Diagnosing a brake problem

Wizardof · Post by **Wizardof** » Fri Apr 23, 2010 10:22 am

Hi all,
I'm on the way to getting my RX back on the road again, but have come up against aminor problem which I would love some help with.

The brake system is a power servo, single master cylinder with brake bias valve that feeds all four corners. I have disks front and rear, with the rears just being serviced. fronts are quite old.

The problem is that when the brak peddle is pushed, both front brakes stay on, they dont release to allow the wheels to turn freely.

I thought it was only one to start with, so suspected a dodgy caliper. I've taken that one off and taken a look but it appears ok. The piston is hard to push back in but I think it always was anyway.

Now I've figured its both front brakes, but not the rears, i cant believe both front calipers would have gone at the same time..

Any ideas?

Many Thanks
Kevin

JSF55 · Post by **JSF55** » Fri Apr 23, 2010 10:47 am

I had this on my 4 pot jag fronts over the winter through lack of use, they were all gummed up inside, a new seal kit and strip down a polish of the pistons and all was fine, john

SuperV8 · Post by **SuperV8** » Fri Apr 23, 2010 11:29 am

Also check your front pads are free to slide and are not binding.

Tom.

Ian Anderson · Post by **Ian Anderson** » Fri Apr 23, 2010 1:12 pm

Depending on your system you may also have a residual pressure valace in the line somewhere.

These valves are like a non return valve and will hold pressure in the pipe up to a limit of XXXpsi - after whih they allow fliuid fo return

Often used on cars where the master cylinder and reservoirs are lower than the top of the caliper to stop the fluid syphoning back

As such the pads will be left touching and with a slight pressure

Ian

stevieturbo · Post by **stevieturbo** » Sat Apr 24, 2010 10:20 am

Is the foot pedal definately retracting enough to allow pressure to bleed back ?

And as others have said...to a manual/visual on the front brakes to ensure everything is free to move.

Wizardof · Post by **Wizardof** » Sat Apr 24, 2010 4:15 pm

Hmm,

ok, had a good look at the front calipers and they are pretty corroded and gummed up. The brake pedal retracts fine, so think I'll invest in a couple of caliper overhaul kits, give them a good clean and see what difference that makes..

Cheers all!
Kevin

CastleMGBV8 · Post by **CastleMGBV8** » Sat Apr 24, 2010 6:40 pm

Kevin,

Be a good idea to check the condition of the flexi brake lines, these have been known to collapse internally causing a return flow problem apart from the obvious safety issues.

Not certain what causes this problem apart from age but someone did mention that an accidental mix of different standard brake fluids can cause such an occurence.

Kevin.

Wizardof · Post by **Wizardof** » Sun May 02, 2010 9:30 pm

Hi guys,

Quick message to say thanks for the check lists and things to look at. Brakes now working again. Turned out I needed new calipers after all. One was really badly corroded and had seized, the other was working but not really in much better condition, so forked out for two replacement ones. Just need to re-bleed the system now, as my first attempt didnt work all that well.

Thanks again!
Kevin