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dual circuit braking system

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maxwedge5281

maxwedge5281

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planning to install in the very near future. utilizing wilwood master cylinder 260-8794 as suggested in an earlier post on the forum. what is the best suggested routing of the hard line for the rear brakes. my car is a 63 bj7 sbc conversion with automatic transmission....no clutch so i do have some flexibility with the pedal box! thanks in advance for suggestions and/or comments.
 
maxwedge5281 said:
planning to install in the very near future. utilizing wilwood master cylinder 260-8794 as suggested in an earlier post on the forum. what is the best suggested routing of the hard line for the rear brakes. my car is a 63 bj7 sbc conversion with automatic transmission....no clutch so i do have some flexibility with the pedal box! thanks in advance for suggestions and/or comments.
Click to expand...

Since you're not using the clutch, you could have a balance bar setup with a separate MC for the back brakes.

Your stock MC, non-boosted, is 5/8". Others may disagree, but IMHO the 1" is going to be too big and will require heavy foot pressure. You have room, why not install another 5/8" cylinder with a balance bar. The bar could be set 1-to-1 as you already have the correct rear cylinders for the 5/8" MC. You would have the exact setup you have now, but with two circuits.

As far as boosters as an option with the bigger MC, you'd need two with dual circuits. Not sure anyone has figured out a place to put the second booster.

Physically - not exactly sure how the balance bar would work - you might have to move the hole for the clutch MC which is not in exactly the same plane as the brake MC.
 
thanks for the replies but i think that i will opt for the simple approach and use the wilwood master cylinder. i have a similar setup on a sebring kit car and the one inch bore does require more pedal pressure. however, this is tolerable for me. i am still soliciting ideas for the rear brake line routing...
 
maxwedge5281 said:
thanks for the replies but i think that i will opt for the simple approach and use the wilwood master cylinder. i have a similar setup on a sebring kit car and the one inch bore does require more pedal pressure. however, this is tolerable for me. i am still soliciting ideas for the rear brake line routing...
Click to expand...


I haven't done mine yet, but plan on mounting compensating valve in the general location of the present 5-way union. I'll run basically a dupe of that for the front brakes down to the input side of the compensator. The present rear line will come out of the output of the compensator. If you don't want to do that you could use a connector between the new line and the existing rear line. You could also ape your old clutch line and go across under the lip of the shroud, then down where the clutch used to be and use the connector to connect to your existing rear brake line.
FWIW.
 
I ran my rear brake line parallel to the front brake line until I got to the 5-way fitting and then just kept going along the original route. The front line goes to the 5-way fitting, where I have the brake light switch and the two lines off to the front brakes. The 5th port is blanked off with a plug. You could replace the 5-way fitting with a 4-way fitting and be a bit neater.

The lines coming from the MC are about a foot long so I could make sure the fittings at the bottom of the MC were tight before installing the MC. It's a bear to try getting them tight with the MC in place. The foot-long piece allows me to have a coupling where I can reach it to connect the rest of the line to the 5-way fitting.

You don't want brake fluid leaking onto headers. Even DOT 5 fluid burns. Ask me how I know!
 
following a couple of the above suggestions. bolted the wilwood master cylinder onto the mounting points for yhe original clutch master cylinder....i have an automatic transmission! purchased 60 inch pre terminated brake line for the new line to the five way distribution block. note,...plugged the rear brake line so it is now a fourway. this was for the front brakes. this length worked very well and after bending mounted directly to the master cylinder. i purchased a 48 inch and a 10 inch pre terminated line for the rear brake line crossover.. the ten inch line hooks directly to the master cylinder rear brake outlet and to the wilwood proportioning valve. the 48 inch line was formed and crossed over to the brake line going from the distribution block to the rear brakes generally following the path of the front brake line. i used a 3/8 by 24 union with inverted flare for this connection. still have to modify the pushrod from the pedal box to the master cylinder. all in all about a five hour job. not having to deal with the srcond master cylinder made working in the pedal box area much easier. thanks to all for advice and suggestions.
 
biggest problem with this modification has been to find an inverted flare female union with enough threads to attach the line to the rear brakes. i talked with moss motors today and ordered a three way union for an austin healey as well as a two way union for a mg. hopefully one or both will have a deep enough female threaded section to attach the original healey line to the rear. the male nut is not threaded all the way and will only catch a couple of threads on the union...not enough for safety sake in my mind!
 
maxwedge5281 said:
biggest problem with this modification has been to find an inverted flare female union with enough threads to attach the line to the rear brakes. i talked with moss motors today and ordered a three way union for an austin healey as well as a two way union for a mg. hopefully one or both will have a deep enough female threaded section to attach the original healey line to the rear. the male nut is not threaded all the way and will only catch a couple of threads on the union...not enough for safety sake in my mind!
Click to expand...

The brass three way union on the rear axle uses a flat-ended crush washer connection for the flex line from the axle to the chassis. Are you trying to insert a male inverted flare connection there?
 
steve, this was suggested by the sales guy and i took a chance that i could use it. and, yes, i am trying to use a male inverted flare connection. the three way union attaches to the main hard line to the rear brakes and to the two hard lines that run to each wheel. i think that is how it works. if not, i may have just purchased a nice 30 dollar spare! hopefully the mg union will work! i searched all over the internet for a long inverted flare female union with no luck. i may have to remove the line to the rear and replumb!
 
just looked under the rear of the car. the flexible line is between the axle and the body....hopefully the two ports on the three way block that are used for the hard lines have deep enough threaded ports to use at the front of the car for the rear brake line union...and i can plug the third port!!
 
maxwedge5281 said:
just looked under the rear of the car. the flexible line is between the axle and the body....hopefully the two ports on the three way block that are used for the hard lines have deep enough threaded ports to use at the front of the car for the rear brake line union...and i can plug the third port!!
Click to expand...

What you need is a 3/8-24 inverted flare union:
BrakeLineUnion.jpg
Also see Earl's - you can call them on the phone with questions, too:
https://www.anplumbing.com/
 
steve, i have purchased a proper union locally...but...it does not have a deep enough threaded area to properly engage the male end...the healey male end is not threaded all the way and there is probably almost 3/16 inch of onverted flare and the unthreaded portion of the nut. so i cant get enough thread engagement for my liking...o need an extra long female inverted flare union. and, i have not been able to locate one.
 
steve, i have purchased a proper union locally...but...it does not have a deep enough threaded area to properly engage the male end...the healey male end is not threaded all the way and there is probably almost 3/16 inch of inverted flare and the unthreaded portion of the nut. so i cant get enough thread engagement for my liking...i need an extra long female inverted flare union. and, i have not been able to locate one.
 
I was going to mention that the MGB (post 68, or 73?) used a two-piece line to the rear brakes, so that union ought to work for you.

I too found out the expensive way (buying a part I can't use) about the difference in threads on a 3-way block. I wanted to add a second brake light switch to run an isolated signal to a 3rd l.e.d. brakelight__I didn't want to mess around with diodes and the original flasher/brake light relay.
 
i should receive the parts tomorrow. i will post my results. and, thanks for the help!!
 
this is the wilwood master cylinder mounted to the car. the proportioning valve is close and easily adjustable. the master cylinder mounts in the original mounts for the clutch cylinder. i shortened the pedal actuating rod and made it adjustable. with just one master cylinder in place this was a very easy changeover......if i can get the one inverted flare female union worked out!
 

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