GM 700R4/4L60 Transmission

well, i tore down a 4L60E and am building a non lockup 700R4. since these transmissions overlap so damn much both in design, upgrades and parts interchange since 1982, i am going to combine both into a general knowledge source to help you out with whatever transmission from this family you may be working on. in my parts books they even list all of them in the same section. so as i add articles, i may seem to be bouncing between the two styles of transmissions….that’s cause i am.

First, i am going to hit on a few basics and some history of this line of light duty overdrive transmissions. Although these are definitely a different breed of transmission than the non lock up th350’s most of us talk about from old iron cars, they are ancestors. you can see a lot of similarities in how they have evolved over the years. To me it all started in the late 60’s when buick and chevy divisions had a demand for a light duty cost effective transmission over the 400 but not a two speed like a power glide. this is where the th350 came into being. during it’s run primarily in the 70’s it underwent several updates, changes, and variations, including a lock up torque converter clutch….or for short a TCC…to add to fuel mileage.

 in the early 80’s with emissions and fuel mileage becomming a major deal GM had a simply approach to it….2.6:1 rear axle gears, more gears in the tranny, and make a smaller engine idle most of the time with a q-jet. in essence robbing peter to pay paul. This is where the 700R4 came into being, as well as the 200R4 (which was a spin off of the th200 metric trannys). where the th350 had a 2.52:1 ratio in first gear the 700r4 had a 3.06:1 in first gear/1.61 in 2nd, 1:1 in 3rd, and an overdrive of 1:.70,  or 4th gear. they also incorporate a TCC, as do pretty much all modern transmissions to date.

I may have blogged about this previously, but the TCC is basically an internal clutch that is applied by fluid pressure in the torque converter to lock the converter solid so there is no give in the converter.  on the 700R trannys some units would start hitting this as early as 2nd gear but most of the time it was programmed to hit it in either third or 4th gear to improve mileage. When a tcc gets fouled up….it will give you that tell tale jerking sensation at cruising speed going down the road. or better yet when you pull up to the stoplight it kills the engine cause it locks the engine solid to the trannys. when that happens you basically start it in neutral and drop it into gear like an idiot teenager trying to get out of the intersection or you abandon it at the light in the turn lane pissing everyone off within a 1/4 mile and call the wrecker.  yeah….been there done that…..towing the old man’s boat to boot!

if you hear about a 700R4 and or a 4L60, they are actually the same thing. 4L60 is the modern designation of the 700R4 the same way a th400 is referred to as a 3L80. where an older tranny like a 400 or 350 would have both a modulator valve and a governor to control shift points, the 700R’s used a cable in place of a modulator valve. now this is not to be confused with the cable used on a th350- on the th350 the cable was simply used for forced downshift(passing gear). on the 700R4 and 200R4…..and most overdrive trannys through the 80’s…..the cable controlled a throttle valve and was used to regulate low speed pressure and timing to the shift valves directly off the throttle position rather than using engine vacuum. although this is more accurate and in a sense kills 2 birds with one stone, it now makes it much more interesting to change a carburetor from one brand to another. the position of the cable to the center of the throttle shaft is critical so the pressure and timing of shift at cruising and part throttle speed is accurate otherwise it can be an unpleasant experience outside of wide open throttle. 

The older style 700R4/4L60 trannys underwent  several upgrades during the 80’s to resolv7004casee several problems including faulty throttle valves and weak input shafts. there were numerous upgrades and i will detail them in more detail in later articles as i get further into my build. starting in 1987 they had most of the bugs worked out of them. in the picture here to the left is an example of how to identify one of these 700R cores. on the passenger side, the casting has what pretty much looks like a camshaft lobe casting mark over the servo boss. in the picture,i circled it and put a red arrow to it. when you are starting out to rebuild a unit and don’t have a core, this is what you shop for at the yard, and an easy way to spot the right one.

 you time and money purchasing and chasing down upgraded components by going with the newer one, however if you can’t find one or the one you got already is not a newer one: don’t worry- it’s not that big of a deal!  upgraded later 700R4 parts  and numerous update parts and kits are available aftermarket and are a must for any serious built you want to last.

TH700-R4_1now after you find the model you want and the generation you got- you need to know the exact year too. yeapers- numerous valve body mid plates-accumulators-springs- yeah you get the point. it can get down to different models for the same year. if you are lucky you may still have the tag on the top of the housing with a bar code- otherwise above the oil pan to the right rear is a number you need. here is a chart i found that explains it pretty simple on how to figure out what you got.

For me i ended up with a 1988 vintage unit-2 wheel drive. i have already torn it down and will be doing a full pictoral and description of the upgrades i will be doing in future articles. these  are a very popular choice for street rods these days not only for mileage of having an overdrive gear, but the higher first gear ratio.  i will also be converting this to a non-lockup transmission and omitting the lock up clutch. i plan on using this in a non-computer controlled engine application: this leaves me with two options- i would either have to buy an extra kit to control the clutch lock up or literally wire up a toggle switch to lock up the converter.  i elected to just omit it during the build using an aftermarket kit and save a big pain in the ass at the sacrifice of a bit of mileage.

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