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Topic: Master Cylinder for a 1968 ????

in Forum: C3 Handling Components

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Master Cylinder for a 1968 ???? (1/9)
4/12/17 5:02pm

rlu1968
Former Member
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427

Joined: 11/28/2003
Posts: 228

I have a 1968 with disc brakes and relative new calipers.

This is probably the fifth master cylinder I have put on this car in 10 years. I am wanting a stronger brake. It seems as each time I replace the MC the brakes are fine and have good stopping power for a few months and gradually return to a spongy pedal and the brakes won't stop as well. I am stopping a 427 hp. Actually 467 dyno hp

I have done all the proper bleeding etc.

I recently was told by a hot rod mechanic shop that they will use a 7/8 bore rather than a 1" bore on the MC to get better stopping power on their hot rods.

I thought about going with a booster brake, but they said I only have 6" of vacuum because of the Cam. They also said to covert over to the DOT 5, with less chance of moisture.

Does all this make sense? Is there another way to go for lasting brakes.

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Re: Master Cylinder for a 1968 ???? (2/9)
4/12/17 8:08pm

manchestershark

Lifetime Member
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Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.

Joined: 10/31/2007
Posts: 2385

The possibility exists that one or more calipers are sucking air and creating the soft pedal. Lip seals in the caliper act like diodes, and allow air to enter, but not leak air OR brake fluid. I have heard that the 1 inch bore is for power brakes, and the 7/8 is for manuel brakes.

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Re: Master Cylinder for a 1968 ???? (3/9)
4/12/17 9:23pm

rlu1968
Former Member
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427

Joined: 11/28/2003
Posts: 228

When you go to Napa, and the general auto stores and ask for a master cylinder for a 68 corvette they give you a one inch bore. That is what I have gotten in the past until I talked to the hot rod shop, I never knew their was another size.

The calipers I have purchased probably from Zip, Corvette Central, etc. were the ones for cars that set up for long periods and not driven daily. So they were mfg a little different and should not fail in that of time. How do you test the calipers for air leaks?

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Re: Master Cylinder for a 1968 ???? (4/9)
4/13/17 8:26am

manchestershark

So...are they power or Manuel. Are the calipers ss sleeves with "O" rings.

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Re: Master Cylinder for a 1968 ???? (5/9)
4/13/17 8:26am

manchestershark

So...are they power or Manuel. Are the calipers ss sleeves with "O" rings.

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Re: Master Cylinder for a 1968 ???? (6/9)
4/13/17 10:21am

rlu1968
Former Member
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427

Joined: 11/28/2003
Posts: 228

It is manual brakes with stainless steel sleeves. All calipers are less than ten years old. Purchased the ones that were for a car that was not driven often. I think this has something to do with the o-rings. That they won't dry out or rot sitting for long periods.

I am going to have the hot rod shop to convert all of the fluid over to DOT 5.

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Re: Master Cylinder for a 1968 ???? (7/9)
4/13/17 1:15pm

rlu1968
Former Member
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427

Joined: 11/28/2003
Posts: 228

All of these calipers on my 1968 are "NOT" the lip seal caliper that originally were installed in 65-82 corvettes.

They have all been updated to the calipers that are for corvettes that are stored for a long period before usage. So they might not suck air as the lip seals did.

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Re: Master Cylinder for a 1968 ???? (8/9)
4/13/17 1:17pm

knotacare
Former Member
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Newark, DE - USA

Vette(s):
1968 Conv, 454HO,500HP-600TQ, TKO-600,3:70 HD rear,hotrod air, custom paint & suspension,1973 Ruby Red,T-top, 383 Stroker, TK)-500,frame off restro, 1967 Dodge Coronet, 340 stroker to 406, Dana 60

Joined: 7/26/2004
Posts: 463

Check the runout on all 4 rotors, if it's more than .005 you will have to put the rotor in a different location & or have them turned. Once you get the runout as low as possible mark each rotor so it goes on the same if you have to remove it. Excessive runout will cause the pistons to move in & out & will suck in air over time causing a spongy pedal. These are not the easiest breaks to get right.

Alan

Almost forgot make sure your frt bearings are not to loose or for that matter your rear bearings too

|UPDATED|4/13/2017 10:17:16 AM (AZT)|/UPDATED|

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Re: Master Cylinder for a 1968 ???? (9/9)
4/13/17 9:49pm

rlu1968
Former Member
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427

Joined: 11/28/2003
Posts: 228

Looks like some very good info. I will forward it to the hot rod shop that I am going to have work on my car.

I know i have new bearings on the front. And new non lip seal calipers.

Over the years I have depended on web sites like this one to help along with trial and error on myself repairing items. I have kept a list on everything I have purchased and fixed on this car since 1989 and have had several different shops to fix the many problems that a older corvette has.

Many fly by night and some pretty good shops.

However do to age and physical ability I have since decided to allow only those shops who have shown good reviews from other corvette friends to work on my corvette. I will continue to closely oversee any thing done and I will continue to speak to people like yourself in the know to help me keep those shop in line on what needs to be done.

Thank you

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