C-5 brake install-GM-abody -newbie question

[Alaska442]

I have ATnS spindles on a 66 olds cutlass and installed a corvette C-5 booster and master cyclander with a bracket mod. i have the 4 wheel disc from a vette as well. I used the stock proportioning valve and some mix of brake lines from the vette and original lines. The system is installed and I have pedal pressure, everything has been bled. problem is i have to stand on the brake pedal to stop and it seems like the booster is bad. is there a way to test the booster? also since i used the stock proportion valve is there a problem there. I think my vacuum is around 12-13.

[dhutton]

I don't think you can mix the original lines with the C5 lines since they are metric. I don't think you would use the stock A body proportioning valve either. Maybe Tobin will respond. I bought special hoses from him to connect my C5/C6 brakes to the stock lines.

[Alaska442]

yes, I bought some stuff from Tobin a while ago. its been a few years since I started buying parts and just getting around to putting the car together.Hopefully tobin chimes in.

[Apogee]

The stock '66 A-body "proportioning valve" is actually just a distribution block if I'm not mistaken, just inlet and outlet ports with a brake balance switch/sensor, no proportioning or metering devices of any kind. The only brake options in '66 would have been drum/drum, so front to rear balance was achieved with wheel cylinder bore sizes, drum diameters, etc.

As for your pedal feel and low brake torque, even with the minimal information provided, it does smell like a booster issue at first sniff. To test that theory, pump the brake pedal 3-4 times to fully evacuate the booster, apply the brakes with firm pressure at the pedal, start the car and note how far the pedal drops when the vacuum assists the application of the brakes. Although not entirely applicable to C5/C6 brakes, Skip Fix did post an interesting GM tech document on this subject here. Several factors come into play when determining pedal travel, however it should drop an easy 3/4 to 1 inch in most instances.

Your vacuum at idle is marginal at best, so I would expect your performance to be somewhat sub par, however pad compound may also be playing a large part, but without more information it's hard to say. Some pads, particularly those that are very hard with low coefficients of friction, can result in shockingly low brake torques that can make you feel like you're rubbing two ice cubes together on a sheet of glass as you're at risk of giving some poor little Civic in front of you a '66 A-body enema.

Just a few questions if you don't mind...what pads are you running? Can you verify your vacuum levels at idle and/or post up your cam specifications? Do you either have a caliper pressure gauge or access to one? It would be nice to know what your caliper pressures are since that can quickly help determine if the problem is hydraulic or something else.

Tobin
KORE3

[Alaska442]

Yes those are some good comments.
The camshaft is big but should still be street friendly. I will post the spec sheet when I can find it.
The brake pads are stock I believe from an 04 vette.
I was thinking of using a vacuum pump to pull a vacuum on the booster to see if it would hold vacuum.
Is this a good way to test them if it wont hold vac it probly is not good. Im leaning toward this as the culprit now as i bought the complete package used from a memeber years ago and it could be just a bad booster.
Do you sell adaptors for the diffrent flare types leading into the distrobution block, I see I have a slight leak there with brake fluid and I believe I flared it. i cut the new style flare off and just flared the end with a tool.

Been many years but im close to getting the ride on the road.
Thanks

[Apogee]

Check your plumbing and vacuum check valve first, then if you wanted to pull a vacuum on your booster to verify it's integrity, there's no reason not to. Odds are though that if it was a significant vacuum leak, you'd notice it with how your engine ran, but it certainly can't hurt to check. Typically, I would start by performing the operational check I noted in Post #4. Assuming that checked out, I would then apply the brakes with the engine running, then stop the engine and wait for ~30 to 60 seconds with the brakes applied. If the brake pedal position does not change, then the booster is air tight under load, where it would be defective if the pedal moved up during that time. Similarly, you can test the air tightness of the booster system by running the engine for a couple of minutes, shutting it off, and then applying the brakes three consecutive time with normal pressure. Wait a few seconds between each application. You should notice a decrease in pedal travel with each additonal application of the brakes, if not, then you more than likely have a defective check valve or vacuum hose, or if the those items appear to be in good working order, then the booster itself.

As for adapter fittings, Weatherhead, Plews-Edelmann and Everco are the most common brands carried by most autoparts stores, so I would suggest you start there. Aftermarket suppliers like Brakequip, Pure Choice Motorsports, etc, should have them as well, but probably not locally to you in AK. The M12x1 ISO bubble flare should be easy to find...M12x1.5 not so much. The '97 C5 MC had (2) M12x1 outlet ports whereas the '98 to '04 had (1) M12x1 and (1) M12x1.5.

Tobin
KORE3