Allison tranny

[Brave Willy]

2004 Brave 8.1 engine 50000 km on engine and trans
When driving with RPM at 2100 the engine will rev to 2300 for a few seconds and than back to 2100.  Not on level ground but on s slight grade    Is the trans slipping or is this an electronic shift problem

 

[PJ Stough]

My first thought is that the transmission is "hunting" a gear.

 

[Brave Willy]

Yes that is what it?s like not really slipping does anyone know what the problem or fix is ?

 

[PJ Stough]

If you have "overdrive", shut it off until the engine is able to maintain at least 2500 rpms would be what I would do.

 

[grashley]

Don't drive on slight grades!  ;D 

 

[JtC-5TH]

Don't drive on slight grades!  ;D 

Kick a brother while he?s down. Haha

 

[Arch Hoagland]

Either it dropping out of overdrive or the torque converter is unlocking.  Not a problem, mine does it all the time. 

Have you switched to Transynd fluid yet?  When was the last time you changed your transmission fluid and spin on filter?

 

[garyb1st]

Ours does the same thing.  Not a huge difference between 4th an 5th gears on mine so I'll take it out of OD when in the hills. 

 

[Gary RV_Wizard]

Agree with all the comments above. The tranny is self-adjusting for the load, trying to find the best combination of power and economy.  On slight grades or if you are varying the throttle, it may react frequently with small changes, e.g. torque converter lock/unlock, and shifts between 4th & 5th (5th and 6th on later 6-speed models). Shifts between the two overdrive gears are almost imperceptible unless you watch the tach rpms.

 

[AStravelers]

2004 Brave 8.1 engine 50000 km on engine and trans
When driving with RPM at 2100 the engine will rev to 2300 for a few seconds and than back to 2100.  Not on level ground but on s slight grade    Is the trans slipping or is this an electronic shift problem

Is this while you are using cruise control, or driving with your foot on the accelerator? 

How long is a few seconds?  2-3 seconds or 15-30 seconds?

If your foot is on the accelerator, are you backing off the accelerator slightly?  Next time press down slightly on the accelerator to see if the RPM's will stay up and feel like normal driving.  If this is the case the transmission is just dropping out of overdrive. 

I know the Ford V-10 frequently down shifts going up hills and highway overpasses.  But my RPM's from 2200 to close to 3000.  But the Ford is a higher reving engine and the Chevy is lower reving and probably more torque at lower RPM's. 

 

[Brave Willy]

Only 2-3 seconds and only on very slight grades almost flat

 

[AStravelers]

Only 2-3 seconds and only on very slight grades almost flat

That quickly, I wouldn't think the transmission would shift down and back up. 

Have you checked the fluid level in the transmission?  Also look at the color of the fluid.  It should be pretty red.  If it is really dark you are in dire need of a fluid change and may indicate transmission problems.  If you have a question about the color, buy a quart in Walmart and compare the new fluid to what you have.