Rear diff problem

[wilkes65]

Changed the rearend fluid yesterday in my 2001 Z-71 and and used the mobile one synthetic 75-90. Loud grinding sound started shortly after. Only happens when decelerating under 30 mph. So I thought it was the fluid. Used the GM fluid instead.(27.00 quart) Still does it. Any guesses? Locker is still working. Only problem is this gear grinding noise. Nervous about losing the rearend.

[Ape0r]

I've heard that non-GM gear oils can cause noise, but wherever I read that, it also read that switching back to the GM stuff would clear up any noise.

 

Could be it'll go away. I've heard of a lot of people using M1 with success.

[vhato]

I've heard that non-GM gear oils can cause noise, but wherever I read that, it also read that switching back to the GM stuff would clear up any noise.

 

Could be it'll go away. I've heard of a lot of people using M1 with success.

 

<{POST_SNAPBACK}>

 

 

 

 

Sounds like bad luck to me. Time for some new bearings.

[CapitalTruck]

All my manual says is synthetic 75-90 gear oil. Used to be you had to add that additive for limited slip, I guess no more.

 

 

I've heard that non-GM gear oils can cause noise, but wherever I read that, it also read that switching back to the GM stuff would clear up any noise.

 

Could be it'll go away. I've heard of a lot of people using M1 with success.

 

<{POST_SNAPBACK}>

 

 

[Ape0r]

All my manual says is synthetic 75-90 gear oil.  Used to be you had to add that additive for limited slip, I guess no more.

 

<{POST_SNAPBACK}>

 

 

 

 

SAE 75W-90 Synthetic Axle

Lubricant (GM Part No. U.S.

12378261, in Canada 10953455)

meeting GM Specification 9986115.

 

Copied from a digital owners manual I have on my comp., 04 model year. Poked around the M1 website, only spec listed as met for the gear oil is API Gl-5/MT-1, doesn't say anything about GM. GM specs are listed on that website for the motor oils, however.

 

On edit: Just stumbled upon this, must be where I read it originally:

 

Posted by Bill W (Member # 7971{not on this forum}) on July 10, 2005 08:11 AM:

 

From another forum:

This ia a letter from Eaton, manufacturer of the G80 diff in the C3, and most all other 1/2 ton trucks (not the Quadrasteer trucks)

 

"Axle tolerances of the trucks are very tight. The recommended

procedure was to change lube after 500 miles of heavy towing, which is considered a break in period. This breaking period generates high heat conditions in the axle which was found to degrade the synthetic After the 500 mile lube change, the axle is broken

in and does not generate the high heat. If you use GM synthetic after the break-in period, it can be considered "lube for life", although some say to change it at 40,000 - 50,000 mile intervals."

And this,

"Back in November, I received the following:

"From Mr. Ralph Holmquist of Eaton, the maker of the locking differential:

"The maintenance schedule for the rear axle was developed by American Axle &

Manufacturing and GM truck based on multiple tests. The Eaton locker does

not require additional maintenance nor does it add heat to the lube. The

lube will darken due to the carbon wear on the clutch surfaces, much the

same as a disc brake pad & rotor. This does not damage axle components such

as seals or bearings. However, a new axle can produce excessive

temperatures (plus 350 degrees F) due to the ring & pinion breaking in that

will break the lube additives down. Avoid high loads, trailer towing and

high speed extended driving during the initial break in of the vehicle.

After the break in period axle temps will level at a much lower figure.

Lube changes are a good idea because the additives are replenished and

contaminates such as casting sand are eliminated. The axle is filled at the

factory with a synthetic 75w90 GL5 rating made by Texaco under part # 2276.

The GM service # is 12378261. This is the only lube we have done extensive

testing with to insure locker compatibility. The only negative to using one

of these other lubes is an increased potential for clutch chatter. This

really doesn't hurt anything and can be corrected by changing the lube. I

noticed in the latest GM owners manual the term "or equivalent" when

referring to the lube specification. Look for a GL5 rating on the bottle to

make sure the ring & pinion, seals & bearings are protected. Limited slip

additive is not needed."

The following information outlines the type of

rear axle lubrication utilized in GM Truck axles.

I. Fluid Type

II. The 1500, 2500 and 3500 GMT 800 Trucks utilize SAE 75W-90 Synthetic Axle Lubricant. The GM part number is 12378261 and the specification is 9986115.

¨ Note: the recommended lube for HD trailer towing is a 75W-140 Synthetic Gear lube, part number 12346140.

III. Inspection/Change Frequency

¨ The 1500 and 2500 GM Trucks recommend rear axle fluid level checks every 7500 miles. Fluid should be added as needed.

¨ Under heavy duty trailer towing conditions the lube should be changed after the first 500 miles of towing. This is due to the extreme heat generated on break-in of the hypoid gear set."

[100R1]

If the noise only happens under deceleration, I can't see where it would be caused from just changing the fluid or changing to the wrong fluid.

 

Now if you said that you changed to the wrong fluid a year ago and now you are starting to hear noises, then I would say that the noise was caused from excess wear or heat from the wrong fluid.

 

Noise under deceleration tells me its not from you leaving tools or foreign matter in the pumpkin when you changed the fluid.

 

Does not sound like a wheel bearing or carrier bearing, But does sound like a Pinion bearing going bad.

 

I don't see how changing the lube can cause a change in the backlash, that could cause excessive noise under 1 condition. Or how chanking the lube could cause any shims to fall out / break /wear into thin air....

 

If you said it was "chatter" sound when you turn corners, I would say it's a limited slip without enough friction modifier in it. But you probally have a G80 and they do not have the same problems as a convential LS & friction modifier.

 

Check your Universals & slip yokes for excessive wear this could also cause noise only under 1 condition (accel. OR Decel)

 

Pull the cover off and check wear pattern of the teeth on the ring and pinion this will indicate problems with worn pinion bearings and backlash problems.

 

As someone posted sounds like bad luck and not from a lube change.

[wilkes65]

If the noise only happens under deceleration, I can't see where it would be caused from just changing the fluid or changing to the wrong fluid.

 

Now if you said that you changed to the wrong fluid a year ago and now you are starting to hear noises, then I would say that the noise was caused from excess wear or heat from the wrong fluid.

 

Noise under deceleration  tells me its not from you leaving tools or foreign matter in the pumpkin when you changed the fluid.

 

Does not sound like a wheel bearing or carrier bearing, But does sound like a Pinion bearing going bad.

 

I don't see how changing the lube can cause a change in the backlash, that could cause excessive noise under 1 condition. Or how chanking the lube could cause any shims to fall out / break /wear into thin air....

 

If you said it was "chatter" sound when you turn corners, I would say it's a limited slip without enough friction modifier in it. But you probally have a G80 and they do not have the same problems as a convential LS & friction modifier.

 

Check your Universals & slip yokes for excessive wear this could also cause noise only under 1 condition (accel. OR Decel)

 

Pull the cover off and check wear pattern of the teeth on the ring and pinion this will indicate problems with worn pinion bearings and backlash problems.

 

As someone posted sounds like bad luck and not from a lube change.

 

<{POST_SNAPBACK}>

 

 

[wilkes65]

Thanks for the suggestions. This morning it was cold and it sounded a lot worse. I could hear it during accell and deccell . Maybe it is bad luck, but it started about three hours after fluid change. That would be very bad luck. The weird thing is it doesn't seem to happen at high speeds. Or it could be I just can't hear it. The locker is still functioning today as well. I am just waiting for this thing to lock up going down the street. Also it doesn't make a peep under 15 MPH. And seems to stop making noise when turning around a corner, but once you start straight again here comes the gear grinding again. Thanks for any help.

[vhato]

Thanks for the suggestions. This morning it was cold and it sounded a lot worse. I could hear it during accell and deccell . Maybe it is bad luck, but it started about three hours after fluid change. That would be very bad luck. The weird thing is it doesn't seem to happen at high speeds. Or it could be I just can't hear it. The locker is still functioning today as well. I am just waiting for this thing to lock up going down the street. Also it doesn't make a peep under 15 MPH. And seems to stop making noise when turning around a corner, but once you start straight again here comes the gear grinding again. Thanks for any help.

 

<{POST_SNAPBACK}>

 

 

 

Yep,

Its a bearing. Could either be 1 of 2 outer axle shaft bearings, 1 of 2 carrier bearings or 1 of 2 pinion bearings. I say it is a pinion bearing, probably inner pinion bearing. Just change or have changed all 6 bearings.

[100R1]

Thanks for the suggestions. This morning it was cold and it sounded a lot worse. I could hear it during accell and deccell . Maybe it is bad luck, but it started about three hours after fluid change. That would be very bad luck. The weird thing is it doesn't seem to happen at high speeds. Or it could be I just can't hear it. The locker is still functioning today as well. I am just waiting for this thing to lock up going down the street. Also it doesn't make a peep under 15 MPH. And seems to stop making noise when turning around a corner, but once you start straight again here comes the gear grinding again. Thanks for any help.

 

<{POST_SNAPBACK}>

 

 

 

OK so side load changes or eliminates the noise.... (turning corners will side load carrier & wheel bearings) sounds more than likely a bearing, which is the least expensive of the repair.

 

If you do the repair OR have a shop repair the axle and the bearing is either a carrier or inner pinion bearing, I would have them replace all of the bearings and seals (axle, carrier, pinion) and crush washers etc.. Hard parts are cheap in comparrision to labor. a rebuild of your axle (not including a rebuild of a G80 locker or new ring and pinion gears) would be around $ 300.00 - 400.00 american dollars.

 

If on the other hand its just a outter axle bearing it's real easy and cheap to replace a single bearing and oil seal.

 

Make sure who ever rebuilds the axle uses quality bearings and seals, no use cutting corners on the parts.