67 Master Cyl power vs. non-power differences

[Brandon K.]

Hi. I am trying to troubleshoot a brake problem I am having on my power brake 67 that is a fresh restoration. Can someone please tell me whether the power brake cylinder is the deeper or shallower recess on the plunger?

Thanks in advance!

Brandon

[Joe R.]

Re: 67 Master Cyl power vs. non-power differences

Hi Brandon:

I believe that for 1967, both the power brake and non-power brake configurations used the exact same master cylinder assembly. I think the piston used in that master cylinder is referred to as a "deep" pushrod piston.

As I recall, John Hinckley has commented on this in the past, so if he does not respond to your post, you may be able to find his previous posts in the archives.

[Brandon K.]

Re: 67 Master Cyl power vs. non-power differences

Hi Joe,

thanks for your response. I'm trying to figure out why I'm not getting full pedal travel and was wondering if I have the wrong cylinder configuration (perhaps the plunger recess is too deep), but I guess not, if they're both the same....

Or maybe the wrong plunger on the front of booster??

Brandon

[Joe L.]

Re: 67 Master Cyl power vs. non-power differences

Hi Joe,

thanks for your response. I'm trying to figure out why I'm not getting full pedal travel and was wondering if I have the wrong cylinder configuration (perhaps the plunger recess is too deep), but I guess not, if they're both the same....

Or maybe the wrong plunger on the front of booster??

Brandon

Brandon-----


1967 used exactly the same master cylinder for both standard brakes as well as J-50 power brakes. They have a 1" bore size and use a "deep bore" primary piston. The primary piston pushrod bore is 1.6" deep. These master cylinders were defined by the "DC" broadcast code. However, it is very possible for a "DC" coded master cylinder which has been subsequently rebuilt to have incorrect internal parts, including but not limited to the primary piston.

1967 with J-56 power brakes used a different master cylinder. This master cylinder used a 1-1/8" bore. It was coded "PG". This exact same master cylinder was also used for 1968-69 (and later) Corvettes with either J-50 or J-56 power brakes. For 1967, though, its use was limited to just J-56 applications.

[Brandon K.]

Re: 67 Master Cyl power vs. non-power differences

Hi Joe,

Thanks for this valuable information. Mine is an original "509" cylinder with the DC code. Seeing that White Post (who sleeved and rebuilt the cylinder) has had some complaints, perhaps it was rebuilt with an incorrect piston....

I had the brake booster rebuilt many years ago by the ASL company in Sparks, NV, who shortly thereafter disappeared. I am wondering if the pushrod in the front of the booster might be the culprit, or at least part of the issue. Do you have any specs on how long that pushrod should be?

You guys are very much appreciated for your help!

Brandon

[Brandon K.]

Re: 67 Master Cyl power vs. non-power differences

Joe,

I reread your response, and was hoping you can clarify a minor point for me. You said the primary piston pushrod bore depth is 1.6 inches on the DC cylinder. Is this measured from the rearmost part of the cylinder to the bottom of the pushrod recess?

Thanks again!
Brandon

[Joe R.]

Re: 67 Master Cyl power vs. non-power differences

Hi Brandon:

Attached are three photos that I took of an unrestored 1967 power brake booster.

I can not confirm that these dimensions are correct because I have not yet installed the rebuilt booster on my car. However, I am quite certain that this is a 1967 booster because it has the 5867 part number stamping and when I bought it, it had a correct 1967 DC coded master cylinder attached. The whole assembly looked like an unrestored original.

I have an unrestored DC coded master cylinder on the shelf, and the depth of the pushrod hole measures 1.61 inches from the back face of the piston.

When I had my 1967 MC rebuilt by White Post, I found that the push rod hole in the piston they used was just slightly deeper than the original, or at least it appeared that way. I had to adjust the push rod at the brake pedal to take out some excess free play.

Please keep me informed about your findings on this, because some time soon I plan to install the rebuilt booster I have, and I would like the process to go smoothly.

[R N.]

Re: 67 Master Cyl power vs. non-power differences

Seeing that White Post (who sleeved and rebuilt the cylinder) has had some complaints, perhaps it was rebuilt with an incorrect piston....

Brandon

I was going to send a 509 M/C to White Post for rebuilding, but now I would like to ask for someone to recommend other companies who do good rebuild/restore work on M/C. - Thanks.

[Jeff A.]

Re: 67 Master Cyl power vs. non-power differences

Based on what I saw when I was visiting yesterday - IMO, you have one of two possible problems...

1) Your Master Cylinder has failed, and is experiencing a "blow by" of the main cylinder seal.
or
2) Your master cylinder is working properly, but your booster has the shorter push rod installed, so as to not actuate the Master.

We will inspect it further, when you get your car down to Ft. Lauderdale next week.
Based on the feel of the pedal - I really believe the problem is #2 - very easy to fix.