BIG Brakes

[TimT]

I'm going to put a SBC big brake kit on the wagon. I found out that a mid 90's midsized GM (like an Olds Cutlass) has a bigger piston on the master cylinder. (stock S has a 7/8 this one has a 1") Went to a junk yard and pulled one it bolts right up to a S brake booster and it has 4 ports on the correct side. I figure this is a direct bolt on. So my question is do you guys think it would be alright if I put the bigger master cylinder on FIRST and test it out for awhile to see if its an actual bolt on. Do you think I'll blow out all the seals on a stock S (has rear disc conversion) What I don't want to happen is put the SBC kit on and get a soft pedal and have to take it off. Right Billy? Oh yea I found a 2 port master cylinder that will work with you guys who have those.

Tim

[SupraCharged007]

heres the thing, the bigger the master cylinder, the less pressure output per given pressure input. for example.


say you put 100#s of force onto the master cylinder. If its a 7/8" mc, it will put out about 60 psi

7/8 = .875(Diameter)
.875/2 = .4375(Radius)
PI*R^2 = .60(Surface Area)

F=A*P(Force = Area * Pressure)

sub in your force and area.

100 = .60 * P
solve for pressure = ~166psi

now same thing with a 1" mc
1.0(Diameter)
.5(Radius)
.785(Surface Area)

again solve for pressure = ~127psi

so by increasing mc size 1/8" you lost nearly 40psi at an input force of 100

but, since its gonna push more fluid due to its larger surface area, the pedal will be more firm, but you will have to push harder on the pedal to achieve the same stopping force assuming that nothing else changes except for master cylinder bore size. Something like that [img]{SMILIES_PATH}/wink.gif[/img]

[TimT]

OK what about the stroke? And if I panic stop will the volume blow out the seals? Did Tyrone get his on? I know he got the rears on, Maybe he can be the guienne pig.

Tim

[SupraCharged007]

naw, we were gonna do it sunday but something came up. And he has to go to a baby shower hehehe

as far as the stroke ...... It should be negelctable. The master cylinder is only going to move as far as you push it. And since no changes are being made to the brake pedal, the stroke should remain the same.

Even if the piston is smaller or larger than the piston in the stock mc, the actual MOVEMENT of itshould remain constant due to the above.

as far as the seals ...... I can't see it happening. The brake system is designed to take very high pressures. And like i said before, by upping the size of the master cylinder without any other changes, you are actually dropping the overall pressure the system puts out.

[TimT]

HEH HEH when are you good to come over and help me bleed brakes??

Tim

[ProDarwin]

What calipers are used on the big brake kit?

[SupraCharged007]

the kit in question in the SSBC kit.

SSBC uses a modified 2nd gen Camaro caliper. Its aluminum and is a 2-piston design

The rear is a modified thunderbird real caliper. Its aluminum as well and I believe its the one from the turbocoupe.


and Tim ..... next weekend Tyrone and I are supposed to be doing the swap

[TimT]

Crap next week end I'll be camping in Tickfaw.

Tim

[ProDarwin]

Well, since it does use different calipers... which will require more fluid volume movement, you would benefit from a larger brake booster. Pressure isn't everything you know. In order to get the same travel with larger calipers (assuming they have larger/more pistons), you're gonna need more master cylinder travel if you stick with the stocker. Plus, you've got vacuum to help you generate the pressure/force.

[TimT]

Well looking at the boosters (in the junk yard) They looked about the same size. Now the master cylinders also look about the same size and I suspect are the same casting. (they have the same casting id marks on them in the same place) They also use the same fittings. But the piston is a differant size. I figure its a volume issue.
Link for the donor master cylinder.
http://www.mvreader.com/multiview/bendi ... mId=00YZZM
Link for the stock S master cylinder
http://www.mvreader.com/multiview/bendi ... mId=00ZQGG

The reservoir is also bigger on the donor and has some sort of sensor. I've been searching for even a bigger one that might work but no luck so far.

[S.Bretz]

Why? You want biger pistons in the calipers, not the master.

[TimT]

You want both. The volume of fluid it takes to move the calipers is more then the stock master cylinder can push.

Tim

[S.Bretz]

I dought it. A caliper squeezes like 1/64 of an inche...if that.

[TytaniumSc2]

yea that is true but u need more force to move the caliper pistons since u are increasing the number of pistons and the overall size of the caliper. i now have nore fluid to move and the master cylinder wasnt designed for dual or quad pistons it was made 4 singles, so it has a little problemm keeping up with the extra demand...

[TytaniumSc2]

why yall wana make me the guienne pig?! its cool though