Author Topic: Changing from single line to dual line brakes  (Read 229 times)

Offline Coalhod

Changing from single line to dual line brakes
« on: November 01, 2021, 09:24:08 AM »
Hello;  After a recent autocross in my MK1 while on course the brake pedal went to the floor making for some exciting moments!  It's the original single line braking system.  Turns out one of the 20 year old steel braided brake lines had come apart at the crimped area of the fitting.

I have read the factory went to a dual line braking system from the late 70's on and am considering replacing the "bean can" master with the newer dual master part number GMC227 and bias valve FAM7821.  Looks like the fittings were changed to metric on both of these items so will have to adapt to fit.

I like the idea of having some sort of hydraulic brakes should this happen again, it was not fun during the hour drive home in the rain with the parking brake!

Any thoughts on this?  Figured the factory probably had a decent setup although I have read otherwise.  Maybe Wilwood or equivalent is a better option.

Thanks,

Andrew

Offline 94touring

Re: Changing from single line to dual line brakes
« Reply #1 on: November 01, 2021, 09:50:05 AM »
I've driven minis with this master and seems to work just fine.  Good as any other mini master I suppose.  One thing you could have done on that drive home when the line burst was "vice grip" the burst line closed and rebleed the others since it presumably dumped most all your fluid.  This would have given you 3 lines instead of no lines. Been there done that.  I wouldn't trust just the hand brake, that sounds scary as hell!
« Last Edit: November 01, 2021, 09:51:36 AM by 94touring »

Offline MiniDave

Re: Changing from single line to dual line brakes
« Reply #2 on: November 01, 2021, 02:07:05 PM »
Unless you do the diagonal split setup, it still could be scary if all you have are the rears!

do you have front discs? is this on the 850 powered car?
Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

Offline skmini

Re: Changing from single line to dual line brakes
« Reply #3 on: November 01, 2021, 02:32:17 PM »
My '79 Canadian Mini has front/rear split, but doesn't use the FAM7821 valve.  It has a 13H7757 inertial proportioning valve mounted to the rear subframe.  This is not the same one as installed on single-line minis.  Keith Calver has a short article on using the MS72 adjustable pressure regulator with a split system:

http://www.minispares.com/article/Technical~Information/Brakes/Brakes~-~Split~brake~systems~and~adjustable~bias~valves.aspx?ids=6|20|977&perma=brakes-split-brake-systems-and-adjustable-bias-valves


This article, by the way, might explain why the rear brakes would occasionally lock up on my mini: the master cylinder also has proportioning built into it and the newer replacement MC has the ports reversed from the original NLA MC.  I'm pretty sure I just put the brakes lines back where they were when I replaced the MC 25 years ago, before you could look these things up on the internet.  I'm anticipating much better braking performance when I put it all back together.

(Edited by moderator to fix article link.)
« Last Edit: November 01, 2021, 03:35:19 PM by MPlayle »

Offline Coalhod

Re: Changing from single line to dual line brakes
« Reply #4 on: November 01, 2021, 03:44:06 PM »
Thanks for all the info!  After all these years of carrying tools with me and I didn't take vicegrips!  Definitely would have alleviated "Flintstone Style" braking.
It's an early thin flange 1275 with AEG163 cylinder head.  Tons of torque.  The autocross club has a "vintage" class where any vehicle 25 years or older can compete but only on street tires.  They figure event results using the SCCA SoloII PAX system.  Trouble is, now I'm up against C4 Corvettes, 240/260/280 Z cars and who knows whatever else from the 90's and earlier.  Still a fun to drive car.
AFAIK the only dual braking system available today at least stock/factory type is a front/rear bias setup.  The article from Keith Calver is interesting - if I decide to go this route it might be worthwhile at autocross "fun runs" after the event is over but able to drive the course to dial in the rear brakes with the MS72 valve.


Andrew
« Last Edit: November 01, 2021, 04:01:52 PM by Coalhod »

Offline mascher

Re: Changing from single line to dual line brakes
« Reply #5 on: November 04, 2021, 12:44:17 PM »
The  GMC227 is the stepped bore master cylinder so it has some bias built in. I haven't used one but I have a lot of the experience with the GMC159 that was used on Canadian Minis starting about 1972 and was also used on Austin Americas. As far as braking is concerned, these work every bit as well as the single circuit brake masters. They do need to be bench bled and I think any of the dual circuit masters should also be bench bled. They seem to like to hold air if installed dry.

I helped install one Wilwood dual circuit system, 2 master cylinders w/ a bias bar. After a few years of driving (not mine) the bias bar had loosened and the brakes became very strange. After sorting it out it appeared that the bias bar wasn't properly locked and given the limited space (V-Tec) it wasn't surprising. If I was to help anyone do this again (and I won't  ;D ) I would add a proportioning valve in addition to the bias bar. The Mini seems to need a bit more brake bias than the bias bar can deliver and the proportioning valve makes adjustments easier between street and racing.
Kelley