Is my AWD Escalade rearend junk?

[73TA]

My project 08 Esky with 234K miles has been pretty good so far. Took it for a 300 mile road trip and got 17 mpg on the freeway. I have been noticing a "clunk" or something like that when taking off "briskly" from a stop or a downshift when accelerating on the freeway. So I jacked it up on the rear diff and the both wheels would spin. I thought this should be impossible if it is in park.
I then got underneath it and checked the u-joints and they looked fine. Then I spun the wheels. The drive shaft was not moving, so it definitely was is park.
I then put the front wheels on concrete with the rear wheels in gravel and tried to power brake it, the rear wheels did not spin the gravel. I assume that I have been driving with only the the front diff taking all of the load and pulling the Esky instead of it being "pushed" by the rear wheels?
Are the rear "posi" clutches worn out?

I am missing something here?

Mike

Project thread

https://www.tahoeyukonforum.com/thr...-mechanic-fixed-my-blown-engine-for-7.123682/

 

[Joseph Garcia]

I can't tell you what to expect, when you try to power brake an AWD truck. Others will chime in with their thoughts.

Regarding the clunk, the slip yoke coming out of the transmission and connecting to the rear drive shaft may be the source of your clunk, coming from some play in the spline, where the slip yoke connects to the transmission. There is a nickel coated slip yoke spline that folks purchase that can eliminate the clunk, if this is the source of the clunk.

Another source of this clunk can be the 2 differential supports brackets, which have rubber bushings at both ends of the 2 support brackets, and these bushing wear, causing a clunk sound. The replacement of these 2 support brackets, along with the rubber bushings can eliminate the clunk, if this is the source of the clunk.

 

[73TA]

Just wondering why the rear end tires will spin if the driveshaft is locked in park while the rear wheels are off the ground, I now have to assume the rear end is basically "disconnected" internally in the rear diff.

Mike

 

[wjburken]

Put the thing back up on jack stands, pull the cover of the differential and see what you have going on. You could also, if you are careful, put it up on 4 jack stands so all 4 wheels are off the ground and put it in gear and see what happens. Either way, you need to pull the cover and take a look. Until you do that, you are just guessing.

 

[02Lightning]

Just wondering why the rear end tires will spin if the driveshaft is locked in park while the rear wheels are off the ground, I now have to assume the rear end is basically "disconnected" internally in the rear diff.

Mike

I think that's normal, did one wheel spin one way, and the other wheel spin the opposite? I'm not sure your applying enough torque for it to couple the front wheels.

 

[73TA]

Every vehicle that I have put on jack stands the rear wheels will not turn when it is park. That is why I assume that the rear end has some serious problems. I agree that I will need to remove the rear diff and take a look if I don't get any information that says this is normal.

Anyone want to jack up there Esky in the rear and see if this is the case?


Mike

 

[Geotrash]

Every vehicle that I have put on jack stands the rear wheels will not turn when it is park. That is why I assume that the rear end has some serious problems. I agree that I will need to remove the rear diff and take a look if I don't get any information that says this is normal.

That's true only with a true posi-traction rear end, or a locked differential. I have 2 Denali's which have the same drivetrain as yours. With the rear wheels in the air, when I spin one wheel, the one on the other side spins in the opposite direction. I know this because I was playing around with it when I changed out the rear air shocks on both of them a few months ago.

 

[gooffeyguy]

When I've had my Denali AWD up on 4 jackstands rotating the tires, I'm pretty sure I could get all 4 wheels to rotate by only turning 1 and also while in park I think. Each wheel rotated the opposite way than the one across from it.

I think it has something to do with hiw the AWD transfer case works.

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[73TA]

Thanks, great to hear that. Both tires do rotate in the opposite direction just like a standard posi does. I never tried the fronts. I guess the GM AWD transmission must lock the front wheels when in park. I guess these rigs are always in basically full time four wheel drive, unlike other vehicle manufactures that bias most of the power to the rear wheels and only activate the front wheels when traction is needed.

If that is the case, wonder how the vehicle can lock into park if all the wheels turn?

Mike

 

[gooffeyguy]

I might have had to move it into neutral when doing this, but I don't remember

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[Jimmyy]

Both tires do rotate in the opposite direction just like a standard posi does.

posi should turn in same direction. One wheel wonders spin opposite direction.

 

[gooffeyguy]

I think the G80 lockers work in a different way. Allows 1 wheel to spin so much then locks up mechanically. That may be why when spun by hand the wheels spin different directions like an open differential.

Now my mustangs with the Trac Loc differencial that uses clutch packs, I have rebuilt them tighter with more clutches and will spin the wheels in the same direction with the rear lifted and turned by hand

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[02Lightning]

Thanks, great to hear that. Both tires do rotate in the opposite direction just like a standard posi does. I never tried the fronts. I guess the GM AWD transmission must lock the front wheels when in park. I guess these rigs are always in basically full time four wheel drive, unlike other vehicle manufactures that bias most of the power to the rear wheels and only activate the front wheels when traction is needed.

If that is the case, wonder how the vehicle can lock into park if all the wheels turn?

Mike

I thought all traction locks both tires spin the same direction? You also have to remember this is all going through a transfer case.

 

[Rocket Man]

Pretty sure this is normal. One note is do not put it on jack stands and run it in gear for more than a minute or two unless you find out for sure if it doesn’t wreck the transfer case. Not sure on the NNBS but on my NBS Denali it will destroy the TC. You should go ahead and pull the rear cover and inspect it but make sure to remove the fill plug first. Quite a few people have drained the diff and then discovered the fill plug was seized and there was no way to refill it. Somebody else should chime in regarding running it on jack stands.

 

[73TA]

According to my vin# search, my ride has a limited slip, posi rear end, and the front is an open diff.

I did bunch of google searches and could not find much on the subject until I remembered to look at the vin info. Can't remember if the wheels spun in the direction on the stands.

Pretty sure there is something wrong with it, if the driveline is locked in park and the both rear tires spin. Guess I will find out when I get back home from my business trip next week and put up on jack stands and see if the rear wheels turn when I put it in gear.

Mike

ADJUSTER RR REAR SEAT, POWER, STOWABLE; ADJUSTER FRT ST POWER, MULTI-DIRECTIONAL, DRIVER; ANTENNA BODY SIDE WINDOW, RADIO; ADJUSTER PASS ST POWER, MULTI-DIRECTIONALADJUSTER,SEAT,6-WAY POWER,SPLIT BENCH,PASSENGER; ASH RECEPTACLE AND CIGARETTE LIGHTER; INSULATION,ACOUSTICAL; VIN IDENT POSITION, MULTI- PURPOSE VEHICLE; BODY EQUIPTMENT ONE PIECE LIFT GATE WITH LIFT GLASS BOD; CONTROL ACTIVE BRAKE; FASCIA FRT, CUSTOM, BODY COLOR; BRAKE VAC POWER, 17" DISC/DISC, W/VSES, 7700 LBS; MOLDING B/S EXTERIOR, BRIGHT; CAMERA REAR VIEW; BAR LUGGAGE CARRIER,CENTER CROSS; COLOR COMBINATION SOLID; CRUISE CONTROL,AUTOMATIC,ELECTRONIC; EXTERIOR COLOR,PRIMARY,BLACK; FEDERAL EMISSION CERTIFICATION; CHASSIS PACKAGE BI-STATE REAL TIME DAMPING; SILVERADO/SIERRA CLASSIC/SLE PACKAGE; CONSOLE ROOF INTERIOR, DELUXE; CONTROL INTELLIGENT HIGH BEAM; DIGITAL AUDIO SYSTEM S-BAND; DEFOGGER,REAR WINDOW,ELECTRIC; OPENER GARAGE DOOR, UNIVERSAL; HEATER,AUXILIARY; LIFTGATE, POWER; COOLING SYSTEM,TRANSMISSION,HEAVY DUTY; EMISSION SYSTEM FEDERAL, TIER 2; ENTERTAINMENT SYSTEM REAR SEAT,SINGLE DISPLAY,REM CONTROL W/HEADPHONE; EQUIPMENT ADDITIONAL DVD SCREEN; PACKAGE OPTION-; CONTROL SALES ITEM NO. 139; CONTROL - SALES ITEM NO. 89; CARPET,FLOOR AND WHEELHOUSE; CARPET,LOAD FLOOR; COVERING,FLOOR MATS,FRONT AND REAR,CARPETED INSERT; COMPONENT FRT LH COMPUTER SEL SUSP (6F4); FASCIA RR, CUSTOM, BODY COLOR; COMPONENT FRT RH COMPUTER SEL SUSP (7F4); GENERATOR,160 AMP; GLASS,DEEP TINT(REAR SIDE WINDOWS AND REAR DOOR WINDOW); GRILLE,SPECIAL; GVW RATING(7400 LBS); HEADLAMPS CONTROL AUTOMATIC, DELAY; HVAC SYSTEM AIR CONDITIONER FRT, AUTO TEMP CONT, AUX TEMP CONT; HEATER,RR SEAT; HEATER SEAT, COOLING, FRT; INDICATOR,LOW TIRE PRESS; CONSOLE,FRONT COMPARTMENT FLOOR(CUSTOM); LOCK CONTROL REMOTE, KEYLESS ENTRY, START; LOCK,SIDE DOOR,ELECTRIC; LANGUAGE CONTROL ENGLISH, FRENCH, SPANISH; LAMP,FRONT FOG; LOCK SPARE TIRE, HOIST SHAFT; LICENSE PLATE,FRONT MOUNTING PACKAGE; CARRIER,ROOF LUGGAGE(PAINTED); CADILLAC BRAND IDENTIFICATION; MIRROR O/S LH & RH, REMOTE CONTROL, ELECTRIC, HEATED, POWER FOLDING; MIRROR,INSIDE,VISOR VANITY,RH AND LH(ILLUM); COMMUNICATION SYSTEM VEHICLE, G.P.S. 1; ENVELOPE,OWNER INFORMATION MANUAL; OWNERS MANUAL ENGLISH LANGUAGE; AXLE,REAR,POSITRACTION,LIMITED SLIP; PEDALS ADJUSTABLE, POWER; PLANT CODE-ARLINGTON TX, CPC; WINDOW,ELECTRIC OPERATED,SIDEWINDOW,POWER OPERATED,ALL DOORS; SENSOR INDICATOR NEAR OBSTACLE DETECTION/REAR PARKING ASSIST; AXLE,REAR,3.42 RATIO; AXLE FRONT (BASE EQUIP) FOR SCHEDULING GVW PLATE; RADIO CONTROL REAR SEAT & EARPHONE JACKS; AIR CONDITIONER,RR AUX; ROOF,SUN,GLASS SLIDING,ELECTRIC; RADIO AM/FM STEREO, WX, SEEK/SCAN, CD, DVD, NAV, CLOCK DSP, RDS, W/VOICE REC MICRO; RESTRAINT ROOF SIDE, LH & RH, INFLATABLESEAT DRIVER,AIR,LOW BACK,VINYL,BOSTROM 910; SPRING,REAR(BASE EQUIPMENT); SEAT,REAR,BUCKET; SEAT,#2 REAR UTILITY; MIRROR,INSIDE,REARVIEW,LT SENSITIVE,COMPASS,O/S TEMP DISPLAY; MERCHANDISED PKG LUXURY EDITION; PROCESSING DIRECTIONS & CONNECTIONS SERVICE PACKAGE; SALES PROCESSING-STOCK ORDERS; CALIBRATION- SPEEDOMETER A; SPEAKER SYSTEM PREMIUM AUDIO BRANDED WITH SURROUND AMPLIFIER; SPRING,FRONT(BASE EQUIPMENT); TIRE SPARE P265/70R17-113S BW R/PE ST TL ALS; STEPS, RUNNINGBOARD SIDE, RETRACTABLE, POWER; SEAT FRT, INDIVIDUAL/NON-BKTSEAT,FRONT DRIVER,PASSENGER; CONTROL STEERING WHEEL,ACCESSORY; HEATER STEERING WHEEL; STEERING WHEEL(DELUXE); TRANSFER CASE ALL WHEEL DRIVE (AWD), OPEN DIFF, SINGLE SPEED; TIRE ALL P285/45R22 BW TL AL2; HOOK,FRONT TOW; TRAILERING PACKAGE(SPECIAL)(REESE TYPE HITCH); TRAILER HITCH(WEIGHT DISTRIBUTING PLATFORM); TRIM COMBINATION,BLACK LEATHER; INTERIOR TRIM COLOR BLACK/EBONYINTERIOR TRIM,EBONY; VEHICLE STATEMENT - US/CANADA; VIDEO FORMAT REGION 1, NTSC; LABEL COMPLETE VEHICLE; SENSOR INDICATOR INFLATABLE RESTRAINT, FRT PASS/CHILD PRESENCE DETECTOR; LEVEL CONTROL AUTO, AIR, HD; WHEEL 22 X 9.0, ALUMINUM, CHROME; WHEEL SPARE FULL SIZE, 17" STEEL; WIPER SYSTEM,REAR WINDOW; WIPER SYSTEM WINDSHIELD, PULSE, MOISTURE SENSITIVE; WASHER NOZZLES, HEATED, WINDSHIELD

 

[gooffeyguy]

Do you have "G80" on the RPO sticker in the glove box? Every option your truck has is listed on this with a 3 digit code.

Looks like this, here's mine.....

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[swathdiver]

According to my vin# search, my ride has a limited slip, posi rear end, and the front is an open diff.

Mike, this differential does not operate like that in a '73 Trans Am or '87 Buick, it is a combination limited slip and locker. Runs more like a locker. No special fluids needed.

Remember, your AWD transfer case operates much like a 3rd differential carrier as well. You can down the Restoration Kit from GMs website for your vehicle and if memory serves there are detailed explanations on how the system works, same with the online shop manual at AllDataDIY.

 

[73TA]

I realize the true options are in the glove box and understand the GM G codes for the rearends. I had used the vin search before I bought to see what options where on it. I will the wife check the glove box.

Regardless of the rearend type, shouldn't the rear tires not spin if the driveshaft is locked in park as the case with my Esky, and shouldn't the rear tires spin at least a little if rear tires are in gravel?

This just doesn't make sense to me.

Mike

 

[mikeyss]

My 09 tahoe has the AXN 9.5" G80 rear end, and when the vehicle is up on the lift, the rear wheels DO spin in opposite directions. While it's still on the lift, you can spin one tire as fast as you can by hand, and it will engage the locker with a loud clunk. It's kinda alarming when it engages and it's kinda hard to do by hand.

 

[thompsoj22]

Thanks, great to hear that. Both tires do rotate in the opposite direction just like a standard posi does. I never tried the fronts. I guess the GM AWD transmission must lock the front wheels when in park. I guess these rigs are always in basically full time four wheel drive, unlike other vehicle manufactures that bias most of the power to the rear wheels and only activate the front wheels when traction is needed.

If that is the case, wonder how the vehicle can lock into park if all the wheels turn?

Mike

Pretty sure you have an open diff G80 in the rear which will rotate the op wheel in the

I realize the true options are in the glove box and understand the GM G codes for the rearends. I had used the vin search before I bought to see what options where on it. I will the wife check the glove box.

Regardless of the rearend type, shouldn't the rear tires not spin if the driveshaft is locked in park as the case with my Esky, and shouldn't the rear tires spin at least a little if rear tires are in gravel?

This just doesn't make sense to me.

Mike

Has the vehicle ever rolled down your driveway when in park with all four wheels on the ground? You have answered your own question. A true locker would not rotate in your test method of being jacked in the air. Your diffs are open and will do exactly what yours are doing when jacked up. If you actually have a true limited slip, lift only one wheel off the ground and you should have enormous effort req to spin the wheel. limited slip clutches wear out, if the wheel spins easily you either have a G80 tracloc or your limited slip is showing the result of 234k miles of urban use.