Home » Public Forums » GMCnet » Rear disk brakes, excessive brake dust on one wheel
| Rear disk brakes, excessive brake dust on one wheel [message #286930] |
Wed, 09 September 2015 09:43  |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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I have the 4 wheel rear disk brakes from JimK. I noticed on the rear driver's wheel, brake dust on the rim which is not on the other 3 wheels. I used my IR temperature gun to read the tire and wheel temps at nearly every fill-up and none have been out of normal. Last time when we got home, I shot the temps of the caliper and disk itself and found them all to be reasonable consider I just braked from hyway speeds. In Celsius, low 50's for the calipers and mid 60's for the disks. The rear driver's disk was hotter, but within 5C of the others.
The pads don't look excessively worn. If it was dragging I would expect it to run significantly hotter.
Any ideas?
Thanks
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: Rear disk brakes, excessive brake dust on one wheel [message #286936 is a reply to message #286930] |
Wed, 09 September 2015 10:41  |
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thesmith
Messages: 589
Registered: February 2015
Location: Cary, NC
Karma: 6
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First thing I would do is jack up that wheel and see if it spins freely....or at least as freely as the rest. Is there a parking brake on that wheel? if so could be that it was adjusted just a little tight, and the dust is from the pad wearing down to the point its no longer tight.
Pete
RF_Burns wrote on Wed, 09 September 2015 10:43I have the 4 wheel rear disk brakes from JimK. I noticed on the rear driver's wheel, brake dust on the rim which is not on the other 3 wheels. I used my IR temperature gun to read the tire and wheel temps at nearly every fill-up and none have been out of normal. Last time when we got home, I shot the temps of the caliper and disk itself and found them all to be reasonable consider I just braked from hyway speeds. In Celsius, low 50's for the calipers and mid 60's for the disks. The rear driver's disk was hotter, but within 5C of the others.
The pads don't look excessively worn. If it was dragging I would expect it to run significantly hotter.
Any ideas?
Thanks
Cary, NC
1978 Center Kitchen Royale.
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| Re: Rear disk brakes, excessive brake dust on one wheel [message #286943 is a reply to message #286936] |
Wed, 09 September 2015 12:41 |
LarryInSanDiego
Messages: 336
Registered: September 2006
Karma: 0
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Are they single piston sliding calipers? Compare pad wear between inside and outside. Could be that either the caliper is not as free to slide as the others and/or the caliper square cross section o-ring (not the externally visible dust seal) has hardened and is no longer pulling back the piston upon release. Or even the brake hose has internally collapsed and is acting like a low pressure check valve.
Larry Engelbrecht
San Diego, CA
'73 26' ex-Glacier
TZE063V100319 03/07/73
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| Re: Rear disk brakes, excessive brake dust on one wheel [message #286957 is a reply to message #286952] |
Wed, 09 September 2015 15:41 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Do you have an E brake on this caliper? A friend found a weak return spring where the cable fastens to the caliper bracket and would allow the brake to stay a little tight. Maybe pull on the lever with an adj wrench and see if it move any more in the relaxed position.
RF_Burns wrote on Wed, 09 September 2015 15:25I'll try to jack it up tonight (or tomorrow) and check if its dragging and the wear. I see the dust on the outside of the rim which points to the piston side I believe.
Its vintage 2012 so I'm hoping its not seizing up.
C. Boyd
76 Crestmont
East Tennessee
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| Re: Rear disk brakes, excessive brake dust on one wheel [message #286975 is a reply to message #286930] |
Wed, 09 September 2015 20:05 |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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Lifted the wheels and there is a slight drag, but no more than the other wheels. Rocking the wheel I can feel/hear the bearing clearance, maybe could tighten the bearing to the next slot. I'll check it, but I don't want to over tighten it.
Looking at the disk, its not as polished as the others, like its not braking as much. I had Paula step on the brakes as hard as she could (engine off, no PB boost) and I could, with effort, turn the wheel. I'm wondering if there is still a bit of air in the line to this wheel?
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: Rear disk brakes, excessive brake dust on one wheel [message #286984 is a reply to message #286975] |
Wed, 09 September 2015 20:30 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Bruce,
Air should not cause that, but a loose bearing could. If this is happening, I would expect that disk to be brighter than the others. Extra run-out or a loose bearing could cause the disk to push on the pads when there is no retarding requested. That could cause extra dust.
Just do not go too tight.
The manual says 0.005" (0.12mm?) but I don't like them there, so I shoot for 0.008~0.010 (0.02~0.025mm).
Only one wheel has ever fallen off - So Far.
Matt
RF_Burns wrote on Wed, 09 September 2015 21:05Lifted the wheels and there is a slight drag, but no more than the other wheels. Rocking the wheel I can feel/hear the bearing clearance, maybe could tighten the bearing to the next slot. I'll check it, but I don't want to over tighten it.
Looking at the disk, its not as polished as the others, like its not braking as much. I had Paula step on the brakes as hard as she could (engine off, no PB boost) and I could, with effort, turn the wheel. I'm wondering if there is still a bit of air in the line to this wheel?
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Rear disk brakes, excessive brake dust on one wheel [message #286992 is a reply to message #286975] |
Wed, 09 September 2015 22:36 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Bruce,
To check the rear wheel bearings (RWB) is a piece of cake! If I were in your shoes I would remove the wheel and hub and check the
wheel bearing in that wheel completely.
Depending on what I found and when the last time I serviced the RWB I would consider doing the other three as well and lubricate
them all with Valvoline Synpower.
Don't forget to review this: http://gmcmotorhome.info/rear.html#BEARINGS
Regards,
Rob M.
The Pedantic Mechanic
-----Original Message-----
From: Bruce Hislop
Lifted the wheels and there is a slight drag, but no more than the other wheels. Rocking the wheel I can feel/hear the bearing
clearance, maybe could tighten the bearing to the next slot. I'll check it, but I don't want to over tighten it.
Looking at the disk, its not as polished as the others, like its not braking as much. I had Paula step on the brakes as hard as she
could (engine off, no PB boost) and I could, with effort, turn the wheel. I'm wondering if there is still a bit of air in the line
to this wheel?
--
Bruce
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Rear disk brakes, excessive brake dust on one wheel [message #286994 is a reply to message #286992] |
Wed, 09 September 2015 23:50 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Senior Member |
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AIR can cause the brake pad to rub on the disc, if the air has gotten down to the caliper where it can get warm and EXPAND. That scenario will also reduce or eliminate braking performance on that wheel. Under no circumstances should YOU be able to rotate that wheel by hand or with tools while the brake pedal is being held down by a helper's foot with the engine running. Especially if the other wheels are locked.
And once in awhile, a brake pad with an erroneous mix of batter gets produced, and somebody ends up with that one on their vehicle. Let us know which pad is thinner; moving or stationary?
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: Rear disk brakes, excessive brake dust on one wheel [message #287007 is a reply to message #286930] |
Thu, 10 September 2015 08:19 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Regarding the bearing, be very careful you don't overtighten it - ask me how I know this....
Also have a look at the back of the disc. One side brighter than the other indicates dragging on one side, for one or more of the reasons stated above.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Rear disk brakes, excessive brake dust on one wheel [message #287058 is a reply to message #287056] |
Thu, 10 September 2015 22:06 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Bruce,
That suggests that the caliper is not moving on the bolts.
Regards,
Rob M.
The Pedantic Mechanic
-----Original Message-----
From: Bruce Hislop
Turns out the inside of the disk has more rust than the outside.
I was able to bleed some more air out of the caliper so I tried the mid wheel too and got some air from it. I'll do the passenger
side before we leave for the joint GMCES / GMC Great Lakers rally on Thursday.
I checked the bearing setting. No way to make one more slot and feel comfortable, so I left it where it was.
I was surprised how rusty the bracket was after 3 years, guess I should have painted it.
--
Bruce
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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