89 c2500 TH400 rebuild or replace???

[tardisguy]

Hey everyone, been awhile. My uncle recently gave me his old work truck and I have been working on getting it back up to ***** after being parked for the past 5 years. Long story short, the truck was stolen 5 years ago, but my uncle got it back a week later with only a busted column and it has just sat since. It has had a hard but very productive life so far (Truck has over 600k and hauled vending machines daily in the bed for 26 years.),so its not a real looker but it was cared for right and I have lots of fond memories of this truck so its a keeper.

Been working through things and it runs good but it doesn't move on its own. Another long story short, the TH400 (or 3l80 if you like) is burnt up. Black, gritty sludge on bottom of pan, awesome burned fluid smell and the outer part of the planetary that you can see when the pan is off has a beautiful rainbow coloring on it. We think when they stole it they overheated the trans some how. Trans had been rebuilt for the third time 20k before and had a fresh fluid & filter done a month before it was stolen.
This is a project right now so I am not in a big rush to get it done ASAP but I am a single dad so the funds are available but need to be spent wisely. This is going to be a weekend driver & tow rig that is not driven too much and will be driven responsibly so I don't necessarily need a "bulletproof" trans. With that being said...
Would it be better to get my trans rebuilt or just get a "new" trans from Summit, Jegs, Monster, etc.

I have talked to a number of local trans shops and nobody can even give me a ballpark figure of what a full rebuild would be. They all want to see it first then shoot numbers. Some even want the whole truck or they wont do it. I'm not too fond of that. I would rather pull it and take just the trans to someone.


Yall are probably tired of reading by now so again:
rebuild what I have or get a "new" trans from Summit, jegs, Monster, Gearstar, Etc.
Any other ideas welcome too, except 5 speed swap. I already did that to my 91 and even though that is pretty stout, I want to keep the 89 an auto. The idea of doing the 4L80 swap does interest me but I don't have that much funding for the trans and the standalone controller.
Thanks in advance everyone!!

 

[stutaeng]

Um, well that's a good story. Usually guys don't give enough information, LOL. 600k miles! Yikes!

I would say get it rebuilt locally. I think some of the online places are hit or miss, and then for warrantee you'll be out for a while while you pull the unit, send it back and wait...

So what does the tranny do? I think "some" grit on the pan may be somewhat normal...something about the frictions having a lot of material on them. But burnt smell of the fluid is not good.

 

[tardisguy]

Before 1st startup I checked trans fluid level and it was low so I added to full mark knowing it will probably take more once motor was running and trans had distributed fluid to all the passages and all. Started motor and quickly check trans fluid to make sure it was not super low. No fluid on dipstick so I stop motor and refill trans to full mark. I figured maybe torque converter was a bit low so it needed to fill it back up. Started motor again and had open bottle of ATF ready. Dipstick was dry again so I started filling. Put a 4 quart bottle in and still nothing on dipstick. I shut motor off then I could hear liquid hitting the ground. Look under and ATF is fast drip , almost running from the dust cover under the torque converter. After it stopped dripping, I got under, pulled the cover and wiped everthing down and ATF leaks out of the torque converter shaft seal, down the pump face and drips off from the dust cover flange. If I start the motor, it RUNS out of the same place. I was going to pull the trans and change the seal but I wanted to pull the pan first to see if it was even worth changing the seal. I don't think it is.View media item 32718

 

[tardisguy]

View media item 32717View media item 32716 screen shots of the video I took while it was running

 

[Erik the Awful]

TH400s aren't rocket science. I remember back in the day when there were a dozen transmission shops in town, and any one of them could rebuild your TH400 for about $700. They're one of the few transmissions I'd trust a transmission shop to build right. On the other hand, if you're the type that enjoys a project, rebuilding a TH400 shouldn't be too hard. If you're wanting to order a replacement, Summit shows a no-name rebuild for $1200, a B&M for $1400, and a bunch more just over $1600.

 

[stutaeng]

Check out this guy. He's got a handful of TH400 teardowns if you want to DIY:

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[tardisguy]

I have watched his videos and he is awesome and very thorough. If he took take offs I would just road trip and go see him! (i love road trips) He has said no take offs in his video's but I might have to call and ask personally. LOL I am pretty DIY but auto trans are a bit much for me. But y'all do have a good point. Its a project and I do have time. Might be the time to learn it!! My only concern is the planetary looking overheated and might be toasted. I'm thinking I might tear it down and see what it looks like, then decide how to move forward. Getting excited!! Thanks and I will update findings!

 

[Schurkey]

Maybe your geartrain and other hard-parts are worn-out. Buy a core trans from Craigslist or the local classifieds.

A Chevy-case core should be under $100. (BOP-C cores about half that. Doesn't matter--the guts are similar.)

Buy a service manual for your truck. Buy the ATSG service manual for that transmission. Buy Cliff Ruggles TH400 book. Buy a trans seal installation tool. Or make one from some piano wire and a piece of steel tubing. Crush the tubing over a loop of the wire.

Buy a rebuild kit, filter, and get a shift kit from Transgo. MAYBE a modulator. Have the core trans' torque converter flushed by a local trans shop.

Overhaul the trans yourself.

The TH400 is "THE" easiest 3-speed transmission on Earth to overhaul. All the clutches in front, all the gears in back. Nothing in the case that needs special tools to remove. And basically bullet-proof to begin with.

For ****'s sake, do NOT buy a mass-market "performance" transmission from Summit, Jegs, Monster, B&M, TCI, etc. They're overpriced by 50%.

 

[Erik the Awful]

I broke my seal installation tool the other day and made a new one today. 1/4" copper tubing and .032" safety wire, crimped in a vise. Easy cheap tool, and necessary when your lip seals face away from you.

Here's a pic of me using the old tool last week.
View media item 32714

 

[tardisguy]

Found out this evening that my uncle has the original TH400 that was in the truck. He had it swapped because it would not shift until high RPM. He didn't have time to fool with it at that time (no truck, no income) so he had another one built and put in. I have read that a bad vacuum modulator or bad vacuum source could cause that. Thinking I might check the function of the modulator and put that one in and see what it does. Worst case is it still doesn't shift right so I will pull and rebuild that one. Only issue it had was the high RPM upshifts. Thoughts?

I have done a fair amount of research from a number of vendors for a rebuilt unit and I am not impressed. Lots of TH400's but just a few are the correct HD units the truck came with & needs. Leaning real hard toward rebuilding it myself.

PS: truck is at my property in the country so I only get to go work on it 1-2 times a week for a few hours at a time. Damn HOA!

Thanks everyone for the advice so far. Stay tuned