TH400 Information Thread

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Jawzjeep

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While on the subject of Th400, if anyone has or trips accross Ron Sessions book,

How to Work With and Modify the Turbo Hydra-Matic 400 transmission

like at a garage sale, book swap event, estate sale or whereever that you can pick up cheap, like $10-$20 or even less, pick that sucker up. It's a great book and is out of print. About the only place I know to find it now is on eBay and it's usually $100 or more used. I was lucky enough to score one a few years ago for like $10 that someone didn't know what they had. Even if you know Turbo 400's, I like it for the Identification Charts. There's great info in it about year model changes, which parts are best and which parts interchange, what year models have the more rare better parts like the dog bone sprag drums. Just get it if you happen to come across one cheap.

I literally just picked this one up. I was going to ask if it was worth having after I read through the thread. Then I saw your your and Nick's posts, awesome.
 

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HotRodPC

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I literally just picked this one up. I was going to ask if it was worth having after I read through the thread. Then I saw your your and Nick's posts, awesome.
Awesome. Great Book !!! Was you able to get a good deal on it?
 

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wow...
pricey indeed.
i bought my copy back in '88 or '89 and paid $20 for it. back then it was the GO-TO as there really was no interweb to speak of then.
almost tempted to sell mine, but nah...flipping pages is better than navigating some bs stuff online
You must be registered for see images attach

just can't belive the prices for a twenty dollar book..
 

NickTransmissions

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I literally just picked this one up. I was going to ask if it was worth having after I read through the thread. Then I saw your your and Nick's posts, awesome.
wow...
pricey indeed.
i bought my copy back in '88 or '89 and paid $20 for it. back then it was the GO-TO as there really was no interweb to speak of then.
almost tempted to sell mine, but nah...flipping pages is better than navigating some bs stuff online

just can't belive the prices for a twenty dollar book..
The BIBLE for servicing, rebuilding and modifying the TH400!

Also, BOLO for his TH350 book as well, if you work on those.
You must be registered for see images attach
 

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So question, our 3/4 ton with th400 seemed to go into gear kinda hard if that makes sense. Park to drive or reverse, like a race horse wanting to get outta gate. Drives fine, shifts fine. Just seeing if that seems...normal?
 

NickTransmissions

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So question, our 3/4 ton with th400 seemed to go into gear kinda hard if that makes sense. Park to drive or reverse, like a race horse wanting to get outta gate. Drives fine, shifts fine. Just seeing if that seems...normal?
The engagement into Rev or Drive is harsh or it's physically more difficult to move the shifter itself into gear?
 

Sgt Gus

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The engagement into Rev or Drive is harsh or it's physically more difficult to move the shifter itself into gear?
Not physically hard to move at all, the engagement.
 

NickTransmissions

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Not physically hard to move at all, the engagement.
Relatively normal for TH400s - some are more abrupt than others...My guess is that both forward and direct drums in yours have no cushion plates installed (the direct clutch is also used in reverse) and the center lip seal in the forward drum has either been omitted during a prev rebuild or left off at the factory, if your has never been gone through (would be interesting to learn it's all original). That drum lip seal helps soften engagement.
 

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Relatively normal for TH400s - some are more abrupt than others...My guess is that both forward and direct drums in yours have no cushion plates installed (the direct clutch is also used in reverse) and the center lip seal in the forward drum has either been omitted during a prev rebuild or left off at the factory, if your has never been gone through (would be interesting to learn it's all original). That drum lip seal helps soften engagement.
Ah, yeah it has a hand written date and initials on it from 08/13
 

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Sgt Gus

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Good info, thx! I took a screen shot and saved it. I was worried could be vacuum or something. Only vac removed was from PO on the cruise control. Thx again.
 

NickTransmissions

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You're welcome, @Sgt Gus!

Keep an eye on it, note that if your shifts start becoming late and real harsh, that could be a sign of high line pressure, which is common in these units as they wear/age...A pressure test can quickly rule that in or out.
 

Jawzjeep

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Awesome. Great Book !!! Was you able to get a good deal on it?
The best kind of deal!

And I'm very happy to find out its not all outdated.
 

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The BIBLE for servicing, rebuilding and modifying the TH400!

Also, BOLO for his TH350 book as well, if you work on those.
You must be registered for see images attach
I do have the Th350 one too. It's still cheap enough. I'd agree the Ron Sessions Th400 is the Th400 Bible without a doubt hands down. I really like the first pages where you can ID any Th400 with the ID tag down to what it came out of originally. When I see Th400's for sale, first thing I do is ask what the #'s and code is on the tag. If it's in the 60's with either dogbone sprag drum I buy it, and have even gotten a couple old Cads where the bell housing wasn't going to fit nothing but that old 64-65 Cad and it had the nice dogbone rear drum. I think I still have 2 of those left that I machined out to take a torrnington bearing from a Th350 front pump instead of a thrust washer, for full rollerizing Th400's and having all dogbone sprags throughout. Great for budget Nitrous launching transmissions.
 

NickTransmissions

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I do have the Th350 one too. It's still cheap enough. I'd agree the Ron Sessions Th400 is the Th400 Bible without a doubt hands down. I really like the first pages where you can ID any Th400 with the ID tag down to what it came out of originally. When I see Th400's for sale, first thing I do is ask what the #'s and code is on the tag. If it's in the 60's with either dogbone sprag drum I buy it, and have even gotten a couple old Cads where the bell housing wasn't going to fit nothing but that old 64-65 Cad and it had the nice dogbone rear drum. I think I still have 2 of those left that I machined out to take a torrnington bearing from a Th350 front pump instead of a thrust washer, for full rollerizing Th400's and having all dogbone sprags throughout. Great for budget Nitrous launching transmissions.
Yep, minimal mods to get TH400s to survive/thrive in high HP, high rom applications. Ill retro a 97+ 4L80E direct drum in to L71+ TH400s that come with that stupid intermediate roller clutch so i can run the BW 34-element sprag instead. Can run a full 4L80E int piston and clutch pack as well if the late 4L80E drum w/sprag assy is installed, top it off with an .085 or .097 thick snap ring from an A518 direct clutch.

I put all of those id tag codes and corresponding years and vehicles into a google sheet, linked in the first post of this thread, for those that dont have the Sessions TH400 book and need that sort of info...
 

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