Hi all,
I hope someone can help with this problem because I'm out of ideas and at my wits end, if I hadn't just rebuilt the rear suspension with a new subframe, welded the sills and replaced the clutch I think the car would be off to the breakers. So, the problem - I replaced the rear sections of the rigid brake pipes while doing the subframe. I bled the system using a pressure bleeder, very little air came out of the rear calipers because there had been little fluid loss as I'd sealed the reservoir. All good so far but when I pressed the pedal it slowly went down to the floor with slight resistance. I bled the system again with the old 'pump the pedal' method, the problem remained. I researched on here and other paces and concluded the seals in the master cylinder had failed so a replacement cylinder was installed. I'm now on my 3rd master cylinder and after bleeding each one behaved the same. Each time I have flushed over a Litre of fluid through the system and haven't seen any air come out, just very clean fluid.
What am I missing or doing wrong? I can't believe that it's so difficult to get the brakes to work.

 

https://www.justanswer.com/car/1cbbn...004-i-put.html

 

If you did all that you are probably a master of "that trade" now, so that I can't tell you anything new, but just in case:
Bleeding of the brakes is done starting on the nipple furthest away from the brake master cylinder - and then coming closer step by step.
When installing a new brake master cylinder, that cylinder needs to be bench-bleed first.
Sometimes air is stubbornly stuck in the "octopus" and hard to get out of there.
I assume you checked for an obvious brake fluid leak somewhere? I had to replace my rear rubber hoses going to the calipers, because they looked might brittle...
And I assume, you have sufficient thickness left on the brake pads and rotors?
Also a possibility: Leaks on the seals of the brake calipers. I already swapped mine. There are replacement kits. But again: If that is the issue, I would suspect a leak there...

 

Just replaced all brake pads on my '06 X-Type and suffered similar embarrassment.

However, by carefully syringing excess master cylinder (m/c) fluid as I pushed back caliper pistons, I had no need to break into any brake lines. None whatsoever! I swear it was so! Moreover, I was careful to ensure sufficient m/c fluid before (and after) pushing brake pedal to properly seat new pads. So . . . imagine my shock when the pedal (albeit with some resistance) went to the floor. I had classic symptoms of spongy brake pedal caused by air in the system. Drove it carefully onto the hoist . . . and went inside for coffee and reading.

Turns out that on this model and many of its era and later, indeed any with ABS, and especially those where the ABS top chamber is at or above the height of the m/c body . . . any air collected in the system (for whatever past reason) can accumulate in the head of the ABS with no ill effect, BUT . . . can very easily be pushed back along the line toward the m/c when resetting caliper pistons!

So, bleeding the brakes never starts at the wheels. It starts at the ABS, and the sequence of loosening and bleeding the ABS unions is critical. Super critical that your assistant presses pedal slowly, or you will send a shower over the mudguard / fender! Only when the ABS lines all bleed clear of air and of new fluid , , , and only then , , , can you proceed to the sequence of bleeding at the calipers. Again, I chose to assume the fluid (which looked fine) had never been changed, so I bled each wheel until I got obviously new fluid. I am still amazed at how few little bubbles of air were in the system to produce that spongy pedal, but I'm now rewarded with a firm stop.

Cheers,

 

Thanks for your comments. I must admit that I've been wondering if I should try cracking the lines on the ABS HU and your experience confirms it, many thanks.

 

Can you explain 'bench bled' please? I'm assuming the purpose is to fill the piston cylinder with fluid but how do you retain it when fitting the assembly and connecting the lines?
What do you mean by the'Octopus'?

 

An update but not progress. I now have a reasonable pedal without the engine running, it can be pumped a bit though. With the engine running and servo assistance the pedal offers little resistance and goes nearly to the floor before there is any braking whatsoever. Pumping improves it but obviously exhausts the servo vacuum.

 

Am I correct in thinking you have never actually driven this car when I had decent brakes?
You have done a huge amount of work and I can certainly understand you not wanting to walk away from all that effort.

One issue that can present itself with brake systems is the flexible lines that connect from the hard lines to the calipers can themselves become over flexible, allowing the fluid pressure to expand the flexi-line diameters.
Perhaps your issue is just old failing flexi-lines that are giving you a very spongy pedal?

 



 

I've been advised by an Independent Jaguar Specialist that it has to be bled with the engine running, using a pressure bleeder and to pump the pedal before cracking each bleed nipple. Also the order is different to what you'd expect, nsr, osr, nsf, osf which is in order from the greatest distance from the ABS unit. Saturday's job, will report back.

 

OK, so some progress. The brakes are working again although not brilliantly. Pedal is very soft to about half way down then there is resistance, one pump and it's great and will stop on a Sixpence. A good half litre of fluid per corner and no air expelled. I can't decide if there is air in the system now? I did wonder about the rear calipers auto adjustment but the hand brake is good.