Grabby or over-assisted front brakes on my '63

OK, my brake woes continue. I took my '63 Riv out yesterday for a spin and no doubt about it: no matter how gently I feather the brake pedal, it still causes the car to screech and lurch and want to stand on its nose at very low speeds. This was really evident when I was going very slowly down a steep hill with a four-way stop at the bottom. It was like some '60s sitcom, where someone's learning to drive for the first time! So to recap...

I had two mechanics tell me that my linings, drums, etc., and everything at the wheel and tire ends look good. Because previously, I had literally no vacuum assist at higher speeds -- but good assist and no screechy stops at low speeds -- I replaced the vacuum booster with a 1967 Riv model for a drum/drum setup as I have now, and with that I had to change to a dual-master cylinder (1964 and later). I also got that special O-ring that goes between the m/cyl and booster from Dewey. After that the brakes started to be real grabby or over-assisted at low speeds, even after backing up the car several times to adjust the self-adjusting brakes. I had also installed a brass 'distribution' block, but per Tim Kaber's advice, removed it and used a three-way tee fitting instead, which made little to no difference in reducing pedal sensitivity at low speeds. Since the car stopped fine with vacuum assist at very low speeds previously, I can't imagine something dramatically changed with the front drums or linings. So using some deductive reasoning, could I have a faulty booster even though it's new? And how hard is it to swap out just the booster?

Thanks/Jan

OK, my brake woes continue. I took my '63 Riv out yesterday for a spin and no doubt about it: no matter how gently I feather the brake pedal, it still causes the car to screech and lurch and want to stand on its nose at very low speeds. This was really evident when I was going very slowly down a steep hill with a four-way stop at the bottom. It was like some '60s sitcom, where someone's learning to drive for the first time! So to recap...

I had two mechanics tell me that my linings, drums, etc., and everything at the wheel and tire ends look good. Because previously, I had literally no vacuum assist at higher speeds -- but good assist and no screechy stops at low speeds -- I replaced the vacuum booster with a 1967 Riv model for a drum/drum setup as I have now, and with that I had to change to a dual-master cylinder (1964 and later). I also got that special O-ring that goes between the m/cyl and booster from Dewey. After that the brakes started to be real grabby or over-assisted at low speeds, even after backing up the car several times to adjust the self-adjusting brakes. I had also installed a brass 'distribution' block, but per Tim Kaber's advice, removed it and used a three-way tee fitting instead, which made little to no difference in reducing pedal sensitivity at low speeds. Since the car stopped fine with vacuum assist at very low speeds previously, I can't imagine something dramatically changed with the front drums or linings. So using some deductive reasoning, could I have a faulty booster even though it's new? And how hard is it to swap out just the booster?

Thanks/Jan

Jan, I was thinking that too! It has to be something in the booster. Where is the old booster? Can you put it back on? That is the only thing you did differently from we did. We used the 67 drum drum master cylinder, Dewey's o-ring and stock booster. Good luck!

Jan, I was thinking that too! It has to be something in the booster. Where is the old booster? Can you put it back on? That is the only thing you did differently from we did. We used the 67 drum drum master cylinder, Dewey's o-ring and stock booster. Good luck!

Tim, do you have a '63 or a '64? I thought that a 1963 booster did not fit a later (dual) master cylinder setup.

Tim, do you have a '63 or a '64? I thought that a 1963 booster did not fit a later (dual) master cylinder setup.

Jan,

My Son's car is a 1963. The 67 Drum/Drum master cylinder fits. I thought the O-ring was only needed on the 63 Booster. I am only guessing but maybe you don't need the o-ring on the 67 set up and perhaps this is causing your issue? Maybe Jim Cannon could shed some light on this?

To recap, on my installation I used a 67 Drum/Drum master cylinder (there were 2 different ones, the difference had to do with the push rod. One had a small 1/4 inch deep pilot hole, the other a 1" deep pilot hole, matched it with the old single M/C), Dewey's O-ring & the original 63 Booster.

The only difference is you used the 67 Booster. Again, I may be wrong but I didn't think you needed an O-ring on that late of a model. Also there could be a miss match in the push rod length between a 63 and a 67. I know it's not much to go on, but that's what we're down to. It has to be something like this if the car braked ok at low speeds before.

Tim

Thanks, Tim. So the question, then, is if the dual master cylinder I installed, which is this one...

http://www.oreillyauto.com/site/c/detail/OBH3/101328/01292.oap?year=1968&make=Cadillac&model=Commercial%2BChassis&vi=1494169&ck=Search_01292_1494169_-1&pt=01292&ppt=C0066

...fits the 1963 model brake booster. I also noticed that my mechanic disconnected the large vacuum tank on the left inner fender when he installed the later booster, since that one only has one tube coming out, not a dual one. Would that have any effect?

The later booster is this one: http://www.oreillyauto.com/site/c/detail/OBH3/5471324/01305.oap?year=1965&make=Buick&model=Electra&vi=1319284&ck=Search_01305_1319284_-1&pt=01305&ppt=C0066

Thanks, Tim. So the question, then, is if the dual master cylinder I installed, which is this one...

http://www.oreillyauto.com/site/c/detail/OBH3/101328/01292.oap?year=1968&make=Cadillac&model=Commercial%2BChassis&vi=1494169&ck=Search_01292_1494169_-1&pt=01292&ppt=C0066

...fits the 1963 model brake booster. I also noticed that my mechanic disconnected the large vacuum tank on the left inner fender when he installed the later booster, since that one only has one tube coming out, not a dual one. Would that have any effect?

The later booster is this one: http://www.oreillyauto.com/site/c/detail/OBH3/5471324/01305.oap?year=1965&make=Buick&model=Electra&vi=1319284&ck=Search_01305_1319284_-1&pt=01305&ppt=C0066

The only experience I have with this swap is our particular project. The 63 booster doesn't appear to have a conventional check valve like the 67. (see Pic) I'm not sure if it has one (check valve) in line? However, and I thought we covered this early on, there are 2 different M/C's (Bendix and Delco). I had to match with the old single M/C upon initial removal. I believe the secondary tank was for additional assist (apparently not your problem, LOL!). There has to be some correlation between the booster swap and the "Over Assist" issue you are having. If your new M/C matches the old single one, it will work with your old booster. (don't forget the O-ring!) It sucks you are having so much trouble with this. You might PM Jim Cannon and run this by him. He was a great deal of help to me when I was doing this conversion and might be able to shed some light on the problem you are having.

Hang in the Jan, we'll figure it out eventually. Old cars aren't easy, if they were everyone would have one!

Tim

Thanks, Tim. So the question, then, is if the dual master cylinder I installed, which is this one...

http://www.oreillyauto.com/site/c/detail/OBH3/101328/01292.oap?year=1968&make=Cadillac&model=Commercial%2BChassis&vi=1494169&ck=Search_01292_1494169_-1&pt=01292&ppt=C0066

...fits the 1963 model brake booster. I also noticed that my mechanic disconnected the large vacuum tank on the left inner fender when he installed the later booster, since that one only has one tube coming out, not a dual one. Would that have any effect?

The later booster is this one: http://www.oreillyauto.com/site/c/detail/OBH3/5471324/01305.oap?year=1965&make=Buick&model=Electra&vi=1319284&ck=Search_01305_1319284_-1&pt=01305&ppt=C0066

Yes and No,

Tom Mooney

Yes and No,

Tom Mooney

Thanks, Tom - you're a man with an economy of words!

So after a little more sleuthing, I think I may be homing in on that O-ring as the culprit - as in the fact that upon inquiry, my mechanic said it was not there when he separated the '63-style vacuum booster from the 63 single-cylinder master and the '63 vacuum booster - and that he also said it was NOT required between the later-style dual master and booster. So that tells me that when the previous owner installed that rebuilt (63) booster, I was most likely losing pedal assist at higher speeds because of the absence of that O-ring as Tim mentioned earlier. So I guess the next step is to reinstall the 63 booster with the O-ring in place, since Tom says it should bolt up to my later dual master cylinder, and then reattach the reserve vacuum tank...

Tim, do you have a '63 or a '64? I thought that a 1963 booster did not fit a later (dual) master cylinder setup.

I know this is a small detail right now but the '64 also has a single master cylinder set-up from the factory.

Hi Tim - just to be sure with the O-ring - it goes on the flat edge of the rear of the master cylinder as shown by the green dot in the attached image of my single m/c, right? Or does it go into the ridge marked by the red dot? Also, do I put anything on the O-ring before installation?

Darren: Thanks - I rechecked compatibility and my dual master is for a 67-70 Riv.

Hi Tim - just to be sure with the O-ring - it goes on the flat edge of the rear of the master cylinder as shown by the green dot in the attached image of my single m/c, right? Or does it go into the ridge marked by the red dot? Also, do I put anything on the O-ring before installation?

Darren: Thanks - I rechecked compatibility and my dual master is for a 67-70 Riv.

[ATTACH=CONFIG]276812[/ATTACH]

Jan,

I honestly don't remember! It has been over a year since I did that and my memory isn't what it used to be. I am going to say Red dot. I referred to the shop manual and this is what I found...

If you look in the second drawing you can see the groove sitting in the opening in the booster body. It appears there to be making a radial seal to the inside diameter of the body. If on the back (Green Dot), it appears it would fall into the booster. The manual had no text that I saw referring specificly to the installation of that particular O-ring. However, the manual recommended brake fluid (Light coat) or silicone lubricant to lubricate other o-rings within the assembly. Like and oil filter o-ring you just don't want it to wad up when inserting it into the I.D. of the booster body so I would use any lubricant sparingly. Hope this helps!

Tim

-I might add that on a manual brake m/c the groove appears to be for a rubber boot, as it does not go into a booster.

Thanks, Tim - very helpful! Has it already been a year since you did this? I just put my old booster into storage so now I have to get it out and make sure that O-ring is in the box. I'll keep you and others posted to see if that indeed solves the problem.

Thanks again for your responses!

This is going way out there, but is there any chance that you got a disk/drum master cylinder? If so, there won't be a check valve in it. I know that when you add disk brakes to an existing drum/drum system you're supposed to remove the check valve. I don't know the function of the valve nor do I know why you're supposed to remove it when you add disk brakes; I'm just throwing it out there as a possibility.

Ed

Hi Tim - just to be sure with the O-ring - it goes on the flat edge of the rear of the master cylinder as shown by the green dot in the attached image of my single m/c, right? Or does it go into the ridge marked by the red dot? Also, do I put anything on the O-ring before installation?

Darren: Thanks - I rechecked compatibility and my dual master is for a 67-70 Riv.

[ATTACH=CONFIG]276812[/ATTACH]

Red dot.

This is going way out there, but is there any chance that you got a disk/drum master cylinder? If so, there won't be a check valve in it. I know that when you add disk brakes to an existing drum/drum system you're supposed to remove the check valve. I don't know the function of the valve nor do I know why you're supposed to remove it when you add disk brakes; I'm just throwing it out there as a possibility.

Ed

The "check valve" is really a "residual pressure valve" that retains some fluid pressure in the line of a drum system to keep the cups inside the wheel cylinders slightly pressurized and pressing tightly against the inside of the cylinder bore. This helps keep fluid from bleeding out and helps keep moisture out of the system. You don't want this residual pressure in a disc system because it would keep pressing the disc pads against the discs while you drive and wear the pads down quickly.

So you would have a problem if you put a drum/drum MC in a car with front discs. But you would not have a problem if you accidentally went the other way around. Not having that pressure against the wheel cylinder cups would not affect performance (just long-term system integrity).

Thanks, Jim. I spoke with "Booster" Dewey today and he said that all 1960's masters, single or dual, have the ridge for the O-ring seal. I'm going to send him my '63 booster for a check and possible rebuild, since it was purchased and installed by the previous owner and I don't know it's history. I do know that the "ears" on the m/c side of the booster were installed upside down, though. Dewey says that shouldn't affect its operation, but I don't want to go through another install and reinstall if I can help it. Thanks again to you and Tim and all on the forum for input. I'll keep everyone updated as I progress.