Downshifting problems

[Clydesvx]

I've just developed a downshifting problem. I recently had Timing belts etc. changed which included spark plugs etc. Since then whenever I'm in cruise control and come to a slight grade my tranny slips into 3rd. I know it's 3rd because if I downshift into 3 the RPMs stay the same. When I looked in the manual I noticed most of the sensors connect to the transmission. It also mentions a vacuum line. Could a broken/leaking vacuum line or a bad sensor cause this problem, or is it just time to start looking for a transmission shop?

[nvrmore100]

Slipping to 3rd would make sense. If the vehicle can not make it up the grade at the current RPM, it will down**** out of overdrive (4th) to 3rd, 2nd or even 1st if necessary. That is how cruise works, hence it let's you cruise.

Maybe I'm not understanding the question.

Ryan

[Clydesvx]

downshifts occur in areas I didn't downshift before the work mentioned in my previous message. Even some slight grades cause a downshift where none was expected or encountered before.

[nvrmore100]

Well from what I know about cruise (which believe me isn't much), yes it works off a vacuum line. I believe the more vacuum, the more its ability to stay at RPM. However to much load and the vacuum decreases and thus it shifts. Someone PLEASE correct me if I'm wrong about this!

If this is the case, it may be possibly that you have a leaky hose. A loss in vacuum from the leak would cause this phenomenon. I honestly have no idea where this line is, but it shouldn't be to hard to check out.

Good luck,
Ryan

[Aredubjay]

Originally posted by Clydesvx
I've just developed a downshifting problem. I recently had Timing belts etc. changed which included spark plugs etc. Since then whenever I'm in cruise control and come to a slight grade my tranny slips into 3rd. I know it's 3rd because if I downshift into 3 the RPMs stay the same. When I looked in the manual I noticed most of the sensors connect to the transmission. It also mentions a vacuum line. Could a broken/leaking vacuum line or a bad sensor cause this problem, or is it just time to start looking for a transmission shop?

This happened to me when I got my first tranny re-built (the legacy). It was acting, essentially, like I had the manual button in (when in manual, the tranny will downshift on lesser up-grades to prevent wheel slippage). If the battery was disconnected during your service, your TCU may simply be trying to "re-learn" your habits. I don't think you need to look for a tranny shop if you're actually "downshifting" only if the revs "flare" on the upshift. The "downshift" gremlin left after I had the "real" SVX tranny installed.