No Reverse 4L80

[Rschap]

This time last year I rebuilt my 4L80 and now reverse isn't working, when I manually drop into 2nd on downhills it also doesn't work though manual 3rd works fine. Works great going forward in drive and it appears to work fine manually shifting through the gear except for the downhill downshifting. I did replace the intermediate and reverse bands and the 1-2 accumulator piston when I rebuilt it. I've only put around 12k miles on it and everything seemed fine until about a week before it went out, reverse didn't seem as though it was engaging right away and seemed to take longer than normal to move the vehicle until it gave out completely. There was no sound, it just stopped working while I was backing my trailer in to park. Any thoughts on what it might be before I start to tear into it? Any help would be appreciated.

1999 K3500 Classic

 

[JOHNGAAA1]

Any codes???

 

[someotherguy]

This time last year I rebuilt my 4L80 and now reverse isn't working, when I manually drop into 2nd on downhills it also doesn't work though manual 3rd works fine. Works great going forward in drive and it appears to work fine manually shifting through the gear except for the downhill downshifting. I did replace the intermediate and reverse bands and the 1-2 accumulator piston when I rebuilt it. I've only put around 12k miles on it and everything seemed fine until about a week before it went out, reverse didn't seem as though it was engaging right away and seemed to take longer than normal to move the vehicle until it gave out completely. There was no sound, it just stopped working while I was backing my trailer in to park. Any thoughts on what it might be before I start to tear into it? Any help would be appreciated.

1999 K3500 Classic

If you built your 4L80E you already know 1,000x more than I do about them as I've never built a transmission. However, I do know that reverse failure is one of the 4L80E's few weak links, so there's tons of information out there about it. A quick search turned up an interesting link from a trustworthy source, maybe it will be helpful? https://www.sonnax.com/tech_resources/88-diagnosing-the-elusive-no-reverse-with-the-4l80-e - if not, there's a bunch more out there to read.

Richard

 

[454cid]

I believe reverse and 3rd use the same clutches..... I just watched a Youtube video on that the other day. It was a case of a cooler line coming off, and the guy smoked a 300 mile rebuild. I'm guessing that info may not do you any good since you rebuilt the transmission yourself.

I've read, and I don't know that it's true, that downshifting on a hill is not good for the 4L80e. I have no idea why. I stopped doing it.

At a previous job, we had a work van (350/4L80e 3500) that would often not want to reverse, and it was some sort of seal under the valve body, I think. I was in charge of getting it looked at, and fixed, but don't recall what the shop told me exactly since it's been several years. I do remember that the shop said shifting between reverse/drive without braking will cause it. The man that then drove the van daily, said it's previous driver did that ALL the time.

Sorry, I'm no real help. Transmissions are mystery boxes to me.

 

[tayto]

do you have engine braking in manual low/1st? did you check/measure the low/reverse servo pin?

 

[Rschap]

Thank you for the responses, I've been working so much I haven't been able to even think about this. I hope to be able to get back to it in a couple of weeks.