Strange Problem, please help

Skumguy · February 10, 2004

Hey I have something happening which I am wondering if someone can help with. it is a 00 1500 4x4.

Every now and again when I have been turning left I have been hearing the rear tire chip. Today I actually saw it happen. The inside rear tire would be turning as normal and about every quarter rotation it would jump forward a bit in the rotation and break the tire loose, it would only rotate about 8 inches worth of tread or so when it skipped. This was happening on dry pavement and so far I have only noticed it when turning left.

Anyone have any ideas what it could be? E-brake catching maybe?

Rookie · February 10, 2004

Almost sound like someone put a spool in the rear. Did you buy the truck new?

Skumguy · February 10, 2004

I got the truck used about a year ago. So far lotsa problems, I think I have a lemon!

Shaners · February 10, 2004

Sounds like the locker rear end is stuck.

You're not in 4x4 mode are you? If you are then it is normal for that to happen... (but not good for the driveline)

Skumguy · February 10, 2004

Definitely not in 4x4. Just what I need is another expensive fix!

JayMan · February 10, 2004

Do you have the G80 GovLok "locking" rear end?

If so, it sounds like the flyweight governor assembly is binding and latching the cam when it's not supposed to.

If the flyweight governor is sticky, it could be catching on the cam and that will drive the clutch plates together when they're not supposed to be driven. You want to fix this quick as at the very least you'll cause rapid clutch plate wear and tire wear.

I'd drain the axle, wrestle off the sheet metal cover, and see if the flyweight governor assembly rotates freely without binding. You should be able to access the governor: have the rear axle supported by jackstands, trans in neutral, rotate driveshaft or one of the wheels to rotate the carrier until you can peek inside.

If the truck has really been abused, and it sure sounds like it, this could be one more problem you have to fix. A boy racer who always powerbrakes to light the tires up will quickly destroy a G80.

Hopefully, a simple fluid change will solve this problem.

Skumguy · February 11, 2004

Holy crap was that over my head. Well I guess I will take the rig in and have it checked out. Not enough tim and too cold to start pulling the diff plate off. Thanks for the responses guys!!

I happened to drop my boss off to pick his truck up at a mechanic and ended up talking to the mechanic. I said I put Mobil 1 fluid in the rear diff and he freaked, this was not a dealer by the way. And he said I needed the additive in there along with the OEM synthetic diff fluid. Is this guy for real or blowing smoke up my behind?

I got the truck off a lease, so someone must have abused the thing, I go pretty easy on it.

shelbyd · February 11, 2004

I don't know about the Mobil 1 but if you have a locker you need the additive. you need to find out if people with M1 are using the addative or if the M1 doesn't need it. It is certainly cheaper to put the recommended product in than a wasted tear down if you need to pay someone to do it, to see what the problem is. I am pretty sure you need the friction modifier though. maybe others will chime in with their M1 experiences

1rado · February 11, 2004

I use Mobile 1 with out the additive and it seems fine to me. When I first went to the dealer to get their stuff I was shocked at the price and an additive wasn't needed.

JayMan · February 11, 2004

Holy crap was that over my head. Well I guess I will take the rig in and have it checked out. Not enough tim and too cold to start pulling the diff plate off. Thanks for the responses guys!!

I happened to drop my boss off to pick his truck up at a mechanic and ended up talking to the mechanic. I said I put Mobil 1 fluid in the rear diff and he freaked, this was not a dealer by the way. And he said I needed the additive in there along with the OEM synthetic diff fluid. Is this guy for real or blowing smoke up my behind?

I got the truck off a lease, so someone must have abused the thing, I go pretty easy on it.

If you do a search for "G80" there should be a post I did describing in detail how the G80 actually works. I'm sorry if I threw too much at you at once.

I didn't realize you had already changed the rear axle fluid.

When you say you used "Mobil 1" do you mean "Mobil 1 Gear Oil 75W-90??" Did this mechanic misunderstand or is he anti-Mobil?

It has been my experience that unless you're already having trouble with the GovLok, the Mobil 1 Gear Oil 75W-90 already has enough additive in it so things should work properly. Even the bottle claims "prevents chatter in Limited Slip units."

If the clutch plates are already glazed - perhaps from using the wrong fluid - or worn, you'll need more additive. I've had good luck with CRC Trans-X PosiTrak in the 7 fl oz tubes, check your local NAPA.

Still, what does this have to do with the inside wheel crow-hopping on a turn? Something is making the flyweight governor catch and engage the cam to force the clutch plates together. If anything, using the wrong gear oil the G80 will stop working altogether.

The only other thing regarding limited slip is that your truck does NOT have the factory G80 - it was a factory open differential - and somebody put in an aftermarket Limited Slip or "posi." The regular limited slip works by using a Preload Spring (Either a large S spring or 4 smaller springs held in a collar) to bias the left and right clutch packs together.

When you go around a corner, the clutch packs can bind and release, causing "chatter." This slip/grab chatter can be seen as a momentary slip in the inside wheel. This would only apply to a regular limited slip with a Preload Spring setup, not the factory G80 GovLok.

Or it was a factory open differential and somebody put in an Auburn Gear unit. Those things use cone clutches and work well, but Auburn Gear warns you to NOT use a synthetic gear lube or the thing will chatter like crazy around corners. Auburn recommends a regular 80W-90 and the appropriate friction modifier LS additive. You will have to verify what rear axle unit you have.

Can you verify the option codes on your truck? They're in the glove box somewhere and G80 is the code for the "locking" rear end. If you can't find "G80" on that long list of build options, the truck came with an open diff.

Somebody mentioned a defective e-brake. You never know, would hurt to check. Those "drum in hat" systems don't impress me at all.

Since this thing is a lease return, any chance of the dealer fixing it?

Skumguy · February 11, 2004

Jay,

Thanks for all your help on this. I checked the glove and I have the G80. I will do the search you said and educate myself. When I started thinking about your post I understood what you were saying more. The mechanic was talking about the clutch plates "slipping" but if I understand correctly, that sounds like it would be exactly the opposite of the problem I am having. The problem is, it shouldn't be engaging at all.

I told the mechanic I used the 75W-90 Mobil 1 and he barely let me get in a word in edgewise telling me how I was going to destroy my diff. I think he might be a little set in his ways so to speak. Before I changed the diff fluid I read up on it in this forum and no one has seemed to have any trouble using Mobil 1, I think the mechanic just didn't know what the hay he was talking about.

When I get a weekend I am going to open that thing up and take a look at what you said.

varmint2506 · February 11, 2004

The last G80 replacement we had done the shop forgot to put in the additive. That thing chattered like crazy.

$4.15 from GM Parts Direct.

JayMan · February 11, 2004

Jay,

Thanks for all your help on this. I checked the glove and I have the G80. I will do the search you said and educate myself. When I started thinking about your post I understood what you were saying more. The mechanic was talking about the clutch plates "slipping" but if I understand correctly, that sounds like it would be exactly the opposite of the problem I am having. The problem is, it shouldn't be engaging at all.

I told the mechanic I used the 75W-90 Mobil 1 and he barely let me get in a word in edgewise telling me how I was going to destroy my diff. I think he might be a little set in his ways so to speak. Before I changed the diff fluid I read up on it in this forum and no one has seemed to have any trouble using Mobil 1, I think the mechanic just didn't know what the hay he was talking about.

When I get a weekend I am going to open that thing up and take a look at what you said.

Ok you have verified you DO have the G80.

In no uncertain terms: it should NOT be doing that on dry pavement around sharp corners unless you have a mechanical problem. Since the G80 does NOT have a Preload spring, the clutch plates are barely touching in normal use.

The only way to bias the plates together is when one wheel is rotating and the other is stationary (Or a differential in speed of about 100 wheel RPM ) : the governor experiences centrifugal force and flips out to the latch bracket, which energizes the cam to drive the plates together.

Since the carrier is not rotating but the wheel is, the cam is driven by the energy from the rotating wheel. That's why they refer to this as "self energizing."

To further assist in understanding how the G80 works, check out:

http://www.traction.eaton.com

In particular the section on the G80 "locker" is at:

http://www.traction.eaton.com/prod2.htm

Where you see the blue lettering "what about a boat ramp" and "nastiest off-road terrain" click on the blue lettering which launches an mpeg of a Suburban at a boat ramp and off road.

They have a neat mpeg of the different G80 parts gently floating together, and how the thing works. You'll see what the flyweight governor, trip spring, and cam are and what they look like.:

http://www.traction.eaton.com/images/G80.mov

With Windows you can use Windows Media Player. If you have a newer PowerMac like I do, Apple QuickTime will play it too.

Don't forget to read the Eaton FAQ, which will provide you with confusing and contradictory advice: GM tells us to use a synthetic and NO limited slip additive, and Eaton tells us to use a regular 80W-90 with limited slip additive.

I tried using Exxon SGO 75W-90 in it when new and the G80 quit on me: Exxon SGO is a commercial synthetic designed for extended warranty coverage of 750,000 miles with 500,000 mile drains in Eaton Dana HP-40 tandem HD truck axles. With the SGO the clutch plates would slip and chatter on snow and ice. I had to flush it out with regular 80W-90 and about 6 tubes of CRC limited slip additive.

If I don't add 1 tube of CRC Trans-X PosiTrak every time I service the rear end, it still slips a bit. No sense in paying to rebuild the stupid thing, it was my fault and I can live with adding a tube of additive at every gear oil change.

Question: did the axle act up before or AFTER you drained and refilled with Mobil 1 Gear Oil??

Skumguy · February 12, 2004

This has all only happened since the Mobil1 change. I changed the fluid a few months ago. I talked with a Mobil tech and he said to not even use Mobil 1 in our trucks because he can't verify that GM standard for the fluid. Not sure if the stuff works fine and that is just what he officially has to say, or whether I should be concerned and just use the GM expensive synthetic.

JayMan · February 12, 2004

This has all only happened since the Mobil1 change. I changed the fluid a few months ago. I talked with a Mobil tech and he said to not even use Mobil 1 in our trucks because he can't verify that GM standard for the fluid. Not sure if the stuff works fine and that is just what he officially has to say, or whether I should be concerned and just use the GM expensive synthetic.

That is SO unusual, since many Forum members have used Mobil 1 Gear Oil with no problems at all.

If anything, the wrong gear oil will cause the clutch plates to slip, so the G80 would stop working altogether. It can only engage if the cam assembly is driven to force the clutch plates together.

All I can suggest is a drain and refill like the Eaton FAQ suggests to a cheap 80W-90 and 2-3 tubes of CRC Trans-X PosiTrak limited slip additive, or use the GM Limited Slip additve. That's what I had to do when mine acted up after I used the wrong fluid, though make sure the temps are above 10 F or you might have problems.

After driving around for almost 2 weeks, it came back to life. Then drain/refill with 1 tube of CRC Trans-X PosiTrak, or the GM LS additive, and Mobil 1 Gear Oil 75W-90.

I would still take off the rear cover and carefully inspect the flyweight/governor assembly for sticking. If the axle had never been serviced until you touched it, you may have knocked a lot of crud loose with the fresh oil and the flyweight/governor may be sticking.

Especially with a lot of miles on it, don't be surprised to find heavy sludge inside the housing: use a shop towel and clean gear oil to clean the crap out. The magnets on the sheet metal cover will look so hairy they'll scare you. Carefully clean them off with a shop towel.

Whatever you do, do NOT use any solvents or gasoline to "wash" the housing out. The residual solvent will cause foaming of the new gear oil and rapid gear tooth wear.

If the flyweight/governor appears stick, take cheap 80W-90 and slowly dribble it on while gently working the assembly: that should help clean out whatever is causing the binding. Hope your local parts store has cheap 80W-90 on sale: I used up 12 quarts last time I had to flush my front axle, so let's hope you don't need that much for the rear.

Hope this helps. I doubt a gear oil change to the hyper-espensive GM Goodwrench Synthetic will help, but if you have a spare $75 eating a hole in your wallet ...