Rear End Noise - Pontiac GTO Forum
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post #1 of 16 (permalink) Old 10-23-2013, 12:24 PM Thread Starter
 
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Rear End Noise

Among all the other things that bug me and I'm slowly fixing, is a grinding noise coming from the back of the car. It's not a nasty grind like metal on metal brakes but a more subtle grinding noise and if I had to guess it sounds more like the speed of the wheel rotation and not the drive shaft rotation. I notice it most while decelerating and it's most noticable from 10-20 mph. I was thinking rear wheel bearings and I can get those replaced easy enough but what else should I be looking for? Can I prop up the back wheels and put it in drive while the engine idles and listen or would it be better to take the drive shaft off and spin it by hand?

Let me know what you think.
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post #2 of 16 (permalink) Old 10-24-2013, 09:53 AM Thread Starter
 
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I put the back of the car up on jackstands and spun the wheels. I felt like I was hearing brake noise more than anything so I took off the wheels and brake drums. Everything spun very freely but there was some noise. Maybe it's normal and maybe it's not.

1. The only grinding I heard was from the differentail gear itself. It wasn't loud but noticable. I assume the meshing of these gears make some amount of noise normally?

2. There's a high pitched squeek from the drive shaft area as it spins.

3. There is a clicking noise toward the front pinion on the transmission as the drive shaft spins.

What do you think about my noises?

One more thing, the right brake drum was tight enough that I could spin the wheel/tire backward but not forward. It looks like the teeth on the adjuster are worn down and it moves freely. Is brake drag my issue?
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post #3 of 16 (permalink) Old 10-24-2013, 12:05 PM
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Hey Witt, here's my suggestions....

1. Drain the gearlube from the differential and inspect the gears (and fluid) for metallic particals and visible damage. There are differential bearings too and they could be worn. For now I would refill with a quality gearlube and seal back up . In the future you might be looking at axle diff bearings but I wouldn't worry about that now, lets take car of the easy stuff first.

2. Sounds like possibly dry or worn u-joints. Check and see if they have a zerk fitting to take grease and if they do give em a couple of squirts from a grease gun. I not you may have to pull the DS and inspect or replace them. Be careful, when you pull them apart needle bearings could go everywhere.

3. See above, also make sure your DS is not touching the parking brake cable.

4. On the brakes I would disassemble and inspect thoroughly and maybe invest in a new hardware kit which you should be able to get through most parts stores and comes with springs, clips and the adjusters. Make sure they are assembled correctly too....They can be assembled backwards and tighten up when you brake forwards instead of backwards....ask me how I know . You should just have a light drag on the brakes when adjusted properly.
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post #4 of 16 (permalink) Old 10-24-2013, 01:58 PM Thread Starter
 
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I was thinking the same thing on the differential and brakes so I picked up new hardware and adjusters for both sides. I also got some good gear lube and I'll change that too.

I'll check the the DS and let you know on that too.
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post #5 of 16 (permalink) Old 10-28-2013, 10:23 AM Thread Starter
 
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I got the new brake hardware installed and that fixed the RR brake drag issue but the noise is still there. I also drained and inspected the differential and there was no metal and no signs of bad wear. The ujoints don't have zerks so I'll pull the DS and check em out soon.
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post #6 of 16 (permalink) Old 10-28-2013, 12:44 PM
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X2 on Alky's advice. My money is on dry/binding/tired U-joints. Be sure to mark the driveshaft position relative to the rear yoke before you remove it, so that you can re-install it in the correct position. ANY binding, dryness, hanging up or looseness means time for new joints. I seriously doubt you have bad bearings in the rear end.
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post #7 of 16 (permalink) Old 10-30-2013, 08:15 AM Thread Starter
 
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Alright here's an update. I replaced both ujoints last night. It didn't fix the noise but I'm sure glad I did it. The nuts holding the u-bolts in back were barely more than finger tight! Yikes!

So now I'm thinking that noise is possibly my out-of-round brake drums. What do you guys think?
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post #8 of 16 (permalink) Old 10-30-2013, 10:00 AM
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Out of round brake drums will be felt at the brake pedal. It will pulsate. A slight amount of run-out can result in noises IF the backing plate pads (where the shoes contact the backing plate) are worn, grooved, or dry. These should be smooth and lubed sparingly with silicone grease. Hard to hear your car's noises from CA, though!!
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post #9 of 16 (permalink) Old 10-30-2013, 10:38 AM
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Originally Posted by WhittP View Post
Alright here's an update. I replaced both ujoints last night. It didn't fix the noise but I'm sure glad I did it. The nuts holding the u-bolts in back were barely more than finger tight! Yikes!

So now I'm thinking that noise is possibly my out-of-round brake drums. What do you guys think?
Get louder mufflers.

Okay, never mind but try putting the car up on jack stands and with the trans in neutral, and the engine off obviously, rotate the rear tires and just listen. Also move them in both directions and check for backlash in the gears. Then on each side try to jerk them up and down and in and out to see if there is any play in the bearings. Also was there any wetness/leaks around the axle seals on your rear brakes? That is an indicator of worn bearings.

I'm not so familiar with the GM 10 bolt but 12 bolt Chevy's use the actual axle shaft as the inner race for the axle bearings and sometimes the bearing eats into the shaft. I'm sure GTOguy will clarify this for me but axle bearings are relatively easy to replace. The carrier bearings are a little more difficult but not out of the scope of the confident home mechanic.
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post #10 of 16 (permalink) Old 10-30-2013, 10:55 AM
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Here I am, Alky. 10 bolt axles don't use the axle as the inner race, they have a sealed bearing pressed on that has its own inner race. Very common for the inner race to spin on the axle, causing the axle to groove and become scrap. Also can cause the wheel to come off the car, with the axle attached. BTDT, twice! When rear wheel bearings go out in ten bolt rears, they usually make a grating sound, or no sound at all. They don't squeak. When I lost mine back in the day, I heard nothing. Looked in my side-view mirror and the wheel was outside of the wheel well!! Rear wheel bearings on these cars should have zero end-play.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Undercarriage, Frame, Transmission and Differential Discussions.

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