Brake master cylinder

[Sheepy]

Long shot, but since Ebay has failed me...

Does anyone have a spare brake master cylinder for an '86 3.6l (no abs)? Mine appear to be somewhat defective in that it doesn't pump any fluid to the rear brakes.

I've even disconnected the line out of the unit (whilst also opening a bleed nipple on a front caliper), but no fluid is expelled from the unit. This leads me to believe that the master cylinder isn't working properly

Does anyone know if there is a rebuild kit available?

Or does anyone have a better suggestion about what is wrong?

Cheers

Sheepy

[Mark_B]

Any car spares / motor factors place, (such as Halfords even) stock (or can get the next day) a renovation kit. Quite easy. Master cylinder tends to go at this time of year, especially if car not used much, the rubber hardens. The effect is very similar to that rubber washer thing in a half knackered bicycle pump that air blows past it at first but once enough air get trapped to make it seal it works ok.

[Telsmoneypit]

Sheepy, before you condemn the master cyl it's worth changing the flexible hoses. The one serving the rear brakes is known to be especially vunerable to collapse.

Tel

[Sheepy]

Tel,

My master cylinder is the problem, not the rear pipes. I'd been told to check them, which is why I disconnected the master cylinder from the rear brakes at a junction near where the front line splits left and right. Basically I had a foot of brake line ending with a plastic bottle, and nothing emerged when I pumped the pedal.

New master cylinder on order from my usual supplier.

Sheepy

[Gordon@1962]

I've just found out I need a new Brake Cylinder too!
Mine has ABS though.

Are the seal kits worthy?
My mechanic said he doesn't like the idea of doing this on such a heavy car that relies on a good braking system.
So he rang Jaguar and they quoted £1700 for a new one. OMG!!

He said he's now going to try a few of the trust worthy breakers yard like Eurojag for a good second hand one.

Whats peoples thoughts on this topic.

[greeban]

Hi,

Your mechanic is quite correct - I am studying at Bedford Vehicle College and we were discussing this very topic the other day! The consensus from the professionals is that seal kits are not reliable as you can never remove all the corrosion/pitting if it is there. If the seals are the only problem then would be OK but as you say, with a fast heavy car like the XJS do you want to take the risk??

[ptjs1]

Many different views on this. I've never tried to re-seal an XJS cylinder but I have successfully done it on other cars. I've always taken the cylinder apart and tried to polish out any corrosion before fitting new seals.

Sheepy - I'm not sure what year your car is, but seal kits are still available from Jaguar for VIN 139052 to 179736 for £22 plus VAT. New master cylinders for this series of cars are £120 plus VAT

Gordon - again not sure what year your car is, but even very late VIN master cylinders are available from Jaguar for £220 plus VAT so I'm not sure where the figure of £1700 comes from!

Hope that helps,

Paul

[poprivet]

I've just found out I need a new Brake Cylinder too!
Did your mechanic break the news to you whilst sucking in air through clenched teeth at the same time as a slow shaking of the head?
It wouldn't be the same mechanic that changed your brake pads a while ago by levering back the pistons thus forcing cr@p back into the ABS modulator by any chance?
What are the exact symptoms that you are experiencing, perhaps the collective wisdom of the forum can help you from wasting a considerable amount of cash.
Pop

[Gordon@1962]

No its ok pop.
He's a close friend and I trust him implacably.

The car has been pulling to the left under braking.
Up to now we've the rebuilt the cylinders, changed the pads, bled the brakes, and changed the hoses.
Only thing left we can think of is the master cylinder.

[ptjs1]

Gordon,

I'm sure there are others here with far more technical knowledge than me on ABS systems. However, on an ABS system, I wouldn't be looking first at the master cylinder for causes of the car pulling to one side. I'm sure you've done all the obvious checks so forgive me if this sounds patronising but have you looked at obvious pulling causes such as sticking caliper pistons or internally collapsing flexible pipes?

If the problem is being caused at the centre rather than the wheel, then I think I would start looking at ECM signals that are being applied to the valve solenoids for one of the front wheels, thus reducing the brake pressure on that one side. This could be caused by a dodgy wheel sensor sending a false voltage reading to the ECM which then sends the signal to reduce the circuit pressure. The actual master cylinder on an ABS system only directly drives the front brakes (the rear brakes are actuated only via the accumulator and thence the control valve). The master cylinder is relatively simple compared to the other parts of the ABS system and I'm not sure it can be the cause of a differential in pressure between the two front wheels.

Perhaps when your mechanic refers to the master cylinder, he's talking about the accumulator or control valve block?

Again, I hope of all of this is helping you.

Regards,

Paul

[Gordon@1962]

Hi Paul,

No you are not being patronising at all and I welcome any information this forum can pass onto me.
There is a wealth of knowledge here, more than you could ever get from one mechanic.
So the more information we have the better, to help us get to the bottom of this mystery.

We have already checked for sticking calliper pistons or internally collapsing flexible pipes by stripping down the callipers and replacing the pipes but this made no difference.
He has now been on the phone to a few Jaguar specialists’ contacts that seem to think it is the master cylinder? But I do see where you are coming from on the ECM signals.
I’ll give him a ring on Monday morning and pass on your suggestions.

Cheers guys.

[greeban]

Hi,

All depends on the type of master cylinder you have - being an early car does this mean you have no ABS - Paul's sugestion is valid if you do have ABS. If the master is diagonally split front/rear this might be the source of an imbalance but I am wondering if you have a drivetrain/suspension geometry problem? According to my XJS workshop manual the master is split front/rear which makes it more unlikely to be the master cylinder. The manual suggests worn shock absorbers. Perhaps it could be as simple as this??

[Gordon@1962]

Yes, mine does have ABS and I also thought it was split front and rear.
But thats as far as my technical understanding of the braking system goes.

However regarding geometry set up, I've just had a S/H front subframe fitted with a complete suspension rebuild which included new shock absorbers.
I'm now wondering if this has upset something?

[dhdove]

Gordon
Why bother repair it? Have this and keep yours as a spare!
1989 3.6 Coupe in met. blue, piped cream leather, good aircon, tyres(Pirelli) brake and suspension overhaul, new headlining, fuel tank, swirl tank, very reliable, too many parts to list etc.etc.etc. body needs tlc, .... with new MoT and five months tax (with ABS) all working and v. good sub-frame for £1695.00
Dh Dove
IDEAL CHRISTMAS PRESENT
Sorry for this blatant advertisement

[Gordon@1962]

Oh you are cheeky m8!

I haven't given up all hope yet.
I checked with a retailer and the part is £1500 + VAT.
However not to worry I've managed to track down a good S/H one for £100 + postage.

We're sure this will sort it once and for all. (*fingers crossed*)