Author Topic: 69 Master cylinder bore size? (Read 11080 times)

69 DIRTY RAT · « **on:** November 09, 2007, 06:55:00 PM »

Any knowledgable brake guys out there?

I need to know what size the bore is on a standard master cylinder on my 69? And what size bore is on a C6 master cylinder?

Basically I need a new/aftermarket master cylinder because now that I have C6 calipers on the front rotors the pedal is going almost to the floor! I need to work out what size master cylinder/bore I need to bring the pedal back to normal? ;42

70vette · « **Reply #1 on:** November 09, 2007, 07:54:54 PM »

Check this link out . It may answer some questions.

http://temp.corvetteforum.net/c3/70lt1/brakes.shtml

77CVT · « **Reply #2 on:** November 12, 2007, 12:10:14 PM »

I thought it was 1 inch. I will try and find some info I had on brake pressure and m/cyl sizing.

;42

77CVT · « **Reply #3 on:** November 12, 2007, 01:10:07 PM »

Here is a good site - http://sports.racer.net/brake_bias.htm

It has a spreadsheet for calculating brake bias as well.

"The size of the master cylinders' piston has a direct result on brake fluid pressure. However, it may not work like you would think... higher line pressure will build up on a smaller master cylinder piston to react the force applied by the pedal. A smaller master cylinder will create more brake fluid pressure but will also increase brake pedal travel. The smaller diameter cylinder requires a longer stroke to move the volume of fluid necessary to move the caliper pistons during braking.

Larger master cylinders will create less pressure but will require less travel."

Hopper Stoppers has some good info too - Here

Popular Hot Rodding - Info

Are your rears Wilwood Dynalites? If so they are the same piston diameter as the stock C3 rear calipers (1.75in - I have these at home). How big are the C6 bores?

Stock C3 caliper piston sizes are:
Front - 1.875in / 47.625mm (5.8929 sq in/149.679 sq mm)
Rear - 1.75in / 44.45mm (5.50 sq in/139.70 sq mm)

Front/rear difference = 1.0714 to 1 or the rears are 93.33% of the fronts

I imagine if the % is more than this then you would need a porportioning valve.

I see you are getting some good info from the CF.

;42

69 DIRTY RAT · « **Reply #4 on:** November 12, 2007, 09:48:53 PM »

Thanks 77CVT!

77CVT · « **Reply #5 on:** November 13, 2007, 12:44:20 PM »

How did you get the Wilwoods to fit on the back? (are they Dynalite's?)

I have drawings to make a bracket for the front calipers but not to fit the back.

69 DIRTY RAT · « **Reply #6 on:** November 13, 2007, 11:25:25 PM »

Got them from http://www.hotrodsusa.com/ they make sets up for C3's. They are dynalites! I should have traced the brakets before puttin them on!

69 DIRTY RAT · « **Reply #7 on:** November 14, 2007, 02:35:24 PM »

FIXED!
I havent driven it yet,and you probably wont believe me but once the proportion valve went in the problem was fixed!
It was just getting to much fluid/pressure to the back causing it to lock up. Once the pressure from the back was eas'd more fluid went to the front and now works perfect (apparently)!

77CVT · « **Reply #8 on:** November 14, 2007, 03:30:13 PM »

What piston size do the C6 calipers have? They were probably near the same as the C3's.

Good to hear it is sorted. Did you get the adjustable one so you can spare the rear brakes for the burnouts? ;46

69 DIRTY RAT · « **Reply #9 on:** November 14, 2007, 10:35:15 PM »

Not sure the C6 bore size....I think it was in all that info you gave me somewhere?
Yes I put the bias valve in so I can now wined the bias to the front and do somemore burnouts without hurting the brakes to much...although I think I'll get a line locker at some stage.