Brakes and frustration Mk10

ok the short version, after buying a few new bits and cleaning up a lot of old bit. I have brakes. but they are not so good. the problem I have is that I can not locate the lower master cylinder/ cylinder with the adjustable rod. i took a punt and used the Etype top and bottom but its not working for me. so has anyone found a workaround? or a supplier or an upgrade? 3.8 61

My Mk10 is a 4.2, so I don’t know if this applies. If the pedal box mount is the same, then it does. I know you have the bellows style booster, so it may be different. If the body section is the same, you could find a 4.2 pedal box and swap it in.
I used a Series 1 XJ6 master and booster, basically a bolt-up. It’s easy to just remove the pedal box and bolt the booster and master to the box on the bench. Because the XJ6 rod is not removable from the booster (unlike my original booster), you should drill a 1" access hole in the side of the housing to get the pin and cotter in. Believe me, you can’t do it from below. Then just put a plug in the hole.
My car is off the road right now for an engine rebuild but the 4.2 brakes were excellent when fully rebuilt with the master/booster upgrade.
You should consider trying to find the later calipers if you can, as has been recommended by some of the very experienced Mk10/420G owners. Others on the forum could tell you what’s involved in the swap.

the short story is the early booster and master cyl and most parts are no available and havent been for many years.

Jaguar dealers upgraded early ones to the later parts Ron mentions for this reason

Do you have the original master cyl ?..they can be re-sleeved, and NOS seal kits can be obtained

If you do not have the original master cyl, you can try to obtain a used one off ebay or some other source, then re-sleeve it

Ron is correct, the best way is to replace the booster/master with a XJ (or 420G) system

I wouldnt worry too much about the rest of the brakes, rears are fine, fronts can only be replaced by 420G or later MKX parts…XJ items cannot be used (affects steering badly…dont go down that path

I may have some older items to sell soon, PM me if you want

This is what the XJ booster and master looks like in the car. The master here is actually S2 XJ - I’d go with the S1 if you can find it because of the metal reservoir fittings. Reservoir is non-original.

significant correction to what I said in my last answer…the '61 has the Kelsey-Hayes? booster system…I am therefore of the belief it has the same master cyl as the the E-types.

As penance for my wrong info I will post the part number for the master cyl from my parts books and that may help.

I believe the later system is not a straight swap (cause the boosters are so different)

Just cause the brakes dont work well does not mean you have the wrong parts

best bet is to compare these part numbers with those from the E-type parts book, someone on the E-type list should be able to help you

thank you very much for the photo, I believe i have a secondhand xjs unit on its way, NB it appears you may have fitted you booster to the wrong side of your car? are you a driving instructor? lol

Mine are xj6 parts. I don’t know if xjs is the same. I can tell you that the xj6 series 2 booster can is different and won’t work. You need the S1.

Booster Dewey should be able to rebuild your original booster unit. Sleeving the cylinders is pretty straight forward.
You will never be impressed with the stopping power of a Mk X unless you get real creative with some caliper/wheel changes.

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Hi Dean,
Sorry if I’m late to the party but on reading your post you refer to not being able to locate a part.

Several years ago I dismantled a Mark X 3.8. I have attached picture of brake master - is there a part of this you need?

Kind regards


While your comment may be correct for original 3.8 brakes, it is simply not true for later 4.2 and 420G cars. The restored brakes on my 4.2 are excellent, up to modern standards. And Booster Dewey cannot get the parts to rebuild the 4.2 boosters - I don’t know about 3.8. I do agree with your recommendation of Booster Dewey - they rebuilt the xj6 booster in my earlier photo and were great to deal with. Talk to Steve. Apple Hydraulics did the master.

thank you Tony. if you look at your parts numbers the front and rear master cylinders are different,

right you are…they appear to be physically different in size in the pic posted by Matt,

the '61 E-type shows 2 entirely different part nums

If I was you I would probably reach out to Matt and see if he will sell you his parts, although it may be worth checking (if possible) to see if you can obtain seal kits for them

The bore of the master cyl makes a difference

(wait …seems like it is, as per Google :grinning: )

Brakes, Mk X 3.8 - Brake Master Cylinder & Hydraulics - Brakes - Jaguar Early Sedans | Moss Motors

thanks tony, I have reached out to Matt, I also put a post in the e type page to check part numbers. but your link has them as well. in short I received some poor advice and have fitted two E type master cylinders, close but not close enough. have contacted someone selling parts for an XJ s1 complete but after agreeing on price i have not had a signal since, so mat is the safer bet considering i have just had calipers relined etc. thanks for your input

Hi Dean and others,
I have taken the two brake master cylinders out of the pedal box (previous image) and can describe them now. The casting on both has 03 VBM4053 and DUNLOP. I have added image here in which one cylinder can be seen to have a white tag which says VBM4707. I see this tag number is consistent with the part number details provided by Tony. It would seem then that these are the original/ proper Mark X cylinders (not E type ones).

Having a Mark IX which only had a single master cylinder I am curious about how two cylinders functioned and if in 1961 it was an early form of dual circuit braking. I found this link demystifying the brake system.. This outlines there are two different length pistons in 5/8 inch bore cylinders. The Mark X are also 5/8 inch cylinders but I suspect different pistons. Once I get them out I’ll report my findings. Regards Matt

Could it be that one of these cylinders is a clutch master?

No, it is the same style of brake systems used in the early E-types (Kelsey -Hayes)

Being the Saloon is so much heavier, I suspect the bore or stroke is different to the E-type, hence the different part numbers

The only way to obtain them is buy a used item, later MKX (4.2, after '64 use a single master cyl).

65-66 MKX use a different system to 67-70 MKX/420G

All traps for the unwary

correct in all respects. in addition the lower cylinder has more travel than the higher and closer to the hinge of the brake peddle arm. the larger diameter, longer travel Lower cylinder is the front brakes.

NO defiantly not, smaller upper cylinder is back and larger lower cylinders front

shove them in the post please

OK an update. this has been quite a learning exercise so firstly thankyou everyone who has contributed, the parts numbers eliminated a lot of so called expert advice including some pommy dud on eBay flogging off the wrong cylinders, ------ sucker me!.. after phoning an interstate wrecker for an xj s1 master etc, who actually didn’t get back to me. But did pass my phone number onto an SA guy with a Mk10. apart from his car being a shell up rebuild with a 6lt GM. i got to see his XJ S2 master setup. custom mount ( angle) and mod to the inner Gard. along with 6? pot calipers. very impressive and im very jealous as i know i will never have a car as clean as his ( $$$$$$$$) any way i got his old bits. so not working this weekend and I’m optimistic. another story is the weather was not the best so i ended up spending a day moving landrovers and motorbikes around and i put a few to rest and liven up some others to give them a turn ( rego) . having the garage door open to the street and the Mk 10 visible. resulted in an elderly gentleman walking in on his cane. tells me the story of how he owned a jag workshop and had serviced my car from new for its first decade. he had also raced jags. i gave him a couple of cups of tea, a promise of a drive and he ear bashed me on how to really set up the mastercylinders booster peddle etc. now im very optimistic. i do have the manual but there seems to be a bit more to it.