OK, there are so many questions and confusion on the differential. So here I am adding some more. Please beware that mine is a 2005, 2500 Yukon-XL, and the information below is from 2005 CK8 truck service manual (Tahoe, Suburban, Avalanche, Yukon (XL), Denali (XL), Escalade (ESV, EXT)) However, the principles should apply to all.

As per the manual, there are 8.6”, 9.5”, 10.5” locking differentials and 9.75” limited slip one. QS Trucks come with the limited slip differential.

When the wheel-to-wheel speed difference is 100 revolutions per minute (rpm) or more, differential engages. 100 rpm is approximately 9 mph, that is if one wheel has traction and stationery, and the other wheel is spinning.

Differential does not lock over 20 mph.

Differential does not lock if you step on the gas and cause a rapid acceleration of one or both wheels.

So easy on the accelerator (trick: tie an egg under your foot and accelerate without breaking it…not a hard-boiled egg, no cheating ).

As I said before, I would like to replace the limited one with a locking differential. Look what the service manual says.

“When comparing the effectiveness of the locking differential in terms of percent of grade capability to limited slip units, the locking differential has nearly 3 times the potential of the limited slip under the same conditions. With limited slip unit, in extreme cases of unequal traction, the wheel with the least amount of traction may spin.”

See, if your limited slip is spinning, your forthcoming GM service manager can say it is because of an extreme condition…. (Yes, I know, there are so many honest service managers out there. )


Following tests are described in GM service manual. You can take your truck to a dealer and ask them to do the tests in your presence; or have them done in one of your friendly neighbourhood mechanic shops.


You will need help to do the following test. Get your buddy.

Warnings, cautions and notices…

Do not perform this testing on jacks or stands. Do not crawl under the truck when engine is running. The truck must be firmly supported by a frame-contact hoist.

Keep an eye on the engine and transmission temperature, do not overheat them.

Either pipe out the exhaust or work in a well ventilated area. You cannot smell carbon monoxide, and it will kill you. Keep away from the exhaust pipe, it is hot.

Keep your hands and your body away from rotating parts. First stop the engine and them work on rotating parts.

Make sure your buddy understands what you are saying and doing and you understand what he/she is saying and doing.

Do not forget, this is a volunteer site, information supplied is for general discussions, no guarantees, no liabilities assumed, do it at your own risk. If you are not sure do not attempt, go to a professional shop for help.


First test:

1. Place the truck on a frame-contact hoist, allowing free rotation of rear wheels.
2. Rotate one of the rear wheels, the other wheel should rotate at the same direction. If the other wheel rotates at the opposite direction, you have a straight differential, not a locking or a limited slip one or the differential is gone.
3. Hold one wheel stationary. Slowly rotate the other wheel approximately ½ revaluations per second in both forward and reverse directions. The wheel should rotate freely. The differential is locking and broken if both wheels attempt to turn together. Test both sides.
4. Get your buddy (or you) in the truck, and raise the hoist to a level so you can work under it.
5. Start the engine and warm it. Ensure the engine is idling at low speed.
6. Apply the park (service) brake.
7. Place the transmission in drive (or in first gear if it is manual).
8. Park brake should hold both wheels, no rotation.
9. Lock one rear wheel by pulling one parking brake cable under the vehicle.
10. Release the parking brake slowly enough to start the free wheel turning. The locked one should remain stationary.
11. Slowly press the accelerator to increase the speed of the free wheel. The differential will lock, causing the rotating wheel to stop or both wheels to turn at the same speed. You may need to accelerate the engine until approximately 10 mph. If the speed increases over 20 mph without causing the differential to lock, differential is not functioning properly.
12. Stop, lock the opposite wheel, and repeat the test.
13. RAPID RELEASE OF THE BRAKES OR RAPID ACCELERATION OF THE ENGINE WILL INVALIDATE THE TEST.



Testing Limited slip differential

1. Block the front wheels.
2. Raise and support the truck.
3. Remove the rear wheels
4. Using a spindle remover and a torque-wrench, measure the rotational force of axles, one by one.
5. You should measure between 30 to 200 lb. ft. If it is out of the range, clutches may need to be replaced.

Hope you guys find these useful.

This message has been edited. Last edited by: Ken,

Between 30 and 200lb ft, huh ?!!!!?

Good ole GM, narrowing it down for us !!!!!!


Thanks for the info, Ken. Very useful, despite GM's best efforts !!!!!!!!!!

Thanks for the help! Finally made it to this location. LOL! My GM mechanic used a much more complicated method to test the LSD. We went to the wet grass headed uphill and put one tire on the grass and one on the pavement, then eased on the gas pedal! Yep, the one in the grass spun and no effort by the one on the pavement! Even tapped on the brake a bit, Nope, sitll no lock! Put both tires in the grass heading up hill and both spun! Yep, that can even happen on a single track diff too! Not proof it was working! The facts you mentioned in rotation of a LSD in your test are true, but Ill stick with wheels on the ground testing. If it doesnt work there where its really going to be used then its not working and its useless. If in fact its only going to work in mild conditions, then its a mute point wheater it works at all or not, right? Its never going to be worth having when you really need it. If it works correctly in the air test but wont function efectivly on the ground then its worthless. Am I not right here guys? Ill know after the new one goes in, and Ill get back to everyone with some hard facts as it pertains to my situation. By the way, I didnt know the Denali was available in 2500 GMC! I stand corrected! I do know the LSD on the SILVERADO 2500 is an option and not standard equipment! Denalis tend to come standard with most equipment SILVERADO has as OPTIONS!

Yes you are right, if it don't work on the ground, it is just a boat anchor.

Glad someone agrees! If its not working on the ground its worthless, period! Im not sure where some of these crazy ideas come from on the QS axle! If all the QS trucks out there are rated as 1500 heavy duty or 2500 ligt duty, then the axles are all the same probably! My Silverado is considered a 2500 Light Duty and I know the year 2005 was changed to a 1500 Heavy Duty and the 2500 was dropped in name only! It was still the same truck! I figured it had something to do with trying to bring up the sales numbers. I figured the public may have thought the 2500 was too much truck so they renamed it a 1500 to get more interest in the QS. Just my thought! If you read the fine print for 05 brochers on the QS 1500 , in fine print, it still said 2500 light duty!!!!!!! How many of you knew that?

In 03 the 1500HD and 2500 had different trailer ratings. I think they phased out the 2500 due to the confusion between the 2500 and 2500HD.

Also agree, has to work on the ground. Even though not many people are adding to this thread, I know there are a lot that are following it. Thanks for keeping us updated!

Yes, I agree, it has to work on the ground. However, by lifting the tires they ensure zero traction. On the real world, you will always have some traction; even it is not enough to move the truck, and the wheel slips.

Second test is more important for us as we have the limited slip differential. Attached is the description of limited slip from 2005 CK8 service manual.

I will attach component views in “installing after market differential” discussion

This message has been edited. Last edited by: Ken,

What you have provided here is the operation of what would be the LOCKING DIFF., which is a limited slip as well but a whole different breed than the LSD in the Quadrasteer. GM make a LOCKING DIFF AND a LIMITED SLIP. I just read the difference right off the Service computer in the GM SERVICE DEPT. A QS does not have the LOCKING LIMITED SLIP but the Limited Slip only! Ours also is supposed the have some sort of Hydrolics in it as well, making it a different type LSD than the LOCKINT LSD. Thats my reading on the matter anyway.

Mister Outdoorsman, here is the description of the LOCKING DIFFERENTIAL…

A governor mechanism together with flywheels and latching bracket locks this differential. Our Limited Slip G86 differential does not have these.

Click here for the component views

http://quadrasteerclub.infopop.cc/eve/forums/a/tpc/...2732/m/823100458/p/2

This the second page..

Ya, Mr Ken, gald you agreed with me! So whats your point besides confirming what I said? The Locking Diff is not the one we have as I already said???? If you notice the first description says " The locking differential constis of the folowing components:" Again, a limitied slip too, but the QS is not a LOCKING diff. Thanks!

I never said that we have locking differentials…


I know we have limited slips and planning to replace it with a locker.

The info your providing says LOCKING, does it not? Dont think its the DIFF we have is what Im saying. If you say the diagram you provided is the one we have then Im saying it is not. The correct info according to the computer I read off of at a GM service dept says it only a limited slip not locking at all! Maybe Im wrong!

Ken, what was your point of providing the diagrams of the Locking / Limited Slip if not to say thats what we have? One of us is not followint the posts to well! I thought you were trying to say that was the diagram for the QS diff! Did I not follow you correctly? We all need to be clear on what our point is and not throw information out there thats not correct or is irrelivant to our QS pickups! Ive seen several post that seem to say one thing then the poster of that comment says, I didnt say that??? Lets all talk facts and problems and avoid trying to be experts. Im certainly not one!