Transmission Torment

[Jones]

Jones
94 Explorer XLT

My A4LD is giving me fits. It will not upshift correctly in any gear except OD, and vacuum downshifts into too low a gear for added redline entertainment. I thought it was the speed governer as these are apparently problematic, and I decided to ignore the fact that everyone says the governer controls only first to second shift and maybe OD, and second to third is by far my worst shift and OD my only good one. I took down the tranfer case (which had a bad seal and almost no fluid) and the governer was stuck, had burrs on it, and that part of the case had a lot of pretty good sized grit in it. Well, that's that I thought, and after doing the neccessary and changing the tranny fluid and filter and so on, I happily bolted it back together and patted myself on the back for a job well done.
Until the test drive, when the problem persisted, a little worse if anything, but with all the gears locking up great, and pulling better than ever. Every gear seems as strong as could be. So I wonder if this is a blockage somewhere in the valve body of the tranny, and if that means a soft rebuild, or if there is any possible way (Oh please, oh please) that the vacum solenoid could somehow be communicating an excess of vacuum by being stuck, thereby causing the truck to think it is accelerating hard. In order to get it to shift, you have to run the revs up to around 4300 and slowly, gently ease back on the throttle until it gears in, then even more slowly and gently come back onto it to accelerate up. About two times out of three at this point it drops back into the lower gear, and i throw something out of the window. If anyone has any ideas i would be grateful in the extreme.

Thanks In Advance,

Jones

 

[MrShorty]

So, if I understand correctly, it is acting like it wants shift like it is at WOT rather than part throttle, is that right? Is the vacuum line from the vacuum modulator to the intake intact? That kind of behavior could easily be explained by a vacuum leak, plugged vacuum line, or disconnected vacuum line.

 

[Jones]

Thanks for the note back. I think that it will only shift at high motor rpms because of the speed that the rpms represent. What i mean is that i get to 45 miles an hour or so, then back off the throttle, so the rpms drop but the speed stays high, and the low rpms and high speed sort of meanders into the next gear. I checked the vacuum line to the tranny. The short link between the tubing and the valve nipple might be a little stretched, but the leakage, if any, would be pretty negligible. Could that small a leak cause such dramatic problems? I guess I should replace that anyhow. Does it happen that the vacuum modulator gets stuck? Is there a way to check without taking it out?
In looking at other posts about this sort of problem, it seems often to be the valve body. I worry that with the grit that was in the case, it will be the case here, but i really want it to be a vacuum problem.

 

[Glacier991]

In order I'd investigate the vacuum modulator for a) vacuum from the engine; b) a torn diaphragm. (all easy things to check, look for fluid in the line for b).) Next I might pull the vacuum modulator and make sure the throttle valve moves easily (don't lose the little pin!). Failing anything there, I'd pull and rebuild the valve body.

 

[Jones]

Glacier,

Thanks for the info. I'll have to wait a few days to put your suggestions into effect, but am looking forward to doing so. I didn't see any fluid in the lines when I looked the first time, but didn't know to look for same so i may not have noticed. I'm afraid though, that it is the valve body after all. If it were vacuum related, would the trans downshift into a gear so low that the motor couldn't or wouldn't engage the clutches? Anyhow, thanks as always for the excellent and thoughtful advice.

Jones