# TH400 Rebuild advice



## OrbitOrange (Jul 5, 2010)

Well looks like Ill be tackling this rebuild myself instead of taking it to my trans guy. (Financial reasons after filing taxes today).

So Im wondering what kit do I buy? 
Where do I buy it?
What do I look for in a kit?
Is there a good site that tells how to rebuild the th400?

Im not building a dragster so I just really need it beefed up a little and shifting nice and firm. Hold up to a stock 400. (that will be going in it next year)

Also probably just need stock stall speed on the converter unless someone can tell me why I would need a high stall in a street/show car.


Where get I get a good convertor for less than $200?


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## JustAl (Mar 20, 2010)

There are several good books discussing Turbo 400 modifications and rebuilds, they go into great detail. Also any year GM shop chassis manual that covers the 400 is a great source of info and assembly pictures. I have rebuilt a couple of 400's with good results. TCI, B&M, and others all offer comprehensive rebuild kits with most of the good stuff needed. A 34 element sprag is probably a good addition as well as an adjustable vacuum modulator. These kits also include the necessary parts and instructions for different levels of performance mods not unlike the "shift kits" that have been sold for years. You may have to fabricate a couple of tools for the clutch packs and you should have a dial indicator for end play measurements, some snap ring pliers and an inch pound torque wrench, but aside from that common hand tools are really all that's required. Common sense taking it apart, laying out the parts in order and keep it clean !! Torque converters, not my speciality, best left to people who know what they're doing, talk to a reputable vendor with your cars specs and see what they say.


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## OrbitOrange (Jul 5, 2010)

Ordered my rebuild kit and torque converter today. Explained to my transmission guy that I was wanting to rebuild my own TH400 and he was very cool and helpful. I asked if I could but the parts from him and instead he gave me the phone number to where he buys his parts. That was cool as hell considering he gets his parts from this company and backs his transmissions for 1 year even under racing conditions! 

I have the transmission diassembled and on the bench. Will disassemble the hubs and such when I get the kit so I can put them right back together with new parts.


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## BearGFR (Aug 25, 2008)

I'm very interested in this thread. Would you please talk about what you run into, what special tools (if any) you need, and stuff like that as go you along? Photos would be very cool also.

Thanks,
Bear


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## OrbitOrange (Jul 5, 2010)

Ill get pics of some of it. So far no special tools. I do have a dial indicator to check the end play. I went to the library and checked out a late 60s-early 70s chiltons manual that has some useful information. Only issue I have found so far is a part in the back of the tailhousing its a 3 tang looking spacer. Other than that I do not see any obvious problems as to what happened internally and cause the trans to fail.


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## geeteeohguy (Feb 2, 2008)

The special tools I borrowed from a friend were a must have: they were the seal installers for the lip seals that go onto the apply piston assemblies for the clutch packs. Also, get out a magnifying glass and read the part number on ALL lip seals and match them up with the one in the kit. They look the same, but are not. This includes especially the 3 large diameter seals that go on the clutch pack apply pistons. You can use a pick to try to tuck the lip of the seals in, but the tool (basically a plastic cylinder that fits over the piston, containing the seal) makes it near impossible to screw up and roll a sealing ring. I used a 20 gallon steel oil drum (garbage can) as my custom holding fixture. The TH400 is one of the few transmissions that can be built in a garage with no high tech equipment. Also, be sure to air check all the apply pistons/sub-assemblies before installing them in the trans. If they pass an air check, they'll work under hydraulic pressure. Good luck.


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## OrbitOrange (Jul 5, 2010)

Went out to get some pics and finally took a look in the torque converter. The torque converter is what I thought the problem was because of the noise I was getting at the front of the trans. Heres what we got!
Bearings came loose inside the converter.


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## OrbitOrange (Jul 5, 2010)

geeteeohguy said:


> Also, be sure to air check all the apply pistons/sub-assemblies before installing them in the trans. If they pass an air check, they'll work under hydraulic pressure. Good luck.


I read a little about doing this today. You want to lend some experience on this?


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## geeteeohguy (Feb 2, 2008)

Yeah....use shop air, but not a lot....maybe 30-50psi. That will be enough to activate the apply pistons/servos without blowing the seal. Just a quick bust with a rubber tipped nozzle, canted a bit to bleed off air so you don't blow it up. Takes very very little. Also, with an automatic at home (no "clean room") it's important to keep things as clean, actually cleaner, than when assembling an engine. Bag all ov your sub-assemblies in zip loc bags, and keep a garbage bag over the trans when not working on it. Brake Kleen and shop air are your friend. Also, use a decent amount of trans assembly lube (or Vaseline) to hold seals, check balls, valves, etc, in place. If you take the valve body apart, photo the whole thing as you go, do it on a big sheet of newspaper of newsprint, and lay all the valves, etc, out so you can take a picture. You already pulled the VB, so too late to photo the check ball locations. You can actually tell where they go, or use a manual. Borrow the seal installing tools from the trans guy you got the kit from!!!


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## GTO JUDGE (May 14, 2005)

Say Orbit....... I have the recipe here for my valve body. It was done by a TH400 expert. It shows what's in it, check ball locations, etc. If you want it to reference, or copy it I will gladly send it to you.


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## OrbitOrange (Jul 5, 2010)

YES PLEASE!

I bought a transgo kit, but not installed it yet. Ive been talking to Half Inch Stud somewhat along the way.


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## geeteeohguy (Feb 2, 2008)

I've read a bunch of H.I.S's posts....and he seems to know what's going on. Always seems objective and brings up good points. Jakeshoe and Cliff really know these units, as well. But you klnow that already.


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## OrbitOrange (Jul 5, 2010)

Jakeshoe has great info, but some his stuff isnt detailed enough LOL. Ive had to read it 4-5 times to realize what hes talking about.


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## GTO JUDGE (May 14, 2005)

Orbit, PM me your email I will email you a copy of my recipe.


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## OrbitOrange (Jul 5, 2010)

Well its been pure hell! The next time it wont be as hard. Ive had this thing apart and nearly 90 % together probably 15 times or more. Problem was the direct drum wouldnt drop into the 3rd intermediate clutch causing binding of the input shaft. FINALLY, tonight got that figured out and fixed. Working with H.I.S. tomorrow on the valve body. Ive cleaned it and reassembled it. 

Even with the NTSG manual its been a pain in the ass for sure. Installing seals in the drums is a BITCH! Found a solution to that online using some electrical tape and grease! All in all its not that bad. Had to invent my own tool to release the piston springs. C- clamps werent working for me very well. 

I did leave the 2 seals out for the direct feed modification that jakeshoe has on his site.

Plan was to install trans last night then tonight so , maybe , just maybe tomorrow night.


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## BearGFR (Aug 25, 2008)

Hey Orbit ---- I hope you've been taking pictiures along the way. If so, please post them when you get a chance.

Bear


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## geeteeohguy (Feb 2, 2008)

Hey Orbit, I _TOLD_ you about the seal install tool. Makes the seal installs a 2 minute job with no chance of rolling the seals!! (it works like a ring compressor but has no moving parts) I can't think of ANY easy way to install the final assembly in the case, holding on with dear life by your fingertips, hoping it'll "drop in" and be lined up...I think it took me about 6 times, and then I found out the tailshaft bushing wasn't pressed in all the way....D'OH!! Sounds like you're most of the way there, though. Excellent.


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## OrbitOrange (Jul 5, 2010)

geeteeohguy said:


> Hey Orbit, I _TOLD_ you about the seal install tool. Makes the seal installs a 2 minute job with no chance of rolling the seals!! (it works like a ring compressor but has no moving parts) I can't think of ANY easy way to install the final assembly in the case, holding on with dear life by your fingertips, hoping it'll "drop in" and be lined up...I think it took me about 6 times, and then I found out the tailshaft bushing wasn't pressed in all the way....D'OH!! Sounds like you're most of the way there, though. Excellent.


I gotta get one of those tools. The electrical tape worked great. 

Bear... I have a few pictures. Not really anything to do a write up on. Ill answer any questions you might have. And I have a spare 400 that I also tore down because I forgot how something went and didnt trust my gut so I would tear it apart from the spare trans to see how it was suppose to be. 

The transmission is in the car everything is done except Im going to run new lines and need a larger cooler. I might try to fire it off tonight. Not sure since its Valentines Day and the wife was raising hell last night that Ive been in the garage for a week and Ive had my uncle over everyday trying to help me on the trans.


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## OrbitOrange (Jul 5, 2010)

Finally got her out for a test run yesterday. 1-2 shift good, but 2-3 wouldnt shift til I let off the throttle. Turned out when you do the "dual feed" modification that creates a leak between 3rd and reverse. Theres a hole in the case that feeds from the center support that has to be blocked off. That can be dont a number of ways. I happened to have a transgo VB plate that took care of that problem. So I swapped that out. After some studying I also noticed I had 1 of my 3 check balls in the incorrect location. Put it back together for another test run and she works great now except reverse. Reverse slips and shudders. So no Im going to check the reverse servo and see if thats the problem.


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## geeteeohguy (Feb 2, 2008)

I left mine stock except for the elimination of the waved plates on the clutch packs for a little firmer shifts. I read all about the dual feed mod, and others, and decided that for my application (cruiser, stock HP), stock would be the easiest way to go. Any time you modify, you need to fine tune it a bit. Hope you can get the reverse deal squared away without pulling the trans. Sounds like a fluid pressure issue, so yeah, the servo or the VB would be the thing to check. Good luck.......


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