OD Transmission

[johnw1944]

I have a 2004 chevy Tahoe 4x4. I need to know what should the RPMS be at 70 Mph. My Tahoe tacks 2300 Rpms at 70. Is this correct or is my overdrive not working>

[777stickman]

To tell you if the RPM's vs Speed is correct would need a whole lot more info from you.

Here's an easy way to tell if your OD (aka Torque Converter Lockup) is working.

At cruising speed, add some throttle, not enough to down shift, just enough to maybe get from 60 to 70. Watch the tach!! If you get an immediate 200-300 jump in rpm's, the TCC is not locked up.

If the rpm's steadily increase with MPH then the TCC is locked and OD is working.

Hope this helps and welcome to AF.

[maxwedge]

To add if the o/d wasn't was inop. it would set a code so the cel would be on.

[Blue Bowtie]

3.73 axles? 3.42 axles? 3.08 axles? It all make a difference in final drive and RPM at speed.

What tires?

I won't ask it that's in 4HI or 4LO, but you get the idea.

[j cAT]

Originally Posted by johnw1944

I have a 2004 chevy Tahoe 4x4. I need to know what should the RPMS be at 70 Mph. My Tahoe tacks 2300 Rpms at 70. Is this correct or is my overdrive not working>

my 2000 silverado 4x4 3.73 rear diff RPM is about 2K..@70MPH.. 2300 is too high IMO..... I think your running in 3rd . when I tow my 4K LBS boat I run in 3rd @ 2300 RPM @ 70 MPH ... normally I tow @65 MPH.. with the 4 speed tranny my vehicle shifts into 4th at 35-38 MPH.... my 96 impala shifts also at 38 MPH... 2004 GM used DEXRON III this fluid is no longer an approved GM fluid because it put GM into bankruptcy . If you never changed to the GM approved dexron VI then it is very possible the valve bodies are eaten away from the dexron III fluid turning to an acid metal eating mess. DEXRON III is only good in a tranny for 20K miles then the acid begins .. gm dumped this fluid in 2006 !