98 Blazer Transmission Problem

[darek1211]

Hi. The transmission seem to try to downshilt when driving at a constant speed on a gradual incline between 45mph and 60mph. This happens constantly unless I accelerate or slow down. The RPMs go up by 200 and go down again and it feels as if I hit a bump on the road when this happens. Any help is greatly appreciated.

[DelCoch]

Has the transmission fluid & filter been changed in the last 30K? That's where I would start. It worked on mine.

[MT-2500]

Welcome to AF.
As said filter and fluid level check first.

A 200 RPM change sounds like TCC lock up kicking in and out.

May be wiring or plugin or brake light switch or even engine running problem.
Any check engine lights or codes stored or present or history?
Spedometer working good?

A good engine transmission scanner may show the problem.
MT

[darek1211]

Thanks for the information.
I think it is the TCC problem...as I had the transmission rebuilt two years ago.
It worked fine for over a year and then it started happening. Any guesses on how mych TCC replacement would cost?

[MT-2500]

First thing is to find out what part is bad.
I would start with checking for codes and wiring.
Could even be a engine runnig problem.
Post back any codes.
MT

[aleekat]

Originally Posted by DelCoch

Has the transmission fluid & filter been changed in the last 30K? That's where I would start. It worked on mine.

Ditto. Just had the same symptoms, and did the change.

[peterjon1]

Except for the hitting a bump part, it could also be surging from a vacuum leak. My '94 was doing something similar, found a crack in the main vacuum hose at the manifold.
Edit: Ok took mine on the highway today. I can see where the lean mixture surge would feel like hitting a bump on the highway. Kind of a RPM up and down feeling.
Had myself convinced it was a lockup problem until I found the vac leak, now all is well.