front brakes sticking on help

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martin418
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front brakes sticking on help

Postby martin418 » Tue May 28, 2019 11:53 am

hi all story so far s 2 car 8'' brakes all working fine until a few weeks ago both front brakes holding on slightly ,the rears are fine , it has 2 year old lockheed wheel cylinders .i fitted new flexi hoses , new lockheed master and new wheel cylinder rubbers just for the hell of it . bleeds fine pedal adjustment correct all pedal bushes etc new and free ,brake lines flushed through ,but still slightly sticking let the adjustment off to point where pedal travels nearly to the floor its ok , as is letting the fluid pressure out of the pipes anywhere on the front circuit , even took the 4 way union off and cleaned it through less than 1 mile road test and they are hot especially the passenger side , even tried a spare set of drums ! i am wondering if a new set of return springs is worth a go . any other ideas appreciated

philthehill
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Re: front brakes sticking on help

Postby philthehill » Tue May 28, 2019 12:33 pm

You could try a new set of 8" return springs (Pt No: 27H6555 (MOSS)) and see what happens.

If the new springs do not cure the problem I suspect that the brake wheel cylinders are sticking and need to be stripped and cleaned.

I always recommend that the brake adjusters are left on the slack side as that ensures plenty of wheel cylinder piston movement which reduces the possibility of wheel cylinders sticking.


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panky
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Re: front brakes sticking on help

Postby panky » Tue May 28, 2019 1:56 pm

Could also be the flexible hoses collapsing in side.
Image

martin418
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Re: front brakes sticking on help

Postby martin418 » Tue May 28, 2019 2:59 pm

its had new hoses and cylinders cleaned / new seals [ only 2 year old lockheed ] i have ordred new springs

paul 300358
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Re: front brakes sticking on help

Postby paul 300358 » Tue May 28, 2019 3:46 pm

As Phil has said, the brakes should not need adjusting up too tight as the first press of the peddle should move the shoes into contact with the drum. The residual pressure valve should keep about 10lbs of pressure in the pipes which should keep the shoes adjacent to the drum. A bit of a long shot but you could find that the top hat seal in the master cylinder is leaking, this can cause you to think that the shoes need adjusting and you then over adjust them.
I can't imagine that the top hat seal could increase the residual pressure.

Also, if you have a lot of peddle travel without the front brakes binding, it could be the rear brakes are adjusted incorrectly. You need to ensure that the handbrake cables are fully released (I think that the manual states that the cables never need adjusting). Then you adjust the rear adjusters. If you have any tension at all on the handbrake cables you will never get the rear brakes adjusted correctly.

philthehill
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Re: front brakes sticking on help

Postby philthehill » Tue May 28, 2019 5:32 pm

You cannot exclude the wheel cylinders and hoses even if they are only two years old. Even new stuff fails these days.

As regards the residual line pressure it should be about 8lb/sq inch. (data taken from BMC wksp manual)

If the master cylinder is not adjusted as per the BMC wksp manual the main cup/seal can obstruct the return orifice so causing a build up of pressure in the brake line resulting in the brakes being applied. (see BMC wksp manual.

The brake pedal master cylinder actuating rod must allow the master cylinder piston to return hard against the circlip at the front of the master cylinder.

The brake pedal should be able to move slightly before it engages and pushes the master cylinder piston. You should be able to feel when the operating rod hits the piston.

Details of the adjustment(s) required can be found in BMC wksp man Section M.


martin418
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Re: front brakes sticking on help

Postby martin418 » Tue May 28, 2019 9:13 pm

master new .all brakes adjusted master cylinder push rod all fine the fault just appeared its a regular in use car


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