Hello at all
I have a 1990 Jaguar XJ40 with the 3.2 l engine with SLS system removed. Last week, as some sort of preventive maintenance, I replaced the forward brake caliper pistons and seals by a so called Frenkit (Supplier) I realzized that the Pistons went very hard into the cylinder, and that the sliding part was quite stiff to move (rubber bushes replaced as well). I first tried to blled the system conventionally by brake pedal. The pedal remained soft, but fluid was coming out with no bubbles. I monitored that the piston did not move at all. To do the job more properly I bought a bleed bottle. even with this no success. A friend of mine said that maybe to the full movement of the brake pedal, some seal inside the brake master cylinder could have been damaged, due tto that normally the pedal is not moved to such an extent. He had the same on an Audi Quattro which is the same age of my XJ40.

My question....did anybody had the same experience?

I saw that the brake master cylinder replacement is not an easy task. It is called as the electro-hydraulic braake module according to the workshop manual.

Any ideas and advises are welcomed.

Kind regards,
Wolfgang

 

Hi Wolfgang,

I'm sorry to hear about the trouble with your brakes.

My first question is this: prior to replacing the caliper pistons & seals, were the brakes operating properly?

It is certainly possible that if the brake pedal was pushed all the way to the floor while bleeding the brakes, one or more seals inside the master cylinder could have been displaced due to the piston being extended too far. I have learned to place a block of wood under the brake pedal to prevent it from being pushed too far during the bleeding process.

But I have to wonder if the new pistons are simply too large and will not move as freely as they should? If you still have the old pistons, it might be worth reinstalling them with new seals before you worry about replacing the master cylinder/actuation unit.

One other possibility that comes to mind is that you could have air trapped in the ABS/power assist pump or accumulator sphere. I can't recall the specifics, but I think there is a special procedure for bleeding the air from the pump and accumulator. Hopefully one of our other members will remember.

Cheers,

Don

 

Hello Don,
many thanks for your swift reply.

Ok...the car was 2 times dragging to the right. I started the troubleshooting process and found the L/H brake piston had some marks which I interpreted as bad in a way that the piston is not moving properly and is the cause for that dragging. Anyhow, I made the decision to overhaul the calipers on both sides with an overhaul kit. As I mentioned before, the pistons did fit very hard into the cylinder bore, and the caliper guide pins had been stiff to move. Ok I thaught, its a brake, and hydraulic force is needed to make them going. So I decided to reassembly the calipers. First bleeding action went with no success. Fluid was coming out bubble free from the bleed fittings, but neither the pistons nor the calipers were moving any milimeter. So, I decided to get hold of a standard bleed tool where you pressurize minimally the fluid reservoir. This action worked so far, that fluid was coming out of the bleed valves, but nothing was moving at all. At this point I called up a friend, and he told me the experience he made on the old Audi Quattro, where he damaged the master cylinder by pumping the pedal like I did.

I made another strange observation, which might be important. I reinstalled the cap from the reservoir. Caliper bleed pistons were close. I operated the brake pedal several times in short sequences, and suddenly I saw that brake fluid spilled out of the little hole in the reservoir cap. The fluid went up to the ceiling of the garage. Quite strange, and have no clue by what this event was triggered, and what caused an obvious ''overpressure'' in the reservoir tank.

Now I wait for a set of new calipers, which are supposed to arrive this week. Then I will start from this point.

Luckily a friend of mine is dismantling Jaguars, and always has plenty of spare parts, if it comes to the point that I really have to replace the electro hydraulic module.

The funny thing is, I just wanted to do some preventive maintenance, and created my own disaster. Sad.

I will keep you and the Forum updated.

Best regards and thanks again
Wolfgang

 

Hi Wolfgang,

There should be no pressure in the brake fluid reservoir, so it does sound like one or more seals in the master cylinder have failed or been displaced.

In the past, there were seal kits available for rebuilding the master cylinder yourself, but I do not know if any company still offers a kit. You might try our forum sponsor SNG Barratt.

Cheers,

Don