Rear End Rubbing Sound

[Peter L.]

I have a 63 convertible, with a 327/340hp engine, 4 speed Muncie, ad a 3:36 posi rear. The rear end was rebuild by Bair's in 2012, and the frame off compete car restoration was complete in 2015. I have approximately 9,000 miles on the car, and about 1,000 miles ago, I started to hear a faint chuffing/rubbing sound from the back of the car. It got louder with time, and is speed dependent. That is, as I go faster, the frequency of the rubbing increases. It also goes away if I am increasing speed even slightly, but comes back when coasting or just maintaining speed on a level road. I thought it was coming from the left side, so I took it to my mechanic and we pulled the left wheel and examined the brake on that side. We found the parking brake slightly worn, when It should have shown no wear. The cable was very stiff, so we sprayed it where it went into cover sheaths on it's entire length, both sides, and after much exercising of it many times and reapplying the gel lube, the stiffness went away, and the PB shoes moved freely. I took it for a test spin, and the noise was still there. Next, we pulled the brake on the right side, and found the runout on the rotor was about 0.012 to 0.015", with no appreciable wear on the pads (left side showed no appreciable wear either, but no run out). We skin cut the rotor and re-installed it, and the sound was still there. Next, my mechanic crawled into the back of the car, and listened, while I drove, and he came to the conclusion it was coming from the rear end. When I called Bair's to discuss what could be causing it, they said there is nothing in the rear end that would make a rubbing sound. They said it could be the universals (not, since we checked them for looseness, and they have no grease fittings, as they are permanently lubricated), the half shafts and drive shaft (again, we check them and they were fine). They also said it might be the wheel bearings, but they checked fine. Anybody got any ideas, or heard this type of sound before?

[Gary R.]

Re: Rear End Rubbing Sound

Discussing or explaining sounds can be tricky. If driving the car and letting off the gas and you hear the noise I would say it is either a bad pinion bearing or gear whine.

Wheel bearings replaced 9k miles ago should be fine. If not they typically would be loose and you would be able to feel end play by pulling on a wheel stud, now this may be deceiving depending on how the bearings were setup to start with.

Not saying anything bad about Bairs it was good you called them, just general comments that may or may not help you with finding the issue.

With the rotor you had turned did you confirm the runout afterwards, depending on how the rotor was turned it may or may not resolve runout.

[Douglas L.]

Re: Rear End Rubbing Sound

Peter,

I would suggest changing the differential oil adding in the proper anti-friction additive. Check the old oil for anything that looks suspicious.

[Peter L.]

Re: Rear End Rubbing Sound

No we did not measure it, but once installed we rotated the rotor with the caliper installed and the disc pad no longer rubbed at one point in the rotation as it did before

[Frank D.]

Re: Rear End Rubbing Sound

Help me out here, you have a 63, but with rotors, is that correct ? Yet you talk about PB shoes - confusing to me...
If its a stock parking brake you can't just address one side if its stiff, as, if the other side could have issues and the equalizer won't operate correctly.

You may also want to try a run with the wheel covers off, I have seen some odd symptoms on some cars as the wheels are turning and the hubcaps go through a revolution.

[Peter L.]

[Gary R.]

Re: Rear End Rubbing Sound

Well I would have checked the runout again once the rotor was installed. The method used to turn rear rotors is important as a common brake lathe may cause more runout. If an on the car lathe was used the rotor and axle will be concentric, if the rotor was turned independent then who knows and there's not a lot of material that can be removed.
Hopefully you didn't run the car in the air without blocking the arms to ride height as opposed to just putting it in gear and letting the wheels spin with the suspension hanging.

[Peter L.]

Re: Rear End Rubbing Sound

Yes we blocked the arms so the wheels were not hanging at the end of the suspension

[Frank D.]

Re: Rear End Rubbing Sound

Yes we blocked the arms so the wheels were not hanging at the end of the suspension

Good! I was going to ask that but figured you had enough issues on your hands already.
Listen to what Gary is telling you above about runout for sure.

[Tim S.]

Re: Rear End Rubbing Sound

When driving, can you get the sound to change if you drag the brake?

Tim

[Peter L.]

[Edward J.]

Re: Rear End Rubbing Sound

Peter, have you looked at the rubber components such as the snubber bushings, I have seen them flatten out and the yoke contacts the bracket. Rear cushions on the cross brace for rear end have been known to break away and cause problems 63 more so. Does car have knock off wheels, (I have seen the wheel lug holes elongate and cause noises).

[Frank D.]

Re: Rear End Rubbing Sound

If the OP could capture the audio and post it here I think it would help in diagnosing things...

[Peter L.]

Re: Rear End Rubbing Sound

Ed,
The rubber bumper attached to the rear Kick-ups to cushion and stop travel of the Trailing Arms are intact, and in good condition. They show no signs of even being touched by the trailing arms. Remember, this is a constant banging/rubbing sound, that increases in frequency with speed, and any noise coming form hitting the bumper cushion that often would be obvious.

Frank,
I'll try to make a recording of the sound in the next few days and post it as a file.

Thanks for your ideas guys.

[Frank D.]

Re: Rear End Rubbing Sound

Sounds can travel in funny ways in these cars, I'm more familiar with the 250hp/300hp 63s but if your engine has a flywheel inspection cover I'd look at it closely. Maybe even remove it and run without it for 10-15 miles... There aren't many things I can reconcile against a "banging/rubbing" sound and this is one possibility. Snubber bushing or "egged-out" differential bracket holes don't produce sounds that vary with speed in my experience.

And I presume you've ensured the propeller shaft U-joints are completely clearing the transmission tunnel (another possible source of banging/rubbing noise).