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TH400 Rebuild/Build

H

Hijinx

Guest
Well, I think I am going to tackle tearing apart the TH400 I have in the garage in preperation for the Shark. I was given a (supposedly) race prepped TH400 a couple of years ago for my '70 Z28 that I never installed. I need to go through it and replace all the seals and such. However, I have never torn into a transmission before. Any tips on what I should and should not do? I got a TH400 trans manual, but I dont really know what I am looking for to see how this one is set up. Maybe I should just get a trans pac and go through it again. Thoughts?:confused
 
R

rpounds

Guest
I am certainly no expert on automatic transmissions. However, I work with a fellow who spent many years rebuilding them. His comment on the TH400 was "keep it cool and it will run forever". His other comment, when I told him I was going to go through mine? "Keep the parts clean, keep the work area clean, keep your hands clean, keep your tools clean, keep your teeth clean, keep your underwear clean, wear clean socks . . . " You get the idea. Dirt is a real enemy.

Since he could have given me a number of wonderful tips, I consider the one that he did give me to be of utmost importance.

My 2 pennies.
 

69MyWay

Well-known member
Joined
Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
Hijinx,

I am Mr. Tear into Anything at least once. Gear boxes have scared me for ages since I have personally had the unfortunate experience of having them rebuilt by professionals and still fail not long after the rebuild. The part about the auto that gripes me is for the most part you don't know if it will work until it goes back in the car. Or shall I say it is hard to test what you have done on the work bench.

With that said, I tore into a 700R4 a couple of years ago out of desperation to fix a problem. I bought a sweet 88 rag top camaro from a guy that had just gotten the trans rebuilt by a pro and just over the 90 day warranty it went south. You could start the car and put it in any gear you wanted but it did not move (bad pump).

I poor mouthed the price on the car, then poor mouthed a used pump and some other parts from a local trans shop. Yep, took it apart, slid the guts out, looked at them, shoved them back in with a rebuilt torque converter (said lots of prayers), and it worked like a champion. Turns out that the installer must have misaligned the torque converter into the pump cracking the torque converter shaft and smashing the pump. The car has been half way across the country several times since, and is coming back to rest in my garage again in May 02.

So, if Mr. Scared to work on a gear box can do it, I suppose anybody can. However, I still fear those things as I feel beyond lucky. On top of that, outside of my time I got that car up and running for $80. In negotiating with the prior owner I pointed out how it was going to cost me $1,500. So, as you can imagine I for once in my life got a good deal on something.
 
B

Bullitt

Guest
As Chris mentioned, many mechanics do install the torque convertor incorrectly. They don't seat them all the way on the shaft and then bust the transmission to hell. My uncle, who is a Honda mechanic, has made the same mistake. Another relative of mine did the same thing, but that transmission decided to just fall off completely. He kind of related the story with pride, so that tells you a little about his mental condition. :crazy With an aftermarket convertor that has tighter tolerances, it becomes a bit more difficult. Sometimes just turning the convertor a few degrees and then pushing it in, will finally do the trick. As for the teardown, I have little experience with this myself. There's always a great transmission shop or race shop with a guy that has the know how, if you happen to get stuck. Be sure to go to a hands on shop versus the bolt-on places. The old timers can't be beat. Good luck, man. :) --Bullitt
 
6

68mako

Guest
What's the status

Just wondering if you got into it yet. I have my th400 sitting on
the driveway waiting for me to rebuild. Would like to hear if you
encountered any problems.
 
H

Hijinx

Guest
Have not torn into it yet, but plan to soon. I have the engine torn apart right now. Hope to get it back together in the next few days, and her back on the road. After that I will probably tear into the "spare" 400 I have under my work bench. It is supposed to be a race prepped unit, so it should be fun to try to figure out what "race prepped" meant to the guy that gave it to me. I got a good book on rebuilding the 400. You might look this up. I got it a Barns and Noble. It is "How to work with and modify the Turbo Hydra-matic 400 Transmission" by Ron Sessions. It is really detailed and has both transmission theory, rebuild and modification information. I'll keep you informed on how my rebuild goes.
 
6

68mako

Guest
I'll have to check amazon, no B&N store here. I ordered a 90 min
tape from eastwood, still waiting.

S/B build?...mild or wild?...pics ??
 
H

Hijinx

Guest
Current, is a basically the stock 350 with a Edelbrock Performer intake and a few other look good, clean up goodies. The one I am planning to build will be a 400-425 HP 383 stroker with aluminum Corvette heads. I have the block and crank for this build and need to locate some heads (probably keep an eye out on eBay).
 

69MyWay

Well-known member
Joined
Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
Just a thought,

I will be pulling the stock roller aluminum headed 350 from our 90 vette soon and putting it on ice. It will be complete with intake, heads, valve covers, oil pan, timing cover, etc. less the fuel injectors (unless I locate another good set) and a couple of the sensors. I am thinking about asking an even grand for it.

It runs fine, leaks oil out the rear main or either the back of the intake a little and has 150K miles. However, you would never know it to look at it inside or out. We also put a new timing chain in it about 20K ago with all new valve stem seals, gaskets, etc.

Like I said, just a thought.
 

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