420G-MKX Thread

Hi folks, been meaning to do this for a while,

The purpose of this thread is to be able to:

  1. Discuss and link descriptions of specialist jobs and parts for our cars.

  2. Highligh originality features. These cars had many changes, like E-types. It can be difficult to pin down details

  3. any other discussion or photos of MKX-420G also welcome, including modifications.

I will add a 2nd post to act as a link page to “jobs of distinction” which hopefully I can edit over time


In this post, I will search the forum archives and link some previous postS that may help people trying to do work on their MKX-420G.

Might take a while to accomplish this. I will see if I can lay it out like the FSM


[Saloon-lovers] Adwest Power steer MKX/420G/Landrover - Saloons - Jag-lovers Forums

Land Rover Adwest steering box overhaul part 1. Stripping the box (youtube.com)





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Good idea Tony.
The problem is that we are not many owners who like this fantastic car.
I bought my first one in 1988. Dark blue with light grey interior. I still own it. I have 3 more of which the MOD 420G from June 1970 is going out for sale in the spring.
I can probably add some information to your projecr.

I would love any and all info concerning the MK X. The last of the great saloons…

The beautiful best that is the Mark X/420G. The cause of the demise of multiple cows to cover the seats of the gargantuan interior and with more wood than an Edwardian library, she will empty your pockets quicker than a girl in St. Paulie when you restore her. For those brave enough to endure all this, she is quite a rewarding car to own and drive.


Just got a 420g. . been off road 30 years finding front brake parts my first big problem. Does anyone know if the pistons from other jags fit the larger Dunlop brakes on the 420g ?

I do not think any other brake pistons fit 420G.

I have a pair in my car that I got from David Manners, where I also got new discs, pistons, seals and pads to overhaul the fronts (that was a few years ago, dont know if they still sell them

I need to fit them asap, my original fronts are worn out

420G has a 1/2" thick brake disc

If you cannot obtain new pistons, you can have them SS sleeved

(piston is sealing surface in fronts)

SNG Barrat and others would probably have them

Check Part nums carefully as earlier MKX had different parts in some cases

front calipers are rare and VERY expensive ,be careful not to damage them, seal sits in the caliper groove

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Great advice. Is it same story for rears ? Also trying fit master cylinder seals but no luck getting apart yet . Manual say take a retaining bolt out and it will come apart ?

I just checked and Manners no longer advertises front pistons, (they may have them if you call). 4.2 MKX and 420G re the same

The rear brakes calipers are different. I cannot recall whether the piston or caliper is the seal surface, I had my rears sleeved in SS, they do have a similar piston and caliper to most other Jags with IRS

It is no easy proposition to remove the rear brakes without taking down the IRS

I also had my master sleeved in SS.

To get it apart there is a 1/2" recessed Allen head fastener, I think it is under the tipping valve assembly, have a closer look at the manual

Hi Roy,

If you run in to too many problems with parts shortages and pricing, one option is to replace the Dunlop calipers with an aftermarket kit from Coopercraft. I put their four-pot calipers on the front of my Mark IX with great results. They also make a four-pot kit for the Mark X/420G that is plug-n-play. No affiltation with Coopercraft; just a satisfied customer. Here is a link to their Mark X kit:

Best of luck,

For those in the USA, call Jack White in Luray Virginia at 540 743-4037. Leave a message if no answer. He does not do email or texting. He has a lot of 420G & MX X in his Jaguar retirement facility. He is a source of a wealth of information. He ships internationally .


Bremskolben für Jaguar | 218197 | Limora Oldtimer

edit, shows Limora has front pistons (and all other parts)

117GBP each x 4 needed (if your old ones are shot, which is likely, standard ones are chromed

For that price, I would get a quote on SS sleeve for original piston, be cheaper

Halrays in Lismore NSW Australia are world leaders

You can put a flag on your record here to show where you are located

I bought my front pistons, (which are 2-1/4" diameter and I think unique to the Mk10/420G), the original retractable type from Martin Robey about a year ago. David Manners were also listing them at the same time. And SNG listed as special order goods.
Roy, you need the XJ6 series 1 FSM, brakes section for the Girling MC.
I can post if you if you don’t have it.

Good pick up Nick

The MKX-420G FSM, with supplement make no mention of the later Girling setup for booster and master cylinder

This is confusing to say the least

I have seen dudes lamely picturing the old master cyl in their hand, with its tongue hanging out, no idea that is the older style they have bought.

You have to make sure you have the rights parts

As I understand it, an XJ MC has a dfiferent part number, and may have slightly different output port location, but they do takes the same internals and work. LHD and RHD have ports on opposite sides, so are a different part num

here are the relevant excerpts from the S1 XJ6 FSM

You can see the fastener part num 3. it really wants a 1/2" allen key, if you do not have one, inside pliers may work

The tipping valve screws, part num 6 can be very hard to get undone without damaging the heads. I suggest soaking these with penetrant, they are open from below i think.

Make sure you have the exact size bit

I do not like using heat in this area as it may damage the valve part num 2, which I think has a rubber seal on it

Unless the bore is 100% perfect with no pits, it may need sleeving, have it inspected by an expert, they have a stepped bore

The problem with larger front calipers is that they don´f fit inside the orig 14” wheels.
XJ S1 wheels will cure that problem. They also use the same rim bellishers and hub caps.

Thanks guys for advice so far salvaged one caliber. Run into problem with end stop for brake pad breaks off .I had second set so have one end stop each side . I did buy new discs and pads for the uprated 420g so in too deep too change plan now . Still can not get master apart no sign Alan key bolt talked about

What year is your 420G.

1967 and some 68 models may have the earlier Dunlop system fitted

here is a picture of it

Its easy to see the difference, booster is different having a band that retains the clamshell. Master will have part of the engagement piston protruding from the master, while the later one , the piston is retracted and restrained with the cylinder.

What manual are you using?

Post some pics, that will be a better idea than a “passion fingers” routine

Putting them back together is surprisingly difficult

Make sure you take many digipics that show the orientation of the seals in the master cyl. If you place one backwards, it wont work. I advise measure the “length” of each seal with a vernier. If they are too long, the prevent the rear port from working.

That happened to me, there are 2 sets of MC seals which are very similar

If the crescent shaped metal parts that are retained to the caliper with 2 screws, it common for them to be broken, good luck if you have a spare set, I also have some spares, last time I just JB Weld then together and scrwed back in, they still do the hob like that

I have to do my fronts, and am looking for my spare front calipers so I can dismantle them also, I have noticed, that as per the parts manual, the 66MK10 has slightly different caliper bodies from a later 420G, I believe the internals are the same

I shall post some pics later

To get them apart, I split the caliper, soak them in turps/atf mix, knock the pistons all the way in, fit tight bleeders to the caliper halves, connect a caliper hose, and pump out each individual piston, restrained by a g-clamp, using the cars unboosted brake hydraulics

Yes mine is the early one then . Same as your picture. Will have check have correct repair kit when get it apart . Be next week now .will try take pic thanks for great advice Roy

@nick_banks is probably the man when it comes to these 65-67 Brake Master cylinder seal kits

The later seal kit, which also fits Ferrari is very similar fits 67-70 MKX/420G

The pre 65 3.8 MKX have a similar system to early E-types

I believe @RustfreeMike may have also rebuilt one of these, may be wrong on that

says you just have to take out stop peg 40 and release spring 37, should spring apart.

If it seized rapping on a suitable wood block after allowing penetrant to be absorbed into the body via the ports will allow the pistons to work out

Be careful, it will pop apart, springs and small bits will fly half way across your garage,

Getting nervous take it finding a new one a no go ? It may still be ok but car not been on road for over 30 years been tucked away in a collection so would like know new seals are in it