4x4 problems with front diff...

[GMCheadache]

Hey guys, I have an 87 high sierra with stock diffs. When I put the truck in 4wd, the front passenger tire locks up after about 2 feet and will not turn. It doesn't make a difference in hi or low. Figuring it was the auto locking hubs, I replaced them with some new manual hubs. Still the same issue. If I put it in 4wd and don't lock the hubs, the wheels spin freely which makes me assume that the t-case is fine. I have no issues in 2wd and I hear no sounds from the t-case. I have no brake issues either. Any opinions would be great. I'm going on my second winter with no 4wd and the tires are getting a little tired of spinning.
Thanks.

 

[crazy4offroad]

Pull the cover and check the spider gears and cross bar. It sounds like something is about to grenade in it.

 

[PrairieDrifter]

If the transfer case is a 203 you cant put manual hubs on the axle unless you put a kit in the transfer case

 

[crazy4offroad]

Doubtful an 87 has a 203 but honestly you never know what a PO might have swapped in. The fact it goes about 2 feet then stops sounds a lot like the lock bolt that holds the crosspin in place broke and the crosspin is backed partially out and when the diff rotates it contacts the inside of the pumpkin and stops. Best to catch it now before it destroys everything in there.

 

[Georgeb]

Doubtful an 87 has a 203 but honestly you never know what a PO might have swapped in. The fact it goes about 2 feet then stops sounds a lot like the lock bolt that holds the crosspin in place broke and the crosspin is backed partially out and when the diff rotates it contacts the inside of the pumpkin and stops. Best to catch it now before it destroys everything in there.

Agreed! Open it up and look.

 

[PrairieDrifter]

Doubtful an 87 has a 203 but honestly you never know what a PO might have swapped in. The fact it goes about 2 feet then stops sounds a lot like the lock bolt that holds the crosspin in place broke and the crosspin is backed partially out and when the diff rotates it contacts the inside of the pumpkin and stops. Best to catch it now before it destroys everything in there.

But if the crosspin is sticking out and making contact, then the driveshaft shouldn't be able to move because the carrier and ring gear can't move. So that would burn out the transfer case.

I totally cant think right now.. if the pin is coming out, the driveshaft and carrier wont be able to turn, so shouldn't both wheels not be able to turn? Or just one not be able to turn? Or should they both spin freely. I think both should be locked up instead of one, but I cant figure it out right now lol

 

[crazy4offroad]

Yeah I don't get it either. The 3rd member would be the first place I would look though, just to eliminate it. Most of everything else seems to check out ok. The 208 is chain driven so there's not really a differential between front and rear like the 203. When he says he put it in 4wd with hubs unlocked and wheels spin freely he could mean on a jack, not running.

 

[GMCheadache]

Wow guys, thanks for all the input. The t-case is a 208 and the wheels spin freely when the truck is on the ground, not on jack stands like the last reply said. I will take the front diff apart on my next day off and take a look at what you guys suggested. I havent put swapped out any parts in the driveline since I got it, but who knows with the previous owners did. from what I can tell, everything looks factory.

A friend of mine said it was possible that the gear ratio in the diffs may be different and could lock the front diff when using 4wd because the t-case is trying to spin the two diffs at different ratios. Any input on this? I will have to jack it up and check both diffs for matching revolutions of the drive shaft to confirm the gears. I know there is a formula for limited slip revolutions of the drive shaft, but can I use that formula for the front shaft as well? I guess if I can spin the front diff in 4wd when the rear shaft is disconnected then I would answer my question about the gear ratios being different.

Please bare with me on the replies. I dont have a day off until next tuesday, so I wont be pulling anything apart until then. Can I post a video on this forum to show you guys what the truck is doing?

Thanks again for all the suggestions.

 

[crazy4offroad]

Yeah definitely post up a youtube video. Different ratios front/rear would cause binding and eventual stop, and much difficulty shifting out of 4wd, but not a sudden stop. It's pretty much the same process for the front as for the rear counting revolutions of the driveshaft per 1 turn of the tire.

 

[GMCheadache]

Sounds good. I will get the video up on my next day off.

 

[PrairieDrifter]

Yeah if the ratios are off then one of the axles will have more drag than the other because they aren't spinning at the same speed, which like said above wont cause anything to lock up, its just extreme wear on the driveline.