Caliper seals repair

[pflaming]

DO NOT have your fingers in the caliper when you apply air pressure to remove the cylinder. I am repairing a caliper, my finders were NOT in the path, but that cylinder came out like a bullet!  It was a great reminder of the amount of pressure the brake lines have. Does someone know what that pressure is? 

Old brake lines rust out from the inside. I thought an old line would only leak, but I would guess that with a new MC, especially a dual cylinder MC under a hard sustained emergency stop, I think the line is more apt to burst and quickly increase the size of the object one wants to avoid! 

Edited September 13, 2016 by pflaming

[TodFitch]

Can do a rough guess for non-power brakes: I can put at least 200 lbs force on the pedal. Pedal arm has at about a 10 to 1 leverage between foot pad and where rod to master cylinder attaches. So that would be about 2000# into the master cylinder. IIRC, Master cylinder has a bore of about 1 1/8" or pretty near 1 square inch. So that would be about 2000 psi.

It is a bad idea to use compressed air to break things free like you did: You want a non-compressible working fluid (water, oil, brake fluid) pumped in as when the part gives the pressure immediately drops to zero and you don't get a explosive release. Its the reason they use hydrostatic pressure testing for things like air tanks rather than using air to do the test.

[Plymouthy Adams]

ALWAYS place a nice piece of 3/4 inch wood between the piston and the pad mount opposite to protect not only yourself but the piston for reuse....

[ptwothree]

You could also turn your regulator down to 25/30 psi.  Pistons don't always need 100 or so psi to break 'em free.

[Plymouthy Adams]

I have disassembled calipers that were so frozen that only the use of a grease gun with its similar high pressure equal to the braking system itself would move the piston within the caliper ..if opposing  pistons, one often has to adjust his method of pressure and control movement of each piston with extracting the remote piston first then block the exchange hole for the other....not fun..but totally effective method

[pflaming]

My cylinder did not go in squarely and when I removed it I tore the gasket. When I ordered another one, the bench salesman asked what I had lubricated the inner seal with, I replied "brake fluid".  Bad choice, because brake fluid is NOT a lubricant and the inner seal may bind on the cylinder and not slide. So he sold me some brake assembly lube. He said some when in a bind use brake fluid as a penetrating oil. 

Details!!!!!!!!!!!!!!!!

[pflaming]

I learned how to put a new seal in a caliper, tricky but easy one you know the dance?

First get brake cylinder lubricant, place the square O ring seal in the cylinder wall, push the piston down to that seal, then slowly press the piston down into the cylinder.

Next, lube the top seal and press it into place using the old seal and a brake pad.

Finally via low air push the piston out til the groove shows, now wrap the seal around the piston and roll it down til the top edge settles into that groove. See attached pics.

Keep every thing lubed with brake cylinder oil. 

Took me three hours to learn a 30 minute task, but that's how this hobby is. If something in the above is incorrect, please let us know. 

 

Edited May 28, 2017 by pflaming