Brake peddle is darn hard to push....

[Ezheimers]

I'm running four disc brakes taken from a wrecked 1971 Vette on me 1941 Pick-Me-Up
and it takes a manly man to push the standard Master Cylinder, as is...

The brake peddle is firewall mounted with a 5:1 ratio. Existing New Master Cylinder has a 1 1/8 bore, double feeds and I've got to do something...?

My scouring around for information tells me that I should have purchased a new Master Cylinder with a 7/8" bore.....? And that would solve my problem...?

Any advice for this old man...? What have you found...?

Appreciate anything..... -EZ

 

[Ol Blue]

7/8" bore will help, for sure. I have a 7/8" bore with about 5 1/2 to one ratio with a disc/drum set up and the peddle still takes quite a bit of effort.

Blue

 

[von-zipper]

Did you use residual valves?

Zipper

 

[Sam_Fear]

Why not just buy a master cylinder for a 71 Vette? Seems it should match?

BTW, when did a quick search, I came up with the non-power M/C for a 71 Vette as having a 1" bore.

 

[MercuryMac]

opinion

Hi Ezheimers,
I'm running discs / drums on a '55 Merc pick-up with a standard master cylinder. One of my hired men was a mechanic and he laughed at my set up while guessing that I had to push on the brake pedal awfully hard. He was right; not the part about laughing at me, the pedal push part. He said "Get a power booster in there, you don't have to push disc brake pads very far but you've got to push them damn hard." I took his word for it and bought a smallish vacuum booster and master cylinder and kept them hidden under the floor like the standard master cylinder had been. My brakes came alive, once I got everything adjusted right. That was five or six years ago and the brakes are still working very nicely. Vacuum power brakes 'worked for me'.

 

[donsrods]

Discs do take more pedal pressure than drums, and 4 wheel discs are even worse. If you can get a booster in there, as Mac suggests, it will make them work a lot better. They make some really small boosters any more, so you should be able to get one to fit.

Don

 

[Dirtyrat]

Changing the bore as described, or change your ratio...

Your output pressure with a 5:1 ratio and 1 1/8" bore is 75 lb force input yields pressure output of only 377 psi (change to 7/8 will change output pressure to 623psi)

See here for some really good info on pressures and pedal ratios

 

[BigIrish]

I have 4-wheel disks on 2 rods and just use the standard ford-type MC that Speedway sells with thier brake pedal kits. They are like $40 and work great. I think 7/8 bore.

1 1/8th is an awfully big bore for non-power brakes.

 

[RPM]

I would make the pedal longer to change that ratio to about 7:1

 

[Ezheimers]

Fixed me brakes....

Dirty... You were right on. (Others too...!) The formula figures out that what I needed was the 677# with a 7/8 bore.

Put one on today - What a difference. It works GREAT!

Again to all you very knowledgeable hot rodder's... A BIG "Thank YOU" -EZ