Is a 3/4" master cylinder too small for front brakes?

blykins · #1 (**permalink**) 04-11-2005, 01:44 PM

I'm using Wilwood GMIII single pot calipers on the fronts......would a 3/4" cylinder be too small? Should I go with an 1"?

I'm trying to find some small-sized cylinders since I have floor mounted pedals. Looking for a cylinder with the output fitting on the top instead of at the rear of the cylinder.

Hotfingrs · #2 (**permalink**) 04-11-2005, 02:07 PM

Here's what I know about MC sizing... A smaller cylinder will put more pressure on the pads, but increase brake pedal travel. Mine are either 5/8ths or 3/4. The car had a 7/8 and 1 inch on when I bought it.

blykins · #3 (**permalink**) 04-11-2005, 02:14 PM

So you went down from an inch to a 3/4? I think my clutch and rear brake master cylinders are 3/4. I need a front one.

Anyone else?

Hotfingrs · #4 (**permalink**) 04-11-2005, 02:25 PM

Basically yes. There were 2 different sized MC when I bought the car, 7/8 on the front and 1 inch on the rear. I went down in size because I wanted more pressure on the pads...manual brakes, but the pedal travel noticiably increased.

ItBites · #5 (**permalink**) 04-11-2005, 02:39 PM

In the interest of maintaining reasonable pedal force, I use 5/8 bore MCs. Yes the pedal travel is more than I'd prefer, but when I get on the pedal, at least enough pressure is generated to stop the car.

My pedal ratio is about 4:1, so I am disadvantaged in that way.

For 75 lb of pedal force (75 lb is more than you'd think) at a 4:1 ratio, with the balance bar set for 60% front and 40% rear, and using a 5/8 bore in both MCs, I produce about 586 psi front and 391 rear. I'd rather be doing about 750 psi, but for that I have to push harder than 75 lbs.

Just remember, larger bores require higher pedal force to produce the same braking action...

niles · #6 (**permalink**) 04-11-2005, 03:38 PM

Do you have discs on the back?
My friend with vette brakes(no power) had to go to 5/8 frnt MC and 3/4 back MC inorder to get enough pressure to easily lock them without excessive pedal pressure. Standard is a 6/1 pedal ratio; ie, pedal length being 6in to pivot and 1" length to MC rod
gn

blykins · #7 (**permalink**) 04-11-2005, 03:54 PM

I'm using 4 wheel disc brakes.....10" rotors with single pot calipers on the rear, 10" rotors with big single pot calipers on the front.

I'm also using a Tilton floor mounted pedal assembly. It's showing a 4.5:1 ratio.

Michael C Henry · #8 (**permalink**) 04-14-2005, 02:35 PM

I have an older EM with intermediate GM 10.5" front rotors and Jag inboard rears.I'm usind twin 3/4" Tiltons with an adjustable balance bar, no power assist.
Hydralic clutch came with 7/8" Tilton master cylinder .Not enough travel at slave to get full release and have any free travel clearence for the throwout bearing .I changed to 15/16" master cylinder .Takes a little more effort but have both release and free travel. As i remember a master cylinder kit is about $60.any size.