Pulsing disk brakes doing my head in

[Mikey08]

I got some secondhand Formula CR1 brakes recently. I have cleaned and lubed the pistons, bled them, fitted new rotors and pads, and they are rubbish. Both brakes pulse under gentle baking and dont seem as powerful as I would expect. This is what I have tried so far:

- Cleaned and lubed caliper pistons
- Checked rotors are true/straight
- Bled and re-bled both brakes*
- Cleaned rotors with WD40 aerosol contact cleaner
- Sanded rotors with fresh 120grit emery paper.
- Sanded pads with clean fresh 120grit emery paper.
- Thoroughly cleaned calipers, no leaks visible.

All I can think is that the rotors are out of spec as in not the same thickness around the braking track. They are cheap Clarks 160mm rotors. It must be the rotors right? Im stuck with this and loath to buy yet more new rotors. Am I missing anything that could cause this pulsing other than bad rotors?

*no matter how thoroughly I bleed them they still have a bit of a spongy feel. I mean they are snappy but not as firm as I would expect. The only other brakes I have used were hope mono mini so thats what im comparing to. Are they just crap brakes or is it down to age, old seals, hoses etc?

 

[mdvineng]

Caliper alignment is paramount and use acetone to clean the disc etc

 

[Mikey08]

Thought about that. They are post mount and I've fitted them directly to to fork mounts without conical washers. Looking at how the pads align with the braking surface, adding conical washers would move the caliper too far away from the axle so id lose a couple of mm of pad to rotor contact. Is that much of an issue?

 

[mdvineng]

The calipers need to be centered and parallel to the discs, otherwise all that happens is reduced contact and deformation of the disc during braking. Greatly reducing braking performance and noises etc

 

[Mikey08]

Cool thanks. Have just fitted conical washers either side of the caliper mounting holes and re-centred the caliper. Problem is the pads are now losing about 3mm of contact area along the top edge.

Ive looked at tons of images and most brakes seem to only have conical washers on the top side of the caliper. This would rely on the post mounts on the fork being perfectly parallel to the axle. Maybe I need to get my fork mounts faced?

 

[dyna-ti]

I wouldnt be using conical washers, as the entire thing to work is utterly dependent on right angles. A PM caliper should bolt directly, or with a size adaptor.

 

[mk one]

Pulsing disc brakes are the first sign of warped rotors, same on motorbike.

 

[dyna-ti]

Pulsing disc brakes are the first sign of warped rotors, same on motorbike.

How up to spec are we on truing floating rotors, that still a no go ?.

 

[Mikey08]

Update:

I did a lot of messing with the caliper alignment and checked the rotors for trueness. There is a very slight warp but its not enough to be an issue. What I recently noticed is that the braking track is narrower than the pad surface so Im only getting about 90% pad to rotor contact. In addition to that the rotors are out of round so when looking square on and turning the wheel there's a off center movement of the rotor.

If anyone is considering buying the cheap Clarks rotors be aware they are cheap for a reason!

 

[Mikey08]

Just fitted some brand new Ashima Ai2 rotors and all is well in the hydro braking word! One finger skids and endoes