Backing plates

Stuntmanmike1977

Original poster
Member
Nov 21, 2021
79
Sanford, Maine
Hello all. Had a squeak from the rear on my 03 LTZ and noticed the emergency brake shoe linings are gone as well as the backing plates. I really am nervous about doing this job. I ordered new shoes, plates and seals. Question is what are the chances of the spider gears falling out cause I don't want to damage the rear differential especially when I start tapping the new seals in. Was thinking of slowly pulling out the pin, slide the axle shaft half way out then temporarily pushing the pin back in before removing the axle all the way out. Will that keep the gears from falling out? Doing one side at a time just to be on the safe side. My only vehicle so can't make a tragic mistake.
 

mrrsm

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Oct 22, 2015
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Some Suggestions:

(1) First… Check the RPO Aluminized Sticker in your Glove Box to ID what your Rear Diff actually is, as the Internals do NOT all look and behave the same whenever the need to Pull The Axles occurs. The GM Eaton M-Locker Series is not the same as the Limited Slip or Posi-Traction versions once the Cover is taken OFF The Pumpkin. THIS is what this Job actually looks like when doing it from Start to Finish on a GM Eaton M-Locker Differential:

https://gmtnation.com/forums/threads/2000-2002-silverado-rear-diff-partial-rebuild.20455/

(2A) If you are worried about the Axles Rotating inside of the Diff once you safely Jack Stand Support the Vehicle… Place the Floor Jack under the Tire-Wheel on the opposite side to the Wheel you are working on and raise it just enough to prevent the Axles from turning. Do this only AFTER First aligning the Axle position necessary to Un-Bolt the Pin Retainer Fastener and only AFTER you find the Sweet Spot needed in order to Slide out that Pin.

(2B) Remember… in order to remove the “C” Clips you just need to Push the Outer Wheel Stud Plate of the Axle INWARDS just enough to Free the “C” Clip and then you can spin it around enough to Grab it with a Telescoping Magnet and then Slide it OUT without having to manipulate anything else inside the Differential Gears Cavity.

(2C) Once the First Wheel-Axle Job is Finished… Re-Install the Wheel Lightly on the Repaired Wheel Lug Nuts just to avoid turning the Axles and then Raise the Floor Jack under that Tire just enough to hold the Axles STILL while working on the remaining side. Leave it there until ALL of the remaining work is finished and that includes until AFTER the Pin is finally Re-Installed and the Locking Fastener is Installed and Torqued-Tightened.

(3) Visit THESE Links to the Albums where I have memorialized doing these jobs on my Y2K Silverado… just to familiarize yourself with all the landscapes involved:

https://www.flickr.com/photos/126111508@N07/albums/72157713562564068/
https://www.flickr.com/photos/126111508@N07/albums/72157712806384396/
https://www.flickr.com/photos/126111508@N07/albums/72157712699445326/

(4) Once the Job is Complete… Lower the Vehicle and Check the Wheel Lug Torque Specifications mentioned in your 2003 Chevrolet Trailblazer Owner’s Manual and apply that level of Tightness to ALL Four Sets of Wheel Lugs.

(5) Enjoy Trailblazing… In Safety! :>)
 

Stuntmanmike1977

Original poster
Member
Nov 21, 2021
79
Sanford, Maine
Good info with the floor jack. Will do that. What about the spider gears falling out? Will temporarily reinstalling the pin after the axle is pulled out prevent that?
 

mrrsm

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Oct 22, 2015
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Perhaps... But only if you can manage to insert that Pin and and remember to remove it just AFTER you finish replacing the Axle Tube Seal(s) and BEFORE you Re-Insert The Axle on either Side. Just Remember what I mentioned earlier ... It depends upon the RPO and the Type of Gear Box you are dealing with.

Those components are fairly easy to control as long as they do NOT get yanked around... and other than the hassle of aligning their Curved Thrust Plates (Holes) along with the aligning Spider Gears by Trial and Error to get things back into their correct positioning...its more or less just about the process being a Huge PITA more than an impossibility.

BUT... I can express my seasoned chagrin that if you discover that your "Pumpkin" is any flavor of the GM Eaton M-Locker Style... Whatever you do ...Don't Deliberately Remove that Odd Looking Rectangular Block from inside that Core Area... or you'll begin to Wish that your Mother... Never Met Your Father... I'm NOT Kidding....Read that Thread I posted in my First Response to vicariously experience THIS Nightmare...
 
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Mooseman

Moderator
Dec 4, 2011
25,192
Ottawa, ON
75w90 Synthetic. Any brand really. Doesn't need to have the friction modifier additive for limited slip whether you have a G80 locker or not.
 
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TollKeeper

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Dec 3, 2011
8,028
Brighton, CO
Why not use Mobil 1?
 

mrrsm

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Mobil1 75W-90 Gear Oil comes default with the Limited Slip Additive already mixed in. The GM Eaton M-Locker Diff Design is NOT a "Limited Slip" style mechanism and calls for this information to be considered for LOCKING Centrifugal Differentials:

LOCKING DIFFERENTIAL LUBRICANT (SERVICE INFORMATION) #91-4-109
SUBJECT: LOCKING DIFFERENTIAL (G80) LUBRICANT - (SERVICE INFORMATION)
VEHICLES AFFECTED: ALL LIGHT TRUCKS EQUIPPED WITH G80 REAR AXLE ALL YEARS

Some Light Duty Trucks equipped with Locking Rear Axles (G80) may Exhibit Rear Axle Chatter, especially when turning a corner from a stop.

This Condition of Alternate Engagement and Disengagement of Clutches in Differential Assembly is usually caused by Contaminated Axle Lubricant.

The Use Of Any Additive In Locking Rear Axles (G80) Is Not Recommended. Rear Axle Additives are Designed for use in Limited Slip Differentials which are Normally Installed in Cars. "All Light Duty Trucks Equipped with RPO G80 Make Use of a Locking Differential" and the Use of Additives will Delay the Engagement of the Locking Mechanism and May Decrease Axle Life.

Rear Axle SAE 75W-90 Synthetic Axle Lubricant (GM Part No. U.S. 89021677, in Canada 89021678) meeting GM Specification 9986115.

WARRANTY INFORMATION:

"As Specified in Light Duty Truck Maintenance Schedules, Locking Rear Axle Fluid Drain and Refill is Required Owner Maintenance at the First Engine Oil Change"......Failure to Drain and Refill the Rear Axle as Specified May Contribute to a Later Axle Chatter Condition. Refer to the Appropriate Light Duty Truck Maintenance Schedule or Service Manual, Section OB, for Further Details on Change Intervals."

 
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TollKeeper

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Dec 3, 2011
8,028
Brighton, CO
Nope. No Locker, no Limited slip.. Just a open diff GU6 3.42.

G80 is a Eaton Locker
G86 is a LSD
 
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Mooseman

Moderator
Dec 4, 2011
25,192
Ottawa, ON
The Use Of Any Additive In Locking Rear Axles (G80) Is Not Recommended. Rear Axle Additives are Designed for use in Limited Slip Differentials which are Normally Installed in Cars. "All Light Duty Trucks Equipped with RPO G80 Make Use of a Locking Differential" and the Use of Additives will Delay the Engagement of the Locking Mechanism and May Decrease Axle Life.
I was not aware of this. Learned a new one today. However, the additive will not affect an open diff except that it may thin the oil itself a bit so it's still better to not have it.
 
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mrrsm

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The GU6 Designation just means that the Gear Ratio is 3.42. I cannot swear that this De-Coder List for GM RPO Codes is complete or comprehensive.:

For those of us WITH the GM Eaton M-Locker Differentials... Amsoil is one of the FEW Companies that does NOT include the Limited Slip Additive in THIS particular version of their 75W-90 Weight Gear Oil:


51o5ZQIw3hL._SL1000_.jpg
 

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Stuntmanmike1977

Original poster
Member
Nov 21, 2021
79
Sanford, Maine
Yeah, when I changed the gear oil 2 years ago looked pretty empty inside. So I guess the backing plate job shouldn't be that hard. I'll just put the pin back in after I take the axles out until the plates and seals are in. Thanks everyone for the info.
 
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budwich

Member
Jun 16, 2013
2,021
kanata
Probably heresy, but why are you bothering about the backing plates? There were "gone" and didn't cause an issue. Seems like a lot of effort for limited gain along with potential trouble.
 
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mrrsm

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Oct 22, 2015
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Actually... Without having the Backing Plates ...It's a lot like an Armored Knight, Riding a Destrier whenever Jousting, but without wearing his Beveled Breast Plate... is just asking for a *Different* Kind of Trouble.

Watch the Full Video covering this GM Truck Backing Plate R&R for a Bonus Practical Solution featured at the End:

 
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Mooseman

Moderator
Dec 4, 2011
25,192
Ottawa, ON
Front plates are not essential however the rear hold the parking brake shoes and will expose the internal drum and shoes if missing.
 

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