Thank you Dennis!! Somebody in CT buy that man a cold beverage. I did have to remove the hoses from the master cylinder to get it out but you were spot on. When I had the 2 nuts holding the master cylinder to the booster loose I noticed there was a gap of maybe 1mm between the master cyl and booster. Tightening the nuts without adjusting that rod was pushing on the master cylinder piston slightly, exactly the same thing as pushing down on the brake pedal. I turned that 7mm head bolt half a turn and my before and after test laps around the block went from 10 MPG to 18 MPG and the front rims went from about 170 C down to 110 C (measured near the center of the rim with a non-contact thermometer).

I have no idea why this happened after new brakes, I didn't touch the master cyl or the booster.

 

Changing pads has absolutely 0 to do with the brake booster.

 

@ Erik, really? X's are notorious for the brake booster having a problem after replacement and bleeding. There are dozens of threads on exactly this problem. Here is just one =

https://www.jaguarforums.com/forum/x...3/#post1931807

It causes a misalignment of the brake booster valve rod which member "Brutal", a Jag Tech, has posted the easy adjustment fix.

 

I originally was trying to find if there was some kind of brake pedal adjustment, then I looked into the pushrod adjustment, then brake booster testing. However, I'm thinking that the pushrod adjustment will fix my problem. Which is a hard pedal with dragging brakes. I've already replaced the rubber brake lines,(they were horrific to begin with) rebuilt the calipers with new square cut seals (the pistons were super clean, I was amazed) bled the brakes and the master cylinder (somehow there was air in it), I may have run the reservoir low (tried not to).....weird that the push rod would go out of adjusment, but at this moment it's the only thing I can think of that is preventing the pressure in the master cylinder from releasing. Hopefully this will fix my sticking brakes.

 

Well sorry to say that sounds like what has happened to mine and just had a mechanic come out to look and tell me it's the servo spring inside the servo booster which has gone are you having trouble braking when driving like when you press the pedal it goes to floor and stay there ?? cos if that's the case it's the servo and a local mechanic he just quoted me £1,300 to fix it.
missing info but mine is on a xj 2013 and he said for the part alone is near £900 I just want to get mine fixed then sell it.

 

UPDATE: 5/19/22-- Adjusting the "throw on the push rod was the key to fixing the brake drag issue. It took some back and forth and some skinned hands, but I got it to stop dragging. As a matter of fact, the wheels spin extremely free!, better than any car I've had.

Bleeding the master cylinder is critical if you allowed air to enter the system. The Master cylinder itself could be leaking within and totally fool you because you don't see a leak anywhere, This will cause for the pedal to drop to the floor. The booster itself in my case at least, is fine.

 

I'm happy that this adjustment worked for you. I just don't know why. It would be really nice if a Jaguar tech would weigh in on this topic. I am having the
same problemwhere the brakes seem to tighten up the more I drive the car. After few miles the brakes are near locked up and seriously overheating.
This all started after I installed new front wheel bearings. About the same time, I found a brake line leak on the RR. I repaired the line and did a bleed on
that caliper. All these braking issue began immediately afterward. The part that is so disturbing, is that I had no braking issues before repairing that brake
line. I was simple loosing brake fluid very slowly. I would need to top it off about every two weeks. I've been told that we may have damaged the Servo
during the brake bleed, by pushing the pedal to the floor.
I have looked at your suggestion and it's puzzling why this worked the way it did for you. The position of that shaft head is not the cause of this problem.
That position is preset at the factory and does not move. That is a crimped setting. I have attempted to adjust mine and it doesn't move.
The one millimeter of preload is to ensure that the head stays in contact with the receiving end of the master cylinder. It's to eliminate any slop in that
connection, so the shaft doesn't rattle around.
I sense that what you have done is put a band aid on a different problem. I suspect that the problem is in the Servo itself. The master cylinder
is a simple device that responds when pushed forward and releases pressure when moving back. If the Servo is not venting properly, it will not move
back as it should. Theoretically, not allowing the master cylinder to move backward as it should.
I'm just not so sure this adjustment is the correct way to fix this problem.
Your original post was back in 2018. I can't help but wonder how this worked out long term.

 

This is an update on this previous response. I maintain my opinion in regard to this method of correcting this braking problem. This not the right way to repair this.
The correct way would be replacing the Servo brake booster. Damage must have occurred during the bleeding process. Somehow the Servo is damaged when
the pedal is pushed too far and hits a hard stop. I took my Servo booster apart and I could not identify the one part that was compromised. That was frustrating.
I did find something that looked out of place, but it did not correct this problem where the brakes gradually locking up.
What is happening, is the booster is continuing to build pressure and is not properly venting that pressure to equalize the Servo. As the Servo builds pressure, it
gradually increases the force on the master cylinder. Eventually, the brake begin to lock up and the quick way to remedy that is to remove the vacuum line fitting
from the Servo. The Servo will immediately normalize. This will release the pressure on the brakes. Unfortunately, you cannot drive the car this way. You can't
physically put enough pressure on the pedal to effectively stop the car without that Servo.
All things considered, this method of correcting whatever has changed in the Servo, does work. Whatever damage has occurred inside the Servo is not obvious.
As I stated, I had my Servo completely disassembled on the bench and I could not identify the component that was compromised. Whatever has changed inside this
Servo is not obvious. This change has effectively moved components closer together and reducing the space inside the Servo that allows it to vent properly.
The change is anywhere from one to two millimeters. There is little information in regard to the normal operating specifications inside this device. So, we have
to make certain assumptions. The vent seal sits at the back end of the center pin that enters the back of the master cylinder. We have to assume that when the
brake pedal is not pushed forward, this part sits with a small amount of clearance so the vent is open. This allows the two sides of the Servo to balance out.
There are two diaphragms inside this device. A front and a back. The vacuum balances the two sides and keeps a constant vacuum on the entire device.
When the pedal is pushed forward, this closes the vent and pushes this rod forward into the master cylinder. With the vent now closed. The Servo is able
to assist with braking effort. Whatever damage has occurred inside the Servo is taking up that clearance and the vent is constantly closed. Negative Pressure
continues to build up in the front side. Aside from this imbalance, the Servo is doing exactly what it is supposed to do. So the objective is to regain that
clearance that was lost so that the vent seal is open when in a relaxed state. On the end of the post is a threaded 7mm hexhead with a polished round end.
I found that mine was threaded out and factory set about five millimeter from the end of the post. The post has a crimped and threaded end. So this head
does not just easily unthread itself. I had my wife sit in the car and hold the brake pedal down to the floor. (I know this seems counterproductive) but the damage
has already been done. The objective it to push this post forward so I could get a grip on it with a locking pliers. Then using a 7mm socket to turn the head
in and reduce the working length of this post. This is pretty much trial and error. I would adjust this in one full turn and then put the master cylinder back in
place to check for interference. The objective was to have the master cylinder sit against the Servo with no interference. Then check the pedal to see if
there was any sloppy pedal behavior. Now the vent can sit open when the pedal is not pressed forward. Problem solved without spending a fortune for
a new brake servo. The car once again drives and brakes as it should. I still have the option to replace the servo sometime in the future.

 

So here is a bit of a lengthy read but read through it and see "Jaguar's" finding of the push rod.

https://www.justanswer.com/jaguar/73...xtype-jag.html