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TH400 Rebuild and a have questions... Any experts in the house?

10K views 28 replies 9 participants last post by  sjracer 
#1 ·
Finally got around to rebuilding the transmission on my Suburban Tow rig.
1987 3/4t 2wd TBI 454/TH400 HD 41 case.
The Transmission was fine and had been regularly serviced, and only had one issue...
No L2, or engine braking in 2 as you came down to a stop. If you selected L2 on a hill for engine braking, it just ran away, like you selected neutral.
Scary.
I threw another TH400 I had in a couple of years back, but now that one is bad... Time to rebuild the original and swap it back in.

Ok, so I got a rebuild kit and threw it up on the bench...
Pump and shaft has a little surface rust on...



 
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#8 ·
After looking at that drum... I believe the parts proper name is "Reaction Carrier".
I see that it also carries the planetary or spur gears, which are staked into place.
Read somewhere that it passible to have the outer surface lightly refinished, which would be better as it would mean that the gear set would go undisturbed.
Could I do a refinish and replace ethe rear band?
Anyone know if there is a minimum diameter or dimension?
 
#17 ·
needs a whole valve body, look at the rust on the whole thing. spool valves are probably rusted/pitted by now. ruined.

OP, you better plan on either buying new hard parts or spending hours getting every trace of rust off of every single thing inside there.
 
#19 ·
from a rebuilders standpoint, thats too much.

what you might see as minimal is excess to people that have fought for hours to get the trans to operate when its got a small issue with a valve body being "slightly rusty".

but what do we know?
 
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#21 · (Edited)
OK, OK...
Yep, looks llike I have some rust in the valve body... I stand corrected!

I think its my fault, as I rinsed the oil off the trans last week with the converter out... I bet thats when the water got in.
Looked at it today, and its not bad. I moved all of the spool valves and they are all free and look fine. I sprayed some WD40 in there and left it to soak.

Also looked at the Accumulator, and yes, now I have my glasses on and had looked at what it should look like... boy is it busted!

Now, stupid question, would that be the reason I had no L2????
Where can I get a new one or aluminum part?

Anyone suggest a good converter for Towing?
 
#23 ·
correct on the 2wd, wasnt paying attention to that, was more concerned about the condition of the parts.

that's whats great about this world, you can build it your way, i can build it mine, and they'll both still make it to the point where the tow truck picks it up anyway, maybe in 100 miles or 100,000.......
 
#24 · (Edited)
Thanks for the input and opinions... as entertaining as ever guys!

FWIW, this trans had about 150k on it when I pulled it out, and I had owned the truck since 100k, and 10 years now.
Here she is next to a Rotissary I am building for another resto project.


I had to rebuild the motor at 150k, because the stupid GM aluminum cam gear stripped...
It took out the intake valves and pushrods...



The inside of the trans, aside from the little bit of fresh rust, was clean and sweet smelling, as I had changed the fluid about every 20k miles. It has the tow package, plus what looks like a larger aftermarket cooler.
I think the trans has a shift kit, as it always shifted firmly, and I loved it.
Any way to tell if it has?

It never had engine braking in L2 since I owned it, and assumed it was the front band, but looking at the band it was not burnt or worn out as I expected it to be..
I will measure the thickness later today, and post, but I have new one anyway to go in.


The 2/3 piston is plastic(which I have not seen mentioned in any of the books I have), and the center cone is snapped clean out of the piston, as well as there being a crack down the side of it.
I will replace it with a cast aluminum item.

As far as the reaction carrier, i have examined the sun gears and they are good, and exibit no play or endfloat at all. I will measure the overall diameter, and friction thickness and post.
 
#25 · (Edited)
Here is the VB after I cleaned off most off the gasket..
It looks grim, but as I said, it was all fresh, and all of the valves moved freely, none were stuck.



And here after I removed all teh valves, left it soaking in rust dissolver(Captain Lee's) overnight.
I then gun cleaned and and a good wash and WD40 wipe.



All of the valves look fine, with no pitting.

Here is the broken/cracked 2/3 piston/accumulator... I have a new Aluminum piece on its way..


 
#29 ·
Here is the VB after I cleaned off most off the gasket..
It looks grim, but as I said, it was all fresh, and all of the valves moved freely, none were stuck.



And here after I removed all teh valves, left it soaking in rust dissolver(Captain Lee's) overnight.
I then gun cleaned and and a good wash and WD40 wipe.
just get a new valve body, that one looks really grim. take it from a guy who had his first trans build back in tech school not work because a piece of lint got stuck in a spool valve. i would take your empty trans case to a trans shop and see if theyll stick it in thier parts washer to get it uber clean. also have them check it for wear in the clutch pack guides, you may need case savers.
 
#26 ·
I had the same problem with L2 in my TH400 and the trans guy said the one-way clutch sprags were the issue.

When manually selecting 2nd, the band would hold it. I think thats why you have all the wear on that reaction drum. So replace the one-way clutch while your in there...
 
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