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Matt
Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 21622
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a kia picanto bought new in 2006. I am on my third

Resolved Question:

I have a kia picanto bought new in 2006. I am on my third brake master cylinder and about to replace it again at 105,000kms-we live in spain. symptoms are: brakes squeal when not in use, brake pedal does not maintain its position-it may be right at the top or lower at any moment and the brakes have been known to come on in normal driving. I suspect there is a basic fault with these master cylinders which have all been original Kia parts.
Thankyou
David Bethell
Submitted: 1 year ago.
Category: Car
Expert:  Matt replied 1 year ago.

Hello

I'd strip the calipers down again and check that the pads are in square and true with no debris in the mounting slots, also inspect the caliper mounting faces for any dents, burrs, or debris which would cause them to be bolted up out of true, also remove the disc and do the same for its mounting face on the upright and inside the disc.

If you still have an issue then it could be a flexible brake line has partially collapsed and is producing a one way valve, this can't always be seen from the outside but you can test to see if there's any residual pressure in that caliper by cracking off the bleed nipple after stamping on the brake a few times

Another possibliity is that one caliper is sticking slightly so the piston isn't retracting on its seals

in which case that caliper will need rebuilding with new seals or replacing

One other thing to try is to remove the master cylinder again and have your assistant push down on the brake pedal to expose the pushrod as it exits the servo

on the end of the pushrod there should be a little adjustment nut

try screwing this in a turn or two and put it all back together

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