1992 MGM Tranny Downshift Problem
 

I acquired a 1992 MGM recently. It has the AOD-E tranny. It works fine except for one problem. When I manually shift from overdrive "D" to standard "D" at highway speeds, there is a very harsh, loud, and severe jolt when it downshifts. If I do a "forced" downshift using the gas pedal, it downshifts fine. Therefore, when I need to downshift, I do a forced downshift followed by the manual downshift. Any ideas what is going on?

the transmission engages and THEN then engine catches up. this will tend to jolt the car a bit. if you rev the engine while doing the shift, it should lessen the blow. It's just the nature of the beast.

I assume by "rev the engine" you mean to have the engine under load during the manual shift from overdrive "D" to standard "D" so the engine doesn't have to "catch up" as much? The more the engine is under load, the worse the jolt is. Under engine load, the jolt almost locks up the rear wheels (or at least it feels like it). I doubt the tranny, or something else in the drive train, will withstand very much of it before something breaks and is left in pieces in the road.

hmm... sounds like your jolt is more than what I was imagining. when you goose it and it downshifts, it does so smoothly. But if you downshift on the column it kicks like a mule.

now that I think about it, it could be the transmission cable grommet on the throttle body as well as linkage adjustment out just a bit.

for the grommet issue, check out this site.

if you still have the stock grommet or the cable has fallen off, you will need to replace it to avoid major transmission issues.

also check the level of the fluid to make sure it's ok. To do this, leave the car running after it's warmed up, put it in park and pull the transmission dipstick out to make sure the level is correct. also check the color and smell of the fluid. it should not smell burnt. it should also be a nice red color. if it is amber or black, there's something wrong with the transmission and it should be checked internally.

It sounds like something is amiss in the trans. I would lay off manually downshifting if it as violent as you say. Just let it kick down to drive by by mashing the gas.

What about other manual downshifts? 3rd to 2nd or 2nd to 1st?

Good idea for the AOD tranny, however, I have the AOD-E. It doesn't use the throttle body linkage. The fluid is OK.

I am doing as you say, manually downshifting after the kick down. Works fine that way to hold the transmission in the lower gear. As can be imagined, it can be a pain to need to goose it to downshift when going down a hill.

All other manual downshifts work fine.

sounds like it's probably the overdrive solenoid being an issue. there are upgraded solenoids to be had. If it comes down to rebuilding the trans and that solenoid is singled out as an issue, ask for a beefier solenoid. This may require upgrading the overdrive bands as well, which would cost more, but you'll get better life out of it. Something to think about.