I have a 91 GMC 3500 dually 7.4. I recently had my transmission rebuilt and it ran fine for 6 to 7 months. I give it gas and it will go up to 40-45 mph and will stop accelerating like it goes in neutral. The rpms go up but the truck will not speed up and wont accelerate again until it drops down ...
When I first the post, I thought the OP was getting hosed. They didn't have electronic shift transmissions in 91! I still have a 1991 Z28, and had a 1991 GMC S-15 Jimmy (the small one) neither had electronic transmissions. I decided to look it up in the application guide, and starting in 1991 it was an option available.
I am still baffled at how a Transmission Shop Can't figure it out. I understand regular shops, for a lot of them their knowledge of the transmission stops at changing the fluid, they're just a magic box. But a transmission shop that can't work on an electronic controlled transmission in 2014 is beyond belief .
@Larry ... Yup! I agree on all accounts. The reason I deleted the comment was because I was wrong. I thought the 4L80e wasn't used until the later 90s, then as a follow-on to the 4L60e, but I was wrong. As you found out, the 4L80e was first installed in the HD trucks (and some cars with enough HP/TQ) starting in 91.
They used the 700r4 as an overdrive option until 92, then renamed it to be a 4L60, then they started using the 4L60e in 94 ... at least in the Camaros and all other cars around the same size. I was clueless about the starting time of the 4L80e.
Funny thing about the Z28 transmission, I can't keep one in it. I gave up on building them for that car about 3 transmissions ago. Even bought performance transmissions for it and it chews them up to.
@Paulster2 Trying to rack by brain on the power flow for that tranny. Should be able to narrow it down more that my answer but I can't find my overhaul manual and I can't remember because I haven't build a 400 in about 10 years
@Larry ... I never actually rebuilt a 400, but have torn a couple apart. When you get down to the mechanical side of it, there really isn't much to one. I would assume, since the 4L80e is a 400 with an overdrive, they probably aren't too much different. I had gotten to a point where I was going to start rebuilding 400's for performance builds, had bought a VCR tape (shows how long ago it was) from Darrel Young Racing Transmissions, but never had the opportunity after that to make it happen.
I figured out what the "good" parts for the 400 were, like the correct sprague (sp) unit (which years were better), etc. I found an old BOP 400 in the junk yard I tore apart for the hard parts to put into the one I had in my 68 Chevelle SS396. I sold the car before I had the chance to do the work, though.
@Paulster2 The 4L80 works a lot like the 4L60, it's just build on the 400 frame so to speak. Also google found the 4L80-E Technicians's Guide. I am reviewing it now to see if I can better narrow down the issue for the OP
@Larry ... good on yah. I hope you can help. I've got a lot of answers, just not all of them ;-) I try not to only comment on things where my knowledge is weak.
@Paulster2 I shoot from the hip sometimes and sometimes that bites me. Depends on my energy level and time available to answer. Lot's of the questions I pass on are great questions and I would have a great answers if I had the time to type a @BobCross Wall of words lol
It's not just performance that's suffering if you use a fuel less than recommended.. You're doing unseen damage to your head gasket. By the time it's noticeable, it's too late and you've caused an expensive repair that could have been avoided. If your owner's manual says 87 or higher, go with ...
@Paulster2 Am I missing something here. How does running a higher octane help the head gasket? Or maybe a better question is how does running to low of an octane (in the absents of spark knock) cause head gasket damage?
@Larry ... I've never seen/heard of knock/pinging/low octane causing head gasket damage. The head gasket is completely concealed between the head and deck ... nothing there for it to affect. It will destroy the piston well before it would do any damage to the head gasket ... at least that's my line of thinking.
@Larry - I thought the 700r4 could be made to stand up to a little abuse? Still, aren't the transmissions made weak so you don't have to worry about the 10-bolt? You should convert it over to a Magnum T56 and then you could worry about the rear instead ;-)
@Paulster2 You are suppose to be able to get them to handle it. But for whatever reason they won't hold up. The last one made it about 90 days, and that was just with street driving, I hadn't even took it to the drag strip. It sits more than it gets driven, and I have other priorities for money right now.
It's not just performance that's suffering if you use a fuel less than recommended.. You're doing unseen damage to your head gasket. By the time it's noticeable, it's too late and you've caused an expensive repair that could have been avoided. If your owner's manual says 87 or higher, go with ...
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