Rear end questions

**REVNORR82** · 09-21-2013, 02:15 AM

I have a 2007 Silverado classic z71 and the posi or what ever these trucks have is acting funny. I was pulling my hunting camper out of the yard the other day in 2wd and it started to spin the drivers side started first then went to the passenger side then to both and then the passenger again then I went to 4wd. What the hell is with this it has 115000 miles now and I'm wondering if its a fluid thing or its just worn out. Thoughts please.

**Cutlass** · 09-24-2013, 02:49 AM

Usually it has to spin one wheel a little bit then it'll lock up both. But its not a true lock, it still has clutches. And those clutches can be overpowered and slip. If both tires have pretty much even traction (ie both on a snowy road, both on ice, or both in mud) the clutches won't slip, much. But it the traction is grossly uneven (ie one on ice and the other on dry pavement) and the clutches have some miles on them, it'll slip. Sometimes a lot of slip.
It sounds like your "posi" is a little worn out but still functioning. So maybe you could try replacing the clutches to freshen it up.

**0rion** · 09-25-2013, 05:10 AM

sounds pretty normal to me

**Firebirdjones** · 09-26-2013, 02:50 PM

Those Gov-locs GM uses are pretty goofy like that. GM has been using them since the mid 70's, especially in trucks. One tire has to slip before a centrifical weight takes over and determins it's time to lock the other wheel. On top of that they are linked together with a very small clutch pack like Cutlass mentioned.
When that centrifical weight engages it's a fairly strong shock to the system. It's fine when you are on loose pavement like dirt, snow, grass etc.... However in extreme type conditions of engagement they have been known to come apart. So they got the nickname "gov-bomb" All these issues I've seen (or been a part of myself

) were all in the smaller 8.5" 10 bolts and the GM truck 8.875" truck 12 bolts (up to 79) I've broken a couple of them myself in stock trucks horsing around on solid pavement. I haven't seen a problem in the larger 3/4 ton and 1 ton 14 bolt rears.

**Cutlass** · 09-26-2013, 05:40 PM

If I ever had a problem with mine, I'd like to swap in one of those Tru-Trac diffs. Those are the ones with the helical cut gears like the Torsen limited slip diff in the LS1 F-bodies.

**REVNORR82** · 09-27-2013, 01:04 AM

Well that was the first time that had done that just seemed strange at first. Don't think I'm going to worry too much I do believe I'll be swapping the truck out for a crew cab soon.