Missing overdrive

[techieman33]

On a couple of occasions in the past couple of weeks, the transmission has failed to shift into overdrive while getting onto the interstate. It normally shifts around 3000rpm, but those times it didn't the rpms just kept climbing, once it jumped to over 5500, which scared the crap out of me. And both times if I would let off the gas for a minute and coasted, then got back up to speed then it would shift like normal. Any ideas what could be causing this?

 

[IZwack]

Is the "O/D OFF" light coming on or blinking?

5500 is a tad high (I'm assuming you werent flooring it) but also, engine RMPs are usually a bit higher when the engine is first warming up.

 

['92Bauer]

I think he has a 1991 so no overdrive light.

 

[IZwack]

[QUOTE='92Bauer]I think he has a 1991 so no overdrive light.[/QUOTE]

Oh ... well i guess the first step is to get the computer read for codes then.

 

[TheJMan]

Oh ... well i guess the first step is to get the computer read for codes then.

I thought the first gen trannies were vacuum controlled, not computer controlled.

 

[techieman33]

Yeah, no overdrive light, I select overdrive by the shifter. And i'm not sure if the tranny is computer controlled or not, but I have pulled the codes and didn't pull anything up.

 

[IZwack]

I thought the first gen trannies were vacuum controlled, not computer controlled.

Amazing

 

[Brian_B]

My A4LD had a modulator valve for the shifting, but the lockup converter and OD soleniods were both computer controlled. I would check the mod valve first thing. Pull the hose off and see if its damp inside. If it is, there is your problem. A $15 fix. Also check the fluid level with it hot. That can be a culprit with weird shifting as well.

 

[techieman33]

Where is the modulator valve, i'm at school right now, and don't have my haynes with me.

 

[Brian_B]

If you do have the A4LD, its on the passenger side above the pan. Hard to see, but you can feel it (careful of the exhaust). Just pull the vacuum hose off it and look at the hose. Its a round thing that sticks out and has a rubber hose going to it, if that tells you anything.

If that turns out to be the problem (hope it is) there is one bolt holding it in. Just don't lose/drop the little pin thats behind it. It won't work without it.

 

[techieman33]

ok thanks, i'll have to go check that out tomorrow when it's light out.