Rear end whine from 40 to 60 MPH

[dalekerr]

Well I've had the gears changed three times in my 67 12 bolt rear end and each time it has whined. The first hack did a bad job and they were not set up correctly. Started whining at 20mph.
 The secound mechanic set them up perfectly according to him and they whined around 50-55 mph until I changed the gear oil to Syntheticoil,  (Lucas 80/90) as he suggested and they became much louder and started at 45 mph. He claims there must be something wrong with the rear end housing. Gave my money back and does not want to do them again

Yukon says not so, just not set up properly.

Next guy same thing only worse.  He claimed no whine while on the rack, so it must be something else besides rear end!

New gears, crush sleve etc, each time. 3.31 gears

Is it possble they don't know how to set up and old rear end?

Sure would like to hear the radio while cruising. Hopeing to do a part of route 66 this year. Suggestions appreciated, Located in Central Louisiana

[rich69rs]

The whine you hear is from something, as you already know, not "meshing" properly between the pinion and ring gear.

First two things I'd have verified and WITNESSED BY YOURSELF are backlash and tooth contact.  Out of tolerance backlash is a set up issue; i.e. not shimmed properly.  Tooth contact issue can result from more than one source including the axle tubes not being square to the differential housing, among others.

Mismatched tooth hardness/surface finishes could also cause an issue but that is probably a stretch because that would be a manufacturing issue and probably not the case.

If you haven't personally witnessed a backlash and tooth contact issue, I'd start there.  Also, the rear end won't "whine" on the rack because the gears aren't loaded to any great extent.

Richard

[dalekerr]

I bought a used set of gm 3.31 gears. the last two mechanics did not want to use them since, used. But agreed they look good. Should I jsut use these gears, they have to be better than the after market gears?

[rich69rs]

I bought a used set of gm 3.31 gears. the last two mechanics did not want to use them since, used. But agreed they look good. Should I jsut use these gears, they have to be better than the after market gears?

If it were me, and I hadn't witnessed the backlash or tooth contact checks, I'd start there.

Richard

[z28z11]

A good friend of mine, '69 Firebird 400 car, went through two sets of aftermarket gears before he went back to a used set of GM gears. Whined and howled on him until he went back to OE. This guy is a retired GM drivetrain engineer, knows what he is doing when sets a rear or a transmission up: he's sworn off aftermarket because of the lack of compatible, matched gear sets in his opinion.

Regards,
Steve

[CantRepeat]

When setting up used gears the coast side contact patch is far more critical then the drive side. If not done correctly, used gears will be very loud.

Best bet, buy some new gears.

[Kelley W King]

Just asking, did they install new side bearings, ect? Was it quiet before? Did they check the axle bearings when they pulled the axles? Just thoughts.

[usa1ti]

A lot of different opinions on this one due to Urban Myth and past experience including mine. I have had a lot set up and have zeroed in on this (1) used gear sets are very difficult to re set up quiet in another housing due to the initial pattern being set. (2) VERY few people actually know how to set a gear up correctly and hit it every time. (3) Synthetic vs conventional gear oil makes no difference. Viscosity does. (4) I have had quiet and loud in most all brands so no mfg seems to be the best. (5) The only way to 100% guarantee a good quiet set up that will live is to have Mark Williams, Richmond or Moser set it up. I have used these guys (mostly Mark Williams) at NHRA / IHRA events to set up all of my race cars and 1 street car. 0 issues. Sometimes local guys can hit it but rare. If you are tired of going back and forth and don't mind spending the $ to fix the problem send everything to one of them. Unfortunately with Chevrolet the housing would have to go or if you are lucky enough to be near a national event you might could arrange to bring the car to their service truck/trailer. 

[dalekerr]

Ok I got my gears changed again a few weeks ago with US gears 3.31. I took my car to a shop that does only rear axle repairs and gear changing. The mechanic called and said both tubes were bent forward about an inch on each side? He said he could not straighten them so, I told him to go ahead and change the gears and do his best. After changing the gears he said that they whined a little around 35mph. I said great, I can live with that. He sent me pictures of the pattern on both sides and they looked great.

I picked the car up and drove it gently for the next 500 miles over two weeks, never above 60mph. I changed the oil from 80/90 to 85/140 and added the clutch juice. I also used a striaght edge to check tthe tubes for straightness and I could not see any bend? So far no issues, a minor whine around 35 to 40 mph, but with the AC and radio going you have to listen for it to hear it.

Thanks for all your help. Rt 66 here I come in the fall.

Dale Kerr

[bcmiller]

If the tubes are bent that much, it’s a big problem and bearings probably won’t last long.

There are guys that can straighten housings. I had one done not that long ago, very early 67 3.31 Posi coded. Had to cut about 12-15 inches off each end and weld on used tubes with original GM perches. Perfectly straight now, setup with a big thick 72 inch long rod and “pucks” on each end to verify straightness.

I have had used GM gears setup correctly with no issues.