Brake experts....Need help!
Thread Starter
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
Brake experts....Need help!
Just installed a new Wilwood brake system (calipers, pads, rotors, master cyl.,braided hoses) on my '69. Everything seems to be installed perfectly. Bench bled master cyl. and bled system w/ Power bleeder 3 times. Not an air bubble to be found. When I start it up and press the pedal, it goes to the floor! (I have power brakes). I tested the master cyl. alone, plugged, pushing manually and it will hold hard pedal OK; I attached the front line only, leaving the rear plugged; pushing manually it works OK, but with engine running and booster assisting, the pedal goes straight to the floor!......the same thing happened testing the rear line. I pumped the Pressure Bleeder up to 25 lbs.; no leaks anywhere in the system. Possible bad booster?.....unknown trapped air?....booster worked OK before.......?????
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
What about the rod for the master cylinder? If the internal hole in the new master cylinder is deeper then the stock master the plunger in the power assist will not push on the new master cylinder. I had this exact problem and it was the rod.
Instructor
Joined: May 2003
Posts: 220
Likes: 0
From: Hilton Va
This will be interesting for me. I have done the same thing and I have done everything to get brakes on my 69. I have suspected the rod, but I have ajusted and adjusted it but to no avail. Everything new(twice) everyway to bleed (more than I care to count). Good luck to you C3, hope you can help us both. Please keep us posted. 
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
It's a little late now but you need to compare the back of both master cylinders. Look at the stock master then compare the indent in the new master to compare the depth of the hole in the back piston. If the rod is too short you can push all you want and the piston will never be touched by the rod.
Thread Starter
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
Originally Posted by norvalwilhelm
What about the rod for the master cylinder? If the internal hole in the new master cylinder is deeper then the stock master the plunger in the power assist will not push on the new master cylinder. I had this exact problem and it was the rod.
C6 the C5 of tomorrow
Joined: Nov 2000
Posts: 6,665
Likes: 2
From: Twin Cities Minnesota
What size master do you have?
Which calipers do you have?
You should be using the 1 1/8" bore master clyinder if you are using large piston calipers and a power booster.
Did you convert from Manual? If so your pedal ratio will be too high. You need to switch the push rod to the lower hole, the one the brake light switch is on now. Then of course you need a new brake switch bracket.
Which calipers do you have?
You should be using the 1 1/8" bore master clyinder if you are using large piston calipers and a power booster.
Did you convert from Manual? If so your pedal ratio will be too high. You need to switch the push rod to the lower hole, the one the brake light switch is on now. Then of course you need a new brake switch bracket.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
If the bore size is wrong you still get brakes, just too much pedal travel but you still get brakes. Same with using the wrong hole. Brakes work but you might run into the floor.
If the brakes feel like there is absolutely nothing there I would still suspect the rod. I chased this around for a few nights until I found the rod wasn't contacting the master cylinder piston.
If the brakes feel like there is absolutely nothing there I would still suspect the rod. I chased this around for a few nights until I found the rod wasn't contacting the master cylinder piston.
Thread Starter
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
Originally Posted by norvalwilhelm
If the bore size is wrong you still get brakes, just too much pedal travel but you still get brakes. Same with using the wrong hole. Brakes work but you might run into the floor.
If the brakes feel like there is absolutely nothing there I would still suspect the rod. I chased this around for a few nights until I found the rod wasn't contacting the master cylinder piston.
If the brakes feel like there is absolutely nothing there I would still suspect the rod. I chased this around for a few nights until I found the rod wasn't contacting the master cylinder piston.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Instructor
Joined: May 2003
Posts: 220
Likes: 0
From: Hilton Va
Originally Posted by norvalwilhelm
If the bore size is wrong you still get brakes, just too much pedal travel but you still get brakes. Same with using the wrong hole. Brakes work but you might run into the floor.
If the brakes feel like there is absolutely nothing there I would still suspect the rod. I chased this around for a few nights until I found the rod wasn't contacting the master cylinder piston.
If the brakes feel like there is absolutely nothing there I would still suspect the rod. I chased this around for a few nights until I found the rod wasn't contacting the master cylinder piston.
norval, I have the VBP o-ring calipers. Would it be alright to use the 1 1/8 master cylinder with these?? I looked a 69 up on VBP web site and they list a 1" for 67-76 and 1 1/8 for 77-82.