Brake questions

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RickB56
Posts: 370
Joined: Sun Jan 25, 2009 1:13 am
Location: Melbourne

Brake questions

Post by RickB56 » Tue Mar 05, 2013 6:48 pm

I mentioned a while back that I had pulled the front forks off the shovel to do a service. Turned out that what I thought was a crack in one tube was just a casting mark in the bottom of the tube. No comments please. Anyway, new seals, reinstalled and refilled without further problem. Then I put on new brake rotors and pads. Also put in new pins that the pads hang on. Right off, the left caliper started chattering badly during acceleration. It would stop after shifting up, but resume once revs got a bit high again. At cruise it was fine. The right brake began squealing when braking, especially at lower speeds. The left caliper has always seemed a bit looser than the right. So I bought some bushings and installed them in both forks. No improvement. If anything it was worse. Seemed to improve slightly once things were warmed up a bit, but that is not a firm conclusion. I then drilled the top mounting hole in the caliper and put a bushing in that too. Still no improvement. I finally reasoned that the only real change I had made before the chattering started, was the new rotors. I put the old rotors back on and the chatter and the squeal is gone. WHAT THE????

I've checked the rotors are the same diameter and thickness. The difference are.....old rotor is solid in the brake pad contact area. The new rotors have 3 rings of about 8mm holes in this area. The old rotors have 5 large holes and 5 small holes in a ring between the axle and the brake pad contact area.
Checking the new rotors against each other, there seems to be some slight shift in the hole positions. If I line up the 8mm holes the larger holes and the mounting holes are offset. If I line up the mounting holes, the other holes are offset. Seems like the large holes are not evenly spaced to me.

Anyone have any thoughts?

Bearcx
Posts: 1894
Joined: Thu Oct 18, 2007 12:31 am
Location: Gawler, Sth Aust
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Re: Brake questions

Post by Bearcx » Tue Mar 05, 2013 10:43 pm

Having never owned a HD, take this as you will. :D

Sounds like a combination of disc run-out and new pads vibrating in the caliper housing. The disc rotors can 'wobble' while they are rotating, this causes the pad material and its backing plate, to vibrate in the caliper. Some companies include an anti rattle spring in the box, with caliper overhaul kits, some back yarders used to glue a piece of Weetbix cardboard on the backing plate. All it does is 'absorb' the vibrations from the rotor 'wobbling'.

I've done my share of brakes in my lifetime, mostly on cars, but, even brand new DBA rotors (a reputable brand) have had run-out straight out of the box.

Do the HD pads have rods or pins going through the pads? If so, these need to be lubricated also. Never-seize, Kopr-Kote, something like that.
DO NOT get this stuff on the pads or rotors. Also, try rubbing the rotor faces with 600 wet and dry, to help the pad 'wear in' faster. The holes in the rotor face shouldn't cause the noise, they help shave old pad material off, giving you a good brake feel, every time, especially in the wet.

My 11 cents worth. (GST incl)
The brave may not live long, but, the cautious do not live at all.

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