The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Putting booster on 66 drum brakes driving me crazy

old cool · 10-19-2014, 06:42 PM

I can't get too mechanical or technical here but I may have some info that will help.
1. I have a "66 with an older power booster and dual circuit upgrade. From what I see in the catalogs and on-line, it appears I have a Cardone booster to fit a 67-70 truck.
2. If I recall, I get 15-17" vacuum with carb set at max vacuum read
3. I have a 250 inline 6
4. My brake pedal is almost as high as clutch pedal so I have a pretty long push before pb engages. Different from new cars for sure.
5. My brake pedal touch and stopping is very easy. Stops great. Almost too good. A first time driver always needs to drive a couple of times to avoid sending someone at windshield. Not sure if it's right, but I have no problems now that I'm familiar with braking.
6.Brakes will lock up if sudden stop is needed. (my MC looks a little dingy inside so it may be on its way out)

I sense your frustration and I'm sharing for 4 reasons.
1. My pedal is not firm whatsoever and the booster is prob the same as the one you picked up - though I've read somewhere there is a 2nd generation booster for 67-72's that may be slightly diff in size and color. Mine came flat black.
2. I've read that if you put a hose to back of booster from inside truck, near push rod (vehicle running) and you hear air hissing that gets louder as you depress brake pedal, your booster is leaking and this causes a firm pedal. FYI, I have a very light hiss that is continuous whether brake is being pushed or not. Not sure if that's ok yet although my pedal is NOT firm at all.
3. I went all over my engine for vacuum leaks and did pick up a couple of connections that sounded of leak. Resolved where needed. I also changed check valve and grommet at the booster as the grommet was old and did hear minor hiss. In other words, vacuum leaks can be the culprit in your case.
4. I think my pedal is factory setting for a non power brake system and one of the previous owners used existing push rod and made it work by fabricating the booster bracket on the firewall.

So, I don't have your experiences but I do have your modifications. Good luck. Please let us know how you resolved your issue. Hope this feedback is helpful.

10-19-2014, 06:42 PM	#12
old cool Registered User Join Date: Apr 2014 Location: Rochester, MI Posts: 206	Re: Putting booster on 66 drum brakes driving me crazy I can't get too mechanical or technical here but I may have some info that will help. 1. I have a "66 with an older power booster and dual circuit upgrade. From what I see in the catalogs and on-line, it appears I have a Cardone booster to fit a 67-70 truck. 2. If I recall, I get 15-17" vacuum with carb set at max vacuum read 3. I have a 250 inline 6 4. My brake pedal is almost as high as clutch pedal so I have a pretty long push before pb engages. Different from new cars for sure. 5. My brake pedal touch and stopping is very easy. Stops great. Almost too good. A first time driver always needs to drive a couple of times to avoid sending someone at windshield. Not sure if it's right, but I have no problems now that I'm familiar with braking. 6.Brakes will lock up if sudden stop is needed. (my MC looks a little dingy inside so it may be on its way out) I sense your frustration and I'm sharing for 4 reasons. 1. My pedal is not firm whatsoever and the booster is prob the same as the one you picked up - though I've read somewhere there is a 2nd generation booster for 67-72's that may be slightly diff in size and color. Mine came flat black. 2. I've read that if you put a hose to back of booster from inside truck, near push rod (vehicle running) and you hear air hissing that gets louder as you depress brake pedal, your booster is leaking and this causes a firm pedal. FYI, I have a very light hiss that is continuous whether brake is being pushed or not. Not sure if that's ok yet although my pedal is NOT firm at all. 3. I went all over my engine for vacuum leaks and did pick up a couple of connections that sounded of leak. Resolved where needed. I also changed check valve and grommet at the booster as the grommet was old and did hear minor hiss. In other words, vacuum leaks can be the culprit in your case. 4. I think my pedal is factory setting for a non power brake system and one of the previous owners used existing push rod and made it work by fabricating the booster bracket on the firewall. So, I don't have your experiences but I do have your modifications. Good luck. Please let us know how you resolved your issue. Hope this feedback is helpful.