Intermittent trans shift prob related to brakes?

cdre · September 4, 2006

I have an intermittent shift prob on my ’95 2500 4x4 6.5L w/4L80. Usually when putting the trans into Drive, the truck will feel like it is slipping in 1st gear. Slide the shifter down to 2, and it engages in 1st gear fine with a solid shift to 2nd. Shift to D from there and the remaining shifts usually occur fine. Sometimes the shift from 2 to 3 requires the same manual shift, but more often than not it works fine on its own.

Occasionally it will take off in D fine. Seems like it might be associated with the trans being warm and placed in P with engine still running, but I am not absolutely sure.

Ran the diagnostics and all that popped was a code 41, indicating brake problems (correct as the ABS light is on). SES light is not otherwise on. One thing worth mentioning is that the light just automatically started flashing an un-ending 41 without the 12 beginning and ending indicated in the directions I have read.

I was originally thinking solenoids due to the intermittent nature of the problem, but now I am not so sure. I recall reading about wire harness issues before… could that be a problem here as well? Since I get a solid engagement and shift from 1st to 2nd when placed in 2, I want to rule out worn bands, but not being a trans expert, I cant be sure.

Someone suggested it might be a brake switch issue. I will check the operation of the brake switch, but from what I have read, that is usually associated with TCC problems.

Any suggestions? Thanks!

cdre · September 5, 2006

Looked at the documentation explaining brake switch problems, and it seemed to confirm that it only impacts the TCC lockup. Any ideas?

mmmikkke · September 6, 2006

Could be a plugged filter or failing hydraulic pump. "2" range raises the fluid pressure.

If you have a marginal pressure situation for some reason, like maybe a plugged filter, you could overcome the otherwise lazy 1-2 shift by raising the fluid pressure.

If you haven't done it yet, I'd change the filter and see what happens.

cdre · September 8, 2006

Any ideas GM Tech?

GM-Tech · September 8, 2006

Any ideas GM Tech?

<{POST_SNAPBACK}>

Nope, I'm not a tranny guy. But I can tell you with confidence that the brake switch has absolutely nothing to do with your problem.

cdre · September 9, 2006

Thanks for the reply. That definitely eliminates one potential cause. I think I am going to put in a set of solenoids and the Transgo kit and see how it goes...