found an inexpensive hydraulic brake on ebay so I thought I'd finally get one.

come with 3 options for a master cylinder: 0.75/0.70/ 0.625

which do I get? thx.

I purchased the .625 for my mk2 golf with brakes from a 98 jetta. it worked well but it was tough to use it for parking.

Get a .625.

I used a .7 because it was really, really cheap, and I figured that if it didn't work, it could be the front master in a dual setup. It works, kinda, with a 11:1 lever ratio, but a .625 would be much nicer.

Quote
Pete
Get a .625.

I used a .7 because it was really, really cheap, and I figured that if it didn't work, it could be the front master in a dual setup. It works, kinda, with a 11:1 lever ratio, but a .625 would be much nicer.

Yea go with the 5/8's master. That way it will lock up anything with any tire at any speed with any kind of pads.

Another vote for the 0.625, its what I've got on the BMW and a good quick jab on the handle gets all the lockup you'll need.

Dave

done. thanks for the input.


Another conundrum solved by the RallyAnarchy think tank!

0.625

Lever ratio should be large; 11:1 is OK but could be more. If you like, I can measure 1 or 2 here.

Lever length should be long, like 12" or more.....

Mark B.

Quote
starion887
0.625

Lever ratio should be large; 11:1 is OK but could be more. If you like, I can measure 1 or 2 here.

Lever length should be long, like 12" or more.....

Mark B.

Meaning the (vertical) lever if built to this spec would have hypothetically the clevis pin 1" above the pivot point at the base. with the lever extending 11" above the clevis point? Do i understand that correctly?

11:1 is large? Hmm. I tried finding info online and didn't see anything but pictures so I backtracked from that to about a 9:1 ratio, which sucked, so I moved the pushrod as low as I could without re-engineering everything.

Good to know that I'm not too terribly far off, though. In a RWD with crap stock calipers, it can lock the brakes on dirt or gravel at any speed. On pavement, one must have the brakes applied first or otherwise already have the car partially upset.

The lever is huge, big L shaped thing that sticks up over the shifter.

Quote
Pete
11:1 is large? Hmm...

Thats what she said.

Ok the 5/8's master with an 9:1 lever makes about 650 ft/lbs of brake torque with medium friction brake pads, at only 25lbs of arm force, which is pretty light. If its 11:1 then it goes up to 780ft/lbs torque. Both of which is more than enough to lock up slicks on pavement.

the lever I'm looking at is long....more than 11", but I don't want a long throw either, so .625 it is.

remember, bigger master, more volume, shorter throw, higher lever effort.

I have the CNC staging brake, and i swear the handle is 24" or so. It would not lockup the rears on tarmac without upsetting the car first with my old small crappy disc calipers. Works better now with bigger calipers.

Yah, I've got the weenie stock 1 3/8" bore calipers on 10" rotors in the rear.

Reducing travel required is really down to making a mount that will not flex no matter what. I need about a 50lb pull (estimated - used a torque wrench and a little math) to lock the rears on pavement. 50 times 11 is 550lb of force fucking with the pivot and master cylinder mount.

Quote
phlat65
remember, bigger master, more volume, shorter throw, higher lever effort.

I have the CNC staging brake, and i swear the handle is 24" or so. It would not lockup the rears on tarmac without upsetting the car first with my old small crappy disc calipers. Works better now with bigger calipers.

that comes with a .75" master? What's your approx. throw with that? The brake I'm looking at is just under 24", so I'll have some leverage on it.

Quote
Pete
11:1 is large? Hmm. I tried finding info online and didn't see anything but pictures so I backtracked from that to about a 9:1 ratio, which sucked, so I moved the pushrod as low as I could without re-engineering everything.

Good to know that I'm not too terribly far off, though. In a RWD with crap stock calipers, it can lock the brakes on dirt or gravel at any speed. On pavement, one must have the brakes applied first or otherwise already have the car partially upset.

The lever is huge, big L shaped thing that sticks up over the shifter.

Hmmmmm....reading comprehension needs some work there, Pete> I said 11:1 is OK but could be bigger.

Starion system measurements:
Lever is 13" long.
Motion ratio is approx 16:1 ; 6" of handle throw (a pretty hard pull) results in 3/8" cylinder motion. EDIT: The 3/8" is total rod motion; some of that goes into taking up slack.


Too chilly to go and measure the other system.

Mark B.



Edited 1 time(s). Last edit at 04/01/2011 09:30PM by starion887.