Hi,

Has anyone done a how to replace a brake booster? I'm not mechanic at all, but i can't afford to take my car to the shop! I've ordered a replacement brake booster now i just have to figure out how to install it! I was really hoping someone had taken some photos on how to do it? Thanks

 

Probably covered in this manual well enough. The early 4 bolt booster are easy to change but the interface with the pedal can be very fidley.

https://haynes.com/en-us/jaguar-xj12-xjs-including-xjsc-cabriolet-series-12-and-3-72-85-haynes-online-manual?gclid=Cj0KCQiA2snUBRDfARIsAIGfpqHaHgw3b1fx8 bDAIM-BQ-BbA5t-ceqRadcLhji3Q4EKeiZ9xKqbKDAaAmEiEALw_wcB

 

The booster just bolts up to the aluminium casting that holds the whole assembly to the car by four bolts. The casting carries the brake pedal underneath and it is fixed to the car by four more nuts threaded onto studs. Thus entire assembly, brake pedal, booster, casting and all, is fixed to the car by these four nuts that go onto studs fixed at each corner of a large square hole in the body.
It looks like the booster can be unbolted from the casting and the casting left in place, but it cannot be as the dent in the wing into which the booster sits is too short to disengage the booster from the casting when the bolts are undone!
I suggest that you get your head into the footwell and look at the brake pedal switch, a rather complex lever affair. Make a diagram or take a photo. Remove any other wires fixed to the pedal assembly. When the whole lot goes back you need to ensure all this goes back as it was before you started - which is NOT obvious.
Then undo the four nuts that hold the casting to the body, either (i)carefully disconnect the brake lines from the master cylinder, or (ii) the master cylinder from the booster leaving the lines still attached - if the lines have enough "give" to allow it. Then you can remove the entire assembly: booster, master cylinder, ally casting and brake pedal, in a upwards direction from the car.
If you do not know how to bleed the brakes, then if you have to undo the brake lines from the master cylinder, you will have to get some help to do so after the whole lot is back in the car.
Finally, renewing the master cylinder rubber seals, or buying a new/rebuilt one, and replacing the brake fluid throughout the system is VERY strongly recommended.

 

Thanks Greg, thats a huge help

 

This is the steps im following. (plus gregs photos)

Damn i need a small asian child to get the nuts off the brake pedal box. I can only see two of them, getting a tool in there to work is even harder!

1 Remove the pedal box. To do this, first unbolt the wing stay from the engine compartment rear bulkhead on the pedal box side and swing it clear.

2 Disconnect the vacuum pipe from the brake servo unit.

3 Unbolt (but do not disconnect the fluid lines) the brake maste cylinder from the servo unit.

4 On right-hand drive cars only, release the throttle cable from the throttle pedestal.

5 Unbolt the brake fluid reservoir from its mounting bracket and rest the reservoir on top of the engine.

6 Disconnect the hydraulic pipe from the clutch master cylinder. Plug the openings.

7 Release the nuts on the brake fluid reservoir bracket and swing it upwards from the pedal box.

8 Unscrew and remove the four nuts which hold the pedal box to thebulkhead.

9 Carefully ease the brake master cylinder from its mounting studs to clear the servo unit.

10 Withdraw the pedal box, complete with brake servo unit and clutch master cylinder, clear of the car.

11 Disconnect the return spring from the clutch pedal.

12 Extract the pushrod to pedal split pin, washer and clevis pin.

13 Unbolt the clutch master cylinder from the pedal box.

14 On right-hand drive cars, before the master cylinder can be completely withdrawn, the fluid reservoir bracket will have to be removed. When withdrawing the master cylinder, note the location of any mounting shims.

 

well i have now removed the *******. So many nuts/bolts that don't have clearance for the socket or spanner! also it looks like i did not need to go in from the pedal box end!! i find out after i have spent 3hrs in there on my head, cursing british cars.

 

Quick update to this, I replaced the brake servo, change the brake fluid, bled the lines and still have no brakes. I've just bought a new master cylinder and will be giving that a go to see if I now have some sorta brakes. Car has been off the road a long time now (scar tissue from changing the brake booster), and since im stuck in isolation, I should do something to the car.

is anyone else starting to lose appreciation for these cars the more they work on them? XD

 

Hi 350XJS

There is no way in the World, that I am losing appreciation for the XJS even though I have two of these that are both broken down at the moment, on one of which I've removed the Cage in order to replace the rear Wheel Discs and Calipers

As for the other one I am converting that to Non ABS even though it took Two days to remove the Brake Booster from a Scrap Car, as I'd left my 'Magic Wand' at home!
and so the 'Lockdown' in the UK has given me time to get on with these jobs, in between taking a Tree down that is about to fall on the Car

All of which helps to resist the Temptation to go for a drive in XJS number: 3

The XJS is a 'Cult' Car and Steve Mc Queen would be driving one if he were around today, the only problem being that you very often have to pay for the pleasure of driving one of these Cars in 'Blood Sweat And Tears'

And so of course they're not for everyone, though when She's on Song and running just right there's not another Car on the Road that I would rather to be driving

 

yes it was a bit of tongue in cheek. they a super cool cars just PIGS to work on :P

 

Manners Servo. Ebay decal.