Binding front brakes

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malcolmd
Posts: 8
Joined: Wed Sep 14, 2016 9:17 pm

Binding front brakes

#1 Post by malcolmd » Tue Jun 25, 2019 4:01 pm

I hope someone can help with some advice. I have an Austin Somerset which has been off the road for a couple of weeks and I recently changed over to silicone brake fluid which I have used in several cars with no problems. However, she has developed a ‘hydraulic lock’ with the system being pressured applying the brakes and turning on the brake lights.
I then changed all the rubber seals in the system including new flexi hoses with no improvement. The rears seem fine with the fronts binding and when I took the drum off you can push the shoes back 5mm on the pistons, but they come out again. I
I rebuked the brakes again this morning and all seem well but after 1/2 mile or so the brake pedal is again hard, the brake lights on and the front drums very warm.
I am at a loss what to do next after speaking to both Automec and the Austin Counties Car Club.

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JPB
Posts: 9872
Joined: Fri Jan 07, 2011 3:24 pm

Re: Binding front brakes

#2 Post by JPB » Thu Jun 27, 2019 12:28 am

Sorry, Malcolm, for not responding earlier to your post, but I needed to have a good think about this one! (Though I am surprised that nobody beat me to it..)
Have you fitted new return springs and hold down springs to the shoes? Weak return springs (the ones that cross the backplate and attach to both shoes) would be one possible answer to this conundrum. These can become less effective with age and the fact that the problem arose during a fluid change may be coincidental.

Another thing that may be to blame, and which you didn't already mention, is the master cylinder pushrod being adjusted too tightly or being of incorrect length, though this would usually be more apparent when driving as the clearance is reduced and the brakes gradually become less willing to release as a result of the pushrod expanding slightly and being unable to do so in the available space without causing unwanted brake application. Reliant Regals & Rebels, which also have underfloor m/cs, are prone to this effect, usually caused by one of two things: incorrectly adjusted pushrod clearance at the pedal end or a pushrod of incorrect length, either would cause the brake lights to come up when the switch is operated by system pressure.

Then there's the brake light switch itself. If yours is the type that screws into a four way union somewhere close to the m/c, then the spring inside the switch can fail, which turns [the switch] into a one-way valve, this is a rare occurrence but as these are cheap, I think it would be worth swapping the switch for another if the return springs and pushrod adjustment are both found to be innocent.

Good luck and please come back to tell us how you get on.
JB I didn't go looking for the current fleet, they just sort of followed me home and now they won't leave without an extradition order from the Japanese government..
:|

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