awful scraping noise from rear - Pontiac GTO Forum
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post #1 of 20 (permalink) Old 10-19-2018, 06:38 PM Thread Starter
 
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awful scraping noise from rear

No, it's not the busted shock from my other thread. I lopped off the offending brake bracket and replaced the shocks. It's something else. Only appears to happen when turning right over deep and wide ruts in the street:


I have 5 inches of clearance on everything under the car, and don't see any scrapes, so it's not that. It doesn't quite sound like gears grinding so I hope it's not the diff, although correct me if I'm wrong. Hell if I can figure out what is rubbing against what underneath there.
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post #2 of 20 (permalink) Old 10-19-2018, 07:01 PM
 
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Well, just my 2 cents, sounds like maybe the rear brake drum rubbing against the backing plate or maybe even on the front rubbing against the brake dust cover but when it’s flexing is the cause otherwise something in the differential
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post #3 of 20 (permalink) Old 10-19-2018, 07:11 PM Thread Starter
 
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Well, just my 2 cents, sounds like maybe the rear brake drum rubbing against the backing plate or maybe even on the front rubbing against the brake dust cover but when itís flexing is the cause otherwise something in the differential
Just got 4-wheel disc brakes installed, I double-checked and don't see anything rubbing in the brake mechanism. I really don't want it to be the diff, I just got finished with this car being in the shop for six weeks.
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post #4 of 20 (permalink) Old 10-19-2018, 09:01 PM Thread Starter
 
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Let's assume for the sake of argument the diff is toast and I need to replace it. (My shop will tell me for sure on Thursday.) Car was born with a Safe-T-Track and AFAICT it's still on there (even has the metal tag). Let's also say I don't want to wait weeks to send it out for a specialized rebuild and just want to swap something in there ASAP that works. What do I order? I know absolutely nothing about diffs and have been furiously Googling around for an hour... looks like I need a diff carrier and diff gears at a minimum?

What about these 3.36 gears:

https://www.summitracing.com/parts/yga-24503/overview/

What about this Auburn unit (is the 28 splines correct):

https://www.summitracing.com/parts/aub-5420113/overview

Do I need "bearings" as well, and what kind? Anything else? (Once again, like Rummie, I feel like I don't even know what I don't know.
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post #5 of 20 (permalink) Old 10-19-2018, 09:37 PM
 
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Almost sounds like a tire rubbing. I would have someone stand outside the car at that place where you heard the noise and see if they can pinpoint where it is coming from as you do the same turn/maneuver.
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post #6 of 20 (permalink) Old 10-20-2018, 02:12 AM
 
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I agree with PJ, the best is to have someone outside and listen, video diagnose is hard at times, you can get a bunch of different opinions. If you just did a 4 wheel disc brake conversion, and the noise wasn’t there with the old set up and you know this, to me as I listen it sounds metal to metal, then my money is on the conversion, you might have a rotor rubbing on a caliper or a dust cover, etc. to me ( and I’m not there ) doesn’t sound internal, and I could be wrong, just offering advice. Good Luck
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post #7 of 20 (permalink) Old 10-22-2018, 11:22 AM
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That sound is VERY familiar. Go check for evidence of tire rubbing on the REAR/LOWER corners of the FRONT fender openings... You'll also see rub marks on the tires themselves, right around the outside edges of the tread. See the location I've indicated in the attached photo. (Which, by the way, is a photo of my car that the original owner sent me from when it was brand new. )

Bear
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post #8 of 20 (permalink) Old 10-22-2018, 07:24 PM
 
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That sound is VERY familiar. Go check for evidence of tire rubbing on the REAR/LOWER corners of the FRONT fender openings... You'll also see rub marks on the tires themselves, right around the outside edges of the tread. See the location I've indicated in the attached photo. (Which, by the way, is a photo of my car that the original owner sent me from when it was brand new. )

Bear
I can confirm that my '65 has rubbing in this exact spot (drivers front tire at back of fender) when I am driving downhill (even a small incline) and turning to the right as weight and gravity do their things. Same goes for the opposite (passenger front tire inside of fender) when turning the opposite direction on the downhill. I don't have the issue going uphill as the airshocks on back seems to keep everything happy.

The plan to fix for me is a front-end rebuild as the rubber/bushings/springs/shots have all had better days (years) as well as replace the airshocks/springs on back to keep everything in sync.
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post #9 of 20 (permalink) Old 10-22-2018, 08:18 PM
 
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stressed out exhaust hanger?
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post #10 of 20 (permalink) Old 10-23-2018, 12:44 PM Thread Starter
 
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Originally Posted by BearGFR View Post
That sound is VERY familiar. Go check for evidence of tire rubbing on the REAR/LOWER corners of the FRONT fender openings... You'll also see rub marks on the tires themselves, right around the outside edges of the tread. See the location I've indicated in the attached photo. (Which, by the way, is a photo of my car that the original owner sent me from when it was brand new. )

Bear
Been over every inch of the tires and wheels, they are flawless. Fronts turn through the full range without fouling on anything. I even played the old game of turning them all the way to the right and bouncing the car up and down on each corner with my hands trying to find a clearance problem. All I hear is a suspicious squeaking from the rear left wheel. Hopefully when they get this on the lift on Thursday the problem will become obvious... it certainly isn't to me spending hours crawling under the car with a flashlight. Haven't found a single sign of anything scraping on anything.

I also found they routed one of my front hard brake lines directly on top of the left wheel upper control arm under tension, so every time that wheel bounces it rubs the line. This is clearly not the source of the audible scraping, but it will eventually result in catastrophic front brake failure on the road. So yet another thing to fix. (See, I'm finally making progress with this car... I'm now finding things I can blame on shops I took it to instead of the braindead previous owner! I guess that now makes me the braindead current owner.)
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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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