TH400 Rebuild advice - Pontiac GTO Forum
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post #1 of 20 (permalink) Old 02-02-2012, 09:57 PM Thread Starter
 
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TH400 Rebuild advice

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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post #2 of 20 (permalink) Old 02-03-2012, 03:36 AM
 
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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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post #3 of 20 (permalink) Old 02-07-2012, 06:44 PM Thread Starter
 
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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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post #4 of 20 (permalink) Old 02-07-2012, 06:50 PM
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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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post #5 of 20 (permalink) Old 02-07-2012, 06:55 PM Thread Starter
 
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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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post #6 of 20 (permalink) Old 02-07-2012, 07:50 PM
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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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post #7 of 20 (permalink) Old 02-07-2012, 07:55 PM Thread Starter
 
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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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post #8 of 20 (permalink) Old 02-07-2012, 07:57 PM Thread Starter
 
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Quote:
Originally Posted by geeteeohguy View Post
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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post #9 of 20 (permalink) Old 02-07-2012, 08:59 PM
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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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post #10 of 20 (permalink) Old 02-09-2012, 09:04 AM
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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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