Front Brake Surge .......
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Tourer
Joined: Jun 2006
Posts: 341
Likes: 0
From: Sarasota/Bradenton FL
Front Brake Surge .......
Working on a lady rider freinds scoot last night, oil change and a couple of quick fixes before she makes a trip to West Palm from Sarasota this AM.Ran into a big problem on the test ride. The bike surgesviolently when the front brakes are applied at low speed. Surges pretty good from a moderate speed stop and gets progressively worse as the bike slows. She said the "bumping" started after a run last weekend. The brake pads have plenty of life, rotors appear to be flat & true, no noticable noise when coasting and besides the front brake surge the scoot seems to handle ok. I am thinking head or wheel bearings or maybe fork oil .... other areas to check?
A little background: Its a 2000 Road King Classic with approx 168,000 miles. Has been ridden hard without much maintenence. All miles have beenput on under the lady's seat.The RK is a definite "Road Rat".
I told her that as far as I was concerned the scoot wasnot safe or ridable until we get this sorted out. Got a shoulder shrug which means she will make the trip anyway.
Any wisdom from the RK experts?
A little background: Its a 2000 Road King Classic with approx 168,000 miles. Has been ridden hard without much maintenence. All miles have beenput on under the lady's seat.The RK is a definite "Road Rat".
I told her that as far as I was concerned the scoot wasnot safe or ridable until we get this sorted out. Got a shoulder shrug which means she will make the trip anyway.
Any wisdom from the RK experts?
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Tourer
Joined: Jun 2006
Posts: 341
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From: Sarasota/Bradenton FL
RE: Front Brake Surge .......
Thanks Sleepen.
Cast wheels (no spokes) and afairly new Dunlop (less than 2K). No noticable vibration at speed to 50 mph or so without the front brakes applied (was afraid I wouldn't be able to stop it any faster). I'll have her check to see if it chucked a wheel weight.
Cast wheels (no spokes) and afairly new Dunlop (less than 2K). No noticable vibration at speed to 50 mph or so without the front brakes applied (was afraid I wouldn't be able to stop it any faster). I'll have her check to see if it chucked a wheel weight.
Outstanding HDF Member
Joined: May 2006
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From:
RE: Front Brake Surge .......
doesn't mean the tire can't be bad. Some are bad out of the mold.
Check to see if there are any indicators of hot spots on the rotors. There would be a slight discoloration where there might be hardness. This causes surge in disk brake systems.
Check to see if there are any indicators of hot spots on the rotors. There would be a slight discoloration where there might be hardness. This causes surge in disk brake systems.
Elite HDF Member
Joined: Oct 2006
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RE: Front Brake Surge .......
Guess ah'm confused by what ya mean by "surge"... Are you talkin' about engine (rpm) surge, a feeling like the brakes are being applied/released, or something akin to wheel hop?
If brake surge (applied/released) is what ya mean, ah'd bleed hell outta the brakes and see if that helps. I'd also check the disk with a run-out gauge, or by raisin' the front wheel an' spinnin' it to look for run-out.
If something akin to wheel hop, ah'd look at bearings - but since it happens only with application of the front brakes, ah'm gonna look at the brake system.
A li'l "cheat" that will help ya is to use a belt sander. Put on a mid or coarse grain belt, put it against the wheel (with the wheel jacked up, and hand-rotated as fast as you can) an' bring it up ta speed (it'll give ya an effective speed of about 35-40 mph or so). Then start playin' with brakes, etc. and see if you can repeat the symptoms. If so, you'll be able to SEE what's going on, which should help you troubleshoot.
As others have mentioned, it could well be a balance or out-of-round issue, which the high-speed tire rotation could well help ya find...
If brake surge (applied/released) is what ya mean, ah'd bleed hell outta the brakes and see if that helps. I'd also check the disk with a run-out gauge, or by raisin' the front wheel an' spinnin' it to look for run-out.
If something akin to wheel hop, ah'd look at bearings - but since it happens only with application of the front brakes, ah'm gonna look at the brake system.
A li'l "cheat" that will help ya is to use a belt sander. Put on a mid or coarse grain belt, put it against the wheel (with the wheel jacked up, and hand-rotated as fast as you can) an' bring it up ta speed (it'll give ya an effective speed of about 35-40 mph or so). Then start playin' with brakes, etc. and see if you can repeat the symptoms. If so, you'll be able to SEE what's going on, which should help you troubleshoot.
As others have mentioned, it could well be a balance or out-of-round issue, which the high-speed tire rotation could well help ya find...
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Tourer
Joined: Jun 2006
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From: Sarasota/Bradenton FL
RE: Front Brake Surge .......
Tex,
I would describe it a wheel hop. Worse at low speed with the front brake applied.From a moderate speed stop starts out as a consitant bump and as the scoot slows ends as what you are describing as wheel hop. I was thinkingbearings or wheel weight as this problem appeared so quickly in the last 100 or so ridden miles. I would think that a tire problem or rotor hardness problem would be more of a progressively worsening problem?
Didn't get the chance last night to get it up in the air. But will try your sander trick at the next opportunity. Good tip.
I would describe it a wheel hop. Worse at low speed with the front brake applied.From a moderate speed stop starts out as a consitant bump and as the scoot slows ends as what you are describing as wheel hop. I was thinkingbearings or wheel weight as this problem appeared so quickly in the last 100 or so ridden miles. I would think that a tire problem or rotor hardness problem would be more of a progressively worsening problem?
Didn't get the chance last night to get it up in the air. But will try your sander trick at the next opportunity. Good tip.
Road Master
Joined: Mar 2006
Posts: 1,037
Likes: 2
From: Winslow, Arizona
RE: Front Brake Surge .......
You've got a wrped brake disc. Get the bike up on a jack with the front whel off the ground, tape a pointer of some type (nail, etc.) on the fork close to the edge of the disc and rotate the wheel. You should be able to tell if the disc is good- it will stay the same distance from the pointer through the whole rotation.
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Road Captain
Joined: Aug 2005
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RE: Front Brake Surge .......
Definitley (from what you described) it's a warped rotor(s). As wesd41 mentioned, the only true way is to use a dial indicator to measure out the trueness of each rotor. A warped rotor will cause the front pads to "pulsate" causing the feeling you're getting. If the wheel or tire were at fault you'd be feeling the same thing with or without the the front brakes applied. I had the same issue a few months ago where the stock rotors were warped. I replaced both sides with the HD floating rotors, a new set of Lyndall pads and gave the calipers a good cleaning. The brakes have never been better.
Brian
Brian
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Joe Kucinski
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Joined: Feb 2006
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From: South Florida
RE: Front Brake Surge .......
If the rotor runout is within tolerance,try cleaning the caliper and renewing the pads.A good rotor should have runout of .002 or less.I have had some with as much as .004 and not transmitt pulsation to the brake lever.