I changed the brake pads, rotors and calipers on all 4 wheels on my 06 x-type. Removed all the air using a pressure bleeder. Brakes are great - too great. After a couple miles the brake pedal gets stiffer and stiffer - doesn't take much to stop the car after a few miles. In fact I think if I blew on the brake pedal the car would stop. You can also feel a drag build up on the car over those few miles. When I get out of the car all 4 brakes are hot. I have ordered a new MC but I'm not sure that will solve my problem. I took the old MC off, put bleeder hoses on it and when I push the piston rod fluid is pumped into the reservoir (basically bench bleeding). If I put my finger over the hose and then release the piston rod I can feel a suction on the hose - both hoses in fact. So I don't think it's preventing return fluid - I could be wrong but I'm afraid that a new MC will not solve my problem. BTW I completely flushed the fluid with all DOT4 fluid.

I have checked and double checked all caliper to make sure everything is good - sliders are all grease up, etc... Given the symptoms could it be that I screwed up my ABS block when I tried to bleed them a bit? I can't imagine I did but even if I did would this ABS block create pressure buildup on both sides of the block?

 

By the way I took the vacuum hose off and drove the car - just to see if that was it. The car is MUCH harder to stop without this vacuum hose. The result was the car was much better, less drag but over a longer period of time the same thing was happening. So it's not a faulty vacuum hose.

 

How many times did you bleed the brakes ....If you've drained the system it can easily take 4 times pulling at least 1/2 pint through each corner before the air is gone and if you're using the pressure bleeder make sure you GENTLY press the brake pedal to the floor and make sure it comes back to the top again during the bleeding.
I've known cars that after the fluid running clear all of a sudden release a large dose of bubbles that was obviously trapped somewhere....(some thing a vacuum bleeder can help with BUT vacuum bleeders have horrid tendency to suck in air around old bleed nipples meaning you cant trust the clarity of the fluid travelling down the clear pipe you should have on the nipple)....all of that however that normally leads to brakes that bind up after a few miles or pedal presses but with a softer than normal pedal feel.

If I understand you correctly you describe a rock hard pedal with binding brakes ???.

But if its all 4 wheels binding up it does sound to me like the Master cylinder is the best place to start....Its unlikely the abs pump is at fault just from bleeding ...have you tried braking hard enough to get the ABS pump to kick in ...a gravel lane a great way to test an ABS pump...if you don't have the software to run the pump on its own....some cars ...like most modern french cars ...you have to run the ABS pump whilst bleeding the brakes ...but I didn't have to do that on my X type to get good brakes
or another idea but unlikely is a failing brake hose ...
I've known failing brakes hose when they start to expand to much under braking and act like a hydraulic accumulator effectively storing pressure after the brake pedal is released.... leading to a build up of system pressure.

when you find what ever it is let us know what fixed it.

 

PinkFlamingo: Try removing the brake master cylinder from the power brake booster and adjusting / shortening by ~1-2 mm the length of the push rod in the power brake booster, which presses on the piston in the master cylinder. If the push rod is a few mm too long, the master cylinder piston can't fully retract. The master cylinder piston must fully retract so that, as you drive, the brake calipers heat up, the expanding brake fluid must be able to flow backwards thru the master cylinder relief ports into the brake fluid reservoir. If the master cylinder piston can't fully retract, it blocks the relief ports, and the hot, expanding brake fluid has no place to go other than to push the brake pads into the brake rotors, slowing the car. As you drive, the brake calipers and brake fluid gets hotter, and the problem gets worse.

This post has more details how to adjust the push rod length, and the following post in the same thread explains why it works: https://www.jaguarforums.com/forum/x...3/#post1931807

This post also explains how to adjust / shorten the push rod length: https://www.jaguarforums.com/forum/x...9/#post1929116

 

I bled the brakes several times. The last "flush" was actually just pushing about 12 ounces of fresh fluid out each caliper - no actual draining.

The "stiff" pedal meaning the pedal is high and all it takes is a little push and the brakes are applied - I don't have to push much at all. It's not hard as in hard to push. So in the beginning I have to push the pedal down halfway to stop. After a few miles it's like the fluid is pressing against the pedal - could be the fluid is getting hot and expanding and pushing on both ends of the system - pedal and pads. Doesn't make sense - fluid isn't hot and what could be causing the fluid to get that hot that quick?

I will let you know what I find.

 

That's a great theory, however, it doesn't explain why the pedal is also locking up. If the check valves are not relieving the pressure then I wouldn't expect the pedal to feel like something is pushing back on them too. That's why I just don't see a new MC helping. The fluid level was high (due to the pressure bleeder) and so one theory is the expanding fluid has no where to go and then ends up pushing on the pedal. But I sucked it out last time it was high, brought it down to the max line and it still was the same behavior. Plus like I said the fluid is not hot (stuck my finger in there lol).

I don't know much about the ABS block and how it could be causing this behavior.

 

PinkFlamingo: When you say "fluid isn't hot", I will venture a guess that you are checking the temperature of the brake fluid in the reservoir above the brake master cylinder, where the brake fluid does not get hot, except from residual engine heat.

The problem with hot, expanding brake fluid is down inside the brake calipers, which become very hot after you drive a few miles with the malfunctioning brake pads squeezing on the rotors and generating a lot of frictional heat. The more you drive, the hotter the brake calipers become, causing the brake fluid inside the calipers to get hot and expand. To illustrate the point, in very severe instances, the brake fluid inside the calipers can become so hot it boils, causing spongy brakes, while the brake fluid in the reservoir will not get anywhere near hot enough to boiling.

If the push rod in the brake booster is too long, and this causes the piston inside the brake master cylinder to not fully retract, then the compensation ports inside the brake master cylinder are blocked by the piston, and there's no expansion outlet for the hot brake fluid inside the calipers. This causes the brake pedal to become stiff, and the brakes to lock up after you drive a while. The longer you drive, the worse it gets because the brake fluid inside the calipers gets hotter and expands more as you drive.

I'm not certain that this is the problem and that the solution is to adjust / shorten the length of the push rod in the brake booster by ~1-2 mm. But the symptoms you describe suggest that this could be the cause, it's a relatively easy fix to try, and no parts are required (assuming you already have a 7 mm socket to adjust the push rod length).

The symptoms you describe do not fit the pattern of an ABS problem. 99+% of the time the ABS is inactive because all 4 tires are rolling on pavement at about the same speed. The ABS does not kick in until you brake hard on slick pavement and one or more tires spins at a different speed because it's slipping.

 

great explanation!
ive heard about others using that pushrod
adjustment with success.

 

Not gonna! You can't make me try a fix. I wanna complain some more. If you keep it up, I'm gonna take my ball and go home........

 

Yes - I am checking the temperature from the reservoir with the theory that hot fluid would eventually mix and at least feel a bit warm up there (but if it's blocked then it will never mix - got it).

What you are suggesting is this. The Master Cylinder is preventing all or at least some of the fluid from returning to the reservoir. This is causing the brakes to lock which is causing the calipers to get hot which is causing the fluid to get hot. Once the fluid gets hot, the fluid expands pushing back on the pedal (even harder than cool fluid) because it has no where else to go.

The only puzzling thing is why does the pedal work fine for the first few miles? Seems to me that if he fluid is restricted it would make the pedal stiff after the first couple pumps - hot fluid or not. It's certainly worth a shot - I'm going to try this and let you know. I have the new MC coming sometime today but to isolate the problem, I will make the adjustment with the existing MC. I'll back it off by two turns on the thread. If it doesn't work I guess I'll immediately go with the new MC.

Thanks for your help and detailed explanation!

 

I also wanted to mention I had a hell of a time initially bleeding the system. We beat the crap out of the brake pedal for hours over several days until I finally ordered a pressure bleeder that did the trick. Could have weakened the springs inside or caused the booster pin to come out too far. Now that I think about it I did notice that it was much easier to bench bleed the old one vs the new one (easier to push the piston rod in) - the springs must have been weak. The initial new MC I ordered failed out of the box - kept getting air as I bled it and then fluid started coming out the sealed piston rod wasn't holding any pressure.

 

Quote:

Originally Posted by PinkFlamingo

Yes - I am checking the temperature from the reservoir with the theory that hot fluid would eventually mix and at least feel a bit warm up there (but if it's blocked then it will never mix - got it).

What you are suggesting is this. The Master Cylinder is preventing all or at least some of the fluid from returning to the reservoir. This is causing the brakes to lock which is causing the calipers to get hot which is causing the fluid to get hot. Once the fluid gets hot, the fluid expands pushing back on the pedal (even harder than cool fluid) because it has no where else to go.

The only puzzling thing is why does the pedal work fine for the first few miles? Seems to me that if he fluid is restricted it would make the pedal stiff after the first couple pumps - hot fluid or not. It's certainly worth a shot - I'm going to try this and let you know. I have the new MC coming sometime today but to isolate the problem, I will make the adjustment with the existing MC. I'll back it off by two turns on the thread. If it doesn't work I guess I'll immediately go with the new MC.

Thanks for your help and detailed explanation!

PinkFlamingo: Why is brake fluid in the reservoir not hot?
+ Coolant is circulated by the water pump from the engine thru the radiator and coolant reservoir, which is why coolant in the reservoir gets hot.
+ Power steering fluid is circulated by the power steering pump thru the steering rack, the steering fluid oil cooler (in front of and below the radiator) and the power steering reservoir, which is why the fluid in the reservoir gets hot.
+ The brake system has no equivalent pump, and there is no loop of brake line to circulate brake fluid from the calipers back to the brake fluid reservoir. So when brake fluid in the calipers gets very hot, the brake fluid in the reservoir stays relatively cool.

You ask why the brake pedal works fine for the first few miles. Before you start driving, the brake calipers are cool. After you drive a few miles, friction heats up the calipers causing the brake fluid inside to expand (while the fluid in the reservoir remains cool). If the compensation ports in the brake master cylinder are blocked (because the push rod in the power brake booster is too long and needs to be adjusted / shortened so the master cylinder piston can fully retract and unblock the ports), then the expanding brake fluid in the calipers has no place to go other than to push the brake pads into the rotors, increasing the friction, increasing the heat, increasing the brake fluid expansion, etc., etc. The cycle stops only when you park the car and let the brakes cool.

Makes sense?

 

Makes sense if the booster rod is too long - doesn't quite make sense if the springs in the MC are weak because once the fluid forces the MC piston back those check values should now be open and should have relieved the brakes. But if the booster rod is too long yes makes sense

 

Wait, let me argue this point a while longer instead of fixing the fraking rod.......

 

 

Just curious ...So did the MC rod mod fix the issue for pinkflamingo... I'm still a bit confused as to how the MC rod was suddenly too long ... Or did you change it out for a non oem part.

 

Read the thread links above, it explains why it happens along with the fix.

 

greenestate asks a valid question...… what caused the push rod in the power brake booster to become "too long" and now need to be adjusted / shortened?

Perhaps PinkFlamingo can tell us what changed, e.g., did this problem begin soon after someone install a new power brake booster or a new master cylinder?

I'd start by adjusting / shortening the push rod to confirm if this fixes problem. It's a ~15 minute adjustment if you've done it before, maybe ~30 minutes the first time. If the adjustment (hopefully) solves the problem, then it's worth figuring out what change that cause push rod to become "too long".

The only times I've had to adjust the push rod is after replacing the power brake booster or the brake master cylinder. But I've never had a push rod go out of adjustment on it's own. If someone has a different reason they had to adjust the push rod, please share.

 

greenestate asks a valid question...… what caused the push rod in the power brake booster to become "too long" and now need to be adjusted / shortened?

Perhaps PinkFlamingo can tell us what changed, e.g., did this problem begin soon after someone install a new power brake booster or a new master cylinder?

I'd start by adjusting / shortening the push rod to confirm this fixes problem. It's a ~15 minute adjustment if you've done it before, maybe ~30 minutes the first time. If the adjustment (hopefully) solves the problem, then it's worth figuring out what change that cause push rod to become "too long".

The only times I've had to adjust the push rod is after replacing the power brake booster or the brake master cylinder. But I've never had a push rod go out of adjustment on it's own. If someone has a different reason they had to adjust the push rod, please share.

 

So in the links are several reasons. Bleeding brakes, master cylinder replacement, master cylinder leak, vacuum leak normally from booster hose (causing p0171 &/or p0174), pad replacement with bleeding, using a pressure bleeder has done it in a couple of others not in this thread, air in ruptured lines. There may be some other arcane causes, but these seem to be the most common.