Rear brake lock up has me stumped...
05-22-2018, 11:29 AM
#1
Rennlist Member
Thread Starter
Rear brake lock up has me stumped...
I'm having a strange issue with the rear passenger caliper. Sometimes when I'm driving the passenger side caliper will slightly start to engage and the car will feel like its "dragging". At the same time, the brake pedal starts to feel very firm - like no travel. If I come to a complete stop, push the pedal in good and hard, everything frees up (sometimes I hear a click as the caliper gets free) and the car drives completely normally.
My initial thought was that the caliper was frozen or otherwise extending but not retracting. I ordered a new rear caliper, adjusted the piston orientation per the WSM, installed it and everything seemed fine for a couple weeks, but the symptom returned.
I don't think its an issue with the master cylinder because I think that would affect each of the wheels (or at least pairs of wheels), not just the right rear.
I did a "search" on this at it seems to have been encountered at least once before, but no solution was posted.
Any thoughts? Thanks.
My initial thought was that the caliper was frozen or otherwise extending but not retracting. I ordered a new rear caliper, adjusted the piston orientation per the WSM, installed it and everything seemed fine for a couple weeks, but the symptom returned.
I don't think its an issue with the master cylinder because I think that would affect each of the wheels (or at least pairs of wheels), not just the right rear.
I did a "search" on this at it seems to have been encountered at least once before, but no solution was posted.
Any thoughts? Thanks.
05-22-2018, 11:36 AM
#2
Team Owner
have you ever replaced the brake flex lines?
what fluid are you using?>
When was the MC replaced?
what fluid are you using?>
When was the MC replaced?
05-22-2018, 12:09 PM
#3
Drifting
Failing flex hoses can begin to collapse internally. The hydraulic pressure is enough for fluid to be pushed through to caliper, but fluid returning from caliper at low pressure gets blocked so pistons don’t retract.
if you replace that hose (really all the hoses due replacement if original), then spray penetrant on the union and use a good flare wrench on the hard line nut, supporting the line behind. You don’t want to damage the hard line on that side as it’s much harder to replace than the short one on the left side.
if you replace that hose (really all the hoses due replacement if original), then spray penetrant on the union and use a good flare wrench on the hard line nut, supporting the line behind. You don’t want to damage the hard line on that side as it’s much harder to replace than the short one on the left side.
05-22-2018, 04:26 PM
#4
Rennlist Member
I had a similar issue on my 81 where the rear calipers would drag and eventually lock up. It was due to the brake pedal being adjusted incorrectly with the brass rectangle thing being too far forward and putting pressure on the brake master when the pedal wasn't applied.
I would start with giving the car a brake fluid flush and replacing the rear hoses if they are original or very old.
I would start with giving the car a brake fluid flush and replacing the rear hoses if they are original or very old.
05-23-2018, 12:10 PM
#5
RL Community Team
Rennlist Member
Rennlist Member
If you're going to go to the trouble of replacing the hoses, use a DOT certified braided stainless steel with the protective clear cover. These hoses are Teflon lined and you'll never have to worry about the internal swelling issue again - you'll also get a firmer brake pedal. I'm using the ones from 928 Motorsports with my Big Black upgraded Calipers.
