R & R Brake Master Cylinder Steps?
 

Have searched Google and other sources and no step by step or video available I can locate. Looks like the LHD cars should all be similar. (2003 XK8) The 2 mounting bolts appear diagonal rather than horizontal mounted to the booster. Appears one would need to empty & remove the reservoir to determine next step.
I do not have JTIS downloaded. Will someone share a link or links to the procedures to perform this operation. Seems the R&R is difficult due to limited space by the enclosure bulkheads. Appears after the electrical connectors are removed, the brake lines and other attaching fasteners should be accessible. Please share any methods that worked for you?.

Do you mind sharing the diagnostic that leads you to this R&R? Are there easier steps you could take first? The vacuum line to the throttle body is a known spot for air leaks (weird brass setup) and maybe poor vacuum assist.

From memory replacing the brake switch, you might gather more insight by checking the area behind the pedals.

Best of luck, keep us posted.

The pedal seems to drop excessively once it is pushed. Generally the pedal is at good height when pressed. Have bled the brakes couple of times with the pedal height becoming normal and solid. Indications point to the Master Cylinder perhaps bypassing. Pumping brakes returns the height to normal, but then it acquires more travel over time. No leaks at Calipers or the M/C does not get low. Classic symptoms for internal bypass I think. It does good, but does not seem quite proper. Fluid (Dot 4) is clear at each bleed port and was flushed thru 1.5 years ago.
Guess us Squirrels are too picky. :-)

I have the same, tried bleeding a few times, I have braided hoses all round, still pedal sinks down slowly when pressed. Maybe we are bleeding wrong.. or.. maybe the seals in our master cylinder are going.. From what I have seen you cannot repair the master cylinder as there are no kits available, you'd have to replace with another one. Unless of course someone knows the seals we can use? Mines a 1999 xkr

When replacing a master cylinder, remove the electrical connectors, then the brake lines. Unbolt the master cylinder and remove it from the booster.

The next step is to bench bleed the new master cylinder to get the air out. Installing one and then bleeding will not work if the master cylinder is at any angle at all.

You will need a kit to do this which attaches special nipples into the ports where clear tubing is routed from the nipples into the chambers and held in place. The cylinder is held level in a vise where the chambers are filled with fluid and the piston is slowly cycled with a screwdriver until there are no more bubbles showing in the line. Put the caps on and very carefully reinstall the cylinder, being sure not to tilt it.

The bleed the system your usual way. I suggest pressure bleeding.

If this is not done, it is just about impossible to get a firm pedal.

As further explanation, the booster drive does not produce full excursion of the master cylinder plunger, making the case for bench bleeding. So don't think you can outsmart this procedure, you must bench bleed the master..

Interesting info here... Luckily I never have removed the maser cylinder so not had to go through that procedure..

any tips of maximizing the chances of a good firm pedal from a standard bleed? I have a pressure bleeder. If I remember correctly the pedal has never been good since i had to remove and replace the abs unit due to the normal dry solder joint failure.. The code never came back.. neither did the pedal firmness though

thanks for replies. One could see a need to remove the electrical connections and the brake lines. My request was for someone to share the Jag Tech instructions for the operation of R & R assembly. After looking at the enclosure, it would seem to be best to remover the reservoir prior to attempting any other removal of attached parts. Guess I will keep searching and perhaps i can locate a confirmation of need to remove the reservoir.

Anyone have experience with a Motive Pressure Bleeder? They use a pressurized tank and cap adapter to push fluid thru system. Since the M/C rod does not fully depress, there must be air at end of travel. i will try this since the pedal is not as I expect. BTY, anyone with a link to the JTIS section requested regarding this R&R operation, please share.
Ok to Mark as RESOLVED or close. Will proceed in another direction.

Master Cylinder 3 or 4 bolt.
 

I am having the same issue with needing to do one pump of the brakes to get a solid pedal at the top of the stroke. I have bled the brakes and have a solid pedal feel after the one pump. My car is a 2004 Xk8 with 201,000 km. When I look for a replacement master cylinder it asks for a 3 bolt or 4 bolt, what does this refer to. I have a 2008 Stype with the same 4.2 6 speed powertrain and the brakes on that are just fantastic. The slightest touch on the brake pedal and you have stopping power, my XK8 which I have had for 5 years has never been like that. Does anyone think that a bench bled might be the first step on the XK8?

Viewing the M/C from above, I expect it is referring to the number of studs that mount the unit to the booster. My car has 3? and they appear difficult to access. Reason I posed the request for the share of JTIS article. Guess we just have AIR in our system. :icon_toast:

I use a Motive pressure bleeder. It works well but removing it can be tricky, watch for spillage. Brake fluid eats paint. The reason is that brake fluid is basically antifreeze (ethylene glycol) adapted for the brakes.

If you have gotten air into the master cylinder, you will need to bench bleed it. Never let the master cylinder suck air while bleeding or you may be pulling the whole thing off. If you have bled the brakes and still have soft pedal, you might have air in the master. Don't forget to get the bleed kit.

Even a pressure bleeder may not get at air between the two rubber piston seals that gets trapped between the ports. When you bench bleed, you push the piston seals past the ports and clear the air, the booster cannot do this.

If you are considering rebuilding the master, it is usually futile due to the built up ridge in the bore that causes the new seals to leak. I always install a new unit.

Next project, bench bleed.
 

I am going to do a bench bleed sometime this week, will let everyone know if it solves the problem. Every winter one of the jobs on my to do list is change all the fluids; and I do the brake fluid. Although I doubt it I may have gotten some air into the system. After 60 years of working on cars starting as far back as I can remember pushing the pedal while my mechanic father bled the breaks I am pretty aware of not letting air in the master cylinder.

@kstevusa, have a look at this link for the Workshop Manual and other technical information:

https://www.dropbox.com/sh/mkchxc77m...PEiFn8_aTP2Tga

Help! Removing master cylinder. 2004 XK8
 

https://cimg8.ibsrv.net/gimg/www.jag...789e18bb66.jpg
2004 XK8 master cylinder.
Trying tonight to bench bleed the Master Cylinder. Do I have to take out the booster to get the Master Cylinder out. I have tried to remove the reservoir with pulling the 2 clips under the reservoir that I saw with a mirror. It is very tough and I don't want to pull on it too hard. I just need another 1/4 of an inch to get it off the studs. Maybe if the reservoir wasn't there I could get it but I am afraid of breaking something.

Thanks Daro31. Did not know about the CLIPS. No one mentioned them in any previous posts. It would appear once the reservoir is removed, the access would be adequate. Please keep us informed, Good Luck!

Possibly a retaining bolt for the reservoir
 

https://cimg1.ibsrv.net/gimg/www.jag...3c87f13756.jpg
Instruction for reservoir removal -Stype
I have not been able to find a hint of the method to remove the reservoir on line, and no one has gotten back to me with anything on 2 other XK8 Facebook groups. I do have the factory manual for my 2008 S-type so thought I would look there. It shows a retaining screw under the reservoir, so tonight I will get out the scope and take a look around under there.

Hey, how did you get on? did the bench bleed work?

No bench bled.
 

I struggled to get the reservoir off, it turned out to just a hard gentle pull. I thought if I got the reservoir of it would give me room to get the M/C out, it didn't. You need another 1/4" to get it off the mounting studs. I ended up buying some plastic nipples and clear tubing and bled it in the car. I did get air bubbles out of the M/C. I am sure you must have to pull the booster out to remove the Master and I just wasn't up to that job. Of course with the brake lines detached you get air in the lines so I had to bleed the brake lines. In the end I have good brakes again and definitely got air out of the Master Cylinder.

Finally got a short pedal stroke.
 

The length of stroke of the brake pedal before you feel has bothered me since I got the car. Some people say this is normal but it just didn't feel right. I got into it big time this spring. I rebuilt all of the callipers, jot because of anything wrong just because it is a 17 year old car with over 200,00 km. All that went well, aand blasted repainted and all new hardware and rubber bits.
the ling pedal strike still bugged me so I order a Master Cylinder from Auto Reserve.
I got it in yesterday, you do have to remove the booster bug it turned out to be a 3 hour job that was all completed from the engine compartment. Bench bled the new M/C and then bled all 4 wheels. I only have about a 1/2 inch of stroke before brake pressure. Feels normal again.