Better Stopping
- Thread starter Gospel Runner
- Start date
Gospel Runner
Well-Known Member
There is so much conflicting information. Do I just go with Cass and buy his brake system he wants me to purchase, as he is the expert? Is his system guaranteed to work for my RR. If it works, I will be glad to pay the price. I don’t want to waste my money on something that will lot work! Is anyone using his system that is successful? Thank
diesel_lv
Well-Known Member
You have an aftermarket front disc brake kit already, but you never stated what it is. Disc diameter, single or double piston calipers. I use the larger Dr Diff rotors and single piston calipers. Manual brakes w 15/16" master cylinder. My car was already manual brakes so my pushrod and pedal lever are correct for it. Mine stops on a dime w minimal pressure.
Gospel Runner
Well-Known Member
I have the SSBC front disc brake system. It has four pistons. 10.25” rotors, 1” MC and bendix style booster. I have a separate vacuum pump and separate vacuum canister. Drum rear brakes. I stand on the brakes and it barely stops. It is a hard pedal that does not move! I don’t mind changing up, but I just don’t want to purchase something that does not work.
diesel_lv
Well-Known Member
Completely understand you wanting whatever you get to work. I enjoy my manual brakes, 4dr '67 Coronet w BB n automatic. The larger 11" rotors require 15 rims. I cannot in good faith give you a recommendation on the correct master cylinder for 4 piston calipers. I can say that my larger disc manual front disc kit from Dr Diff works great for me. I would badger SSBC a bit 1st though, as their kits are supposed to be good.
steve340
Well-Known Member
Sounds like the booster is not right - if your description of a really hard pedal is on the money.
Connect the pump straight to the booster with none of the check valves and see what happens.
Make sure the booster is seeing the full vacuum.
You only need one check valve in the whole system.
Connect the pump straight to the booster with none of the check valves and see what happens.
Make sure the booster is seeing the full vacuum.
You only need one check valve in the whole system.
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About 10 years ago, I wanted to try a manual brake setup. I've had a 75 Dart booster and master cylinder in my '70 Charger since 2000. It worked but I wanted something simpler and NOT reliant on engine vacuum. I have the Cordoba 12" front discs, 2.75" single piston calipers and out back I have Dr Diff's 10.7" rear disc setup with 1.5" single piston calipers. I had 3 known good master cylinders in the shed to try so I went to it.
I pulled the Dart booster and master cylinder and swapped in a 1 1/8" master cylinder. The brake pedal was as firm as an 18 year old cheerleader but the car wouldn't stop right. I then tried the 1 1/32". Same thing. Hard pedal but terrible braking action. Next was the 15/16" iron MC that was attached to the power booster. It stopped better but would barely skid even on gravel.
Finally I called Dr Diff, explained the situation and asked for advice. I must have caught him on a bad day because he wasn't much in the mood to solve the problem. He was willing to sell me an aluminum 15/16" master cylinder. I doubted that it would be any different from the iron one I last used of the same size but I gave it a try.
Yeah, it didn't help. The brakes still sucked. I ended up putting the power booster and iron MC back in.
A couple of months later, I was under the car and suddenly realized that I had a disc-drum proportioning valve in the car. 4 wheel drum and 4 wheel disc cars don't use them! The proportioning is determined by the wheel cylinder or caliper bore sizes. I changed to a drum-drum distribution block and the car actually seemed to brake quite well. All along, the booster was masking the mismatch of parts and making up for it.
Here I am, 10 years later and I'm ready to try again. I bought another 15/16" MC and plumbed it to the drum-drum distribution block. The engine, trans and suspension are out for a refresh so I'll know if it stops well once it is all back together.
Good luck.
Geoff 2
Well-Known Member
Gospel,
Have you tested the booster to see it works? That is the first thing to do & a really simple test.
With your foot on the brake pedal, start the engine. Pedal should move slightly with engine running. No pedal movement means booster is not ' boosting', for what ever reason.
Have you tested the booster to see it works? That is the first thing to do & a really simple test.
With your foot on the brake pedal, start the engine. Pedal should move slightly with engine running. No pedal movement means booster is not ' boosting', for what ever reason.
Gospel Runner
Well-Known Member
The booster is not connected to the engine because the engine is 13.5:1 compression ratio and makes no vacuum. It is only tied to the external vacuum pump and canister. Forgive my ignorance, but where is the check valve that I may remove it to see if that is the problem. The proportioning block that I have is original to the car, for drum brakes front and rear.
steve340
Well-Known Member
The check valves are generally built in to the plastic inlet fitting of the booster or vacuum tank.
You only need one at the booster, but for checking purposes they can be bypassed to ensure the vacuum is getting to the booster.
With full vacuum on the booster if it still will not operate it would be faulty.
You only need one at the booster, but for checking purposes they can be bypassed to ensure the vacuum is getting to the booster.
With full vacuum on the booster if it still will not operate it would be faulty.
Sixpactogo
Well-Known Member
You may have two problems.........One for sure......You need a proportioning valve for disc / drum brakes. Fix that problem first. Then if your brakes still don't work, either get rid of the booster and go manual or get a dual diaphragm booster for disc brakes. The single diaphragm booster for drum brakes does not provide enough boost for discs.
Geoff 2
Well-Known Member
If the m/c is bolted to the booster, then it should be working & providing assist. The test in post #28 is still a valid test. If no assist or pedal movement then the problem is the booster, vac pump, vac canister, check valve or lines. With an ext vac pump, I do not see why you need a vac canister. Should be able to eliminate it & just run the pump to the booster.
Sixpactogo
Well-Known Member
Just because the booster is working doe not mean it provides enough boost to operate the front discs. Disc brakes have more volume and need more boost because of it. I upgraded my 60 Dart to front discs a few years ago. The booster has been rebuilt and works fine but does not provide enough boost even with 20" of vacuum. I tried adding a vacuum pump and it made no difference. IMO, you could add 30" of vacuum and it wouldn't help. You need the volume provided by the dual diaphragm booster to get the job done. No one makes a dual diaphragm booster for my dart so I am pretty well stuck with what I have. It stops the car quick enough but won't lock any wheels no matter how much pressure you put on the pedal. I have spoken with Cass at Dr Diff a few times about my issue and he agrees with me that my single diaphragm booster just doesn't have the boost needed.
My 68 Charger had the same problem when I upgraded to front discs. Once I changed the booster from the single diaphragm to the dual, my problem was solved.
Geoff 2
Well-Known Member
Six pack,
Well aware that the booster may not be good enough. The point of the test was to see if it is providing any boost or assist.
And if not enough assist, it needs more diaphragm area, not volume. That is what a dual diaphragm or larger OD booster does: adds more diaphragm surface area for atmospheric pressure to act against. Disc brakes require about 50% more line pressure than drum brakes, all else being equal.
Well aware that the booster may not be good enough. The point of the test was to see if it is providing any boost or assist.
And if not enough assist, it needs more diaphragm area, not volume. That is what a dual diaphragm or larger OD booster does: adds more diaphragm surface area for atmospheric pressure to act against. Disc brakes require about 50% more line pressure than drum brakes, all else being equal.
Sixpactogo
Well-Known Member
Well......Maybe volume was the wrong choice of words. My point was and still is. Just because a booster is working does not mean it is up to the task. Some people think since the booster is working, they need to replace the master cylinder and or hoses or push rod adjustment when all along it is the booster not up to the task. I went down that road myself and it cost me a lot of money before I got educated. I'm just trying to help others not have to make the same mistakes I did. I have not heard your comment about the 50% more line pressure needed for discs before but it makes sense to me.
steve340
Well-Known Member
A larger diameter or double diagram booster will give more "assist" and that is definitely true.
So this means the selection of the correct booster type for a 4 wheel disc car becomes critical due to the requirement for far more line pressure.
But it does have factors like pedal ratio, size of pad and pad material etc.- these things all need consideration.
Geoff 2 is right about the drum/disc pressure thing.
A drum needs about 300-400 psi and discs need somewhere around 800-1200 psi.
You can get away with less line pressure if a car is light.
A standard B body is fairly heavy - so you need callipers with big pads, correct lining material and lots of line pressure.
So this means the selection of the correct booster type for a 4 wheel disc car becomes critical due to the requirement for far more line pressure.
But it does have factors like pedal ratio, size of pad and pad material etc.- these things all need consideration.
Geoff 2 is right about the drum/disc pressure thing.
A drum needs about 300-400 psi and discs need somewhere around 800-1200 psi.
You can get away with less line pressure if a car is light.
A standard B body is fairly heavy - so you need callipers with big pads, correct lining material and lots of line pressure.
Gospel Runner
Well-Known Member
This is much more complicated than I ever thought or knew. My education is costing me time and money. My booster is a dual diaphragm aftermarket new style. The canister is being used because it stores vacuum so there is ample reserve in the event the brakes have to be used multiple times in succession and the booster or vacuum can't keep up with what is needed. At least that was my understanding. I have 18lbs. of vacuum pressure at the booster. Cass suggests that with his brake kit and his disc/drum proportioning valve, my problems will be solved. I bit the bullet and purchased both from him. When they arrive next week, I will install them and let you know how things go. Because Cass is not receiving phone calls, this process has taken way longer than it should have, since we have been emailing each other. He answers what I consider to be simple yes or no questions with statements about equipment, as though I know what he is taking about (when I have no clue). So, his answers for me just raise more questions, that could have easily been concluded with a phone call. Anyways, I want to thank each of you for your knowledge and sharing here. Cass has told me to keep my booster, M/C, pump and canister, just add his kit and I will be fine. I have prepped my car so that when his kit arrives, I will be done that same day. Have a great fourth of July weekend, and I will respond as soon as I get this kit installed! Peace!!!
Geoff 2
Well-Known Member
Gospel,
Whatever booster you end up using, & the brakes are still poor, the simple test in post #28 will tell you if you are getting any assist from the booster. If no pedal movement, you have no assist. If this happens, could be the booster as well as other components, but at least you have a starting point for troubleshooting the problem. If the pedal does move, it tells you that there is assist there, but it doesn't prove that every component is working 100% effectively. Good luck.
Whatever booster you end up using, & the brakes are still poor, the simple test in post #28 will tell you if you are getting any assist from the booster. If no pedal movement, you have no assist. If this happens, could be the booster as well as other components, but at least you have a starting point for troubleshooting the problem. If the pedal does move, it tells you that there is assist there, but it doesn't prove that every component is working 100% effectively. Good luck.
Gospel Runner
Well-Known Member
Ok I took the advice of Cass and purchased their brake kit with the new disc/ drum proportioning valve. I got the kit installed Friday, I plumbed new lines yesterday. I stripped the old ones when trying to get them out. Today I will bench bleed the master cylinder, reinstall it and test it today or at the latest tomorrow morning. I will let you know how things go.
Gospel Runner
Well-Known Member
Ok I took the advice of Cass and purchased their brake kit with the new disc/ drum proportioning valve. I got the kit installed Friday, I plumbed new lines yesterday. I stripped the old ones when trying to get them out. Today I will bench bleed the master cylinder, reinstall it and test it today or at the latest tomorrow morning. I will let you know how things go.
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