Mk10 booster revisited

Starting a new thread here as I meandered a bit on the prior. I did de-install the original P90 booster attached to a chevy master. I was given a series 2 XJ master and servo from a driver that seemed to clean up well on the bench as I flushed new fluid through, but I found that the bolt pattern was different than the original, square rather than rectangular. Attached is a comparison.

Tony said that the Girling Supervac servo will work, but descriptions online are vague, and I don’t have a way to get my hands on one without buying one sight unseen. The bolt pattern looks square in the photos.

On further research, I find a reference to three series 1 XJ boosters with part number 11963 advertised as a replacement for the first two systems. these have a designation of a rectangular bolt pattern.

So, the question is whether that series 1 booster will work with the series 2 master that I have - I’m guessing yes. If not, then I am looking for a used series 1 master to rebuild.

Another idea that I am considering is simply to disassemble the series 2 servo and weld new mounting bolts on the rectangular pattern. I see that a question has been asked before about adapter plates (apparently not done), but changing the bolts seems simpler. Anyone try that?

Thanks in advance

give me a couple of days…I have some servos sitting around, will take pics and measurements

As I have owned both S1 and S2 XJ, as well as 420G, I cannot be 100% sure which is which, but will look at the bolt pattern etc etc

In Thorleys book, it states that the 420G was “standardised” with S1 XJ in 1968
afaic, this means the brake booster and master (but not front calipers)

swapping pedal box as well might be required

preliminary findings from inspecting some XJ booster/pedal boxes

there appear to be differences between the bolt pattern of MKX/420G booster (rectangular) and XJ booster (square bolt pattern). This is supported by the S1 and S2 Parts Manuals I have

All 3 appear to have different pedal box

The 420G booster is not shown in any official Parts Publication I have
The official Parts Manual for 420G is designated IPL4

It may be difficult to mate the actuator rod and pedal mechanism via the pin, if anything is not the same length

Apart from fitting a 420G booster & master, you could probably fit a complete XJ pedal box/ booster/master, by drilling new holes in the body to accept the pedal box, you would possibly need to weld some metal into the old cutout in the body, maybe not.

I did take all this out to inspect and make any needed metal repairs…another bad rust spot, on most old XJ, and other vehicle…under the brake cyl, and under the battery side, adjacent to the firewall, made a new gasket, will check for pics

I will be very busy over the next 2 days, so cant inspect my 420G/MKX wreck with brake parts, it is at another property

some further info…but more confusion to

I have verified that the S1 XJ6 booster, mated with S1 pedal box 26712 has the same bolt pattern as a 420G…that is 110mm x 90mm…different pedal box from mkx/420G though

My S2 XJ6 manual shows the S2 booster has a rectangular bolt pattern also…and a change of master during production, different pedal box from MKX/420G and S1 XJ6

I also have some “square” pattern boosters, 90x 90mm, different pedal box again
These may be out of S2 XJ12

Thanks very much for that information, although, as you said it’s still confusing. The series 2 pedal box does not work in my car, so that’s a no-go.
Plan a. Weld new studs (very carefully with cooling) to the case of the s2 booster and try it. If it doesn’t work, no loss, as I’d discard it anyway. This style booster is difficult to disassemble.
Plan b. buy a new series 1 booster with the rectangular pattern and see if the series 2 master works with it.
Plan c. if the master and booster don’t match, find and have rebuilt a series 1 master.
One of these ought to get me going.

In my Spare Parts Manuals, the S1 and S2 XJ6 Master cylinder is shown as the same part number for an EARLY S2…11965LH…then a metric one, then one with a resevoir on top

I cannot give you a part number for a 420G master cyl, as it is not shown in any Jaguar publication I have ever seen, other than to say, I am as certain as I can be it is the same as S1 XJ6

The Booster shows as 11693 for S1, so that should be the right one…with rectangular holes

btw, do you know how they are taken apart ?..they have a kind of crimping, which appears to need to be individually pried open, then the clamshell twisted…I asked 2 pros how it is done, but they were unwilling to tell me, which I found strange.

I do believe a (could be homemade) tool is placed over the 2 master cyl studs to impart a forceful twisting action…this may be enough to displace to crimps

So, the real question on “b” is whether my metric master will work with a series 1 rectangular booster. Although the part numbers are different, that could be related to fittings rather than a functional difference. The only way to find out will be to try.
The early cans like the P90 and remote e-types aren’t hard to get apart and I’ve rebuilt a couple of those. The XJ can has crimps which will have to be raised, and I’m not confident that I can reassemble it without a leak. Thus the external careful welds trying not to burn the internals. So I can do method “a” now for the cost of the bolts, method “b” in 10 days for $300, or method “c” for around $800 and at least a month delay. I’ll let you know how it goes.

I strongly believe so

You would have to make 2 new shortish lines down to the proportioning valve on the inner fender

The other thing is that from distant memory, I was told the booster has a part shaped a bit like an engine valve that actuates the master cyl…this will fall back inside the booster if it is tilted back…I dont know whether this is true…I have a lose old booster here…I may try taking it apart, wont matter if its destroyed

I got a call back from the booster restorer today, Booster Dewey in Portland Oregon, and have a plan that I’m sure will work. Steve checked his spare boosters, and confirmed that the early series 1 XJ is the same rectangular bolt pattern as the P90. I’m going to ship him my series 2 booster and he will rebuild it for $200, replacing the back part of the can with the series 1 can and I will have a bolt up, matching series 2 booster/master cylinder. The only trick is that the XJ parts do not have the slip-in push rod that the P90 has. I don’t think this is a problem, as I believe one can attach the integral XJ rod to the fully depressed pedal before bolting up the booster to the pedal box.
The only bad news is that they are backed-up with work and it will be 4-6 weeks turnaround. However, that will give me time to check the master and rebuild it as needed. Also might be time to drop the rear end and fix the rear brakes, which are not working.
I want to clarify one point you made. I believe the rear brake line comes directly off the master cylinder (rear port), and the front gets split at a 3-way - there isn’t a proportioning valve on my car, and I think the arrangement is original. The rear line is long and difficult to replace, so was previously spliced with a union. No reason not to do the same now, as the line is good.

right you are, not prop valve, but brake light actuation switch

If you have anything metric, you will have to make (or alter) the lines

All seems doable

I started pulling one apart earlier…afaic, all S1/2 have an actuator that presses on the master cyl…2 of my spare boosters are missing this piece…it falls out the front

Your OLD master cylinder should have the guts poking out the rear of the body, the NEW MC has the guts retained by a circlip, almost flush

ie , a booster without the valve stem poking out cannot actuate a later master cyl

pictures if required

you will notice a difference with rear brakes!..

420G brakes very well in my opinion, I can never understand why people talk about upgrading 420G brakes to XJ

Tip; I have a dual brake light system, LED mounted inside my rear screen, actuated by a pedal mounted switch…comes on up to 1/2 sec before the incandescent brake lights, which are too low for many modern cars to see well

Update,further info and clarification

So I dismantled a Girling booster today after 20yrs of wondering

You do have to pry loose each individual crimp. I did this with pry tool and multigrips, then split the shell by wedging a screw diver into each side, which has a tab.

Its a job for a pro to rebuild these imo, as the 2 big rubber diaphragms inside look a bit difficult to replace, for the price, and getting them apart…and probably back together is not easy. The rubber appears ok…they tend to rust inside the shell, I think this would be the No1 cause of failure

I did find one of mine appears to be an NOS part, it is plated, not painted black, and has the rectangular pattern, so that was handy to find

The 420G/S1 Girling should have an internal pushrod to activate the master…it can slip out and be missing…your rebuilder sounds like he would have this part, if it is missing & needed. It looks like an engine inlet or exhaust valve

correction; The master cyl internals are retained by the tipping valve assembly, not a circlip as I said before

RHD and LHD are different part num, but you could make new pipes

Its worthwhile getting your master cyl re -sleeved in SS and rekitted

I will take a few pics in the next few days

a couple of people have been thru these problems in the past, but 65-67 MKX are a rare breed, and many were upgraded by Jag dealers back in the day, if any problems arose

Nice tip about the extra light. I’ll consider that. Might be a nice touch behind the AC unit on the rear shelf.

I agree about the booster - best left to the professional with the right equipment to do the job right. As to the internal connection between the booster and master, since mine will be both series 2, it’s just a stock connection. The only thing changed is the rear can, which is the rebuilder confirms is the same except for the stud location. Hooking to the pedal box will be a fiddle, but I’m sure can be done.

So, I’ve now got massive work to be done - reinstall the fuel tanks, R&R the senders and left fuel pump, repair the header tank and replace all the coolant hoses, drop and R&R the rear suspension, rebuild the front and rear brakes as well as emergency brake, finally reinstall the brake controls. Shouldn’t take more than 3 months!

One last question, then I’ll probably go silent for awhile. The e-brake hardware is all missing, but I have most of it on a spare rear suspension and a new cable is on order. There is a bracket on the lower left rear frame rail for routing the cable. It has a cross hole for somehow mounting nylon guides, C19771. Is a photo of that possible? The parts book doesn’t give me a full understanding about how it goes together, although I expect quite simple.

Again, many thanks for your input. Too bad Australia is too far away to pop over for a look. Besides, as an American, I’m not allowed out of my kennel for the time being.

I will try to take some pics today, although I think a jack might be needed

I think you may find once dropping the IRS that you need to replace many parts, which is what I did, and it did in fact take me 3 months and about $1500 in parts

I was told that to overhaul one by a pro is about $A4500

XJ rear calipers will fit…(dont use metric)

It will be nice for you to cruise around once its on the road, they are a big head turner, as no one has ever seen one before, mine is the only one on the road in my City for many years

I cannot forsee Australia allowing USA citizens to visit Australia unless they spend the first 2 weeks of their holiday in quarantine, probably not within the next 12months, its a shame, as we have been free of any covid cases at all for over 2months, and I can now do whatever I want, altho places must be ~ half capacity, and “social distance” maintained

Thanks in advance for the promised photo, Tony. No rush, as I’ll have plenty of time to source or make parts while waiting for the booster. I did the rear suspension on my e-type a couple years ago, and it’s pretty straightforward, but there is significant time and expense. The E was pretty bad, and I had about 2K in parts and outside labor (half-shaft issues) in it before all was said and done.

XJ rear calipers sound really interesting if the late series 2/series 3 will bolt up - not sure if the series 1 and early 2 are different from the 4.2 Mk10 and the 420G. I see that they changed calipers in 76. I’ll have to see which calipers are on my car.

My wife and I normally travel a lot, but have been nowhere since February, haven’t eaten at a restaurant since March. Australia is smart to keep Americans out, since as a group, we lack the discipline to do what is needed to contain the virus. I’m looking forward to an effective vaccine.

I am 99% sure the change took place to metric mid S2…that means new brake pipes…or cut and make new ends

will check my parts manuals

and the seal kit being the same as S1/S2

most rear calipers will fit most cars (apparently), with a tiny bit of grinding needed sometimes

I had my rear caliper pistons sleeved in SS.
This was not much more than new rear pistons, and less than new SS pistons

Before I forget, I did have trouble getting the seal kit to work. I believe the internal parts to all master cyls may be the same bore, but seals are not always the same length

cross that bridge when you get to it

I think so.

Good stuff, guys. I’ve not seen this illustration, and it is helpful. I was aware of when to tell that I needed a bubble vs a double flare, but not some of the other points. I can simply change and reflare, but it’s easier if I get calipers with the pipe nuts.

So, the question is, is it worth it in braking effect?

In a word, No,as far as I know rear calipers are all basically the same, which is why they cross fit

there may be some variation is piston size

just having them work will transform your driving experience :smile:

1st pic underneath a bracket towards front half

2nd pic rear bracket

3rd pic, shows bracket and rear cable outer part

thesespics are from my 66 MKX wreck, I just lay down on my back in the grass

I have the entire booster/pedal box/master/steel line assembly in the boot, its been refurbished at some time. They removed the brass sleeved original master, and have replaced it with one that seems a fair bit bigger…maybe a S2 XJ ?

It appears they all have different part nums on them, I will check tommorow

It mentions in the last paragraph that metrification does not apply to rear calipers