Transmission slipping 1985 M1009 TH400

[GreggVA]

And so the saga begins.....

This is a first for many things for me - first military vehicle, first diesel, first time working on automatic transmissions. I picked up the vehicle from a fellow SS member and it test drove okay but the trip home through the mountains brought on the below symptoms. Ended up trailering it back after a ticket too!

Symptoms:

- will not shift into third. It did seem to float between second and third and I would rev it and third would catch for a while but then is would slip out again.
- shudders when in reverse and have to rev to get it to catch
- worse when warm

The PO told me that he had changed the filter but I thought maybe he left off an o-ring that I had read about. I went to the parts store and the "smart" kid behid the counter told me that I should remove the valve body and clean it too. He said that there were only 15 bolts and it was easy. I did a little more research and found that there were check balls, a detent, and a solenoid.

I got under the truck and made the big mess. Dropped the pan and the magnet in the pan had about an eigth of an inch of sludge around it looking like a black donut. I think the fluid smelled somewhat burnt but I don't have the nose for it yet.

I pulled the valve body off, heavier than I expected, and had to wiggle it back and forth a little to get the two tubes to slide out of it. I found six balls - one of which I need to remove from my drain pan. I also found what looks like a pump that appears to have broken. Pictures below:

A couple questions:

- Is this a pump?
- Could this be my problem?
- What would cause this to break?
- Who is a good source for parts = Autozone/NAPA?
- Where can I get a good TH400 rebuild manual?

I am confident you all will guide me through this!

Thanks!!!

 

[Cleptomaniac]

I have assisted in rebuilding a 700r4 and l would not want to do it alone! The th 400 is the same just without OD.
Good luck
Danny

 

[BigRix]

I beleive the pictured part is the 2-3 accumulator. That would most likely explain your symptoms. You may have done further damage though from driving it after it broke. Get some valve body gaskets and a new accumulator and seals and put it back together. You should be able to find a good picture online that details where the check balls go. I recently rebuilt my TH400 but don't know off the top of my head which reference book I was using. It is at work. The worst that could happen is it needs to come out and get rebuilt. Pretty straight forward trans to dig into. Parts are also readily available.

 

[jwaller]

400 is way different from a 700. much easier in some aspects and a little tougher in others. 400 overall is easier. You could easily get away with just swapping the clutches and band and be just fine. these trucks dont have any real milage on them and so you bushings and bearings will be just fine.

its not like your going thru a trans with 200k on it.

 

[GreggVA]

Hopefully the fix will be relatively easy or this may be my first transmission rebuild or swap. The truck only has 61k miles on it.

I found this diagram for check ball location

http://mtech360.com/tmblog/?p=777

Some sites say not to put all the check balls back in place. Has that been the practice for anyone?

 

[baddy3]

here is the diagram with the locations of the check balls. Use some transgel to keep the balls in place while you're reinstalling the valve body.

 

[GreggVA]

here is the diagram with the locations of the check balls. Use some transgel to keep the balls in place while you're reinstalling the valve body.

Thanks - that's the best diagram I have seen yet! I see in this one it says to leave out the one check ball.

Still looking to see if I can find an accumulator pump somewhere.

These guys seem to have most of the parts

Transmission Parts 3L80, 400 GM Rear Wheel Drive

 

[WARWAG]

If it doesnt work out for you PM me. I will be swapping out my TH400 for an OD trans soon. My TH400 is in excellent shape. Also check all of your vaccuum lines as well. Especially that little one on the bottm passenger side. Its about (guessing 1-1/2" long. That will usually dry out and create an air leak as well. That really screws up your shifting. Hate to see you down and not running. Try your rebuild. It may just work right again.

 

[GreggVA]

If it doesnt work out for you PM me. I will be swapping out my TH400 for an OD trans soon. My TH400 is in excellent shape. Also check all of your vaccuum lines as well. Especially that little one on the bottm passenger side. Its about (guessing 1-1/2" long. That will usually dry out and create an air leak as well. That really screws up your shifting. Hate to see you down and not running. Try your rebuild. It may just work right again.

I appreciate the note and insight. I am going to order some parts today. The local store just carries the whole rebuild kit for about $125 and I really think all I need is the gaskets for either side of the hard plate above the valve body and the 2-3 accumulator pump. Looks like I can get those online for less than $10. The accumulator pump that they show is made of aluminum

http://www.makcotransmissionparts.com/A34927.html

Instead of the Bakelite or whatever the current one was. The valve body seems like it is made of cast iron and would win in a fight anyway.

 

[GreggVA]

Ordered my accumulator piston, which turns out to be aluminum, a new seal kit for it, and the upper and lower gaskets for the valve body. Will see if this is my fix!

 

[Cucvnut]

I bet its one of the seals in the pump they are usually what go bad in a transmission and then the bands.

 

[GreggVA]

I bet its one of the seals in the pump they are usually what go bad in a transmission and then the bands.

The seal around the accumulator pump piston was not completely on and looked like it had been that way. One of my pictures above shows how it came out and the position it was in when I removed it. I am going to try replacing that first. If that doesn't work, I will have to decide to rebuild or swap. Hope my parts get here soon.

 

[3dAngus]

Oops, disregard this post.
(It was a failed attempt to rehost the OPss pictures here using copy and paste to make the pictures SS compliant (and preserved for history and search), but it just pasted the links all over again to photobucket. Don't you just hate it when you do that?)

 

[GreggVA]

My parts came in today.....but I have a question!

All of them -

Accumulator and gasket - but which one?

I could not buy the seal that goes around the accumulator by itself and had to buy a set which had more than I hopefully need. The two seals pictured by the accumulator are the closest ones to fit. They both seem to be about the same size and hardness.

Any ideas which one is right?????

Thanks!!!

 

[badassissimo]

I think my transmission has similar problems. How much did your rebuild kit cost? The one at oreillys that was recommended was like 200. Don't want to spend that much on a guess. I think I found a transmission to replace the th400. Might do that since its about the same price.

 

[gungearz]

For what its worth, I wouldve took out the th400 and took it to a shop. Swapped it out with a th700 for a couple hundred. Bucks more.... And never looked back...

 

[clandr1]

For what its worth, I wouldve took out the th400 and took it to a shop. Swapped it out with a th700 for a couple hundred. Bucks more.... And never looked back...

I'm thinking that 3.08 gears would cause a 700R4 to smoke itself in no time due to going in and out of lockup in OD, unless the 6.2 is able to keep the truck moving in OD at a much lower RPM than the 5.7 gasser.

Heck, I was running 33's with 3.42's in my 350/700 and it hunted in and out of OD on the highway pretty bad.

 

[gungearz]

If it has 3.08 differentials. It won't touch the trans... Stock civilian 87 6.2 suburban came factory paired to a 700r transmission. So you don't have to worry about that. Besides, a 700r has the option to put it in drive or overdrive. Unlike the 4L60e which is an automatic overdrive. The only problem with the swap is that you need to shorten your driveshaft down (I think 1 3/4"). Which is very easy to do if you know how to weld...

 

[gungearz]

Once you get bigger then a 3.83 gear is when you have to worry about continuous highway speeds.

 

[gungearz]

And worrying about it going in and out of lockup all depends on your stall speed converter (torque converter). Talk to a tranny place. They will point you in the right direction...