Dual circuit conversion

[DADAMS]

I'm in the process of converting to a dual circuit system on my SIIA. I have the SIII pedal tower with servo and MC and a set of Automec lines.

Do I need to find a shuttle valve, or can I send the lines directly to the front and rear from the MC through the old 5-way union? I understand that if I do that, I will lose pressure throughout if there is a failure in one part of the system.

Is there a common replacement for the shuttle valve?

Any advice would be appreciated --Dave

[SafeAirOne]

If you have no way of isolating one circuit after a loss of pressure in the other, you might as well keep the single-circuit system. This occurs when you don't use a shuttle valve and use one big union that combines the fluid from the 2 circuits into one common system.


The shuttle valve sort of "compares" the pressure of the two circuits and shuts off a circuit if the pressure is very different between them (as when one circuit has failed and the other one is still intact).

[lrdukdog]

brakes

If memory serves... you can get two three ways from Victoria British. You then have the three for the front and just plug one outlet for the rear. You have then isolated the front and rear and the dual MC will work.
Jim Wolf

[greenmeanie]

Most owners in the UK where they were commonly fitted on MOD trucks and a lot of SIII end up removing the shuttle valve as they are notoriously unreliable. They make brake bleeding a pain as it is very easy to have them move off centre and you then have to mess around with the thing to get it back in position. They also tend to stick once moved which can cause a whole slew of issues that are fun to diagnose. The seals are also known for failing in which case you now have a single circuit system as the previous poster mentioned.

You are far better to have to entirely separate systems either using unions as described above, or swap over to a SIII brake line set up entirely with one line dedicated to the rear axle and one, incorporating a 3 way union for the fronts. It also has the plus of being cheaper.

[TeriAnn]

A lot depends upon your trucks wheelbase as 88s & 109s have different brake systems that share some components and the systems change over time.

I already have my comments on a web page.

http://www.expeditionlandrover.info/dual_brake_conv.htm

[greenmeanie]

A good thread explaning a lot about the shuttle valve, its problems and the common solution.

Linky

[109 Pretender]

Meanie, I'd agree about the shuttle - somewhat troublesome and not necessary. LRDUKDOG is spot-on w/his advice! Totally seperate your lines w/2 &3 way unions. Try Victoria British (MGB's) as a parts supplier for the brass ones if you can't find them somewhere else. Every British car I ever worked on had these unions and there are a variety of styles.

Cheers!

[thixon]

Forget the shuttle valve, and seperate the circuits. Also, you don't have to use the british equipment for the unions. You're making new lines anyway right? If you want to save time, go get american unions and fittings from napa/autozone/wherever.

And for everyone who's about to give me feedback on why you shouldn't mix american and british fittings, think really hard about what I wrote above.

[SafeAirOne]

Also, you don't have to use the british equipment for the unions. You're making new lines anyway right?

What??--Use a mixture of different "standards" on a single vehicle? Next thing you know, you'll have a vehicle that has metric fittings, standard fittings, BSF fittings, whitworth fittings, NPT fittings, etc. What a mess that would be!

[DADAMS]

Thanks to all for the responses. I'll keep the circuits seperate.

Mine is an 88. I'll have to look closely at the MC that I have and compare to the photos on TeriAnn's write up. (thanks for the link, I've found a lot of useful info on your site)

Greenmeanie, your link doesn't agree with my computer. What is the address?

Thanks again --Dave

[SafeAirOne]

Greenmeanie, your link doesn't agree with my computer. What is the address?

Try it first. When you get the "forbidden" message, go up to the "address" box up at the top of your browser and delete " &highlight=shuttle+vavle " in the address and hit "go". Then it'll work.