67 master cylinder uniqueness??

[Timothy B.]

According to vendors at the Houston Corvette show this past weekend (you experts can confirm), a uniqueness about the 67 year master cylinders was that only that year the same part number MC was used for both regular manual brakes and for J50 power brakes. J56 heavy duty power brakes used a different part number. In reviewing my AIM, this appears to be the case (but I didn't know it was only 67 like that). Other later years (according to the brake vendors at the show) used a 1 1/8" bore MC for power brakes and a 1" bore for manual brakes. When you go out to buy either a new or rebuilt MC for a 1967, chances are you will be asked if you have manual or power brakes, and get a different part based on the answer. So, that means there are probably many owners of 67's out there with 1 1/8" bore MC's even though all factory units were 1" and vice-versa, and I am one of them!

So, the question to the experts, what is the end effect of having the larger bore unit compared to the smaller bore with power brakes? The engineer in me would lead me to think that with a smaller bore MC, it would be easier (with more stroke) to apply the brakes on a manual brake car. This might lead to grabby brakes when the same MC is mounted on a booster? I'm thinking that using the 1 1/8" bore on a 67 might actually be a good thing since GM switched to that in 68? Comments?

[Wayne W.]

Re: 67 master cylinder uniqueness??

The housing is the same, but the rod depth is different. That is why they ask the question.

[Timothy B.]

Re: 67 master cylinder uniqueness??

So are you saying the AIM for 67 is wrong, and there is a difference in master cyclinders between manual and J50?? My AIM shows the same P/N.

[Wayne W.]

Re: 67 master cylinder uniqueness??

No the AIM is correct. The MCs are the same part. But other years and applications have different rod depts and parts store parts fit multiple applications. So they just ask the question for all of them.

[Frank H.]

Re: 67 master cylinder uniqueness??

The larger bore master cylinder was for the added pressure needed for the semi-metalic pads,so what kind of pads do you use?

[Timothy B.]

Re: 67 master cylinder uniqueness??

I installed organic pads this time around since I hardly drive the car and life isn't an issue. So were semi metallic pads not used originally on 67 Vettes???

[Frank H.]

Re: 67 master cylinder uniqueness??

Yes more or less GM called them cerametalic, in a sence semi-metalic ,they are used on the 67 J-56 brakes,hence the larger 1 1/8" bore master cylinder and booster.
Also Used on the 68-69 Camaro Z-28 H-D brake System.Which don't grab till warmed up.
Which needed a production run of 200 units to qualify as factory part for racing.
My 82 collectors edition had all the same basic setup as the j-56,and was the best stopping C3 corvette I ever had.large bore master ,semi-metalic pads,proportioning valve,P-booster

[Timothy B.]

Re: 67 master cylinder uniqueness??

Thanks for the info Frank. Well, since I believe I have the larger bore MC on my car, with J50 brakes and organic pads, what do you think the effect is compared to having the 1" bore on the same car? Worth switching? I don't plan to show the car. I also have new O-ring calipers if that makes any difference. I have only just got the car drivable again, and so far the brakes seem OK, if maybe a tiny bit mushy, but of course that could be bleeding.

[Michael W.]

Re: 67 master cylinder uniqueness??

A larger bore master cylinder will give LESS pressure output (for a given input), not more.

[John H.]

Re: 67 master cylinder uniqueness??

The "Cerametallix" linings were last used on 64's with J-56 Heavy-Duty Brakes (J-65 Metallic Facings used sintered metallic linings). The production 1969 Camaro JL8 4-wheel disc brake package used Corvette calipers with conventional pad material; "race" pads to fit the calipers were available as an over-the-counter item for the racers.