22mm Master cylinder

John Rogers · 05-09-2000, 07:52 PM

I have been told by good authority that a VW Transporter 73-on master cylinder is 22mm and will bolt on to a 914? I threw my old 19mm away and don't have anyway to check this out? For those with bigger than stock calipers, this would cure the soft pedal we feel. Anyone have any way to check?

Germain · 05-10-2000, 05:25 AM

This is a bit off subject, but a question about the size. How is a 22mm differant then a 19mm? Let me rephrase that, why is the 22 "better" then the 19? I guess I don't understand how they work, so I can't understand why a 22 is better then the 19.

neilca · 05-10-2000, 06:11 AM

The 19 and 22 are the diameter of the cylinder measured in millimeters. The difference in the two is the amount of fluid moved per stroke. When running larger brakes (ie larger pistons or more pistons) then you need more fluid to fill the void. Balancing this will give you the pedal feel you want. The larger the cylinder the stiffer the pedal. Too large a cylinder can require you to use both feet for braking. Too small you get a very "long" pedal or require pumping the pedal to move the required amount of fluid.

Hope that helps,
neil

John Rogers · 05-10-2000, 06:17 AM

Come on now, someone must have a bus master cylinder and a 914 master cylinder???

Germain · 05-10-2000, 09:09 AM

Oh, I get it... I think.

When the pedal is actuated we need say 100 units of fluid to travel to the brakes to stop the car quickly. With a bigger cyl, we move more fluid with less distance of a downstroke. So in reality it doesn't provide more stopping power persay, just less effort (or more) on the human part. Thanks.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Yes, at least for the most part.

IF you assume that you can move enough fluid, then you can look at it another way. (This is relevant in 17mm vs. 19mm master cylinder discussions.) By changing the size of the master cylinder, you are changing the "advantage" between your foot and the brake pad. You can think of it as changing the length of a lever between your foot and the pad.

A larger-diameter M/C is like a SHORTER lever. You have to press harder to get the same amount of force on the brake pads. But with a shorter lever, you do not have to push as far.

The math works out that the you have to press about 25% harder on the 19mm M/C than on the 17mm one to get the same clamping force at the brake pads. (Assuming the same brake calipers in both cases.) Some people don't think this is any concern. The extra effort required plus the 25% shorter travel makes the pedal feel "harder" to many people.

To carry the lever analogy further, the M/C size is like the length of the lever between your foot and the fulcrum. The total area of all of the caliper pistons is like the length of the lever bewteen the fulcrum and the brake pads. It makes sense that you'd need more lever length between your foot and the fulcrum IF you had increased the length between the fulcrum and the pads.

--DD

John Rogers · 05-10-2000, 01:41 PM

As posted earlier, I have (like MikeZ) put BMW320i calipers front/rear, much larger than stock. What I need to know is: are the mounting flanges for the bolts the same place and spread, is there one or two fluid feed lines and one or two high pressure outlet line. I don't care about the pressure switch as it is disconnected on the race car.

oredith · 05-10-2000, 04:59 PM

hey John,
not sure if you are an active "lurker" on the rennlist, but Sam's (turbo 2.0) looking into putting Volvo front calipers in the front. from Mike Mueller's guess, it's 40% bigger than the 320i's, and it's 4 piston.. he's got me interested.. can't wait to see how it turns out..

Jeff

John Rogers · 05-10-2000, 09:00 PM

I would not go any bigger with calipers unless there would be thicker i.e. vented rotors since the gasses and heat produced by the bigger pads would probably warp the rotors pretty quick. This is from the experts at CNC brakes in San Diego. I have found that a bus 1968-1970 master cylinder has dual inlets, dual outlets, 22mm bore and close to the same stroke front/rear the 914 master cylinder has?

[This message has been edited by john rogers (edited 05-10-2000).]

TDI Driver · 07-21-2000, 09:29 PM

I was told a few years ago that a 23mm master cylinder from a Mercedes fits but I've lost track of the guy so can't confirm nor deny this.

John Rogers · 07-22-2000, 07:56 AM

the 23mm master cylinder is in fact from a Mercedes and I bought one through RennSport Systems and it forced the replacement of the steering rack support with an alloy one but it sure works great.

Scat(\/)an · 07-27-2000, 10:28 PM

I don't know which Volvo calipers he plans on using - only 4-piston units I've seen had 3 bleeder screws. The front and rear pistons are on a seperate circuit of the MC IIRC. It'd be interesting to see how he runs the brake lines.

Just out of curiosity, has anybody thought about using calipers and rotors off a Toyota 4x4? Massive 4-piston calipers, 12 inch rotors, fairly large pads (~4.5x2.5"), relatively inexpensive. Downside? You would have to figure out a way to attach the rotor to the spindle and a way to mount some wheel studs - plus the calipers are pretty heavy.

turbo2.0 · 11:09 AM

The Volvo calipers are off a 244 DL. The Volvo does use two seperate hydraulic lines, just in case one fails (safety feature designed to sell cars, not stop them). There is no reason the two can't be tied together with a tee and run off of the stock line.
The calipers sit too far from the center of the rotor to suit me, so I am in the process of engineering the changes. I plan to slot the holes, then fill them with inserts to keep them where they are supposed to be after the move closer to the center. I hope to be done with them in a couple weeks, so i will post the results.