Sizing of brake lines on revised system

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walterclark
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Sizing of brake lines on revised system

Post by walterclark »

I am past the point of no return on the changeover from the stock brake system (dual 20.65mm master cylinder, vacuum booster, diagonal connected) to the new racing system (2 independent .75" MC, Wilwood manual pedal cluster with balance bar, F/F R/R connected).

The old firewall has been removed in the area of the pedals and a new flat wall welded in, bracing for the new cluster is done, throttle pedal mount done, steering column lower mount done, and everything has been test fit. Just waiting on the seam sealer and paint to cure...

Now I need to revise the brake lines. The stock system has all 4 lines going to dedicated ports on the dual MC with the 2 lines to the rear going thru a variable pressure regulator that was originally attached to the axle beam for rear bias. The new MC's have 1 port each. To me the obvious and simple approach is to put a Tee at the front MC port and feed the front brakes from that, then remove one of the lines going to the rear and insert a Tee where the old variable regulator was located and connect to the rear lines back there.

Although the balance bar permits tuning the F/R MC pressure ratios, at some point I expect to install a lever selectable pressure regulator for the rear brakes on the inside of the center tunnel. This would be to permit me to instantly increase or decrease the rear bias in the event I want to change the balance while on course... For instance, Mt Washington. I generally prefer minimal rear braking on grippy pavement, but it would have been real handy to have been able to up the rear bias on the gravel section to help me rotate the car at Cragway with LFB. As it was this year traction was low enough that LFB would not bring the rear around before the brakes started sliding the fronts. I have never really learned how to handbrake turn well but I was thoroughly schooled at TON using LFB but I need to add more rear bias than I usually use to make it work comfortably on dirt. So to add the levered regulator it would be simpler to have one line going to the rear. Anyway this is not my issue/question at the moment.

My question is, do I need to upsize the brake line going to the rear, or should one of the original lines be fine? I am assuming on origunal should work fine but maybe I am missing something.

All the original lines are the same diameter and I made new ones from the stock 3/16" OD (4.75mm) size brake tubing when I built up the car for rally about 12 years ago.
Last edited by walterclark on Wed Dec 17, 2014 1:47 pm, edited 1 time in total.
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sdwarf36
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Re: Sizing of brake lines on revised system

Post by sdwarf36 »

3/16" should be fine. And just Teeing the line is ok too. I'll look in the garage-I think I have one of those lever style proportioning valves kicking around.
Do some tests on your pedal mount-set up and indicator and try to push the pedal thru the floor. I've made a few different mounts-added braces-gussets-and I still get some movement. It doesn't affect performance but it bugs me knowing its there. :(
Translating road racing to hillclimbing:
Proper tire selection== nothing hooks up on moss or wet leaves.
Staying on the racing line==anything paved is considered good.
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walterclark
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Re: Sizing of brake lines on revised system

Post by walterclark »

Thanks Sherm! I was hoping that would be the case. Now all I need to do get a couple suitable Tees and some fittings. I found a couple Earls Tees that are M10-1.0 outlets and 3/8-24 IF inlet, so I will probably go with a system that is metric from the Tee's to the brake cylinders and SAE J512 from the Tee's back to the master cylinders (the new brake MCs have 1/8" NPT ports and the clutch MC is a 3/8-24 IF). That should make connecting to things like a proportioning valve (and maybe a hydraulic hand brake someday) and master cylinders easier and cheaper. Those things seem to all be 1/8" NPT and adapting them to the common 3/16" brake tube nut - the SAE J512 3/8"-24 IF - is cheap and easy.

If you have a lever proportioning valve, I would be very interested. Let me know how much you want for it if you locate it.

I assumed the firewall and pedal cluster would require a good bit of bracing. To date the pedal cluster bolts to the firewall with the studs that mount the 3 master cylinders on the engine side, and there are 2-1" square tube braces from the outer ends of the pedal pivot support bracket up to the bottom side of the plenum and a plate in the plenum to distribute that load. These 2 tubes have a round 1/2" tube welded between them onto which the lower steering column hanger slides in a manner similar to the way it mounts in a stock arrangement. The steering column itself runs below the pedal support bracket and between the pedals. Vertically, this pedal cluster bracket and square tube arrangement is very rigid so the pedal support bracket cannot twist downward under pressure. What is left for me to do is stabilize the firewall itself against being pushed forward. That part starts today. I am planning on sandwiching a flat 6061-T6 aluminum plate between the firewall and the master cylinders with 6061-T6 aluminum L welded to one or more edges of plate and those bolted and reinforced near the edges of the firewall. The plate will be from some of the stuff I have on hand which I think is 3/16". The L has to be obtained and I am inclined to go with 1/8" thick 2" L. The 6061 will be re-aged after welding to restore the T6 temper partially taken out by the welding process. I am probably going to use vertical L braces since these would be shorter distances to the edges of the firewall and I need to position them to clear the steering column and its firewall opening that is directly below pedal cluster.
Last edited by walterclark on Wed Dec 17, 2014 1:50 pm, edited 1 time in total.
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Super1303
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Re: Sizing of brake lines on revised system

Post by Super1303 »

I agree with Sherm. 3/16'' is fine, it ain't a dump truck with Dual 3" piston calipers.
One line to the back tee it off before the axle, less to go wrong.
Only thing I can think of is, if that hand brake you mentioned would be the dual lever type.
Then you'd want to put the tee before that and run two lines to the rear brakes.
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walterclark
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Re: Sizing of brake lines on revised system

Post by walterclark »

If I go with something it would look more or less like this:
Image
It just plumbs into the line going to the rear like a proportioning valve will.
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sciroccohp
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Re: Sizing of brake lines on revised system

Post by sciroccohp »

My biggest problem has always been sizing the masters, I think you will find that have the same front and rear will max out your adjustment and give you too much rear brake. I don't remember which sizes I ended up with on my car. the only difference is I was still running drums on the rear.
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sdwarf36
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Re: Sizing of brake lines on revised system

Post by sdwarf36 »

Sorry Walt-I don't know where it went. But it wasn'y anywhere near that fancy. 8-)
Translating road racing to hillclimbing:
Proper tire selection== nothing hooks up on moss or wet leaves.
Staying on the racing line==anything paved is considered good.
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walterclark
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Re: Sizing of brake lines on revised system

Post by walterclark »

Thanks Sherm. The pic is of a hydro handbrake. ..Way fancier than a proportioning valve. The proportioning valve is going to happen now, the handbrake maybe later.

Since the stock MCs are the same F/R (cross coupled of course) and a proportioning valve is used on the rear to get balance, I assume this new equal setup will work with the added valve in the rear. Seems redundant I know, but the valve will be a lever type to let me quickly and accurately increase or decrease rear bias while driving if changing conditions suggest I need it. I didnt pick the MC sizes by the way. Greg Haley had these along with the clutch MC and pedal assembly (he raced his turbo 8V Jetta in hillclimbs) and put them up for sale in our classifieds. They werent brand spanking new, but didnt look like they had seen any real use so I dont know if he installed them in the Jetta or not. The seem like the right choices for the Golf/Jetta compared to stock.
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