# 67 GTO 4 wheel Disc Brakes



## novafreak69 (Dec 16, 2012)

I have recently installed rear disc brakes on a 67 GTO that had already had a front disc conversion installed. Both front and rear kits are SSBC. The car puls 19" of vacuum. The entire system has been bled (many times to make sure no air was in the lines or master cylinder) fronts have 1200 psi and rears have 700 psi at the calipers. it has an 11" booster.. and the pedal does not move but 3 - 4 inches before it is solid... car does stop decent.. but the brakes will not lock up at a panic stop. The rear brakes do not seem to hold much back with the car in the air and giving it gas. I have replaced the Master cylinder with a factory replacement for front power disc brakes. Just does not seem to stop as well as it should.... Am I missing something??? ANY help would be appreciated.


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## 05GTO (Oct 6, 2004)

Did you change the original drum/disc prop valve to a disc/disc prop valve?

Here are several on ebay;

Disc Disc Proportioning Valve: Parts & Accessories | eBay


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## ALKYGTO (Mar 29, 2010)

novafreak69 said:


> I have replaced the Master cylinder with a factory replacement for *front power disc brakes*.


You need a MC for 4 wheel disc, not disc drum. You have pressure but not enough volume. I have a manual 4 wheel disc setup on my car and originally I use MC for a 68 Corvette w/manual 4 wheel disc. It worked very well. I would recommend changing to the correct type MC, the chambers will be of equal size, not a larger front smaller rear.

If you are not concerned with a "stock" look there are several nice units out there to choose from, I have a Wilwood MC now and it is very nice looking and rebuildable.


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## novafreak69 (Dec 16, 2012)

The MC that was on the car was from SSBC and was supposed to support 4 wheel disc. the chambers were of equal size... I have recently bench bled that MC finding A LOT of air in it. I will be replacing it back on the car this evening. 

Should the car lock the tires during a panic stop?


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## the65gto (Oct 9, 2008)

I would chat with SSBC and ask for their assistance/opinion.


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## novafreak69 (Dec 16, 2012)

I have spoken with SSBC and done all of the testing and checks that they asked me too... which was a LOT of time wasted... They say that the pressures are correct and that nothing is wrong.... well when I cannot get the brakes to lock up during a panic stop... something is wrong...


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## geeteeohguy (Feb 2, 2008)

My stock manual drum brakes lock up in a panic stop, easily. What Alky said. You do not have enough line pressure due to low fluid volume being stroked at the master. While disc brakes are superior to drum brakes, as a technician, I have found that rear disc brakes on a street driven car are very over-rated and the perceived performance gain is minimal. You end up with more pedal travel, a softer pedal feel, and an inferior emergency brake. For the road race course, rear discs are the way to go.


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## SANDU002 (Oct 13, 2004)

I'm sure this will help, but did you replace brakes lines? When I did my SSBC kit, I put in all new stainless brake lines.


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## Bensjammin66 (May 12, 2009)

I had the same issue and I used a corvette master like said above for disc/disc, still wouldnt feel as tight as they should. My booster leaked, replaced it and now they are super responsive and tight. Even better than my '01 F150s brakes. Just a thought.


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## novafreak69 (Dec 16, 2012)

I am unable to find a MC for a 4 wheel Disc for a 68 Corvette... They only stipulate front disc manual or power... can either of you guys give me a part number or any specs off of yours so that I may purchase the proper one?


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## novafreak69 (Dec 16, 2012)

ALKYGTO said:


> You need a MC for 4 wheel disc, not disc drum. You have pressure but not enough volume. I have a manual 4 wheel disc setup on my car and originally I use MC for a 68 Corvette w/manual 4 wheel disc. It worked very well. I would recommend changing to the correct type MC, the chambers will be of equal size, not a larger front smaller rear.
> 
> If you are not concerned with a "stock" look there are several nice units out there to choose from, I have a Wilwood MC now and it is very nice looking and rebuildable.



Is there a difference in the manual vs the power MC other than the manual has a 1" bore and the power has a 1.25" bore?

This car does have a power booster on it.... parts store has one for a 68 vette... but it only specifies front disc power or manual...


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## ALKYGTO (Mar 29, 2010)

I don't believe the 68 vette was even available with drum brakes, I think 4 wheel disc were standard.

I would go to an O'rielly's or NAPA for parts, stay away from Advanced and the Zone.


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## novafreak69 (Dec 16, 2012)

I think I am going to get the Right Stuff booster and master cylinder... I have heard good things on here about them...

http://www.getdiscbrakes.com/g91210572


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## ALKYGTO (Mar 29, 2010)

novafreak69 said:


> I think I am going to get the Right Stuff booster and master cylinder... I have heard good things on here about them...
> 
> G91210572


That link is for a Disc-Drum setup.......:rolleyes2:.......

Seriously, you should have no problem going to a local auto parts store and getting what you need. The bad thing about ordering everything online is if it is wrong or not what you need or bad you have to ship it back and wait and deal with all the associated hassles. :banghead:

Napa should have what you need. :cheers


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## novafreak69 (Dec 16, 2012)

I saw that that said disc/drum... but it is what is in their 4-wheel disc conversion kit...

AFXDC41C

I installed a NEW MC for a 68 Vette power brakes... 1.125" bore... and it changed nothing... I guess time to replace lines... only thing that is not new on the car...


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