Dual circuit brake master cylinder

Silly question of the week

Our cars have single circuit hydraulic brakes.

Dual circuit is patently safer.

What master cylinder might be a straight (ish) swap to provide a dual output?

‘Donor’ car should be remote reservoir / remote servo set up I s’pose.

Anybody done this?

For the MK11 use the complete 420 system.
Peter B.

Thanks Peter - I’ll have a look.

Not a silly question at all.
The 420 system seems unnecessary complicated.
I seem to recall an artical in Jaguar Driver or Jaguar World about 15 years ago where someone had retained the single master cylinder but fitted a dual servo, off, (I think), some sort of VW.

There have been people in the forums looking into this but nobody has seemed to find a simple replacement. Wilwood and others make “generic” MC’s which would be ideal to find one that works but not sure if it’s ever been fully investigated.

The VW M/C is single body but dual cylinder as fitted on my `71
Karmann Ghia or same age Beetle, do you then fit dual servos?
The 420 pedal box is a straight change, bit of fiddle to fit the servo,
and some pipework, after all the system is Jaguar spec.
If there is a suitable dual M/C and dual system remote servo, with both
hydraulic lines activating the servo reaction valve available,
then way to go.
Peter B.

2-liter Rovers did the same, late ‘68-on. Impressive looking system!

If I remember correctly, he retained the original mk2 master cyl. The servo was a single remote unit, with a common vacuume chamber with a slave cyl on each end. One cyl worked the front brakes the other the rear. Obviously no alternative protection was offered should the master cyl fail or the single pipe to the servo fail.
It was a fairly compact unit, which may have come from a 1980s VW Golf or something like that. Unfortunatly I no longer have the artical.

Having looked on Google, I see that a UK company specialising in special builds, lists a dual servo, although I doubt that it would be powerfull enough. It’s about £350, is 140mm diameter and has a 2:1 boost ratio @ 600mm Hg. The mk1 and early mk2 had a servo of around this dia, but was increased on later models. Worth a look.

Thanks for the input. I confess to going off the idea a little - seems very involved and for every additional part / connection / union there is additional risk, and I would not like any reduction in servo assistance.

I’ll keep getting the car MOT’d and a regular eye on the brake fluid…

Personally, I think dual-brake systems are a solution in search of a problem. Rather than going to all the trouble of plumbing the extra lines you could more easily make sure the original lines are not rusty or pinched.

Mike Eck

New Jersey, USA

www.jaguarclock.com

'51 XK120 OTS, '62 3.8 MK2 MOD, '72 SIII E-Type 2+2