Brake Master Cylinder Conversion

As you will have read on the page called 'Four Pot Calipers & Vented Disks' the increased piston area in the Princess calipers means that the pedal travel is now excessive, they require a larger volume of brake fluid to do the job.  The brakes work fine and pull up cleanly, but there's just enough time/travel for that sickening feeling when you hit the brakes in a hurry.

I did some research and calculations to work out what I needed and arrived at some numbers which showed that to move the Princess brake caliper pistons (and hence brake pads) by 1 mm, I would need 25.45% more fluid than the Marina calipers.


From this I was able to calculate how much bigger diameter master cylinder I would need to displace the extra 25% brake fluid for the same amount of travel.  To replace the Marina 19.0mm (3/4 inch) master cylinder would need a 22.2mm (7/8ths inch) diameter master cylinder which will displace 27% more fluid - a good match.

Strangely these are thin on the ground, there are lots of 22.2mm dual line mater cylinders, but the only single line one was from an early Transit van and that didn't have a servo.  The next best opportunity is a 25.4mm (1 inch) master cylinder - little oversize with a 60% increase in fluid handling but hey - "beggars can't be choosers".

I search to find a single line master cylinder, and found that a Landrover Series 3 (1971-80) Girling PML157 single piston master cylinder with a 1" bore will do the job and what do you know, it seems to be the big brother to the Marina one (see below).  Parts for old Landrovers are no problem with a vast industry providing backup, I was able to source a brand new master cylinder for under 25!



The Marina one is on the right.  I stripped off both reservoirs/cups, gave the Marina one a good clean and swapped it over to get the correct angle in the car, it all bolts across no problem; the new parts are at the top (below).




Here's the hybrid Marina/Landover master cylinder, it mounted straight onto the Marina servo!



The only thing that I had to do was make up a new brake pipe from the master cylinder to the union. Although the Landrover uses 3/16" pipe like the Marina, the union fitting is 7/16" UNF rather than the Marina 3/8" UNF. As luck would have it, I found one in the autojumble at Shuttleworth Classic Car Show at the weekend.



So how does she feel - in a word - brilliant!  Firm pedal, short travel, very confidence inspiring, although not necessary with standard brakes, I recommend this mod to anyone upgrading their Marina brakes to something bigger.


Footnote: If you are running a twin/tandem line master cylinder in your Marina/Ital, then there are a series of  tandem Landrover master cylinders you could try, depending on the bore size you need.


1.00" (25.4mm) bore Girling 4008161 (Landrover GMC319 or 90577520)

15/16" (23.8mm) bore Girling/TRW 4007184 (Landrover NRC9529)

7/8" (22.2mm) bore Girling/TRW 4006200 (Landrover GMC320 or 569671)


All will fit the Marina servo.



When I get round to fitting the dual lines to the Marina, guess what I am fitting?