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Brakes Locking On, Urgent Help Needed!


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#1 Relatively Normal

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Posted 24 October 2013 - 05:37 PM

Hi,

 

Over the last week my brakes have been locking on after approximately a mile of driving. its a 1992 cooper and has new master cylinder, compensator , both front 4 pot  calipers, vented discs, pipes and  rear wheel cylinders basically everything is new.

 

what the F is going on? I have had to cancel 2 rolling road sessions because of this problem.

 

Thanks

 



#2 Relatively Normal

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Posted 24 October 2013 - 05:42 PM

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#3 freaker

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Posted 24 October 2013 - 06:02 PM

i assume after driving a mile, the car stops completley ? 

 

and you can not get it to move again ? you would normally have a brake servo aswell ?

 

how long does it take  for you to get it to drive again ?

 

freaker



#4 greenwheels

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Posted 24 October 2013 - 06:16 PM

Had this problem on a Maxi years ago. It was a  fault in the servo. Think I ended up overhaulling it.

Wish I could remember more.


Edited by greenwheels, 24 October 2013 - 06:16 PM.


#5 Relatively Normal

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Posted 24 October 2013 - 06:58 PM

Hi,

It doesn't have a servo, and yes it grinds to a halt and will only move again after 15mins or so, or I crack off one of the pipes to release pressure. I'm in the process of dismantling the master cylinder but have only managed to get the bottom part out, for the rear circuit the top part for the front circuit seems like its not coming out. how do I take it out?



#6 greenwheels

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Posted 25 October 2013 - 06:21 PM

Hi,

It doesn't have a servo, and yes it grinds to a halt and will only move again after 15mins or so, or I crack off one of the pipes to release pressure. I'm in the process of dismantling the master cylinder but have only managed to get the bottom part out, for the rear circuit the top part for the front circuit seems like its not coming out. how do I take it out?

It should just come out! Try tapping the master cylinder downwards on a piece of wood to encourage it to drop out.

That could be your problem - it's sticking and not returning when you take your foot off the pedal.



#7 tiger99

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Posted 25 October 2013 - 07:32 PM

You probably do not have sufficient free travel between pedal and master cylinder If the piston does not return fully to its stop, fluid can't escape back to the reservoir if it expands due to heating, so pressure is trapped.

 

Next time it happens, try loosening the two master cylinder bolts and pulling it up slightly. If that releases the pressure, you have located the problem. It may be that there is a problem with the pedal box or the stop light switch is adjusted too far, preventing the pedal from returning fully, or thepedal return spring may be damaged in some way. Pibly even problems with the push in teh pedal, or the pivot shaft.

 

If it is an accumulation of tolerances that is causing the problem, master cylinder shims are available from Somerford.



#8 Relatively Normal

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Posted 27 October 2013 - 03:25 PM

Cheers guys, I put the master cylinder together and went and bought a new one. I have fitted and just bled the brakes but went to go test and the batteries flat. Spacing the master cylinder is something I hadn't thought of but surely that's a bit of a bodge solution, after all it wasn't designed to be like that?

Thanks again for your help

#9 Relatively Normal

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Posted 02 November 2013 - 05:16 PM

Small update,

 

It was the spacing of the master cylinder after all. Putting a new master cylinder on it solved the problem short term. Spacing the master cylinder with some washers did the trick perfectly. Tiger99 i am forever greatful



#10 Ethel

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Posted 02 November 2013 - 06:27 PM

You shouldn't need to spacer the cylinder, it isn't actually attached to the pedal linkage. It will always uncover the reservoir ports unless it's faulty or the pedal stops it. As said, just make sure the pedal can move freely away from the cylinder.

 

If you're trying to dismantle a dual cylinder, you need to remove the reservoir to get at a little pin under the rubber seal.






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