I got myself the Factory Parts Manual on CD for $5 many years ago (also has the Service and Parts Manuals for all MKX/420G…worth its weight in gold)
I strongly advise to see if its still available
I promise you almost all vendors will tell you any old crap about part numbers for these cars, and they are almost always wrong
I have a 420G, and the brakes are completely different from the 3.8 MKX
Hi, I can now provide some hopefully useful insights about Mark X brake master cylinders which may be of use to Dean, and others, and a difference from the early E Type which had a similar braking system.
In my previous post I provided a link to the E Type forum which demystified the system and provided measurements with which I will make comparisons.
So, for Dean I needed to see if the master cylinders were serviceable before posting them. The grease gun method succeeded in removing the stuck pistons. The cylinders look to have a stainless sleave. Cleaned up with new rubber they could be good.
The cylinder with tag 4707 I gather is for the front brakes and it has the short 50 mm piston and the other one has a longer 59 mm piston. The overall length of the ‘ensemble’ for both is 100 mm (being the piston and valve rod under the spring). This is the same as the dimensions of the pistons described for the E Type. I note the suppliers have the rubber seals common to both models.
Next we look at the pushrods.
My measurement from tip to clevis pin is 72mm (E type 52mm) for front brake master and 86mm (E Type 42mm) for the adjustable rear brake master. I wont attempt to explain how this works or why other than the pedal box and length of levers and their travel is probably different.
On further reading on the early E Type discussions it seems some had problems involving repairers having installed masters with both short pistons presumably because externally they look the same. I can’t be categoric what I have measured is the correct original or a ‘mix and match’ but hopefully it is original and what I have identified may go someway to solving Deans frustration and others trying to get a brake.
Other than that, if Dean has now sourced alternative parts, I have these cylinders looking for a new home…
Kind regards
Matt
great work Matt, did you measure the bore sizes? and yes I will still take them and any other brake bits you may have. i suspect you have actually hit the nail on the head with the fitment of the wrong masters IE E type, using your measurements for the Etype and it stacks with what i have. in short we run out of foot travel. you have how ever got the cylinders mixed up, the lower longer master is the front and the shorter higher is the rear. Matt you work has been invaluable, now we can match a part number to some actual dimensions.
Thanks Dean,
Check your PM, I sought your address, payment, postage…
By my school ruler the bore size is 5/8". Going over details I have provided again, the casting on the two cylinders is the same. There is no bigger or larger diameter cylinders. As pictured, they differ by one having a long piston and the other one shorter. My comparison with the E Type cylinders had them matching until I looked at the pushrods which are different lengths. Possibly the cylinders you have got could work with the right combination of piston and push rod. As for having the parts mixed up I suggest you review starting at the parts table VBM4707 being the lower/ front then look for the tagged cylinder in the pictures. Your initial post referred to the adjustable lower pushrod and the pedal box photo I provided has it at top?
Thanks again,
Matt
Dean, Perturbed about the difference I have now verified by finding the manual. It appears that my wreck had the cylinders upside down! Maybe brakes were among other issues why the person who had it ten years ago had sent it to a repairer and then abandoned it.
It had my head spinning with the photo of the pedal box - but readily understood when it is viewed upside down. The adjuster pushrod is correctly the lower ( page 308 of manual.) Under the adjuster should be 4707 which has the longer travel (the length under the spring) of the piston assembly. Manual page 302 has length of long stroke 3.68mm and short 2.75mm.
Thanks
Matt
Can you post up the pages of your manual. i now have the same as Tony wich seems to have less info than yours.
This may be a year too late but the booster is a Kelsey Hayes as mentioned, suits early 57-61 chrysler and dodge vehicles and is not too hard to find in the USA (power brake x-change inc). Seals for your Dunlop master cylinders are easily available from Powertrack brakes in the UK. I however replaced mine with two willwood cylinders of the right diameter and reused the original actuator rods. I got sick of the silly recuperation valves in the Dunlops spliting the seal and only leaving the back brakes working. To do this the firewall hole needs to be a bit bigger and the brake lines need to be re bent or re made, essentially the suction and discharge ports swap positions. It also looks like i had to fabricate a new bracket for the return spring. Sorry i cant remember the willwood part numbers but I am pretty sure it is 260-6087. I got the original idea of an Alfa Romeo guy, they also had Dunlop masters. The diameter of both the willwoods is 0.625 (5/8"), same as my originals. For the record my mark 10 is a 1963 3.8l model.
I hope this helps someone.
Can someone tell me what “The grease gun method succeeded in removing the stuck pistons.” where can i find the answer to this?
You use a grease gun to push out the pistons. The usual fitting should fit the caliper.
My MK IX were stuck solid. I plugged one side of the caliber and modifed another with a zerc (sic) fitting. I applied a hand pump grease gun and the piston popped right out. I must say I was surprised it worked.
Par H
Thank you.
Peter you also need to put a bit of wood or similar between the pistons to prevent one popping out completely, leaving you with the other one still stuck firmly.
You can do this just as well with compressed air, but wrap the whole thing in a towel or similar to stop pistons flying across the room.
I may have misled you. I have trouble removing the pistons out of my Brake Master Cylinders, not my Calipers. I am told it’s the same method by grease gun. I am having trouble finding a grease nipple to fit the master cylinder. I will keep perservering.
Just use a compressed air gun. The resistance is probably corrosion at the opening of the cylinder. Push the piston back and try and remove as much gunk as possible with steel wool etc.
Again. wrap the cylinder in a towel so it doesn’t become a cannon.
No problem, the advantage of fluid is that it is far less dangerous (and the grease gun puts out a lot of pressure). Air is like a spring so do take precautions, best also contain it in a vise or box in addition to the towel, and make sure you haven’t got a pin or reaction valve in the way, and clean out any corrosion. The clearances are pretty tight.
Since they are stuck they will need to be partially, or fully rebuilt. It is best to remove the cylinders. I seriously doubt if an air compressor can deliver sufficient pressure.
Works well although as alluded to you need to be cautious about things flying around the shed 
are you a PURIST? i upgraded my 1959 jaguar mk1 with a 1996 jaguar xj8 power brake booster and master cylinders. with the pedals also. removed ALL other reservoirs and old brake lines. wilwood brakes kits are available
Rebuild is a given. Air pressure almost always works and grease (+ water to reduce the mess) always works.
