14 bolt FF G80 stuck in posi

[99BurbK15]

Today I took my truck to school for the first time in over 3 months (updates coming on build thread) and when I left school I managed to chirp the tires when I took off from a red light (didn't intend too). I initially didn't think anything of it because it was raining and my Firestone Transforce aren't the best but as soon as I pulled into the parking lot at work the truck shuttered and hopped like when its in 4wd so knew the rear didn't unlock. After work I tried going in reverse for a few feet to disengage but didn't help. So when I got home I popped the rear diff cover off just to take a look and wanted to change the fluid anyway but everything looks fine to me nothing surprising. No chunks or foreign matter. Hardly any wear on the gears. I am hoping some fresh 80w90 and some additive will do the trick. My truck is a 1995 Chevy k2500 with 14 bolt full floater 8600lb G80 GT5. Has anyone else ever experienced this? Any tricks I should try before putting it back together?

Thank-you to all in advance who respond, Ben

 

[grampadirt]

I have the same setup and have not experienced what you have.My diff has locked and un-locked many times flawlessly.Just a thought...since you have the cover off,try jacking up the rear so both tires are off the ground and lightly tap the diff with a hammer as you spin the tries.Maybe get a friend to turn one of the wheels back and forth as you spin the diff.All I could think of....

BTW no additives in these diffs.

 

[someotherguy]

"and some additive" = if you used any in the past, you need it out of there. best of luck to you

Richard

 

[99BurbK15]

I have the same setup and have not experienced what you have.My diff has locked and un-locked many times flawlessly.Just a thought...since you have the cover off,try jacking up the rear so both tires are off the ground and lightly tap the diff with a hammer as you spin the tries.Maybe get a friend to turn one of the wheels back and forth as you spin the diff.All I could think of....

BTW no additives in these diffs.

I will definitely try that. My truck has locked and unlocked before just fine too thats why Im was kind of shocked. Its a low mile truck so hope some fresh fluid does some good. I know its a G80 but I though they were pretty stout in a 14 FF.

"and some additive" = if you used any in the past, you need it out of there. best of luck to you

Richard

Okay I didn't know for sure. I didn't put any additive in my Suburban with G80 but didn't know since it is a heavier truck. This would be my first time serving the rear differential on my 1995 and after draining Im glad I did. I bet the fluid was never changed in the 146k miles, so fresh fluid should in theory help.

 

[99BurbK15]

Alright so an update...
I tried tapping on the carrier while I had a friend spinning the wheels however no luck, still engaged. So I figured since my axle shaft flange seals were weeping I would remove them both and see if anything out of the ordinary was going on there. Everything looked like new, hardly any noticeable wear at all. I then reassembled everything with new gaskets and refilled with 80w90. I drove it for a ride around the block but now when I turn it clunks and kind of clicks like its trying to disengage. So I checked the fluid level and just let it sit, don't want to do any more harm. Even for the truck being 20+ years old still running the original fluid the internals were immaculate no damage or wear at all, the magnet was fairly clean no big chunks neither did the gear oil. So I don't know what to think, It appears to be a very well built rear end and should have many miles left. Maybe it just needs to be driven? Any ideas or advice is greatly appreciated!