# awful scraping noise from rear



## Stereolab42 (Apr 6, 2018)

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.


----------



## Cafr119 (Dec 9, 2017)

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


----------



## Stereolab42 (Apr 6, 2018)

Cafr119 said:


> 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


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.


----------



## Stereolab42 (Apr 6, 2018)

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.


----------



## PontiacJim (Dec 29, 2012)

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.


----------



## Cafr119 (Dec 9, 2017)

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


----------



## BearGFR (Aug 25, 2008)

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


----------



## HickBoy (Aug 5, 2018)

BearGFR said:


> 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.


----------



## john23 (Mar 6, 2016)

stressed out exhaust hanger?


----------



## Stereolab42 (Apr 6, 2018)

BearGFR said:


> 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.)


----------



## L Oden (Jun 1, 2013)

For what it's worth, is it scraping or "clunking" ? My 68 GTO, which had been restored a couple of years earlier, was doing the same thing, but in the front. Took me forever to figure it out. Mine only did it when I turned also so I though I'd add my two cents. It ended up being lose body mounts. I tightened all of them and it repaired the problem. Maybe it's worth a check.

Larry


----------



## Stereolab42 (Apr 6, 2018)

L Oden said:


> For what it's worth, is it scraping or "clunking" ? My 68 GTO, which had been restored a couple of years earlier, was doing the same thing, but in the front. Took me forever to figure it out. Mine only did it when I turned also so I though I'd add my two cents. It ended up being lose body mounts. I tightened all of them and it repaired the problem. Maybe it's worth a check.
> 
> Larry


Definitely a scraping, which implies a moving piece is impacting against a non-moving piece. Since I can't see any marks at all on the wheels/tires or surrounding hardware, and nothing on the lowest points of the car which have plenty of ground clearance anyways (5+ inches everywhere), the mystery remains. Maybe an axle in one of the rear axle tubes is scraping (assuming it's not the diff itself)? I know they had to remove/modify/reinsert the rear axles when doing the full disc brake kit. Luckily I'm taking it back to the same shop tomorrow so they are already very familiar with this problem child.


----------



## L Oden (Jun 1, 2013)

Odd that it only does it when you turn however. Does the scraping stop when you straighten out? That was my issue. I though I had tires that were too wide or the wrong length shocks. Ended up being the lost body mounts and the body was shifting on the frame. Let us know what you find out. GOOD LUCK.


----------



## HickBoy (Aug 5, 2018)

Could one of the rear axles be loose and possibly wiggling around during the turn and causing the rotor to move against the backing plate?
Could the new brake conversion of changed the clearance or length of the wheel and somehow causing the rub?


----------



## Sean Lyddy (Oct 4, 2018)

what Hickboy said..maybe it spit out a C-Clip on the axle and the whole rear axle is shifting in the housing?


----------



## Stereolab42 (Apr 6, 2018)

Took it to the shop... had me drive up and down a dip turning right while he crawled underneath... says it's the driveshaft impacting against the muffler. Apparently the car was bending a bit when turning over a dip which was causing that contact. I looked for myself and do see where the end of the driveshaft is very close to the right muffler, and there is indeed a gouge there. So the muffler just has to be shifted.

Lesson for today is that clearance between different components under the car should be enough to account for torsion and bending.


----------



## Cafr119 (Dec 9, 2017)

Sweet, issue solved, no axle disassemble, no Tires rubbing, not anything to do with the disc brake conversion, etc, etc. Glad to hear it’s a easy fix, good thing for all of us to keep in mind when working or modify our exhaust system


----------



## BearGFR (Aug 25, 2008)

Stereolab42 said:


> Took it to the shop... had me drive up and down a dip turning right while he crawled underneath... says it's the driveshaft impacting against the muffler. Apparently the car was bending a bit when turning over a dip which was causing that contact. I looked for myself and do see where the end of the driveshaft is very close to the right muffler, and there is indeed a gouge there. So the muffler just has to be shifted.
> 
> Lesson for today is that clearance between different components under the car should be enough to account for torsion and bending.



Great! Glad you figured it out. Isn't it amazing how confounding mysteries can turn out to be so simple once you know the secret?

Bear


----------



## Stereolab42 (Apr 6, 2018)

BearGFR said:


> Great! Glad you figured it out. Isn't it amazing how confounding mysteries can turn out to be so simple once you know the secret?
> 
> Bear


Yup. I of course knew that one has to pay close attention to clearance in the vertical direction between sprung and unsprung components, for obvious reasons. I simply did not anticipate there could be a half-inch of clearance necessary horizontally to account for body flex. Probably something auto fabricators learn on the first day on the job. The moar you know...


----------



## Stereolab42 (Apr 6, 2018)

The story gets even better... took it in today for the shop to actually fix the scraping, which was accomplished quickly. I mentioned that in addition to the scraping there is a groaning noise when I brake below 10 mph. They found the cause of that too... the upper rear control arms had been installed on the wrong sides! Instead of stopping to consider whether he had them swapped, the PO just went "hold my beer" and whaled them into place, bending the arms, the bolts, and the bushings in the process. $300 later for all-new parts and this will be fixed too. Yay!


----------

