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4L80E Disengages when coasting Will Mayberry 4-14-08  
Howdy! I have a 1998 Chevy Suburban 2500 4x4 w/ 6.5L TurboDiesel. It currently has 205,000 miles. We bought it in 2001 w/ 65K miles and have had no tranny problems until recently. This includes three coast-to-coast trips towing a 26ft travel trailer.

On a trip a few months ago, as we came over the top of the mountain and started down the backside, the transmission disengaged (tach dropped to about 500rpm) and tranny started to make a grinding noise. At the same time, gravity started to take over and accelerate us downhill. It scared the heck out of us. I pumped the gas pedal and got the rpms up a bit, and it re-engages until the I try to coast again.

Now it does it anytime I try to coast down hill (in gear with or without a trailer) or coast on the flats (towing a trailer, in gear).

Last week, I was driving without a trailer and using cruise control on when I crested a small hill. The transmission disengaged, and the RPM tookoff up above engine redline before I could disengage the cruise control. Once the RPM's came down and I pressed down slowly on the gas pedal, the tranny re-engaged.

Any ideas?

Thanks, Will
Re: 4L80E Disengages when coasting Mr. Lt1 7-21-08  
When you tow do you have the od off? and you need to replace the tcc solenoid, if this still does not work have your pcm reflashed at the dealership for about $50 and you should be good. Hope this helps
Re: 4L80E Disengages when coasting terry 8-18-08  
I have a 1992 gmc 3500 hd trans would not shift into od. took to trans shop they said trans was bad it needed a rebuild. they rebuilt it and still same problem no overdrive. whats wrong??? now its at the dealer.
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