2001 GMC 2500 Not Going Into Reverse

Duane WI · Sep 27, 2019

My 2001 GMC 2500 with the 4L80E transmission won't go into reverse after it sits for a few weeks. This doesn't happen all of the time. If I put it in drive and then back into reverse it works fine. It only seems to do it after it has sat for a few weeks. Any ideas what to look for?

Sprint 6 · Sep 27, 2019

Converter drain back most likely, try starting it in neutral and letting it run for a second. Filter may also be getting restricted, slowing fluid flow, but that should affect drive also. It is not an electrical issue, reverse is all hydraulically controlled on a 4L80E, it will have reverse and direct forward even when unplugged.

miangus · Sep 27, 2019

Does it show a code. That system checks for voltage before shifting. My 2004 showed shift range inhibited and would not shift into reverse. Let it idle for a minute and then it would shift. Changed ignition switch and all fine.

Sprint 6 · Sep 27, 2019

Your truck must have an Allison. Allison has to be told what to do for any gears, forward or reverse. Totally different animal than a 4L80E.

Duane WI · Sep 27, 2019

No codes. It just won?t go in reverse. Go to drive and it moves forward against the brakes. Back to reverse and it moves backwards. If I drive it regularly it doesn?t happen. Only after it sits a few weeks. It has happened maybe five times in the past year. It is for sure a 4L80E.

4play · Sep 27, 2019

It's just a guess but I bet the rear band (low/reverse) is probably worn and the servo pin can't apply enough pressure for the band to hold. I bet if you shift to manual 1st gear you probably won't have engine braking when you decel. There is also the chance that the servo piston could be broken too. Either of these are an easy fix after the pan is dropped and servo cover removed.

If you are able to drop the pan and filter, the servo is just another 5 bolts. It is the big can shaped cover in the rear or behind the valve body. Often times you can buy a longer pin ( try ebay) or weld 1/8" tab on the end for extra length, you can chuck pin in drill and shape it on a grinder to match pin size. If none of this sounds good to you, take it to a trans shop and lube up.

Duane WI · Sep 28, 2019

I found a You tube video saying the same thing about building up the length of the pin with a
welder. I have replaced the solenoid plate in the 4l60e so I have an idea how to do this. I will try
the first gear hold back test. Thanks.

NEKS · Sep 28, 2019

Have a 92 Chev 3500 with same tranmission acting about like your. First it started like the brakes were on when put it in low range. Could drive it in other ranges. Then it lost reverse, but have low range again?????

2001 GMC 2500 Not Going Into Reverse

Duane WI

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Sprint 6

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miangus

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Sprint 6

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Duane WI

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4play

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Duane WI

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NEKS

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