Overdrive not working ??

[dhartles]

I think the overdrive gear on my 99' Silverado 4.8L has gone out. It doesn't fell like it shifts into OD anymore. She runs ~2300 RPM now at 60MPH (I thought she used to run under 2000RPM at 60MPH). While I'm at 60MPH I can manually shift back and forth between 3rd and OD, and can't feel any change. Do you think the OD gear has gone in the tranny, or could there be another issue?

TIA,
Dave

[2000CAYukon]

I would think it is more of a valve body issue. Take a look at this http://www.transmissionspecialty.com...77964-01K.htm#

OD is achieved with the 3/4 clutches and the 2-4 band applying pressure to the planatary gears. I would look at the valve body issue in the link above or the 4th apply piston (applies pressure to the 2-4 band). If the band was bad, 2nd would also be gone.

Both of these can be done without removing the tranny from the truck.

//2000CAYukon

[dhartles]

Thx 2000,

The Sonnax description of the problem sounds exactly like what I've got. I'm gonna give replacing the valve a try.

Thanks,
Dave