Brake pulsation question
 

My front brakes pulsate, and I need to know what is acceptable? I checked the wheel and it appears to be true within 1/16th of an inch or less. The spokes again appear to be tight (when plucking the tones are similar with slight variations). When I spin the wheel with the brakes almost closed I have one area that grabs, it looks as though the sidewall of the rim is thicker in one area. at first it didn't bother me as I used mainly my back brakes. After reading that front brakes should be used as the main brakes I have found this to be very annoying and somewhat dangerous on descents.

I am a newbie so take what I have said and checked for what it may be worth.

I bought the bike 2 months ago, and less than 500 miles from my LBS. After much reading in this forum I feel that I now know more than the people at my LBS. I have had to adjust countless things on my bike that were not correct and have been less than satisfied with my experience. So before I take it in to them what should I expect or am I just to anal.

If the rims are round and true, then are the rim and brake pads clean? Are the brake pads toed-in?

YES

YES I did have to adjust the Height, Roll angle, Pitch angle, and Toe in. I also had to adjust the Spring Adjustment to center the brakes on both the back and front wheels.

I am very mechanical and although a bike newbie I have read many articles on bike maintenence and repair.

The sidewall of the rim (where the brakes contact) is a little thicker in one spot thus causing the pulsation. the wheels are ever so slightly out of round again less than 1/16 of an inch. will adjusting the spokes help or do I have a defective rim?

The wheels are Bontrager SSR and the brakes are Shimano M421 Direct-pull if it makes a differance.

Thanks for any input.

Are you saying the rim is slightly out of true and the brake pads are contacting the rim because of this, as the wheel spins? If so, then you'll need to either have the wheel trued or do it yourself. Yes, this will involve adjusting spoke tension............As for the rim being thicker in one spot, is it a seam? Pinned rims (if that's what you have) often have imperfect alignment at the seam and will therefore have a little bump at the seam. If this is the case, then you can smooth the seam somewhat with steel wool if it's noticeable when braking; otherwise it's nothing to worry about. It's also possible the sidewall of the rim is bent a little outward on one side, or maybe there's a manufacturing defect. Especially since it's a relatively new bike, I'd take it to the shop where you bought it and have them check it if you think it's bent or has a defect.

Although they are very slightly out of true there is only contact when the brakes are applied and that is when I get pulsating or a jerking affect.

yes I checked and there is a seam but that is not where the thick spot is.

I am thinking there is a defect as the problem has always been there. I just wanted some input so when I go to my LBS and they look at me funny and tell me its normal I know what I am talking about. Like I said they either dont know much or dont care. The service I have recieved has been less than favorable (granted I am anal and expect good service).

If the braking surface is noticealy different, you should be able to just take it to the LBS and have them exchange it. A new set of wheels shouldn't be like that.

look for an outward dent in the rim.

Well I took my bike to my LBS today. both techs were in, one looked at it and said I must have spilled pop or gatoraid on it. I explained I only drink water. He then filed my brake pads and cleaned the rim. Still had pulsating, so the other trued the wheel wich was in pretty good shape. Still had pulsating so they said they didnt know what was wrong. I showed them how it looked like the rim had a small wave in the side wall (you could tell a little better on the truing stand). They told me that they didnt know what to do and to come back tomorow and talk to the owner.

Boy I wish there were more LBS's around me!

Were it me, I hammer & dolly the bulge out. But then again, I'm whack! :)

Since they've trued the wheel, and they agree that there's a bulge in the rim's sidewall and that it's causing pulsation when braking, you should get a new wheel unless the sidewall's just bent a little and the shop can bend it back, getting rid of the pulsation. You say it's been this way since new, so I wouldn't take no for an answer, and if you don't get satisfaction from the shop I'd contact Trek and see if they can help, at least in dealing with the shop about it. You should have taken it back in and let the shop know about it the first time you noticed it, of course, when the bike was brand new, but you should explain that you tried adjusting the brake pads, etc., hoping you could fix the problem..........When you say "pulsating," do you mean you can feel it (when you're braking) when the wheel comes around to the spot where the bulge is each time the wheel goes around?

edit: after re-reading your posts, it's not clear when you first noticed the problem. Has it been this way since brand new?

Yes I should have but it didnt bother me, as it was in the front and being a nubie I didnt use my front brakes.

Yes when I brake, now with my front brakes the stopping motion is very jerky. It would be like you pumping the brakes very rapidly

They didn't agree they said that wouldn't cause the pulsating, but something is. The only thing they agreed on was that there was pulsating and they didn't know what was causing it.

I am not going to worry about it until I talk to the owner.
Thanks for all the input!