Front brake.... pulsating???

[mattmcuomo@yahoo.com]

I don't know any other way to explain, when I pull the front brake on my CB it feels like it's pulsating, like hitting ABS hard. But I don't have ABS!!
The pads look good, not worn more on one side or other, I bled the system, all seems to be good. Could the disc's have warped??? Anyone else experience this on their bike??? :huh:

 

[Macduff_imp]

You may have pad deposits on one or more of your disks . I found with previous rides if I did a lot of stop /start riding where I held the bike stationary using the front brake the hot disk meant the pads left deposits in that spot. PITA as it didn’t want to clean up so new disks were used to fix it.

 

[Lord Popgun]

I’d say you have what Macduff says or one or both rotors are warped. I think both have been reported here.

You can check for runout with a dial indicator if you have one, or you can rig up a pointer to look. I can look up the spec if you need it.

Try cleaning the rotors first. Its cheaper.

 

[mattmcuomo@yahoo.com]

Yeah, the disc’s do look like maybe a film is on them. I’ll try that. Thanks!!


Sent from me

 

[Macduff_imp]

When I hot spotted my last disk (on a KTM1190Adv) the deposit was a very hard copper coloured mark on the disk. Couldn't shift it with wet and dry or wire wool. I suspect it needed a proper skim to get it off and not cause low spots or other unevenness.

 

[mattmcuomo@yahoo.com]

I cleaned the rotors, it’s better but still feel a little pulsating.


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[camoto_imp]

How did you clean them? Did you rebed the pads after doing so?

Discs being physically warped is a far less common cause of this than pad material buildup. You can clean them with scotchbrite and brake cleaner but anything more aggressive should be done with care. Spinning the wheel and pinching can prevent hi/low spots. After doing this you will want to follow a bedding procedure to re-bed the pads (see the internet for plenty of arguments on the best way to do this). Be careful as braking will be diminished right after cleaning the rotors as you will have removed the necessary layer of pad that is transferred on to the rotor which increases friction.

If you get through all of this and still have a shimmy here's a list of things you can measure/check to try to eliminate the issue:
1.) Measure runout of rotors for physical warping (mentioned above) You can often rent a dial gauge from an auto parts store if you don't have one.
2.) Remove and inspect the pads and clean and lubricate the retaining pins to ensure they are in good working order
3.) Check balance of tire, you may have lost a wheel weight
4.) Check tire for cupping, uneven wear, flat spots etc.
4.) Inspect wheel bearings, replace them if there's any question whatsoever
5.) Check steering stem tightness (hold front brake and rock bike forward and aft-- if there is clunking in the steering tube, you need to tighten it up or replace bearings if shot)
6.) Ensure you have fresh brake fluid and no air in the system

Another thing to try and focus on is if the pulsating is felt in the lever or in the bars. This can be very difficult to distinguish but is very indicative of the problem system.

If you're certain that all of the above is OK, you're in "unlikely land" and you might need to start throwing money at the problem to figure it out such as an internal tire defect not externally visible.

Unfortunately I've been battling the same issue. I believe my issue is tire or bearing related but still haven't gotten to the bottom of it and it's not that severe so I am waiting for winter to tear into it.

 

[mattmcuomo@yahoo.com]

I cleaned them with a rag and rubbing alcohol. I did not rebed the brake pads. I’m sure a better cleaning and rebed of pads would do the trick. I was just hoping for the quick fix to work..... thanks


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[mattmcuomo@yahoo.com]

Cleaned the rotors with steel wool, scuffed the brake pads with some 150 sandpaper and “bedded” the brakes. Much better!!! I’m wondering if the brake pads I put on are making too much buildup????


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[mattmcuomo@yahoo.com]

I think I solved the problem. I removed the cups from calipers, a couple were stubborn so they must have been the guilty sticking ones causing brake drag. Cleaned everything up nice, reassembled and finally, no pulsating. Ir also cleared up the 45 mph front end shimmy. Brake drag must have caused that too.

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[mattmcuomo@yahoo.com]

Well, it’s happening again!! I believe the pistons or “cups” are not distributing even pressure. Would rebuild help? How far can I go with “cleaning” or resurfacing the cups? Or, are the calipers not getting good pressure? I’ve bled the system many times.... this is frustrating to say the least!!


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[Speed_imp]

It has been happening to my bike also since it was new. Braking at low speed I can feel an ABS like vibration but I never paid much attention as it is happening seldom, rarely. In 4 years and 60.000 Km maybe it has happened 10 or 20 times.

 

[max]

MMC i had an identical situation on my cb919, it was fine when i got it but i think putting it away with wet disks got it started, tried to clean the rotors but never got it cleared, lived with it for some time and it gradually got slightly better and it felt that over time the patch grew longer to finally cover most of the surface by gradually applying the brake, it felt like the "resin" that binds the brake material together ( i don't know ) covered more and more of the surface, it definitely improved the friction until i replaced the pads which cleared it instantly, no more pulsing or at least very light and not very noticeable.

To isolate the problem you could swap one caliper inside with the outside pad, if that makes no difference swap the other caliper, swapping this way will at least point out which pad is pulsing the brake.

Not knowing the history of your bike it may be time for a different brand of pads, it does not add to the driving pleasure does it?