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Master cylinder bore size question
Posted: Thu Aug 30, 2018 10:41 pm
by 69ss
Hello, I have a 69 Chevelle with the stock power disc/drum system. Stock uses an 1-1/8 bore master cylinder, I had a brand new Wilwood master cylinder given to me but has a 1inch bore. What kind of difference in pedal feel do you think the smaller bore would make if I were to go with the Wilwood master cylinder? Thanks for any input!
Re: Master cylinder bore size question
Posted: Fri Aug 31, 2018 8:01 am
by John Wallace
The Wilwood would give higher pressure if no other changes.
But will the smaller volume of brake fluid be enough to activate the brakes?
(disk brakes or drum?)
Re: Master cylinder bore size question
Posted: Fri Aug 31, 2018 8:37 am
by 69ss
disc front, drum rear, power brakes
Re: Master cylinder bore size question
Posted: Fri Aug 31, 2018 11:57 am
by John Wallace
Your master cylinder now isn't a dual chamber one?
(would have 2 different sizes for front and back)
Re: Master cylinder bore size question
Posted: Fri Aug 31, 2018 12:06 pm
by 69ss
Yes, it's a dual chamber. The whole sysrem is the factory 69 Chevelle power front disc/rear drum system
Re: Master cylinder bore size question
Posted: Sun Sep 02, 2018 7:05 pm
by MadBill
69ss wrote: ↑Thu Aug 30, 2018 10:41 pm
Hello, I have a 69 Chevelle with the stock power disc/drum system. Stock uses an 1-1/8 bore master cylinder, I had a brand new Wilwood master cylinder given to me but has a 1inch bore. What kind of difference in pedal feel do you think the smaller bore would make if I were to go with the Wilwood master cylinder? Thanks for any input!
The pedal pressure for a given decel rate will go down by ~ 12% and the pedal travel will increase in the same proportion.
Re: Master cylinder bore size question
Posted: Sun Sep 02, 2018 10:17 pm
by rustbucket79
Running a 7/8 bore Wilwod master on my 79 Camaro factory disk/drum setup. Pressure isn't a problem, volume is. You need to pump the brakes once to push out the rear shoes, then the second pump you are good to go up to 1200 psi. Going to rear disk for next season, hoping to eliminate that first pump.
Re: Master cylinder bore size question
Posted: Sun Sep 02, 2018 10:19 pm
by rustbucket79
Pedal effort is greatly reduced. Haven't run the car for a few years, but I believe effort is similar to power brakes with great vacuum.
Re: Master cylinder bore size question
Posted: Sun Sep 02, 2018 11:58 pm
by MadBill
MadBill wrote: ↑Sun Sep 02, 2018 7:05 pm
69ss wrote: ↑Thu Aug 30, 2018 10:41 pm
Hello, I have a 69 Chevelle with the stock power disc/drum system. Stock uses an 1-1/8 bore master cylinder, I had a brand new Wilwood master cylinder given to me but has a 1inch bore. What kind of difference in pedal feel do you think the smaller bore would make if I were to go with the Wilwood master cylinder? Thanks for any input!
The pedal pressure for a given decel rate will go down by ~ 12% and the pedal travel will increase in the same proportion.
Err... make that ~27%
Re: Master cylinder bore size question
Posted: Mon Sep 03, 2018 9:24 pm
by pdq67
I have a really old mag with an article in the very back of it that David Freiburger wrote. He put a 1.25" piston dia. M/C on a Chevelle that had been converted both front and rear to disc brakes. He said it worked great. I figure it was a volume thing...
pdq67