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Faulty Brake Master Cylinder ????????????????? 

 

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 Post subject: Faulty Brake Master Cylinder ?????????????????
Posted: Sun Nov 21, 2004 7:02 pm 
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Hi guys,

Have a brake problem consisting of:

Loss in brake fluid; and

Long pedal travel.

Brakes still work well, but obviously with longer pedal travel and loss of fluid is a concern.

No noticable external leaks other than fluid / oil around rear brakes.

Note I have Jaguar Series 3 inboard rear brakes.

Do you think it is the master cylinder playing up?

Don't like messing with brakes other than replacing pads so will nake a visit to the local brake centre.

Any advise would be appreciated so that I'm armed.

Intend switching the brake lines to braided steel as heard that they work better - why???????
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Posted: Sun Nov 21, 2004 7:35 pm 
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if the only noticeable leaks around the rear calipers, i'd suspect they need a rebuild

long pedal..... does the pedal bottom out? if not, i'd say it's just a part of the pedal box/master cylinder combo you have

braided brake lines...... standard brake lines, especially when older tend to baloon out a bit under high pressures, the steel braid cover stops this balooning, giving slightly higher fluid pressures at the calipers, and having the side effect of firming the brake pedal feel up a little

 

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Posted: Mon Nov 22, 2004 11:11 am 
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Thanks Interceptor

No the pedal does'nt bottom out, but has got spongier over the last few weeks.

If you press hard the brakes still lock up so obviously are functioning.

Regards the fluid around the calipers when I recently changed the pads did'nt notice any leaking from the calipers themselves although there is definitely fluid / oil on the diff housing.

Concerned that it may the master cylinder leaking back into the booster.

Is there anyway of checking that the master cylinder is okay without simply dumping it and replacing with a new one?

Also, thanks for the advise on the braided lines - as I thought.
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Posted: Mon Nov 22, 2004 1:55 pm 
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check underneath the master cylinder on the booster and see if there's any flid there, if not, unbolt the master cylinder and have a look where the m/s sits in the booster

the brake lines to the callipers...... how old are they?

 

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Posted: Mon Nov 22, 2004 4:09 pm 
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A hard pedal usually means air in the system. Gets worse when hot.
A long pedal could mean the booster has a crack/split in it.

Until the leak is fixed, it'll be hard to diagnose as one problem could amplify another. Rekit the brakes, make sure proper washers are used where lines go into callipers. Always bleed Fr/R, Fr/L, RR, RL, position as sitting in the car, with the motor off.

If you accidently used, lets say power steering fluid like i did, then the rubbers in the master cylinder and callipers will sieze and a full rekit is on order. Pedal is usually very hard.

It's not my fault that these oil makers use similar shape containers! :?
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Posted: Mon Nov 22, 2004 6:02 pm 
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No leaks from either the master cylinder or around the booster (will unbolt the m/c this week and check for any leaks from the booster.

The brake lines are only 3 years old (same age of the car).

Rossi, no hard pedal, just spongy.

When I replaced the pads callipers seemed to be moving okay.

Note - I have a jag brake system (Series 3) with 2 pots on front and single inboards on the back.

Because I don't think that I have a fluid leak from the lines or calipers that is why I am drawn to the master cylinder.

I presume that when I disconnect the master cylinder from the booster there should be no leaks visible????

Then if so - that is MY PROBLEM yes????
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Posted: Tue Nov 23, 2004 6:24 pm 
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Had a look at the rear brakes as clear fluid on the diff shield.

Took shield off and could see that one of the rear brakes was oozing fluid out of the pistons.

Upon inspection the outer rubbers are stuffed and one side is definitely leaking.

Can the pistons be rebooted in position or is it easier to do with the caliper off?
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Posted: Mon Mar 28, 2005 5:50 pm 
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Fluid Could need replacing. Brake Fluid is hygroscopic - absorbs moisture -
Once brake fluid starts to absorb moisture, it lowers its boiling point. If pedal firmness and travel is different as car warms up, then fluid could be rooted. Replace with highest DOT rating you can get - 5 - The higher the rating, the less moisture effects it.

Brake fluid shouldnt be leaking into your booster - your booster is just that - a booster. It just uses vacuum to make your pedal easier to depress. If the diaphragm in your booster is rooted, it would make your pedal harder.

The fact that your fluid level is down could just be worn pads. the self adjusting nature of disc brakes means your fluid level will go down in the resovoir.
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Posted: Mon Mar 28, 2005 6:05 pm 
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BTW, bleeding should always be done first at the wheel furthest away from the master cylinder, working your way forward so the wheel closest is done last.

A hard pedal would not indicate air in lines, quite the opposite. A hard pedal could be a faulty booster (no assistance)

Could be just a mismatched master cylinder-booster-caliper setup?
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