TH400 Advice

I'm just picking up a 1986 Scottsdale from a friend today, it's a 2WD and it doesn't move any more... He told me I could have it, if I'd get it out of his driveway, so I'm having it towed back to my garage in a couple hours. I have ridden in it a few times, and noticed it was always very loud and high RPMs off the line, sounded like a race car, but accelerated slowly, although the transmission seemed fine, it never had any trouble shifting that I could tell. He drove it home from work one night with no problems, and the next morning when he started it up, he backed out of his driveway, put it in drive, and nothing, the engine just revved up. He said he put the shifter in 2 and stomped it hard, and it crept forward slowly, then back in reverse and it wouldn't go backward at all any more. So he put it back in 2, forced it around the block, and back into his driveway. At that point he said he heard fluid bubbling like it was boiling.

I don't know a lot about automatic transmissions, but from what little I know, I am suspicious of the torque converter being completely toast. If it is the whole tranny, my girlfriend's father said he could help me rebuild it, and I have found nice full overhaul kits on ebay for around $150 and I could throw a shift kit on at the same time, but there are a few people around town selling rebuilts for around the $300 range, listed as off of 2WD vehicles, that would be a lot easier.

I am looking for advice from those experienced with this tranny, or similar ones, if I should replace the whole thing, or just the converter, and if I do replace the tranny, what should I look for in a replacement? I have heard I need to get later year TH400's because of a change that was made since the really old ones, and I need to make sure to get one from a 2WD because of the drive shaft length, but do I have to worry about the number of splines being different among these transmissions, and is there anything else I should look out for?

Usually one needs to replace/rebuild the entire transmission and converter. These components obviously share fluid. So, any failure in one component, such as a bearing or gear set, tends to pump metal particles throughout the transmission, affecting many components.

It is possible that your transmission has been neglected and has a clogged fluid filter. A clogged filter would prevent the fluid from being sucked up in sufficient quantity to provide sufficient hydraulic pressure to engage the clutches fully. So the clutches slip, causing the high revving. Unfortunately, it does not take much slipping to completely ruin the clutches, so yours may already be done.

Another possible source for the problem is a bad oil pump. When these go, they can be noisy, as you describe.

So, it's best to get a replacement/rebuilt transmission and converter. If you simply get a used one, its important to remove the pan, clean it out and replace the filter. Make sure the pan magnet is in place, inside the pan. The problem with a used one is that most of these transmissions are getting pretty old and, unless rebuild, they may not have too much life left.

Rebuilding your own transmission with a kit is not such a good idea. These things are very complicated inside. One needs a rebuild manual (Haynes makes one for GM autos) a clean place to work and LOTS of patience and time to rebuild one for the first time.
$300 rebuilds sounds pretty a little too cheap to me...... I wonder what they are not doing to get the price so low.

Another point...... what are you using the truck for? If its for heavy hauling or towing the 400 trans is great. But if you are doing lots of highway driving it might be better to get a post-1987 THM 700 trans with an overdrive.

I do plan on doing a lot of highway driving. Mostly, it's just for driving around the corner to work and back, but I have to drive my girlfriend to visit family 45 miles away at least once a month.

I considered picking up a 700-R4, there are several of the 2WD versions around here on craigslist, cheap and easy. One for only $350 because someone had picked it up not knowing they needed a different version for a 4x4. What worries me about this swap, is that I have read so many sites talking about swapping 350s, 400s, 700-R4s, and 2004Rs all in the same article that it's hard to keep track of which tranny needs what. I gather that if I go from the TH400 to the TH700-R4 that I need to move the crossmember, and then shorten the driveshaft. I'm not really sure how to go about shortening the driveshaft. I think I would also need some sort of kit for the converter lockup. I've seen those around. But do I need a different torque converter and do I need to worry about spline count? Any different linkage for the carb, speedo, etc? Is this a swap that requires something special for mounting the new transmission to the old crossmember? I'm trying to get this thing running again for around $1000, or hopefully less.

I did just get the truck home and garaged. It still runs, goes in gear, but gets up in the 4000 RPM range before it starts creeping. At idle speeds there's just nothing, at high RPM's it makes grinding sounds, smokes, and sprays tranny fluid all the way up to the front bumper, and this stuff is a very dark rust color. My buddy first thought it was engine oil, until i spread some on my finger and found it to be a very dark but obvious red.

Sounds like the torque converter is shot, probably even leaking fluid. Pull the access cover off and see if the torque converter is leaking.

On the age of the trans, If I were going to pull it out, I'd rebuild it for sure and not just throw in a new converter.