Shifting Problems on 1997 Chevrolet Suburban 2500

When I am driving downhill the transmission slips out of gear. It usualy happens between 50 mph and 65 mph. It only happens when I am coasting or braking. Once it slips, slowing down dosen't get it back in gear but pushing on the accelerator gets it back in gear. The fluid level is full and light brown-red. I am having no problems on the flat or under a load. Any Ideas on what might be happening?

by in Salt Lake City, UT on August 07, 2009
3 answers 6 comments
ANSWER by on September 25, 2009
Hi, Were you able to find out why the transmission was behaving like this? Was there any diagnostic trouble codes stored in the transmission control module? Thanks for any feedback you can provide! bret
ANSWER by on July 13, 2010
My '99 K2500 7.4L Suburban has started doing the exact same thing that you describe. I have visited with a couple of techs who give me ridiculous perspectives that aren't worth mention here... more or less, they don't have a clue. Anyway, I keep looking for answers. Does anyone else have any ideas? Thanks.
COMMENT by on January 22, 2011
I also have a 99 k2500 7.4 Burban with the 4L80E transmission and it has the same problem. I've been told to change fluid and filter, speed sensor on rear of transfer case and TPS. I've done all of these things and no change, still will do it but not every time. I would think that somebody would have figured this out but no answers yet. Has not thrown a trouble code to this date. Keeps on going so far and haven't noticed any abnormal operation or hard shifting. Has 172994 miles on it now. Let me know if anyone finds a solution I would greatly appreciate it. I will keep searching and let you know if I find any answers.
COMMENT by on January 22, 2011
I did find and fix the shifting problem I was having, here are the details. The problem was actually in the transfer case not in the transmission itself. The transfer case was low on fluid which i belive caused excessive wear to the shift pads on the range and mode forks. I found that if I shifted into low range that the slipping problem went away. (As the problem progressed it was happening at low speeds as well as at high speeds.) This helped point me in the direction of the range fork in the transfercase. I removed the transfercase and sure enough the pads on the range fork were completely gone. This allowed the fork to actually move out of position and "slip" when a reverse force was applied either by coasting or by shifting into reverse. The high pitch grinding noise I was hearing when it slipped was the fork rubbing on the slider gear as it was moved out of position by the reverse force. The fork fingers were almost completely worn away so it was nessecary to replace the entire fork assembly. The pads on the mode fork were worn but still intact. I replaced all the pads and the range fork assembly. I could see no other wear in the transfercase so i cleaned and put it all back together. I did all this in January of 2010 and have been driving it each day since then with no problems at all. I couldn't be happier with the results. I hope this helps you in your search for awnsers. let me know if you have any further questions. Spicy
COMMENT by on February 05, 2011
Thank You. That makes sense! Shortly after buying my burban, about a month I was checking fluids and found my transfer case completely empty. I filled with fluid to proper level and about 2 weeks later was driving from Denver to California through the Rocky Mountains and that's when I first noticed the slipping problem while coming down a steep grade. I really appreciate the tip and will pull the transfer case this weekend. Was wondering though, When adding fluid to transfer case I found every housing bolt on case loose, some of the bolts on the top I was able to turn out with my fingers, did you have this problem also? Possibly caused by the slipping and no fluid? Thank you this is the only answer to this problem I have been able to find. TAVEN16
COMMENT by on February 05, 2011
I'm glad the info was helpful. I didn't have any loose bolts on my case. I didn't have any noticeable leaks at all, I am not sure where my fluid went. Good luck with pulling the case you may find some debris of the worn out shift pads inside. I hope that is all you find. Let me know how it all turns out. Spicy
COMMENT by on February 09, 2011
Did not get to pull transfer case this last weekend, weather here in Denver has been awful. Going to pull it on Saturday and open up, weather is going to be in 50 degree range and clear. Heat wave!!!! Will let you know what I find. Any recommendations on a rebuild kit? Thanks again. TAVEN16
COMMENT by on February 15, 2011
I got my seals, shift pads and range fork from Six States Distributors in SLC Utah. They beat the dealer by quite a bit. I didn't need bearings or a chain. Good Luck! Spicy
ANSWER by on May 15, 2015
My truck is pulling I put transmission fluid in it and I don't see a difference
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