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.

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