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brake master cylinder for CB 4-wheel discs

FM Former Member
what do people suggest for 4-wheel cb discs as the master? i am working on a customer tenzin's car. we will use CB wide 5 discs all round and the stock pedals. i have been researching and getting lots of different answers about master cylinder choice. CB says any 67 or later dual circuit master, plus add the 2lb residual pressure valve in the rear line. but this doesn't seem to quite do it for me. even if you get a ghia or superbeetle master it is designed for rear drums. i found a quote below on a site of a mfg of aftermarket brake hydraulics, mpbrakes.com:

"A four wheel disc brake master cylinder is designed to supply more fluid pressure and volume to the rear disc brakes than the disc / drum master does. This is acheived through an internal piston re design. The piston that feeds the rear brakes on a disc / drum master will run out of stroke, limiting the amount of fluid pressure and volume that may be supplied to the rear disc brakes.

The four wheel disc master redesign delivers the extra needed volume and pressure to the rear allowing your rear disc brakes to function properly. If you attempt to use a disc/drum master on a four wheel disc system you will get poor rear brake function and experience a spongy brake pedal with a long pedal travel."

i think we will be better off with a master designed for 4-wheels discs. the problem is finding one that will bolt up ot the pan and that is designed for no servo. the only thing close i have found so far is a 914 master. it might fit. looking for other options or ideas.

thanks,

scott lyons

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FM Former Member
what do people suggest for 4-wheel cb discs as the master? i am working on a customer tenzin's car. we will use CB wide 5 discs all round and the stock pedals. i have been researching and getting lots of different answers about master cylinder choice. CB says any 67 or later dual circuit master, plus add the 2lb residual pressure valve in the rear line. but this doesn't seem to quite do it for me. even if you get a ghia or superbeetle master it is designed for rear drums. i found a quote below on a site of a mfg of aftermarket brake hydraulics, mpbrakes.com:

"A four wheel disc brake master cylinder is designed to supply more fluid pressure and volume to the rear disc brakes than the disc / drum master does. This is acheived through an internal piston re design. The piston that feeds the rear brakes on a disc / drum master will run out of stroke, limiting the amount of fluid pressure and volume that may be supplied to the rear disc brakes.

The four wheel disc master redesign delivers the extra needed volume and pressure to the rear allowing your rear disc brakes to function properly. If you attempt to use a disc/drum master on a four wheel disc system you will get poor rear brake function and experience a spongy brake pedal with a long pedal travel."

i think we will be better off with a master designed for 4-wheels discs. the problem is finding one that will bolt up ot the pan and that is designed for no servo. the only thing close i have found so far is a 914 master. it might fit. looking for other options or ideas.

thanks,

scott lyons

JogyverJogyver
Scott , I was never fond of the VW brake system. I changed over to a CNC duel master cylinder setup. I have a master cylinder dedicated for the front and the rear brakes. I am also able to adjust the bias of front to rear brakes. It took some major pan modifications to complete. Very solid brake feeling now.Also went with the hydrulic clutch system.I'll post some pictures later.
jschlotzjschlotz
When I converted to 4 wheel disc brakes and tried to utilize a standard VW dual circuit master cyclinder I found that the larger fluid volume of the new brake system was too much for that master cyclinder and created a long pedal(pushing down 5 or 6 inches before firm pedal), this was unsatisfactory to me. I did some research and spoke to some car builders, who told me that the stock unit is what they used. I still wasn't satisfied with the brake performance.

I obtained a master cyclinder recommended for 4 wheel disc brake systems and mounting kit from CSP USA, a German company with a distributor in L.A. area. That master cyclinder has an inside diameter of 20.64mm, a stock unit has a 19.05mm inside diameter.
The mounting kit changes the front fluid circuitry as well as does the conversion mount, and these parts are approved by the German Auto Inspection Bureau. Master cyclinder part#611 015 000, mounting kit part#611 017 111. Cost about $300.00. Contact website is
www.customspeedparts.com, L.A. area phone# 626-445-0108. They usually have the parts in stock in L.A.
Good Luck, Have Fun
Joel
FM Former Member
ok, those are some good ideas. CSP make good stuff, i will look into that. i am quite sure the standard beetle parts will not do it. the 911 master seems like it may work, the bolt-up looks promising.

joe - i peeked at your setup in the photos section, it looks good, but i don't think we can get into the pedal modifcations so deeply as you have done. we are going to use a neal hydraulic clutch designed for stock pedals, plus this brake master issue to be resolved, and stock or roller gas pedal. i did notice the tunnel mod you have made and i may do that, the footwell of this car (a CMC clone made in canada in the 80's) is very narrow, so the extra width would be a great benefit.

will keep you posted.

scott lyons

FM Former Member
Joel I'm getting ready to convert my system from disc/drum to disc/disc. It's on a VS. I have the pedal height and feel where I want it now, and had heard that the conversion would change that. It seems this is what you ran into. Unfortunatly I'm getting different advise from different people. Can you give me the straight scoop?
Thanks Alot Eddie
jschlotzjschlotz
Hi Eddie,
I did not think that the stock master cyclinder was satisfactory for 4 wheel disc brakes. Some of the speedster builders may disagree. It's a matter of fluid volume, the disc brake calipers have a larger fluid capicity/volume, therfore you need a larger master cyclinder to move the fluid and to obtain a good short pedal(2-3 inche throw).
You can look around at VW bus, 914, 911 master cyclinders, but to me time is money and I decided to pay CSP for their research, not to mention, German DOT approves the parts. Although CSP is a little pricey $300.+, the parts work, the installation is relatively easy. Make sure you bench bleed the master before installation, you will also have to adjust the pedal push rod. You will not need to install a proportioning or any other type of additional valves.
You must also be aware of the fact that the CB rear disc brake setup for "wide 5" if you are doing that, increases the track width by about 3/8" to 1/2" per side, which my affect tire to body clearance. If that happens, and your rear tires rub, you will need to talk to Stockton Wheel to have your rear wheel offset changed, I had to do that. I have more information and a few upgrades I would also recommend to you. Feel free to call me if you would like at 650-483-6221.

Good Luck, Have Fun
Joel
S shambly
I've got the complete CSP setup on my car now. wide-5 front and rear discs, plus the CSP 20.64mm 4-disc master cylinder (having previously had rear drums and the std. master cylinder).

One important note about the CSP rear discs is that they reduce track by 10mm each side. Useful, to gain all too valuable tyre clearance with wide-5 rims.

Simon

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JogyverJogyver
Scott, If you have a tight budget you could install a VW bus master cylinder and install a 2lb residual valves. It does work well. The resid valve is sort of a diaphram check valve that eliminates the roll back of the fluid back to the master. This usually happens when the master cylinder is at a lower elevation than the rear disc brake system or your brake line sort of goes up hill. As stated in previous notes the capliers do have more volume. The more expensive master cylinders you are paying for a few extra "O" rings. If you do use a bus master cylinder hook up the rear brake line to the further out opening of the master.
FM Former Member
joe,

do you have any idea which bus master? there are 4 different bus masters from 68-79. the one thing i have seen with them is most have the lines on the wrong side of the master. they also use 2 switches.

i thing we will use the CSP kit, though the master is ridiculously expensive. i am trying locate a master that will match up with the one CSP uses. i have a few to choose from and since i have wholesale accounts with several distributors it should be possible to find a good match.

on the ohter hand, i agree with joel, that the value in the CSP setup is that the R&D has been done, and i applaud them for their well-though-out products. if you spend some time on their site you will see what i mean, they have lots of very good products that they have desinged and manufactured themselves.
WildBillWildBill
I have discs on all four corners. I have the residual valve that CB recommends installed at the master cyl. for the rear circuit. Using a bug master cyl with the valve installed, bled properly,and the piston rod adjusted just right, I happy as a pig in s**t with my set up.
One must remember that we are dealing with manual brakes here. I have about an inch and a half of pedal travel, but can lock 'em up at will.
Unless you install a booster, you'll never have that "power brake" feeling that most are accustomed to.

BD
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