OR VietVet Is Still Throwing $$$ at 2005 Z71
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915_Tahoe
Your GM Parts Specialist
OP
OP
Does anyone know if the first signs of an a/c compressor fail/slam starts with a moan from the compressor when start in cold weather and defroster is on? Heard that noise a couple of times in cold weather here and goes away after about 5 seconds. Need to get under there with my stethoscope and listen while it is started by a friend.
OP
OP
First comment, "tongue in cheek" of course, thanks for all the help and info from my last question about the a/c compressor noise. 
Do have another concern that is going to be looked at on the 27th. If my radio is off and just maintaining speed between 40-65 mph, I hear a very slight minute tiny little howl noise that as soon as I lift from the gas pedal, goes away and as soon as I just touch the pedal ever so slightly, the noise comes back. My tech friend specializes in gears and is convinced that just needs backlash checked and while in there, if the gears themselves look ok, he will do all the bearings and re-shim it. I will post back here with the results.
Do have another concern that is going to be looked at on the 27th. If my radio is off and just maintaining speed between 40-65 mph, I hear a very slight minute tiny little howl noise that as soon as I lift from the gas pedal, goes away and as soon as I just touch the pedal ever so slightly, the noise comes back. My tech friend specializes in gears and is convinced that just needs backlash checked and while in there, if the gears themselves look ok, he will do all the bearings and re-shim it. I will post back here with the results.
OP
OP
Recently I have heard a very slight hum noise at the rear diff. Has 10 month old GM 12378261 75W-90 synthetic oil in it. Last night my friend had me over to his shop and we checked the backlash and found that the backlash was dead center of the preferred measurement and the coast and accel side of the gears looked like new.
The only time I heard the slight hum noise was when accel or maintain hiway speed and when let off the noise goes away. What is everyone's choice for the gear oil instead of the GM oil? Amsoil, Redline or Royal Purple?
While we were there we did the rear shaft u-joints with new Genuine GM joints and dropped the spare and checked it for my upcoming trip and cleaned and lubed the spare tire mechanism.
The only time I heard the slight hum noise was when accel or maintain hiway speed and when let off the noise goes away. What is everyone's choice for the gear oil instead of the GM oil? Amsoil, Redline or Royal Purple?
While we were there we did the rear shaft u-joints with new Genuine GM joints and dropped the spare and checked it for my upcoming trip and cleaned and lubed the spare tire mechanism.
pwtr02ss
Full Access Member
I bought Mobil delvac for the rear of my Yukon. I haven't changed the fluid yet. This seemed to have great reviews and does not have the friction modifier. From what I've read, that's what we're supposed to use as sometimes to friction modifier can mess with the g80. That being said, I've never had an issue using fluid with the modifier, I was just being safe since I'm still under warranty
Mobil Synthetic, SAE Grade : 75W-90, 1 gal. Jug 122035-1 Each https://www.amazon.com/dp/B007WVI5G...abc_6GQHKCS1Q0AQE2MG3VRX?_encoding=UTF8&psc=1
I've ran royal purple (used royal purple in the front of Yukon and rear of Camaro) and mobil 1 in past vehicles. The front on the avalanche recommends non-synthetic so I've used valvoline on it. I can't say one is better than the other though
iamdub
Full Access Member
I put Mobil1 Synthetic LS in mine as well as my brother's '05 Sierra (4WD non-Z71, if that means anything). IIRC, it has the friction modifiers required for some GM limited slip differentials but works fine in those not requiring the modifiers. Two years and ~20K not-always-easy miles with no complaints. Actually, the diff didn't wanna unlock after locking. It returned to working like it should when I put this oil in.
swathdiver
Full Access Member
In 2018 my compressor started making a whirring, whining type noise when engaged, intermittent at first and then constant. Still does it to this day. The Sierra started doing it and just about every 800-900 we hear in traffic does it too. I was going to replace the clutch but didn't want to upset the apple cart.
OP
OP
Since it is warmer here now, the a/c area noise is not there. I think it is a belt noise now instead.
Update on the rear diff fluid. Did the Royal Purple and after a full day of driving at different speeds/loads, no noise.
Update on the rear diff fluid. Did the Royal Purple and after a full day of driving at different speeds/loads, no noise.
OP
OP
Two updates: The rear diff noise is back but not as loud and with the great lash reading, I am gonna leave it all alone.
Second update: As you know, I am moving back to Mo. and today I gave notice here at work and will be leaving end of this month to go to Paradise, Ca. and then leave there toward end of March. This trip/move is also a very large factor for all the work I have done to my Z71.
Second update: As you know, I am moving back to Mo. and today I gave notice here at work and will be leaving end of this month to go to Paradise, Ca. and then leave there toward end of March. This trip/move is also a very large factor for all the work I have done to my Z71.
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