A4LD Downshifting Constantly

[dcpppf]

Been searching the forums with no solid luck so thought I'd try a new one.

The A4LD in my 88 2.9L is not wanting to stay in third. If I modestly accelerate and hold throttle steady it'll upshift and then immediately shift back down. And it'll do that every few hundred rpm until I let off. After I do let off it'll shift up and hold fine, but the second I get back on the gas it shifts back down again.

No t fluid in the vacuum line to the modulator and the modulator is holding vacuum. Fluid level is good. I'm planning to flush fluid and replace the modulator this weekend just to check those off but I'm hoping others can throw out some other ideas.

Thanks in advance!

Also, hello! new to the forum lol. I inherited my grandpas 88' XLT 4x4 a few years back. Truck has been great, replaced the water pump prematurely b/c i didn't realize this thing just runs hot. Great little truck (brown/tan), has some rust which sucks, leaking power steering fluid slowly but surely, 130k miles.... and some ass hat at work just backed in to it a few weeks back.

 

[Dirtman]

I would actually test engine vacuum and the line from the modulator to the intake. A leak in the line, port, or just generally poor engine vacuum will trick the modulator into thinking the engine is under more load than it actually is and want to command a downshift.

 

[adsm08]

First thing to check is to pull the line off the modulator and see if it is full of trans fluid.

 

[dcpppf]

So there was no trans fluid in the line when I pulled it off the modulator, and i was unable to suck any through when i put a hose on the modulator port and pulled my own vacuum so the diaphram is good.

I was going to add pulling the line from the engine side and testing the line itself for leaks to the list so this confirms i need to do that lol. Will check that in the coming days.

The frustrating part about this is that this was after I let a buddy borrow the truck for about a week. It had never had any issues and now that I got it back he's telling me it did it ever since he had it... So it wasn't a gradual thing. not sure if a lead foot could cause something to break internal to the trans and cause this or if it really was just coincidental timing. Thanks for the initial thoughts guys.

 

[dcpppf]

Line itself holds pressure. And when I started the truck the vacuum port up on the block was reading 20inHg. I drove the truck with that vacuum port plugged and it didn't slip or act funky at all it just did not down shift whatsoever. Only time the rpms would drop is if I fully let off the gas and it dropped to idle speed. There was no middle.

Can anyone explain to me what all the computer uses to determine when to down shift? I can't get my mind away from thinking this is some form of modulator/sensor issue and not the trans itself.

 

[dcpppf]

Bump... Getting the vacuum modulator this weekend. Just curious if anyone else has thoughts on things to try before pulling the entire trans.

 

[dcpppf]

still looking for any insight lol. got the new modulator in and now it is acting the same as it did when I had the vacuum line disconnected entirely and when in D or OD it just stays in 1st gear the entire time. I adjusted the new modulator out (CCW) quite a bit and never made an impact whatsoever. Planning to put the old one back in to see if the problem returns or not. I didn't realize the old one was adjustable as well so if I put it in and problem returns I will try adjusting it slightly to see if anything changes.

 

[dcpppf]

... Dropped the pan, plenty of glitter and small bits of what looks like paper. grabbing a M5od this weekend.