The rear diaphragm rubber has fragmented like a busted balloon!

I understand a Girling Supervac 100 is a bolt-in replacement, but googling and an eBay search has turned up nothing. Is there a better way of finding one?

Trying to make it for a local Jag club event in 9 days, after working on the car for nearly two years.

Sorry to drop in to this forum with a "first post of desperation". I'll eventually get around to properly introducing myself and my interesting project car. Thanks for any help.

 

Try contacting White Post Restorations at 540-837-1140 to see if they have the parts you need.

 

Or Booster Dewey. https://www.powerbrakebooster.com/

 

Thanks for the replies.

White Post offered to rebuild both the booster and MC for $550, turn-around 4 weeks. They do not sell parts, but said they do have what it takes to rebuild my old Dunlop unit.

Booster Dewey has what I guess is the Girling Supervac unit, from an XJ6, used (rebuilt?) for $950.

Here's my plan, at the moment: Order a Bosch iBooster, a frequently used electric brake booster (Honda CRV, for example). Around $250. I may or may not be able to do the modifications to install it by next Saturday, so I'm going to also try to fix the ruptured rubber in my bad unit. I will use superglue on the fracture surfaces (ever seen how well this works for re-sizing 0-rings?), and then apply some big tire patches on both sides. A rigorous test program will follow.

 

50yrs ago I use to rebuild power booster, the diaphragm look like gasoline vapor weakened it. The root cause for the failure is the vacuum check valve failed allowing gas vapors into the unit

I hope this helps

 

As a matter of fact , there was some fluid in the booster, probably brake fluid, where those ruptures occurred. MC leakage?

 

Hi Curt,
From your statement, fluid was in the vacuum chamber of the booster. The gas vapors can destroy other seal such as the seals between the master cylinder and the booster allowing brake fluid into the vacuum chamber the booster. I would recommend that you have the master and booster rebuilt. I wish I could help you with getting the parts but the company that i worked for back then doesn't rebuild brake boosters anymore.

 

Thanks, all. Great to have this help. An update:

I patched together the ruptures of diaphragm with rubber cement and pieces of a bicycle tire tube. The genuine tire patch material I got seemed too thick. I put the patches on the side of the diaphragm that would be in tension as it folds inwardly. Two layers, partially overlapped - not easily seen in the photo. I gave it a 50:50 chance of holding at all, and zero chance with strong braking.

Well, it's actually working with up to moderate braking! Have avoided hard braking thus far. But unfortunately, other issues with the car (and the threat of rain) kept me from the Jaguar Club gathering in Saratoga Springs. Boo.

As I mentioned, the plan is to install a Bosch "iBooster" from a Honda. I have one on the bench now, and have measured it up for an adapter plate. Another challenge is connecting the proper wires; as is often the case with such parts, I did not get the plugs/pigtails. I have the pin-outs, though; have soldering gun, will connect.Will I need a brake balance device? Don't know. I'll let you know how it works out - this is something that people do for a variety of reasons.

 

Oh, how about a beauty shot of the car? The exterior is near-perfect (headlights and trim are now in, also hub caps and beauty rings). The woodwork is 95%; the seats, trim, carpet, etc. - bad. The suspension is sublime! The power train - that will be the subject of another post.

Willow Green, though the computer-generated label on a can of paint I had mixed up said "Slime Green". Or perhaps a human was messing with me?

 

Update and question:

The booster I half-assed repaired blew out again, in a different spot, so it was time to install the Bosch iBooster. The piston rod is longer, requiring about a one-inch spacer between it and the pedal box. I machined a new clevis to fit the existing brake pedal arm. I also needed to angle the booster up to clear the inner fender; that required an angled spacer between the pedal box and the fire wall (horizontal at that location). I only got it close to fitting, so some minor medieval action was required to make room between the booster's brain box and the inner fender. Once hooked up and bled, I got firm braking — except for a strong pull to the left. Right-side pads were shot.

The question part of this post is how to retract the pistons for new pads. The WSM refers to a special tool, but not a Jaguar part. More than a simple retraction tool? The retraction pin (?) thing inside the piston is new to me. I don't own a retraction tool, but I've never had trouble pushing the pistons back by other means with any other brakes.

Is there a secret? My searching only suggested my pistons are seized, but the left brake seems to be working fine.

TIA.

 

I found the answer to my question. You retract the pistons like you would any other, except it will take more force than modern brakes. Much more, because the retraction pin washer doesn't want to slip that way. Doing it with the calipers in place, with pry bars, meant using shims to keep the disk from possibly bending as I pried against it — that's how much force was needed. I had to block the wheel on the opposite side so the hub on my side would stay at a convenient angle for the outer piston.

I also found out the new pads would likely be too thick (sourced from Moss). Yes, indeed: I had to mill off about 0.100 inch. Fortunately, this project car led me to acquire an old Bridgeport mill. Hot tip: brake pad material will quickly destroy a steel end mill.

So, I first drove this car around without power brakes (not recommended!), then with a booster likely to fail at any moment, at the worst possible time (even less recommended), then with a good booster but worn-out pads on one side (the bad side), and now — I hope — really good brakes. Stand by for an update.

Some of you may have guessed the nature of this project, which makes the friction brakes somewhat less important: I have converted it to electric. As received, the car was powered by a small block Chevy. I have many other cars with combustion engines — one British — but the Mark 10 will be better with a smooth, reliable electric powertrain. Once I get the driveshaft balanced, that is. It will still leak at the differential, preserving a bit of originality.

 

The Bosch electric brake booster has worked very well over the past few months and a few hundred miles. It's a bit over-boosted, perhaps. I think someone makes a CANbus dongle thing that could be used to reduce the boost, just like someone does for a Volvo electric power steering pump (one version includes GPS to automatically make adjustments).

People who do restomods and similar projects often use these electrically-powered devices to simplify engine connections - fewer belt worries and vacuum leaks. If your 60-year-old PS pump or brake booster fails, you might consider using them, too.

Updated beauty shot, with hubcaps, beauty rings, and all four headlights (LED, inners function as daytime running lights):