Category Archives: Th400 Transmission

Simple TH400’s are not so simple

when it comes to a turbo 400, as transmissions go, it is a fairly straight-forward 3 speed beast of an automatic transmission, with a fairly simple design as automatics go. produced from 1964-1991, it is largely obsolete for street use by modern standards, leaving the th400 basically either for classic cars or performance use. now there is this myth that all th400 were basically the same and the parts interchange. this is not exactly true, although if you look in any parts catalog or on-line source you would get that impression. for the most part anything from 71-87 will interchange, and thats a large chunk.

to start at the drive clutches: there is somewhere around 18 different pistons that could have been used in the forward and direct clutch packs, 4 different direct drums, three different styles of clutchs produced by 3 different manufacturers, and around 3 different types of steels in both kolene and regular steel(6).

now to keep going, there are two types of center supports, two different pressure regulators, up to 9 different ways you can mix and match up different pump halves for the front pump(some aren’t correct), 3 different case designs at the hydraulic circuitry,two different forward hubs,two different mainshafts, 2 different valve bodies, two different int pistons, 3 different accumulator pistons, 3 different pick up tubes to the filter just for the shallow pan, and two different pump gear designs. these are all the differences that you cannot see from the outside.

doing a quick math check, this leaves us with the possibility of somewhere around 20,150,000 different possible combinations of how a th400 can go together internally-not including aftermarket parts.

now, for the most part if you tear down and rebuild a th400 as an individual unit and take your time using all the same parts that came out of that particular unit, replacing stuff as necessary, there is hardly ever a problem. when you start tearing down multiple trannys at the same time and build parts ahead of time, this is where the fun begins. the thing you really got to watch above all else is how you pack your forward and direct clutches. too tight and you burn up the trans prematurely- too loose of a tolerance and parts will have a tendency to smack together and break the backing plates…..and worse yet certain clutch to piston combinations can snag the steels and keep it from applying all together.

for arguement sake, lets leave the clutches and steels out of the equation: there is still nearly 72 different ways to screw up mixing and matching up how you put together your pistons and drums. ok lets say you pack your foward and direct clutches ahead of time to be ready for a customer. you take his chevy 400 truck trans apart, simply grab a ready to go packed forward clutch off the shelf and put it back together. it went together fine right. but by mistake you grabbed a forward drum out of a 65 caddy trans with a large drive hub and you have a late model gearset. oops. you will be destin for an angry phone call.

Transmissions cannot and should not ever be mass produced. you have to treat them as you would treat a performance engine build: as an individual beast. even though you can go fast you have to take your time and be purposeful in how you build. it is a mistake that i made early on myself, and i watch shops do it all around me these days. when i started building newer transmissions i slowed down and was more meticulous in how i build. i then went back and took the same methodology to a th400 again and i tell ya what, i think it really made all the difference in the world. moral to the story: Don’t ever sacrifice craftsmanship for profit, it will bite you in the ass in the long run.

now a th400 is relatively a simple design, they get worse/more complicated from there.

Parasitic Drag/Oil Shear Effect on Clutch Packs

so something i have been trying to find a happy medium on transmission builds is what is largely known as parasitic drag. this is the amount of power it takes to make the transmission function. on a stock th400 it is around 30-35hp it taxes off the engine, whereas a th350 is about 10hp less than a th400 on the average.

parasitic drag i always thought was due to rotating mass and power requirement of the hydraulic pump. simply put, a hydraulic pump needs power, and the resistance to flow creates a power loss as well. you also have slippage in the torque converter as it is a fluid coupling(essentially a pump). internal components also have some weight to it. basically the more it weigh’s- the more it takes to get it moving. i’ll spare you the law’s of physics.

there is also something i have been trying to deal with lately called oil shear. on your clutch packs, oil circulates from the center out for lubrication and cooling. when the clutch is not applied, the surface area of both the clutches and steels are still covered in circulating lubricant oil. now, if we are spinning a dissengaged clutch pack at any kind of an rpm, the oil will sling to the outside…..literally sucking the flat clutches and flat steels together and causing them to drag. i want to say it is fairly similar to a kind of capillary action caused by centrifugal force. obviously a dragging clutch pack will increase tranny temperatures, and if severe enough, clutch failure.

the solution is basically put a relief area in the clutch pack for the fluid to escape. the easiest way to battle this is to loosen up your clutch pack clearances. this though is a catch 22 as if your clearances are too loose you will have other consequences.

the use of radial grooved clutch discs and waffle clutch discs are the best solution to resolve the problems caused by oil shear on most of your older trannys. gm did it on different clutch packs in both the th400 and the th350.

later model 4L80E’s and 4L60E transmissions used what is termed as turbulator steels. basically they are steels that have an oblong hole in the middle to relieve the oil shear caused by centrifugal force. they are found in the 97 and newer 4L80E’s in the overdrive clutch packs.

on the 96 and newer 4L60E’s , they used turbulator steels in both the reverse input drum and the low 1/reverse drum. ironically it is erie similar to the same areas that fail on a th350 in a demolition derby….anyways the late model turbulator steels can be swapped into earlier 700R4’s as an upgrade.

now as an example of oil shear. on my 1st/reverse th400, i got a guy that gives it time to shift, but floors it from one side of the track to the other all night in forward. after 40 minutes of running the piss out of his suicide lincoln……he loses reverse or it starts to slip. upon teardown there is nothing wrong with the seals- the seal rings-the pistons- the forward clutch is fantastic- gearset is fine. the direct/forward clutch is burnt to a crisp- i mean no linings. on a 1st/rev the direct drum spins just as fast in the opposite direction but dissengaged. even when using stiffer trans brake springs to keep the clutches dissengaged- the discs still suck together!

this is chronic oil shear….and can happen on ANY transmission used for demo derby. even with the use of waffle clutches, chronic oil shear still can happen. we are experimenting even to this day with combinations of different linings-number of discs vs number of steels, different fluids/additives, and clutch pack clearances to prevent this. there is no answer at this time for derby transmissions.

Performance Transmission:Full Manual Valve Body Th400

Sorry it took me so long to get back to this section i was writing on in my Blog. The last little bit of information i have to share with everyone on the th400 is the full manual valve body. in fact i have had other builders on wecrash asking me about how i do this. well, it is remarkably simply. this is for a forward pattern full manual valve body modification. if you want a reverse pattern valve body you are better off buying an aftermarket kit. reverse pattern requires some bridgeport machining and cross tubes installed into the casting of the valve body and it just isn’t worth the hassle for the cost savings.

First off, if you have been reading along you have read into how i design the 1st/reverse only. well for full manual, rather than plug one side of the ports leading to the governor we are going to plug both channels to the rear of the valve body that both supply and return oil to the valve body. again i use set screws but some builders also use check balls stacked in place with a small punch. 400v-body-7400v-body6 we are than going to bridge the supply and return oil within the valve body. show here in these pisctures is where the modification needs to take place. the pick is pointing to the supply line to the governor, just above it in the same passage is the return oil line from the governor to the 1-2 and 2-3 shift valves. drill a hole right there. i use a cut off wheel in the groove. basically any way to cut the casting just above the pick in the groove to bridge oil directly to the shift valves. so whenever the car is running, there is full psi holding both shift valves open.

This maked D range or drive full time 3rd gear. you then manually pull it back to low 2 to force downshift to full time 2nd gear. However if you pull to low 1 you will not get low 1 you will still have low 2 due to that little design gm put in there from the factory, so you must also do you hold 1st gear modification to the spool valve for the 1-2 shift as i described in a previous blog. you will now have full manual operation.

now although it is not necessary critical, it is a good idea to modify your boost valve to have consistant psi in all gears, and obviously you don’t need a  modulator valve any longer. you basically have a full manual valve body transmission. now for street or drag racing full manual, i omit the center seal out of the direct drum block the reverse port for added apply psi at the 3rd gear shift. i also block the port on the 3rd gear accumulator as well for the same reason. this creates a hesitation on the reverse shift though so for derby application leave the direct drum seal set up stock to prevent the hesitation.


316600931one issue that must be addressed on ANY build with one of these piece a shit plastic accumulators is that it MUST be replaced. the picture here to the left is a typical cracked piston from a mid 70’s bop tranny. starting in the mid 70’s most of the gm trannys had these in the valve body. the older ones had an aluminum pistons which are the replacement of these. over the years as trannys are rebuilt in the name of normal service, good builders replaced these with aluminum. so it is hit or miss as to whether or not you will have a plastic or an aluminum piston in your valve body. one thing is for certain, if you rebuild a tranny and don’t swap this out knowing full well it can crack, melt, and fall apart….you’re an idiot. so, this is first and foremost an obvious performance upgrade for any th400.  when this cracks it makes 3rd gear sluggish and you usually have to gun the throttle to get it to move in reverse.

3 setNow, the spring below the piston was different from one th400 to another….BOP’s may have had a softer spring vs a chevy truck would have had a stiffer one. quite often once there is severe abuse, these springs will break. so for heavy duty/race applications i chose to remove the spring render the accumulator useless. this omit’s a fluid cushion and make for a more crisp shift for the 2-3… well as reverse depending on your build.  you can accomplish this in a couple of way. if you have an older piston you can simply take the spring out and install it upside down. newer aluminum pistons have 3 tabs toward the top so you will have to grind those off to fit the valve body bore. the way i chose to do it is to install the piston in the bore completely, then install a 5/16″ set screw in the oil port next to it to block oil flow. the picture above is pointing to the port you tap and plug. i like doing it this way simply because your piston is installed correctly in the bore and the servo piston to the low 2 band will seat against the top of it correctly. now, if you have been paying attention……yeah the set screw might leak a bit, but the rest of the plumbing of the tranny via the servo will equal that of the 3rd gear circuit and the servo spring holds the whole works down .

the 1-2 shift accumulator sits inside of the rear servo. this is one of the places where bypassing an accumulator can effect numerous things. i have tried sealing off screws in the case-omitting accumulator piston seals, and all sorts of chicken shit. i wouldn’t suggest doin anything like that unless otherwise specified in an aftermarket shift kit or valve body per manufacturer. Gm had 2 or 3 different large servo springs over the years…not the small inner spring on the servo shaft itself the larger outer one….the most common are a blue spring and a yellow spring. i have found that the yellow springs were most common in heavy duty chevy truck applications and seem to be stiffer, so i prefer using that one and saying piss on it. the softer the spring-the softer the shift…and vice versa. it is not uncommon to find these springs busted upon disassembly. there usually isn’t much point in doing much with the 1-2 accumulator other than a large servo spring change in my book.

TH400 Direct Drum

351788749Now, one of the achilles heals of the th400 is the direct drum, which houses the 3rd gear/reverse drive clutch. the drum itself is a very strong piece. however, the intermediate sprag set up located to the rear of the drum is a weak link. some of my earlier blog post’s from way back address the different drums over the years so i am not going to rehash all of it. from the factory there were two styles- shown here is a pre 1971 drum with 16 element lug type sprag. 71 and later had 8 rollers…and they let loose and explode in heavy duty or race application. so, you want to start off with an early model drum. you then can get an aftermarket 34 element borg warner sprag that fits the older drum. the more lugs there are- the more it evenly spreads the load. when in 1st gear, the direct drum spins the opposite direction as engine rotation. to hit second gear, this drum comes to a dead stop to give you planetary action to create second gear. that shock load is immense in a racing application….and it’s not a matter if rather than a matter of when it will explode the roller clutch. in normal driving conditions….and to be honest anything up to 400 hp nbot using a trans brake or manually shifting….will usually handle a stock roller clutch. for full manual, trans brake, or heavy hauling, the 34 element sprag upgrade is a must. as a matter a fact on the 4L80 transmissions they went back to the 34 element lug sprag. i have been told the 4L80 drum and sprag assembly will interchange with an older 400 but never tried it as a total assy.

another weak link is the direct drum backing plate358343488. these things are prone to breakage primarily where system pressure has spiked or there was a clutch failure-it burned the clutch and overheated the backing plate causing it to crack. to keep this from happening, i ALWAYS make sure i use a rigid aluminum piston for the direct clutch . it is not quite as critical on the forward drum as it is not considered a shifting clutch. the stamp steel pistons will have a tendency to belleville/crown when installed in the direct drum from slam shifting and high pressure. this creates a wedge and in effect breaks the backing plate from the inside out as you can see by the picture. notice this one has an aluminum piston- the piston was cracked at the center  from a pressure spike due to a hung psi regulator-doing the same thing. so using an aluminum is not fool proof, but it drastically reduces fail rate. you can also use the backing plate out of a 4L80 which is made of a stronger material than the replacement 400 backing plates.


Another upgrade for a th400 that is a standard feature on the 4L80 is the spiro wound clip that retains the intermediate sprag. at high rpm, the stock retainer clip(laying on top in the pic) will have a tendency to release  due to centrifugal force. i have even seen some performance trannys go as far as welding in the stock clips to prevent this. although it is a bit of a pain to get it in, i suggest using the 4L80 spiro clip on all  performance trannys using the 34 element sprag. cheap insurance.

now last, but not least, is to apply both sides of the direct piston in 3rd gear application. primarily this is done by omitting the center seal of the piston and blocking oil port to reverse either using a set screw installed in the center support OR using a small freeze plug in the oil port of the case. you can also wedge a check ball in the port and stake it in place lARS017either. any one will work. you can also remove the second sealing ring down on the center support as well. this will allow the oil to flow more evenly into both passages of the drum to the piston. shown here to the right is an aftermarket direct drum and notice there is no provision at all for the center seal or seal ring for this reason. lightened billet drum are the cat’s ass, but they are not cheap and usually only last about 5 seasons for someone running a trans brake and a large bracket racing schedule. your wear rate may vary depending on manufacturer. you can also omit the center seal on the forward drum to achieve a similar effect for derby application only.

if you forget to plug the reverse oil port, it will lock itself up so don’t forget. what this does is give you full surface area of the piston to give apply force to the entire surface of the clutch. you will still have reverse as it will backfeed through the 3rd gear circuit. however, this mod will delay the reverse apply and for this reason should never be done on a derby tranny. this is only for street and forward race applications where reverse is not critical.


now, i am going to divulge a bit of a trade secret. shown here in the pic to the left is a center support and i am pointing to the 3rd gear apply port. this IS NOT the ony you plug for racing. the one you want for the modification above is the one to the right. the port at the center is the hollow bolt going to the intermediate clutch. now, i mentioned before that omitting the center seal creates even strong apply for 3rd gear. by omitting the center seal in a 1st/rev tranny you do the same in reverse. so you basically do the same racing modification ass396007831 backwards. ya plug the 3rd gear port and meter all your reverse apply through the reverse port. you control your reverse apply using a drill bit similar to the 3rd gear port.

another thing that i also do on 1st/reverse is to omit the intermediate sprag all together. like the check balls, it is unnecessary. you can then spot weld the lubrication ports to force extra oil to the planetary gearset

TH400: Check ball locations,shift kits, and mid plates

this is one of the things that a lot of guys will struggle with on both a th350 and th400, especially with all the rumors of guys leaving this one out-leaving that one out-drilling plates. well first off, for anyone who does not do this every day, you should really get yourself an ATSG manual, which is an Automatic Transmission Service Guide. they are available for most transmissions across the board and have very helpful charts and specs including check ball locations. i must also stress that although you can leave out check balls and drill ports, a QUALITY shift kit like the ones from trans-go are the way to go as they have not only a custom mid plate, but new springs and check ball locations to get the job done right. some kits also include extra springs for the low 1 band piston to severely limit accumulator action and/or make apply more aggressive.

but, if you are a cheap bastard like me, you want to try doing it yourself. well, yes you can, but it may or may not bring good results depending on the wear of the valve body springs you are using.  this is where a good kit with the springs will make a difference. i have fairly good luck with the th400 fabbing up my own stuff  so that is what we will be doing here.  on the th350’s, usually just buy a shift kit for street/strip, but fabbing your own kit on a th350 can be done.  i have never really persued it much to be honest and don’t see the point. i’m rambling again…..anyways, figure out what you want to spend and what you want to accomplish, then make your decision there. if you’re going to buy a kit, don’t waste your money on a cheap one that simply omits a few check balls and gives you a tin plate for a mid plate….that’s what we are going to do here.

bomber check ball


these are the 6 check ball locations found in most th400. i did a rather shitty job with a paint program to number them, but you should be able to get the idea here. 1 is for the modulator, 2 is the check in the 2nd gear oil passage that leads to the low 2 band, 3 is the check for oil going to the intermediate clutch(which gives you 2nd gear, 4 is the check located above the accumulator port(which to be honest i forgot wtf it really does), 5 is the check that bobbles between the low 1 and reverse oil ports to keep the tranny from locking itself solid while in low 1, and 6 is the 3rd gear check ball.

the only real critical check balls you must have under any and all conditions is numbers 1 and 5, the rest are there to block the port during clutch application but unseat to releave pressure rapidly. so, obviously by omitting 4 of the 6 check balls, you application and shift will be dramatically quicker….sometimes too quick. when i build 1st/rev or full manual set ups i only use these two check balls since there is no real point in having the rest of em if you aren’t shifting is there? for an aggressive street/strip i also will only use these two check balls and drill the 3rd gear port  in the mid plate to a 3/16″ diameter. you then calibrate your shift by modify’n the governor and adjusting the modulator valve so you get a hard shift at the right time. what we are doing here is controling the atittude of the shift, not the timing of the shift point, that’s the job of the modulator valve and/or the governor.

check ball number 6 can be omitted during ALL rebuilds, and even suggests that in the ATSG manual for a th400. on some of the 77-80 bop short shaft transmissions, there was no check ball port in the mid plate(even thoug there was a check ball for some odd reason), so to increase flow of oil to the 3rd gear you must drill the mid plate at this location for aggressive street/strip rather than the port shown in the picture below.


i found this picture that illustrates  both the second and 3rd gear oil ports in the mid plate of a th400. you are looking at it here from the upper valve body- or rather the case side of the mid plate. you will notice that while the 2nd gear port has the larger check ball  port next to it, while the third gear oil port does not. that would be the number 6 check. all oil is metered through this 3rd gear port for 3rd gear both in apply and disengagement, therefore you really don’t need the check ball. for agressive street or full manual valve body, you would simply leave out the 2nd gear check ball and drill the 3rd gear port with a 3/16″ drill bit. if you wanted to step up you shift to “firm” it a bit, you could leave the 2nd gear check ball in and drill both 2nd and 3rd gear ports to something like a 1/8″ or less to meter the oil orifice that controls the rate of apply. obviously the larger the port- the quicker more harsh the shift becomes. some shift kits even suggest just leaving 5 of the 6 check balls than drilling ONLY the 3rd gear il port to a whopping 5/32″ to give added oil flow for heavy towing conditions. i can only assume this is to improve holding of the 3rd gear clutch that drives you down the road most of the time.

now, modify’n the mid plate and leaving out check balls will only do as much as the rest of the tranny is built for. by that i mean you still have fluid accumulators for both the 1-2 and the 2-3 shift. so if they are still functioning, the shift with a 3/16″ hole may be just what you want whereas if you disable the accumulators(which is another article), a 3/16″ drill size may seem VERY aggressive.  in several builds for heavy towing, i will disable the 3rd gear accumulator, use 5 check balls, and omit the center seal from the direct clutch(here again another future article). depending on the mid plate you may or may not need to drill the 3rd gear port as well. you must know what the other components in the system are going to do before you go apeshit drilling everything out than….ooops.

TH400 :Holding 1st gear from automatic upshift in low 1

Well, i get this question 3 or 4 times a year. “When i am hauling ass across the track in low 1 the damn thing upshift’s right at the last second to 2nd gear and i lose all power before the hit!”  the other complaint is those of you guys using th400’s still for heavy towing applications, but you don’t see that very often these days because of gas prices, so pretty much the th400 is more of a performance item these days. i digress…….GM designed the th400 to force upshift even in low 1 to prevent engine damage. you usually have to hit 3500-4500 (depending on wear)and be on the throttle to make it upshift, but it does happen.  well, here’s the simple mod’s to hold the low 1 gear at all speeds .


First off, you must drop the oil pan and remove the valve body. you then remove the 2nd gear shift valve exposing the spool and sleeve assembly. there are three valves on this end of the valve body, all of which the pins remove from the case side of the valve body, so therefore the valve body must be removed to do this. there are the 1-2 shift, the 2-3 shift which has a spring at the rear against the retaining pin, and the smaller 3-2 downshift valve to the opposite side. you want the large 1-2 valve assy as shown.

On the spool valve, you then grind 3 small lands in the large area to the rear of the spool, of which there is an arrow pointed to it in the pic. this is to allow oil flow to bypass this area of the valve. you then must plug the exhaust port in the valve body itself, which is the other arrow in the picture. to do this you can either wedge a check ball in place, or what i do is tap it for a 1/4″ set screw and plug it using loctite….being careful not to tap and install it too deep preventing the valve from moving at all. i suppose you could also spot weld it…..but never done it that way since this is an area you do not want to warp otherwise the valves for the shift will bind! remember you must plug the exhaust port AND grind the land for relief on the spool valve otherwise it won’t work.

once you are done with this, re-assemble it and beat on it. it is obvious that this kind of a mod is a pain in the ass for something installed in a car, but it is a piece of cake during a rebuild. i do this for most all serious street/strip builds and derby guys who insist on a normal shifting tranny for derby. this way they can still hold 1st gear without issue.

TH350/TH400:modulator block off plug mod’s

302049547Well, this is the first in a new series of posts in the name of performance upgrades you can do for your transmission. what you see in the picture here is an aftermarket aluminum block off plug you can get from most any performance autiomotive supply outlet for about 10 bucks. it not only makes for a much cleaner appearance on you tranny, but in demo derby application it keeps the modulator valve from ripping off on the floorpan and causing a major leak.  unfortunately as i have stated a few other times  throughout my blog, this creates a major pressure spike while in reverse causing severe internal damage to the tranny. usually the modulator valve will act as a blow off valve while in reverse, but with this rigid plug it doesn’t move and deadheads the psi. well, i am going to show you the simple mod’s to get around this.

396007828Basically, what we are going to do is render the boost valve of the pressure regulator useless.  on a th400 shown here, the pump is removed to expose all the oil passages. the pick is pointing to the oil supply port from the reverse circuit. this supplies oil to the boost valve of the psi regulator that is in the front pump of a th400. we need to block this oil. here i have tapped it and installed a 5/16″ set screw to block the oil. some builders simply jam a check ball in here with a punch. Aftermarket valve body kits will simply omit the supply hole in the valve body mid plate to accomplish the same thing.

400boost01Now, this is not a total seal to the boost valve when using a check ball or set screw. Even though it stops the signal pulse of the oil, some oil may seep through and slowly raise the boost valve off it’s seal and trap the oil in the circuit so even when it is suppose to dissengage the boost valve- you have a high psi situation causeing internal damage in all gears- not good.  To solve this issue we grind two small lands on the large face of the boost valve. this insures the boost will not come off it’s seat.

using this modification, your th400 system pressure will remain a constant 155psi or there abouts in all gears where a stock blue psi spring is used. your main regulator spring is the sole psi adjustment now and obviously can be inceased with a stiffer psi spring, which are available aftermarket. you can do these mod’s and not install a plug-leaving the modulator valve in place to go along for the ride- it will still maintain the constant 155psi. this is more than enough oil and psi to make a th400 do whatever you want it to in my opinion. if you have to run more psi to make it shift harder- you really ought to be looking at modify’n your valve body and/or mid plate rather than increasing system psi.

Now, these modulator plugs can be used on the th350 asth350 boost well, and yes they also need some internal mods as well, but ironically we are going a slightly different direction. pictured here is the psi regulator valve ocated in the valve body of a th350. Basically, the reverse/modulator boost valve needs to have a “slight” relief cut into it on the land the arrow is pointing to in the picture. what we are doing here is creating a small shallow groove on the large land of this valve to bleed some of the psi off the circuit while in reverse. now, this is somewhat of a trick as if the groove is too deep you will bleed way too much psi off in reverse and burn up the clutch packs: not enough and it won’t bleed enough and it will spike your psi and also cause damage. the goal is to create a slight bleed of psi in reverse to keep the psi realistic in reverse. don’t get the brilliant idea to just weld the valve in place through the sleeve cause then there is no movement and your pressures will do goofy shit in several different gear range.  i usually don’t mess with it on the th350’s as the short modulator valve sticks out the back of the tranny and really isn’t in the way anyways.

What transmission do i need?

what do i need to get for my transmission and how much will it cost. Well, i truly feel that everyone needs to have a transmission built for their particular needs and desire. this is why i truly believe no “off the shelf” transmission will make everyone happy. usually you end up paying a lot of money for something that gets the job done but really isn’t exactly what you want. i mean you have your engine built to your desire with a cam of your choice and compression/power/budget you want right…..well to me the same applies to your transmission AND rear axle. really they need to compliment what your trying to do otherwise you aren’t taking full advantage of your engine. you’re making due with a one size fits all tranmission. 

when it comes to the th400, it is a very sturdy platform to begin with so to beef it up to handle descent power is relatively affordable. although debatable, i feel in stock form it can handle up to around 400hp in stock form with good stock replacement clutches like a raybestos or borg warner. if you’re going to be using any kind of a shift kit, the next thing is to insure you have an aluminum direct drum piston as not all th400’s had aluminum pistons. when you push near the 500hp mark and are going to hammer on it at the drag strip or upgrade to a full manual valve body of some kind, the next thing is to upgrade to a 34 element performance direct drum sprag. this is the most common weak point of the 400 in 71-later transmissions…..and when it was retired and replaced with the 4L80, they went back to the older stronger sprag.

the next level is over 500hp+ and above 5000rpm, trans brakes, and nitrous oxide. this is a level that most derby engines never get to and if they do-they never apply the power fully. the first thing that needs to happen is to upgrade the input shaft and mainshaft must be upgraded to a hardened aftermarket shaft.  they loosen and snap. the direct drum and intermediate clutch should be upgraded to a 4 disc set up instead of the 3 disc stock….and you must modify or replace the direct drum and sprag to accomodate this. also thrust loading of the rear planetary can become an issue and planetary gears can snap when you get toward the 700hp mark and both straight cut and aftermarket 5 pinion carriers can be used as well. torrington bearings at the rear of the planetary and be machined and installed also.

now spinning a th400 over 6000rpm and up is somewhat of a rarety as a lot of bracket racers usually will opt of a lighter th350 or powerglide as they do not have to rotating mass and do not eat as much power as the 400 does. there are aluminum and lightened components out there to help the 400 in high rpm application hp, and you bend over and take it in the ass on price. so when you get to that point you should definitely consider all options on the table and look across the board at other transmission options for the price. you may want to go powerglide, th350, or even crower or a top loader manual at some point. i mean if the 400 was that great pro stock cars would use them….ya know what i mean? know when to say when.

the th350 pretty much was light duty from the get go and to put any real hp for anything over 250-300hp, you need to upgrade the center support to one out of a later model 4L60 or 700R4, and completely replace the direct drum and sprag assembly to an aftermarket sprag similar to the 34 element th400 sprag. also machining the aluminum piston down to accept 5 clutch discs on the direct is a good idea as well. there were numerous gearsets used on the th350 so you may or may not need to upgrade things like planetary’s and sun gear shell. BUT if you spend the money….the th350 WILL out perform the 400 as far as weight in the car and power put to the ground through the power range. here again- know when to say when.

the powerglide is the choice of transmission for bracket racing in my book. you pretty much have to gut it and use all aftermarket parts, but the consistancy is undeniable when you only have one shift point to worry about.

but as far as derby, the 400 can be built fairly affordable with stock parts and literally has the raw strength needed for the application over most other transmissions period. as i have stated in other parts of my blog, the th350 is not well suited for derby in my opinion, but some people have good luck with them. here again it doesn’t work for everyone.  a lot of guys like running a manual clutch, but for big shows most people go back the 400 and run their clutch set ups at the county fair to have fun. manual trannys for derby are inconsistant and to me it seems like it is a matter of when not if they will fail. the 727 chrysler is a descent tranny, and will work for derby. still not a th400.

1st/reverse only th400 works well for guys running less than a 4.56 gear in old iron and 4.10 in new iron. after that you wind the piss out of your engine. BUT i do know guys running 1st/reverse with 5.13 gears and scream across the track from one end to the other without a care. for the guys that like the 4.88 and up gears i suggest either a regular shift 400 that is modified for holding 1st gear(which is actually quite simple) OR a full manual valve body so you basically have a 3 speed manual transmission without a clutch. a lot of guys prefer the fulll manual over a regular shift as they can hammer 2nd gear to reverse and if they get to a point where they need to move a pile out of their way or their engine is overheating, they kick it down to 1st gear and bull doze around the track with the 5.13 gear. food for thought.

hope this helps guys.

J.W. Ultrabell with a 12″ Converter

S3700003Well, i finally got a 12″ non-lock-up th350 style converter in the shop and went to checking out the new ultrabell designs a bit further. in my previous post i was checking out the raptor fab modified ultrabell with the 13″ th400 converter. Well, with the 12″ it fit A LOT better in the housing. there is no bind at all to the housing itself like the old  design. On the older castings you had to clearance the inside diameter of the housing on some installations to insure clearance to the back of the converter.

However, i was a bit shocked at first when i discovered the conveS3700002rter bottomed out on the installation bolt heads of the housing! i was like”what the hell!” But, this was not a reason to panic as it turned out. after mounting a straight edge to the face of the housing and pulling the converter out to the proper installation dimension, it pulled the back side of the converter away from the mount bolt heads almost a full 1/8″ leaving plenty of room for expansion……well other than ballooning of course.


There have been several reports come up now that these have been in the field of play for a while that some of these 12″ converters will not clear the bolts on the front pump, and others have no problem. i attribute this to two factors….the variance in the quality of the converters guys are buying and the use of mid plates for distributor protectors.  the best overall combo i have seenwith the jw housings is the use of the taper head bolts in place of the stock bolts AND a 12″ converter. all in all i like the JW housing, but do not buy one of these things thinkin it is a drop-in and go. you will need to take some time and make sure everything fits….and don’t freak out if there is a problem. you will have to take some time with shimming the converter-the housing-perhaps sending it off to get taper bolts machined it- or even a smaller converter. when everything is dialled in- they are a very nice set up and they win.

It is also worth mentioning that you can now buy the new style jw ultrabell directly from jw performance. i talked with a sales rep directly and got about a 10% discount on the total order. so if you order  3 or 4 at a time it saves you a good chunk of money. it took less than 5 minutes and  you will have merchandise in less than 3-4 business days.