I've been overhauling the brakes and although I've managed to remove the air one of the front brakes is sticking. It appears (after dismantling) that the rubber seal has swollen and needs replacing. Of course I can't just order a zenit seal kit from wiggle...

Anyone have some experience with these and can offer some advice as to what to fit?

Having taken a further look it actually appears that it's the piston itself that is sticking. I still need some new seals, but I also need to give the cylinder a good polish too.

Spent the evening cleaning the bore of the cylinder, first with 1500 grit then polished. The surface is now free of any marking but the piston still sticks when pushed home. It appears that the end of the piston where the pin locates into is slightly enlarged and although I have spent the best part of an hour carefully sanding I haven't removed enough material to fix the problem.

After some research on the web the seals appear to be a type of o-ring called a Quad-Ring. Although a straight o-ring would probably make a suitable replacement the Quad-Ring does offer several benefits such as reduced drag and better sealing properties. I'm going to have to speak to some places tomorrow and see what they can turn up, especially as it feels like a silicone or viton rubber.



Edited 1 time(s). Last edit at 05/09/2010 03:40PM by enak.

Front brakes now working :)

I received a new seal p/n QR-4013 which is smaller but fits well. I think the QR-4110 may be a better fit but will need to order some to find out. The original I think was a QR-4111.
Part ID OD CS
QR-4013 11.1125 14.2875 1.5875
QR-4110 9.525 14.2875 2.38125
QR-4111 11.1125 15.875 2.38125

Having had time to dismantle the other brakes also I've found there was only one with the quad-ring. It is possible that the o-rings have been replaced! Going by the wear on the remaining quad-ring this is very likely especially as the pistons have been made to imperial sizes and have metric o-rings fitted... Although this could just be my measurements

Piston measurements
14mm dia
17mm long end to end
3mm deep 11mm dia recess for shoe pin
4.68mm to first o-ring from shoe pin recess
2.38mm @ 10.55mm dia
1.60mm @ 14mm dia
2.38mm @ 10.55mm dia
2.36mm @ 14mm dia
3.6mm @ 5.8mm dia





Edited 1 time(s). Last edit at 05/09/2010 05:26PM by enak.

Nice work Enak. Was wondering about O-ring replacement eventually too...

Could you name the supplier where you got your replacements, or was it via your work and not available to individuals?

I've only got one so far as a sample... But a local bearing supplier is enquiring for me.

I think the part numbers above are generally available but a fairly specialist part.

Are you able to have a look at what seals you have fitted currently?

Not just now sadly - it's in the loft and I'd rather keep it in one piece for storage. After the rear end broke:

[www.velovision.co.uk]

it'll take a fair bit of effort to fix - probably involving getting the old block out and machining a new rear block for it from solid. With two mags on the go I just don't have time to get into that at the mo...

enak:

You are now using o-rings successfully for the brake seals? As opposed to a 'square-shouldered' seal?

I don't know which are used on my Zenit. There is a chance that I'll learn when I return the brakes to the original front/rear split, and in that case I'll let you know. I expect the brake seals are the original as from the 'factory' (ASE).

How are your brakes working since your 'intervention'?

Thanks...

Peter B.

-----

I finished fitting new seals I ordered last night. I am now using the QR-4103 Quad-ring seals. The o-rings fitted previously dragged causing the brakes to stay on.

I only had one of what I assumed were the original seals, the rest having been replaced with o-rings. The original seal was a quad-ring although a custom size from the standard ones offered. While the QR-4013 is a good fit, it is smaller and may allow some fluid to pass. Only time will tell. If this were the case it will be neccessary to either have a custom size Quad-ring made or remake the pistons to accept the QR-4110.

Either way, I have bleed the brakes and they are working very well.