Front disc brake rub issue when under load
08-16-23 | 12:47 PM
#1
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Front disc brake rub issue when under load
Hi there,
I'm building up a monstercross type bike. I have an issue with the front disc rubbing when i'm sat on the bike. When there is no load there is no disc rub. Just wondered if someone here could diagnose and help me resolve this. I am beginning to wonder if the lower fork bearing race might be out of alignment forcing the wheel out of of true or the wheel? The problem happens in both laternal and forwards movement.
Parts
160mm rotor, SRAM road Rival caliper on a 160-180 adapter plate. Hydraulic hose as yet unattached. 2.6" tyre, 29er mtb wheel rim, carbon mtb fork with QR drop outs. The front wheel bearings feel tight and both the wheel and the rotor are true.
Any ideas?
I'm building up a monstercross type bike. I have an issue with the front disc rubbing when i'm sat on the bike. When there is no load there is no disc rub. Just wondered if someone here could diagnose and help me resolve this. I am beginning to wonder if the lower fork bearing race might be out of alignment forcing the wheel out of of true or the wheel? The problem happens in both laternal and forwards movement.
Parts
160mm rotor, SRAM road Rival caliper on a 160-180 adapter plate. Hydraulic hose as yet unattached. 2.6" tyre, 29er mtb wheel rim, carbon mtb fork with QR drop outs. The front wheel bearings feel tight and both the wheel and the rotor are true.
Any ideas?
Last edited by marbles; 08-16-23 at 01:08 PM.
08-16-23 | 05:37 PM
#2
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From: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
To diagnose this you have to focus or possible movement between the disc brake mounts and the disc itself. Anything not within those "boundries" doesn't factor.
I'd consider fork flex near the ends, hub bearing play, movement of the axle in the dropouts, etc.
For starters I'd pull the rim across toward a fork blade while watching for movement of the disc in the brake.
FWIW my prime suspect would be axle play, which is easy to confirm and fix or rule out.
I'd consider fork flex near the ends, hub bearing play, movement of the axle in the dropouts, etc.
For starters I'd pull the rim across toward a fork blade while watching for movement of the disc in the brake.
FWIW my prime suspect would be axle play, which is easy to confirm and fix or rule out.
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FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
08-17-23 | 02:10 AM
#3
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From: Palm Coast, FL
Bikes: Diamondback Wildwood Classic
To diagnose this you have to focus or possible movement between the disc brake mounts and the disc itself. Anything not within those "boundaries" doesn't factor.
I'd consider fork flex near the ends, hub bearing play, movement of the axle in the dropouts, etc.
For starters I'd pull the rim across toward a fork blade while watching for movement of the disc in the brake.
FWIW my prime suspect would be axle play, which is easy to confirm and fix or rule out.
I'd consider fork flex near the ends, hub bearing play, movement of the axle in the dropouts, etc.
For starters I'd pull the rim across toward a fork blade while watching for movement of the disc in the brake.
FWIW my prime suspect would be axle play, which is easy to confirm and fix or rule out.
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JoeTBM (The Bike Man) - I'm a black & white type of guy, the only gray in my life is the hair on my head
08-17-23 | 08:51 AM
#4
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From: Rochester, NY
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB
The first thing I think of is fork slop between the uppers and lowers. Andy
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AndrewRStewart
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08-17-23 | 11:39 AM
#5
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From: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
I would have thought that the brake bridge at the top would have provided enough rigidity to the lower fork/wheel assembly.
But, you work on far more suspension bikes than I ever have or will, so I defer to your experience.
08-17-23 | 05:24 PM
#6
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From: NW Oregon
Bikes: 1982 Trek 930R Custom, '91 Diamondback Ascent w/ XT, XTR updates, Fuji Team Pro CF road flyer, Specialized Sirrus Gravel Convert, '09 Comencal Meta 5.5 XC, '02 Marin MBX500, '84 Gitane Criterium bike
i've seen only a couple "carbon suspension forks" EVER... two Super-high dollar Lefty Cannondales... they were MTBs.
As to the issue the OP is having.. i'd be looking at the Dropouts REAL CLOSE, and also the triple clamp/tube junctions...
there's a strong chance that the Quick Release is bottoming out on the axle before the thing can clamp solidly, too......
OR The AXLE IS BROKEN.
Carbon tubes fitted into aluminum Triple clamp and dropouts, right? Brand? Model?
Last edited by maddog34; 08-17-23 at 05:27 PM.
08-17-23 | 07:41 PM
#7
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From: Mt Shasta, CA, USA
Bikes: Too many. Giant Trance X 29, Surly Midnight Special get the most time.
The first thing I’d do is replace the skewer with a closed cam design if you can’ haven’t already. It can be hard to get the skewer tight enough to work well with a disc otherwise.
Also check the alignment of caliper carefully. If the disc tabs aren’t machined perfectly perpendicular to the disc you may be able to get it to not rub in the stand, but not have enough clearance in real world conditions. Having the mount faced at a shop with appropriate tooling isn’t a bad idea.
Also check the alignment of caliper carefully. If the disc tabs aren’t machined perfectly perpendicular to the disc you may be able to get it to not rub in the stand, but not have enough clearance in real world conditions. Having the mount faced at a shop with appropriate tooling isn’t a bad idea.
