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LR rotor is scraping on rotation ('94 855T)

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LR rotor is scraping on rotation ('94 855T)

Post by BlackBart » Fri Aug 23, 2019 11:31 pm

My left rear rotor has a scrape scrape noise on rotation. It might be sightly worse when turning. Loud enough to hear inside. It scrapes every rotation with the car lifted and turning the wheel.
I pulled that corner apart, inspecting pieces at each step to see if there are marks on the rock shields etc.
The rotors and pads are fairly new, Plenty of pad left. The pistons retracted back into the calipers easily with a channel lock pliers.
The rotor spins easily with no pads and by eye doesn't look out of true at the caliper.
I cleaned the ABS ring and sensor. Nothing contacting there.
The caliper pins might be a bit corroded but are pretty new - replaced with the rotor and pads. I'll have to look up which ones I bought - ipd or fcp. They look like they need some emory cloth and a re-grease.
I don't see any marks on the dust shield where the rotor might hit.
The outer pad is just touching the rotor, and only in about a 1/2" to 3/4" swath. NOT the whole swept area at all. The rest is rusty.
The inner pad seems to be riding on the rotor more solidly.
The car was sitting for a long time this winter and the rotors have surface rust, but the others have started to clean off after a few days driving.
The parking brake shoes look fine, not close to the backing plates. I have them too loose and the brake handle isn't tightening them.

So I'm trying to figure out if it's that outer pad making the scraping noise, and why isn't it riding on the rotor? Could the pistons be retracing fine with pliers, but not coming out to the rotor? Because of the pins?

I had Mrs BB push on the brake pedal carefully (car not running) to watch the pistons come out of their bores, but there was no movement. Does it need to be running to make hydr pressure?

Could it be coming from the parking brake pads? Wouldn't there be a mark inside the drum area?

Thanks for any advice -


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Re: LR rotor is scraping on rotation ('94 855T)

Post by abscate » Sat Aug 24, 2019 5:00 am

Do you get the noise with the pads removed? That will settle the parking brake question

The backing plate could be slightly bent and is touching the rotor , which makes a scrape.

It sounds like one piston isn’t moving enough so that you aren’t getting full paid contact. Eventually that’s piston will seize up. Try flushing 500 ml brake fluid through and work the piston back and forth with brake pressure while you do that. Make up a shim about half as thick as the brake pad so you are flushing the working part of the caliper. The real solution is to source Orings, open up the haliper, and hone the cylinder shiny clean, replace piston seals.


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Re: LR rotor is scraping on rotation ('94 855T)

Post by BlackBart » Sat Aug 24, 2019 8:28 am

OK, I'll try that. Should the pedal force the pistons out even if not running? They slid easily into the bores.

Some pics from last night....
IMG_4261.JPG

Pad contact on outside
IMG_4262.JPG

Then there's a funny spot of the inside face. Could it be where the pad sat while parked outside over the winter? And now maybe it's trying to scrape off this rough spot? That doesn't explain why the outer pad isn't pressing again the rotor.
IMG_4266.JPG
IMG_4267.JPG
IMG_4269.JPG
IMG_4264.JPG
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Re: LR rotor is scraping on rotation ('94 855T)

Post by BlackBart » Sat Aug 24, 2019 10:51 am

OK, the scraping is there without the pads and caliper. There's also a single wear area inside the drum part of the rotor.


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Re: LR rotor is scraping on rotation ('94 855T)

Post by BlackBart » Sat Aug 24, 2019 1:14 pm

I loosened the parking brake adjuster all the way, the handle has no tension at all on it, pulls straight up. Put the rotor back on and it's still scraping on rotation. One spot per rotation. There's at least a 1/4" of parking brake pad left, they don't seem worn out. Are the springs not pulling the shoes away from the drum surface?


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Re: LR rotor is scraping on rotation ('94 855T)

Post by abscate » Sat Aug 24, 2019 3:50 pm

You are either rubbing the backing plate or the shoes are slightly out of arc with the drum.

Put the shoes back on and just them to locked up, then back up 3 clicks. Now set brake cable tension to full brakec5vlever clicks up.

Drive for 500 miles using parking brake
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Re: LR rotor is scraping on rotation ('94 855T)

Post by BlackBart » Sat Aug 24, 2019 5:15 pm

Yep, I looked at all the parts I could throw at it - shoes are fine, springs are fine, clips are fine, adjuster is fine, wheel bearings no play. So, I just took everything apart, cleaned it all, and reassembled the parking brake. Adjuster full loose, tighten 'til rotor is locked, back off 4 or 5 'til no binding per the book...should be good. Did the right side as well, rotors back on, and the brake lever comes half way up and both sides are locked correctly! So that seems to be ok now.

Next step is piston travel and pad pressure. The rotors have very few miles, but I may have them turned for a clean flat surface again.


"Drive 500 miles using parking brake"...? Parking brake on? Parking brake to stop with?


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Re: LR rotor is scraping on rotation ('94 855T)

Post by Eddystone » Sat Aug 24, 2019 9:57 pm

Don't rule out a bad rotor.

That spot on the rotor looks very much to me like what I got on a car with very cheap Chinese rotors some years ago. The problem was with the steel that the rotor were made of not being "pure" and uniform all the way through. The results were hard spots that did not wear down uniformly with the rest of the rotor. Aside fro making a noise, they were also making a groove in the pads.

I am guessing that this is not what's causing your noise, but you could try swapping rotors side to side...

When I got my '99 T5, I bought all of the usual brake parts only to find that a caliper piston was complete seized on each rear caliper. I had to quickly buy a pair of calipers locally which are nothing special but seem to work just fine.

No car does well when it sits for very long. That when any moisture in the brake fluid collects at some point and corrodes something. This was especially common in the olden days with cars such as the MGB or anything British.

All of this rambling may not be much help to you, but I'll be interested to hear what you finally discover is the cause.
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Re: LR rotor is scraping on rotation ('94 855T)

Post by abscate » Sun Aug 25, 2019 4:19 am

abscate wrote: ↑
Sat Aug 24, 2019 3:50 pm
You are either rubbing the backing plate or the shoes are slightly out of arc with the drum.

Put the shoes back on and just them to locked up, then back up 3 clicks. Now set brake cable tension to full tension on brake lever 5 clicks up.

Drive for 500 miles using parking brake
Horribly worded, sorry. I meant just drive the car, using the hand brake as you normally would. I actually make a couple of handbrake stops then gone back and adjust them again when new shoes go on. You are trying to make sure the shoes radius matches the drum radius

Try to compare pressure needed to move each piston, if it isn’t equal then that’s the uneven problem

With the bleeder slackened m you can press the pistons in with strong fingers, if you can’t, it’s rustimg up. Replace bleeders of course. 500 ml fluid through calipers too.
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Re: LR rotor is scraping on rotation ('94 855T)

Post by scot850 » Sun Aug 25, 2019 3:55 pm

Volvo has a bedding in/cleaning process recommendation for parking breaks involving driving for a short distance with the parking brake engaged. Can't recall the exact details but think it was around 50 meters.

The insides of your drums for the parking brakes look really rusty. If I have a car with drums like that I uses a rotary wire brush on a drill and clean all the rust off first and then rub the faces of the drums with a fine emery paper to roughen the surface a little for better grip.

I am also assuming you checked the parking brake cables are not kinked or broken and move freely. Finally make sure (FWD cars) that the plastic tie back is in place on the parking brake cable to keep it off the back of the rear tires.

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