I have a TH400 in my 89 Wrangler. Just today, it started clunking when going from drive to reverse. It does not clunk going from park to to reverse, only from drive to reverse. It shifts fine, and the reverse works fine, just seems to really be slamming into reverse. Any ideas. This tranny only has about 2000, miles on it.

I could very well be wrong on this, but I had a TH350 that did the same thing. Before jumping to ay conclusions you may wanna check a few things first. Check the fluid level on a flat surface once it has warmed up a bit. You may also want to notate the color of the fluid and if you see any shiny specks or flakes in it. One question for you though, when you are shifting from "D" to "R" are you at a complete stop or are you even slightly still rolling? The valve bodies may be very sensitive. Or maybe when the tranny was built/rebuilt they didn't do so hot of a job and stuff got in someshere it shouldn't be. What kind of warrantee did they give you with the purchase?!? IF it's still under the warrantee I take it into a couple other shops and play kinda dumb. Feel 'em out for what may be the potetial cause so when you go back to where you bought it you have a good idea if they are blowing sunshine up your rear, and I don't mean the diff on yer rig.

Good luck! :beer:

I was at a complete stop. I am wondering if my idle adjustment could have caused the clunking. It was idling a little high, but I had to stop working on it for the day, and didn't have a chance to adjust it.

I think I would look at two possibly three things. First: have someone watch the rear driveline when you take it from R to D. There may be excessive play in the drivetrain that is causing this. I had that in my 77 Blazer, it got worse the more I pounded it through the rocks. Secound: Internal slop will cause this, the only wat to test for this is to tear it down and check the splines on the inside. Third: and hopefully the cause, the tranny filter may be plugged some or have allowed some garbage past it. Valve bodies are very sensative. In this case try changing the fluid. While it is down, drop the valve body and clean it in a solvent tank that has clean fluid (or a good ol can of brake parts cleaner will do). You should be able to get a TH400 diagram from a tranny shop, you may need it to assure you get the check balls in the correct location. Don't stress, this is actually easy. If people only knew how easy trannies are to build & work on, we would put a lot of tranny shops out of business.
Greg
PS. Vasaline will hold the balls in place if needed, it's safe to use too.:D

OLDMULE ... good call for a Newbie. j/k Welcome!! :flipoff2:

BRACKNEYC ... IF you were at a stop, Oldmule has some good points. Check for driveline slop when going from "D" to "R" and vice versa. And also like I had said, check for crap in the fluid. The pan and filter will be good indicators as well as the dipstick. But if the filter is clogged like Oldmule said then you could have a real easy fix. Good Luck!

A new twist in the tranny saga. I started it up today, and it was fine..or so I thought. It seems this clunking problem only happens when the tranny is warmed to operating temperature. The guy at the shop that bult it said it was fine (surprise) and that I had the RPMs set too high. I thought 600 RPMs was adequate in this application, and told him I didn't think that was the case. It is out of warranty, and I am screwed as far as having him do anything about it. I plan to take the pan off this weekend to check the filter. Someone here said something about the pump? Is that a possibility? One shop mentioned the vacuum to the shift module? One guy said it might be toohigh, and one said it might be too low. There sure are a lot of possibilities for such a simple tranny.

On a side note, today I accelerated to about 40 mph in a somewhat quick fashion, and when I let off the gas, it made a slight clunking noise. Not as pronounced as the shifting clunk, but a clunk nonetheless. This gives me concern that the shift module may be a part of this problem. Since it is vacuum activated, maybe I am losing vacuuum when I let off the gas. I am getting my vacuum from the manifold though, and I don't notice any other problems except where the tranny is concerned.

IMHO, kinda sounds like it has been narrowed down to either vacuum issue or driveline slop. Have you checked for slop yet? Once you have ruled that out you won't have to worry about wasting time and $$$ tearing the tranny down when its fine. Checking for the slop is pretty easy. Good Luck! :beer:

I have checked for driveline slop as far as u-jonts and overall tightness goes. The curious thing here is the hot/cold thing. Why only when it is warm does it do this?