Need trans help ASAP! Chevy/GMC

[redrussell]

Ok wife and I are down to one vehicle, our 1994 3/4 ton GMC suburban. It has the 7.4(454)/4L80E drivetrain, yes it is 4x4 but I don't remember the tcase. We were driving last night and decided to take a road we have driven before near the house to see deer. There was some snow but nothing major, so I thought. We slid a little when I slammed on the brakes as a doe tried to commit suicide with the grill, dropped the right rear into the ditch. I started to rock it back and forth between D and R, eventually getting out, thought nothing of it. We pull out onto the main road and now it won't shift out of 1st gear, I still have reverse and N as well. I find a clear spot and crawl under it to check it out, not a damn thing looks wrong, all the connections are good, no wires pulled out, nothing looks wrong. Limp home at 15mph drop the wife and kids off at the house and go to the shop and put it on the lift. I spoke around, disconnect every connection and plug it back in, pull the fuses and check them. Still can't find anything wrong. I check the fluid again, has ok color, not bright red but still red but smells like gear oil. I did new fluid and trans filter almost a year ago. I decide to call it a night(2300). Now I don't have reverse. I have N and 1st gear only now. Anyone have ideas? I have never rebuilt any of the electronic transmissions, only rebuilt a th350 once. Whatever it is we need to get this back on the road as soon as possible. This vehicle is used for towing/camping and hunting as well as foul weather. I'm lost please help.

 

[Utahtrucker]

with the 4L80E it could be anything,could be a burnt out plate, or a spine is mis-alianed,4L80E is a pain in the ass and expensive to replace,better off putting in a 700R4

where are you @ my Brother inlaw has a shop in Magna, he is pretty reasonable and with work with you!!! Magna's automotive center on main street!! ask for Donnie

 

[Tacoma]

4L80e's are great transmissions, there's a reason they didn't put 700r4's in 3/4 and 1 ton stuff.


As for your issue, I'm not sure. If the pan didn't get hit, no obvious linkage or wiring issues, it's hard to say.

 

[redrussell]

I could be missing something but I am stumped. Luckily I live on post and my wife isn't working right now so limping to pt in the morning(Its too cold to walk or ride my bike, I do draw a line somewhere) isn't too bad, just slow at 15mph. Then I ride my bike around post. I am stuck though if we need to go to town. I'm to the point of I will trade my project cj7(the one I have posted for sale here) for a 4l80e that is guaranteed since when I pcs this will be towing a loaded trailer. I can also trade parts or labor for something. You have something you don't want done, guess what I will do lol.

 

[boogie_4wheel]

I know on the 60E the vss (vehicle speed sensor) worked for both the speedo readout and trans function (was the case on my '97). Does the tbi have a single point of reading the vehicle speed for determining shifts? I read once upon a time that the early 90's had issues with the vss getting wet inside from fluid and it thinks it isn't moving, but you are recording a speed readout correct?

 

[zmotorsports]

with the 4L80E it could be anything,could be a burnt out plate, or a spine is mis-alianed,4L80E is a pain in the ass and expensive to replace,better off putting in a 700R4

I don't necessarily agree with this. The 700R4 is a good transmission but a bit undersized behind a big block. The new nomenclature for the 700R5 is 4L60E which is just the littler brother to the 4L80E. For comparison's sake, figure the 4L60E(700R4) is equivalent to the TH350 in terms of clutches, steels, sprags, etc., then think of the 4L80E as the equivalent to the TH400 in terms of clutches, steels, sprags and overall strength. That is about the best comparison I can think of.

As for the original posters issue, I suggest you get with a shop that can check the input and output sensors on your 4L80E. Don't confuse them with the Vehicle Speed Sensor (VSS) which is for overall vehicle speed and mounted at the final drive output (ie. transfer case). There is a sensor that measures the input shaft RPM and one the measures the output shaft RPM before going into the TC. If these are incorrect at any of the predetermined parameters then the PCM interprets them that there is slippage and the trans goes into "limp mode". That is the first place I would start. Then you can start to determine whether the problem is mechanical or if it could be electrical.

Mike.

 

[redrussell]

I'm out in Dugway, not a shop near by and my trailer is broken and in Idaho being repaired still. This is also my tow vehicle since it is my only running and license-able vehicle right now. I am getting speed and rpm(on the tach) readings. I do 15ish mph at 2000rpm, no attempt or pause to try and shift. I pulled the negative terminal last night and pulled every fuse in the fuse block and checked them. Let it sit over night and then hooked the negative back up. Now I don't have reverse, just N and 1st. I'm confident this is a senator or selinoid of some kind. I just don't know how to trouble shoot it.

 

[TRD270]

I'm out in Dugway, not a shop near by and my trailer is broken and in Idaho being repaired still. This is also my tow vehicle since it is my only running and license-able vehicle right now. I am getting speed and rpm(on the tach) readings. I do 15ish mph at 2000rpm, no attempt or pause to try and shift. I pulled the negative terminal last night and pulled every fuse in the fuse block and checked them. Let it sit over night and then hooked the negative back up. Now I don't have reverse, just N and 1st. I'm confident this is a senator or selinoid of some kind. I just don't know how to trouble shoot it.

I don't have a trailer, but if you can source one i'd be happy to come give you a tow.

 

[boogie_4wheel]

What happens if you manually select 2nd?

 

[redrussell]

Nothing, I tried manually running through the gears

 

[jeepin4x4james]

What about the small auto shop on site out there? They happen to have one of the old scanners that can read OBD1?
When my 4L60E had similar issues it was the internal harness...

 

[boogie_4wheel]

You can read obd1 using a jumper on the diagnostic port and counting the flashes.
https://www.obd-codes.com/faq/read-gm-2-digit-obd-codes-free.php

 

[neagtea]

4L80e's are great transmissions, there's a reason they didn't put 700r4's in 3/4 and 1 ton stuff.


As for your issue, I'm not sure. If the pan didn't get hit, no obvious linkage or wiring issues, it's hard to say.

^^^^^^X2
My guess is a sensor. Does the base have a auto hobby shop? Not sure what DPG has on post.

 

[redrussell]

Yes we have a shop(I have keys and run it monday nights) our reader does not have the module to read a 94 GMC/Chevy. Have tons of Ford modules. And a gmc/Chevy up to 90, for shits and giggles I tried that module and nothing came up. If anyone has a reader I could borrow I can get a ride to come get it or if someone wants to come out I would pay gas money or whatever for you to look it over, I'm stuck. Talked to a few shops and all but one says it needs a rebuild. I have no warning lights of any kind on.

 

[larrybenny]

To save alot of time diagnosing, I would pull the pan 1st and cut apart the filter. If it is loaded full of crap and metal fragments then you know the the rocking back and forth took out an already tired trans. I would never replace the 4L80E with a 700r or 4l60e. The electrical won't work, the driveshafts would have to be altered since the 700 or 4l60e is shorter and the t-case input gear is different. Plus the fact mentioned here is that gears and shafts are much smaller and weaker.

 

[redrussell]

Yeah dropping a 700 or 4l60 in isn't going to happen. This vehicle isn't abused but it is used on occasion. We hauled a 12,000lb trailer from salt lake clear to San Diego, a few other things like that as well. That definitely isn't the norm but it happens.

 

[redrussell]

Ok I have a 93 4l60 now, question is; can I drop this in place if the 80 till I get a rebuild and then put the 80 back in? What would need modified or is it just not going to work?

 

[UNSTUCK]

Off the top of my head, I believe the 60 is shorter, different output shaft, different t-case adapter, and different programming.

Have you figured out whats wrong with the 80? This thread is almost a month old. I got the impression that you needed this rig up and running ASAP. Pull the tranny, have it rebuilt/repaired, and be up and running next week. Why dump time and money into a bandaid that you will remove to go back to what you had? I see no logic in this.

 

[redrussell]

I just happen to have the 60, I have been borrowing a vehicle in the mean time.

 

[mbryson]

I'd throw the $ at the rebuild rather than try to adapt something. I've always spent WAY more than expected trying to put something where it's not intended to go (well, some things work out but if you go off percentages, I stand by my previous statement)