Mountain Cycles - Early ProStop disc brake

[deelam]

Is anyone familiar with these? Cable activated hydraulic. Along with it came 2 syringes with tube ends attached, I assume for the two nipples on the caliper body. I've no experience with disc brakes at all. Does anyone know of a link to some service info on the web? At the moment, it works fine except the return action is weak so the brake stays partially applied.
As usual, any info greatly appreciated!
(It's a weird disc this, it "floats" on nylon bushes instead of being fixed solid.)

 

[stevet1]

not much use but I recall the Hope cable actuated discs also dragged a little, maybe its a 'feature'

 

[deelam]

Yup, this certainly drags a little. Even with the pressure right off the disc "sings" as the wheel spins, no noticeable friction though. I've not ridden this yet but it's going to be pretty musical!

 

[scant]

the "float" of the rotor allows it to cope with any minor warping or damage (IE bending from rock dings).
I have a friend whos had good experience with pro-stop, what do you need to know exactly?

 

[stevek]

Not intending to teach you how to suck eggs.

Does it drag with the brake cable disconnected? Even a small amount of tension from the cable onto the actuating lever will slightly apply the brake.

 

[deelam]

Scant: Thanks, I want to know how to top up the fluid. I suspect it is a lack of fluid or presence of air which is causing the sticking. I have 2 syringes and 2 nipples (sounds like a dodgy german specialist film already!) but I don't know what to do with them.

Stevek: yes it drags with no cable. Once I let go of the small black arm on the caliper housing, it never fully returns. Thanks for the thought though!

 

[pete_mcc]

Think this one is a cable actuated hydro system. The two tubes are a bleed system much like that on a hope system. To flush through attach syringe filled with fuild to one, tube to the other and the push the syringe. (a bit of a simplistic 'how to bleed brakes 101' but you get the idea). Just read the hope bleed manual (there should be a pdf on their website) to get an idea.

There should be a return spring in there to help push them back out, so you may need a stronger one, or the seals/pistons maybe sticking, so they may have to be cleaned or replaced.

Those discs are very floaty (totally unlike the modern hope floaters), they have up to 5mm of movement in them - bonkers (I have one sat in my front room at the mo', 1st thought it was broken, then that the bolts were loose, then remembered that it was from the early 90s so probably did all manner of bizarre things!)

 

[pete_mcc]

On second thoughts probably more like the magura Hs-33 bleed manual, not the hope one, sorry

 

[Grobbebol]

This is a very old brake and maybe not frequently serviced?
If so, the piston rubbers might be sticky causing the piston to stick. The best solution will be to open the system and clean all parts. if this is a DOT brake there's a chance for dirt in the O-ring housings (pistonrubbers), we call it coliflower in the workshop. Best to remove this is by scratching with a thin screwdriver and remove all the dirt. I also like to leave the O-rings in a bath of teflonspray, the same one that you use for the chain. This will bring the old rubber back to life. After a day you can check the O-ring on cracks, this is better to see after the treatment than before.

If you don't know how to deal with these brakes you can always ask a motormech, they should understand these brakes since Yamaha used one back in the 80's (if I'm correct model TR1).


Is this the Fisher that was for sale on eBay a few days ago? Or did you borrow the pic?

 

[deelam]

Nope, it's my pic all right! I did win this on ebay but going back several weeks now. Still not been out for a ride yet :cry:

Thanks for all the advice!