64 TH400 refresh

[Matti Roth]

 Next task with my 64 DeVille project is to check TH400 condition. Gearbox came with the car but was already removed. It is 64 but not possible to say if it is the original to this car as there is no VIN stamped like in later gearboxes. And again we have one-year-only part, so I hope no need to replace mechanical parts. I got 64 gasket kit already but probably will need some more rubber for inside parts.

Two bolts from extension housing were so corroded that they broke when opening, otherwise no damages yet. O-ring in filter was not properly in place, and was cut actually. Modulator is not holding vacuum so need to be replaced. Governor valve is stuck, I hope cleaning will solve that.

I will clean all parts and replace gaskets, and other parts if necessary. Oil was very clean and red inside but I think oil has been changed or added not long time ago. 
 I can see that 64 is slightly different from 79 which I repaired year ago. All hints and advice are highly appreciated. Shop Manual is in heavy use.

[Matti Roth]

My first TH400;project was from 79 Seville, and that was in much worse condition. Friction and metal plates in forward clutch were melted together and car was running forward all the time, even with Reverse or Neutral on! Lack of oil and maintenence can damage these trannies like others. I think TH400 might wear but not break easily. You just replace those worn parts, clean the rest, and then back to the road and keep oil clean and correct level.
TH400 was in production more than 30 years and for a reason!

[Matti Roth]

I have checked every piece I could think of and there were 3 possible causes found: o-ring in oil filter supply pipe was damaged which could cause low oil pressure inside. Governor valve was stuck but I don`t know if it is due to transmission staying out of use. Small dirt accumulation was fould inside valve body and that could have caused some errors in operation. I cleaned all parts, dismantled the forward clutch and replace all plates, replaced most of the bushings and seals. Everything should be in order after that. 

[Matti Roth]

Extension housing got new bushing and new seal. Excellent service from MrMechanic in Sweden to supply rare parts for one-year-only 64 TH400!

Simple tools can be handy! Normally I use my 10ton hydraulic press.

[Kurt]

That's AAMCO beep beep. In case they don't exist in Finland, here you go:

https://youtu.be/jPcX9P9JYDM

[Matti Roth]

Thanks Tony

Local transmission shop asked 2500 USD to fix the TH400 in my Seville so I thought I will first try myself and pay that huge amount only as a last chance. So far I have kept the money in my pocket.

Thanks Tony

Local transmission shop asked 2500 USD to fix the TH400 in my Seville so I thought I will first try myself and pay that huge amount only as a last chance. So far I have kept the money in my pocket.

[Matti Roth]

Hi Tony

I made short video to see how the piston has to move freely up and down inside governor. 

https://youtu.be/AtV53UE1OmQ

[0bs08u1yjf40z]

Btw where did you get the trans mount?

[Matti Roth]

TA Motor on Sweden. (I live in Finland).

They were available in Rockauto some months ago with very good peice but not anymore.

[Matti Roth]

During rebuilding my 64 TH400 I found out some technical features which are related to our year 1964 or a bit later, but are different to TH400 from later years. Good to check these if you are repairing your gearbox or sourcing parts for it. Most of this is defined in Shop manual when you read it very carefully. I am far from specialist regarding transmission so please correct and add data where needed.

First of all, the main case is one-year only for 1964. Probably similar case can be found in 1964 Buicks. Case is installed to 429 with adapter ring which is not needed in later models. So please handle your 1964 TH400 with extra care because it might be not so easy to find a replacement!

The control valve assembly is 1964 one-year only. It means that the spacer plate and spacer gaskets must be 1964 model. One of the fixing screws has copper washer which is not used in 70’s and later.

Oil pump is 8 bolt version which is regarded the strongest and the best. I believe it is possible to use 6 bolt version from later years as well if 8 bolt version not available.

Inside the case 1964-1966 TH400s have a sprag assembly instead of a roller clutch assembly. Sprag is regarded stronger and recommended when building hi-power modifications.

The extension bushing has 1.8” outer diameter whereas 68 onwards has 2.0” diameter. Extension housing seal is smaller as well, it has 2.502” outer diameter in 1964-67.

1964 TH400 has a center support locating screw which is not used in 70s and later. It helps to position the center support before tightening the center support bolt.

1964 TH400 has 5 pcs of 0.068 wawed metal plates in Forward clutch whereas later models have only 1 wawed plate. Thanks to this 1964 has extra smooth engagement of gears! I was lucky to find a NOS kit.

Oil filter in 64-67 is different from more common flat type filter used since 1967. In our filter the o-ring is installed to filter neck before installling the filter to gearbox.