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General => Technical | How To => Topic started by: ninuve on July 02, 2016, 12:41:48 PM
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I have an issue with my rear brakes. Basically I have filled rear master cylinder with oil but the brake lever goes down all of it. I have bleeded system several times and ensured that air is out. Have also replaced rubber from master cylinder but to no avail. I was told that air can be trapped in the pipes. Or can it by anything to do with caliper. Until 2 days ago all was working fine. Would appreciate your valuable feedback
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If there is even a TRACE of oil left in the lines or in the caliper, it will either destroy the caliper seal or it will work its way back into the master cylinder and ruin the new rubber seals that you just installed in the master cylinder. Make certain that ALL traces of oil have been removed from the master cylinder by using brake Kleen to clean it all and then making sure that the brake Kleen is COMPLETELY evaporated before installing the seals and reassembling the master cylinder and/or caliper. Then immediately bleed, bleed, bleed the lines. You should then have brakes again.
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Thks. But i cannot understand why. I mean removing all oil. I did this process but all remain same..there must be air somewhere
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Oil contamination in the brake system causes the rubber parts (master cylinder seals, rubber brake hoses, and seals in the brake caliper or wheel cylinders) to swell up and all have to be replaced at the same time along with flushing/degreasing of any hard lines otherwise as Forbes1964 said the problem will still be there.
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Am I real thick-headed or are you interchanging the term "oil" for "brake fluid"? The brake fluid should be DOT 4 I think for all disc brakes. Somebody will chime in if that's wrong.
Karl
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Yes, he means brake fluid when saying oil.
If you have bled the lines several times - there is probably little air in there - might be master cylinder is not sealing and is moving when you pull brake lever - but not pushing along the brake fluid because of broken seals - or it is at the other end ? (but if seals broken at the wheel - would not fluid be leaking out down there??)
His lever is going all the way down with no effect on the brake.
Fluid is either not being pushed, or is coming out somewhere, yes?
Look for leak along the brake fluid line - from the brake lever down to the wheel.
Any brake fluid on the floor?
If lever fully squeezes and nothing happens at the wheel -
1) leaking seals in master cylinder by the brake lever
2) leaking brake line, or line connectors
3) leaking at the caliper
4) still much air in the line
No brake expert here by any means - but this is what I would look for before taking it to an expert.
Stig
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Stig's explanation is better than any textbook and spot on!
Karl
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Thanks guys for all the help. I have taken Agility to be checked by a m/cycle mechanic and he found out that master brake cylinder was defective. Basically this was changed and it is on the road again :)
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Am I real thick-headed or are you interchanging the term "oil" for "brake fluid"? The brake fluid should be DOT 4 I think for all disc brakes. Somebody will chime in if that's wrong.
Karl
I guess we were the thick headed ones. Thanks for moving us in the right direction. A ONE track mind is not good. It's always wise to make sure we have the right understanding.