Delima. Had just front ssbc disc brakes and rear drums and all worked good. Went ahead with adding rear disc now jamming on the brakes just coasts to a stop. Bleed them several times. Do I need a bigger bore master cylinder for 4 disc brakes?? Using a stock master cylinder and have a adjustable proportioning valve in the rear brake line just under the drivers seat. Any help would be appreciated.
SSBC disc brakes won't stop
- Thread starter 71Demon
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67Dart273
Well-Known Member
Just a guess but you might want to remove the prop valve.
If anything you want a SMALLER bore master.
Bigger pistons or
bigger wheel cylinders
or SMALLER master gives you more braking effect with less pedal effort while requiring MORE pedal "movement."
As an example, I have 73/ 74 Duster brakes on my 67, with a Linc Versailles 9" Ford rear axle, factory disk. I am using the factory drum master with the residual valves punched through and no prop valve.
If anything you want a SMALLER bore master.
Bigger pistons or
bigger wheel cylinders
or SMALLER master gives you more braking effect with less pedal effort while requiring MORE pedal "movement."
As an example, I have 73/ 74 Duster brakes on my 67, with a Linc Versailles 9" Ford rear axle, factory disk. I am using the factory drum master with the residual valves punched through and no prop valve.
nm9stheham
Well-Known Member
Is the pedal going to the floor or do you get a hard pedal part way up?
Any info you can give on the conversion parts/kit used? Is this the stock drum/drum 1971 MC?
Have you pinched the rear brake line and seen if the front brakes came back? Be careful; if the line is old, the internal lining may break up inside and cause problems. So be aware.....
Any info you can give on the conversion parts/kit used? Is this the stock drum/drum 1971 MC?
Have you pinched the rear brake line and seen if the front brakes came back? Be careful; if the line is old, the internal lining may break up inside and cause problems. So be aware.....
Using the 1.1/32 factory disc brake master cylinder.
Pedal pumps up. Doesn't go to floor but seems squishy a bit.
Part way down gets solid but doenst lock up the brakes
AJ/FormS
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The no one thing is to get a hard pedal, on the first pump, with about 50% or less travel.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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From here it looks like an extreme amount of rear pad travel may be the culprit, accompanied by air in the front system.
When you apply the brakes, the first chamber nearest the firewall, is supposed to go to the front brakes. If the front does not immediately respond,as in the fluid going out meets no resistance, then the piston inside the M/C collapses but continues to move until it activates the rear brakes. If the front brakes have air in them or excessive pad travel, then you get your situation.
The best solution is to pinch the rear flex-line to isolate the systems. Then get a hard pedal in the front by bleeding.
Then re-examine the rear system to make sure everything is correctly assembled and adjusted. The pads must be in intimate contact with the rotors, and the calipers well centered over the rotors. Then very slightly release the clamp pressure on the flex-hose until fluid can pass thru with a bit of pedal effort. The re-bleed the rear system until you get a hard pedal.
If you absolutely cannot get a hard pedal, then it possibly a faulty M/C that is internally bypassing fluid.
Also, when switching to rear discs from drums, you have to defeat the residual valve in the m/c. The R-valve will maintain a low pressure in the rear line, which will keep the rear brakes applied,which is not good.
BTW; the rear bleeders are at the high point of the calipers, right?
When finished, remember to remove the clamp.
The 1 and 1/32 will be fine with a power booster.Without it,you will need a good braking leg!
If you have an aftermarket P-valve, I'm assuming you gutted the factory one?
When you apply the brakes, the first chamber nearest the firewall, is supposed to go to the front brakes. If the front does not immediately respond,as in the fluid going out meets no resistance, then the piston inside the M/C collapses but continues to move until it activates the rear brakes. If the front brakes have air in them or excessive pad travel, then you get your situation.
The best solution is to pinch the rear flex-line to isolate the systems. Then get a hard pedal in the front by bleeding.
Then re-examine the rear system to make sure everything is correctly assembled and adjusted. The pads must be in intimate contact with the rotors, and the calipers well centered over the rotors. Then very slightly release the clamp pressure on the flex-hose until fluid can pass thru with a bit of pedal effort. The re-bleed the rear system until you get a hard pedal.
If you absolutely cannot get a hard pedal, then it possibly a faulty M/C that is internally bypassing fluid.
Also, when switching to rear discs from drums, you have to defeat the residual valve in the m/c. The R-valve will maintain a low pressure in the rear line, which will keep the rear brakes applied,which is not good.
BTW; the rear bleeders are at the high point of the calipers, right?
When finished, remember to remove the clamp.
The 1 and 1/32 will be fine with a power booster.Without it,you will need a good braking leg!
If you have an aftermarket P-valve, I'm assuming you gutted the factory one?
Last edited:
pishta
I know I'm right....
I thought disks self centered/adjusted due to the shape of the seals? They sort of relax and get off the rotor ever so slightly just by the way the seal sits. Are you using DOT5 fluid? You must bleed them: with the bleeds wide open and the M/C higher, you could probably just let them weep and then cap them if the bleed is at the high point of the caliper. Tell us what works. You may have to open the adjustable prop valve to bleed them?
69_340_GTS
Well-Known Member
A) Residual pressure valve in M/C must be removed. It may or may not be there.
B) You can probably eliminate or completely open up the proportioning valve with 4 wheel disks.
C) You will probably need to bleed them a couple times.
B) You can probably eliminate or completely open up the proportioning valve with 4 wheel disks.
C) You will probably need to bleed them a couple times.
I have had that problem with the OEM KH brakes. Make sure the rotors are clean. The pads can make a huge difference. I switched to EBC Yellow pads and they grab a whole lot better. Ran last night at Pocono with racing pads and they really grab.
Didn't gut the old prop valve but added another one in the rear brake line. You said you have to defeat the residual valve with rear discs? How is this done? Im going to isolate the fronts like you said today and see what I have on the fronts. I have no peer booster but Im used to that. Guess I need to remove one of the prop valves or ca I just ope up the adjustable all the way? Not sure its a Dot 5 fluid is this a must?
nm9stheham
Well-Known Member
If it pumps up on successive rapid pumps of the pedal, then there is definitely air in the system. More bleeding is needed.
As suggested, if the MC does not move enough fluid, then the rear will never apply. But, changing to a different MC with the same bore size will not move any more fluid unless there is more stroke. Changing to another MC as suggested may be needed; the internal springs and stops can be set differently to allow the rears to have more of the available piston stroke.
nm9stheham
Well-Known Member
Yeah, you don't want 2 prop valves in there. Don't open up the adjustable one all the way; close it down all the way, to take its action out of the system for the time being. The residual valve can be dealt with later; it would not cause lack of brakes but just the rears dragging slightly all the time.
momoparman
MOISMYHOME
You also need to bed the brakes on a disc setup. Once you get them bled properly and verify that you have no leaks, read up on the procedure and try again
SSBC Performance Brake Systems FAQ
SSBC Performance Brake Systems FAQ
rmchrgr
Skate And Destroy
I went through a similar scenario with my SSBC brakes, they pretty much suck. Not sure which ones you have, are they the small bolt pattern K/H type? I went with their SBP aluminum 4 piston calipers to save weight and keep my wheels. I don't have a booster so it's a manual system - disc front, drum rear with all new components. Essentially, the pistons in the calipers are too small and the rotors don't provide enough surface area. My rear brakes are adjusted almost solid and have small wheel cylinders - I can stand on the pedal with two feet and it still won't lock the brakes. I got some Wilwoods now, hope they work better.
I realize you have rear disc so that may account for a slight difference in bias. You might need a different distribution block for a disc/disc setup, the disc/drum and drum/drum blocks all create different biases. There is no OE disc/disc distribution block to my knowledge, you would probably have to find an aftermarket one and make it work.
You also need a really small bore master cylinder ( I have a 15/16" bore MC from Dr. Diff, probably need a 7/8" bore) to be able to generate enough pressure. With the smaller pistons, there is not a proper amount of pressure available for decent stopping power and good pedal feel.
I had a cool guy prop valve in my rear line but removed it, you really don't need it.
I drag race the car sometimes, the brakes will not hold the car past 1,200 rpm at the line, it would creep so I had to launch from idle which hurt my ET. The Roll Control I installed never worked, would not hold the car.
When I was trying to figure out why I couldn't stop the car and had a low pedal, I must have run two gallons of fluid through the brakes trying to get any air out. The reality was there was no air, I did everything right. The brakes just suck.
I realize you have rear disc so that may account for a slight difference in bias. You might need a different distribution block for a disc/disc setup, the disc/drum and drum/drum blocks all create different biases. There is no OE disc/disc distribution block to my knowledge, you would probably have to find an aftermarket one and make it work.
You also need a really small bore master cylinder ( I have a 15/16" bore MC from Dr. Diff, probably need a 7/8" bore) to be able to generate enough pressure. With the smaller pistons, there is not a proper amount of pressure available for decent stopping power and good pedal feel.
I had a cool guy prop valve in my rear line but removed it, you really don't need it.
I drag race the car sometimes, the brakes will not hold the car past 1,200 rpm at the line, it would creep so I had to launch from idle which hurt my ET. The Roll Control I installed never worked, would not hold the car.
When I was trying to figure out why I couldn't stop the car and had a low pedal, I must have run two gallons of fluid through the brakes trying to get any air out. The reality was there was no air, I did everything right. The brakes just suck.
67Dart273
Well-Known Member
^^THIS RIGHT HERE^^
You certainly don't want 2 prop valves and as I said earlier you may not want ANY
The residual valves ARE NOT this problem. They are a very very low pressure valve, the only thing they would cause, is a slight drag of the pads. Look in the shop manual, which shows how to remove them. On mine, I simply poked nails in through them from the fitting.
Here's a generic photo. You can thread a small screw into the seat, and use a claw hammer to pull the seat out. Discard the valve and spring, and re-insert the seat
Isolated the fronts by closing off the rear aftermarket prop valve I have in the rear brake line. Pedal is perfect in this scenario. Fro its working good.^^THIS RIGHT HERE^^
You certainly don't want 2 prop valves and as I said earlier you may not want ANY
The residual valves ARE NOT this problem. They are a very very low pressure valve, the only thing they would cause, is a slight drag of the pads. Look in the shop manual, which shows how to remove them. On mine, I simply poked nails in through them from the fitting.
Here's a generic photo. You can thread a small screw into the seat, and use a claw hammer to pull the seat out. Discard the valve and spring, and re-insert the seat
AJ/FormS
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There you go. Now you know the front system is A-OK.
So now lets talk about the rears.
Go back to my previous post. The whole point of that post is to make sure the rear pistons are out against the pads, and that the pads are all in intimate contact with the disc, and that everything is in the correct working relationship. If the caliper is a slider-type, it has to be somewhere in it's normal working range. If it's a fixed caliper,bolted-to-a-bracket with pistons on both sides, then again it has to be well centered and somewhere in its normal working range.It is very important that the pads not be bent, and that they are exactly correctly installed.
-So now, if everything back there is 100%, then it's time to bleed it.
-Now here's something you need to know; It is often very difficult to bleed disc brakes by yourself. This is because with the rear bleeders open,as you push fluid out on the down-stroke, then sometimes, on the pedal return, the fluid also returns. When this happens it is impossible to bleed. To get around this I often have to clamp the rear flex-hose,just enough to offer resistance to the fluid that it cannot return, and crack open only the nearest bleeder to the MC.I use the special bleeder cup with the hose attached, and the tube that runs to the bottom of the cup. Then I can watch as a helper pumps the pedal. When the fluid gets to this side, I pump a few strokes into the cup and close the bleeder. Then I move to the opposite side, and bleed it the same way ,but completely. Then I return to the first side and finish there.
-With a M/C for a drum brake rear system, the M/C usually has a small rear reservoir. So, you have to keep a very close eye on the fluid level. You have to keep it pretty high or the system will suck air on the return stroke. The compensating port will need to be more than just covered, cuz of that. At least 1/2 inch. More is better.
-If you cannot seem to get fluid out to the back, there is a good chance that the compensating port is not working.If this happens to you,give a shout back and I'll walk you thru proving it.
- The M/C that you now have, will work just fine; if A) you remove the R-valves, and B) you forever keep a close eye on the rear fluid level, and C) you don't mind the pedal effort.
-Once the system is working,the big bore M/C should have a hard pedal very early in the pedal stroke. I find this hard to modulate, but lots of guys like this.
-Don't worry too much about the P-valves right now, but run the aftermarket one wide open during this bleeding exercise.Later after the road-test is successful, you can dial in the rear pressure.
-The R-valves maintain about 8 to 12 psi in the line(s). If you do not remove them the piston-seals will not be able to retract the pistons, and the pads will drag. The engine and tranny torque-multiplication will overcome this and you may not notice this. But the rotors will run hot.
-Make absolutely sure that if you have a factory P-valve that it is correctly plumbed.Only the rears should be proportioned, and the amount of proportioning is application specific. The factory set-up was playing it way too safe. They must have been really afraid of law-suits due to premature rear loc-ups sending people into spins.I am running Zero rear proportioning, with Zero problems.
-Oops, I see you say you didn't get the old P-valve. So I guess you still have the safety switch then?
Okay so good luck.
So now lets talk about the rears.
Go back to my previous post. The whole point of that post is to make sure the rear pistons are out against the pads, and that the pads are all in intimate contact with the disc, and that everything is in the correct working relationship. If the caliper is a slider-type, it has to be somewhere in it's normal working range. If it's a fixed caliper,bolted-to-a-bracket with pistons on both sides, then again it has to be well centered and somewhere in its normal working range.It is very important that the pads not be bent, and that they are exactly correctly installed.
-So now, if everything back there is 100%, then it's time to bleed it.
-Now here's something you need to know; It is often very difficult to bleed disc brakes by yourself. This is because with the rear bleeders open,as you push fluid out on the down-stroke, then sometimes, on the pedal return, the fluid also returns. When this happens it is impossible to bleed. To get around this I often have to clamp the rear flex-hose,just enough to offer resistance to the fluid that it cannot return, and crack open only the nearest bleeder to the MC.I use the special bleeder cup with the hose attached, and the tube that runs to the bottom of the cup. Then I can watch as a helper pumps the pedal. When the fluid gets to this side, I pump a few strokes into the cup and close the bleeder. Then I move to the opposite side, and bleed it the same way ,but completely. Then I return to the first side and finish there.
-With a M/C for a drum brake rear system, the M/C usually has a small rear reservoir. So, you have to keep a very close eye on the fluid level. You have to keep it pretty high or the system will suck air on the return stroke. The compensating port will need to be more than just covered, cuz of that. At least 1/2 inch. More is better.
-If you cannot seem to get fluid out to the back, there is a good chance that the compensating port is not working.If this happens to you,give a shout back and I'll walk you thru proving it.
- The M/C that you now have, will work just fine; if A) you remove the R-valves, and B) you forever keep a close eye on the rear fluid level, and C) you don't mind the pedal effort.
-Once the system is working,the big bore M/C should have a hard pedal very early in the pedal stroke. I find this hard to modulate, but lots of guys like this.
-Don't worry too much about the P-valves right now, but run the aftermarket one wide open during this bleeding exercise.Later after the road-test is successful, you can dial in the rear pressure.
-The R-valves maintain about 8 to 12 psi in the line(s). If you do not remove them the piston-seals will not be able to retract the pistons, and the pads will drag. The engine and tranny torque-multiplication will overcome this and you may not notice this. But the rotors will run hot.
-Make absolutely sure that if you have a factory P-valve that it is correctly plumbed.Only the rears should be proportioned, and the amount of proportioning is application specific. The factory set-up was playing it way too safe. They must have been really afraid of law-suits due to premature rear loc-ups sending people into spins.I am running Zero rear proportioning, with Zero problems.
-Oops, I see you say you didn't get the old P-valve. So I guess you still have the safety switch then?
Okay so good luck.
Last edited:
rmchrgr
Skate And Destroy
Well, sorry for the useless info on my part.
I still hate my brakes.
Good luck.
I still hate my brakes.
Good luck.
When I went to 4 wheel discs I had to go with a 1 1/8" bore M/C to supply enough volume to the calipers. Prior to that the pedal was low, wouldn't stop well, and felt like I was running out of pedal before full pressure would get to the brakes.
AJ/FormS
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Your info was not useless.
I went thru the same motions when dialing mine in.
I do have the HK set-up from a 70 Duster, and 10 x 2.5s out back. I am running a 15/16 M/C cuz I like the long pedal travel, cuz it's easier to modulate when coming to a stop. (I did try both the 1 incher and the 1&1/32). I have 7/8 rear W/Cs (down from 15/16) so as not to overpower the rear tires. I do have a booster, which I have dialed back the assist on.I run Zero proportioning. I'm running 235/60-14s and 295/50-15s;all BFGs.I am at 3650 pounds with me in it.
-This system stops "HolyCow" awesome with organic pads and linings. This is the best stopping street car I have ever owned since 1969.
- I know nothing about your SSBC system, but many guys have had success with them.
-Pressure is adjustable, in all sizes of systems via pedal pressure or boost assist. But if a two-foot,max effort can't get 'er locked-up,at under 30mph, the first place I would look, is the pad to rotor interface. Either they are not compatible, or the pads are not running flat to the discs, or there is a mechanical error. The issue could be hydraulic, but if you have a hard pedal, I doubt it.
best of luck with your new Willwoods.
AJ/FormS
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This sounds like a mechanical issue. As in bent pads or those pesky anti-squeal shims between the pads and pistons, or some kindof flex in the system,including but not limited to,the rubber flex-hoses, or pads not running flat to the rotors,or even the bracketry.
When the system is set up and working correctly, the pistons only need to move out a few thousands of an inch to do their work. If you calculate out how much fluid that adds up to, I think you will find that even the 15/16 M/C has enough volume.Even a pair of 2.75 pistons, moving out .005 only makes about .94cc. And 8 of 1.25ers moving out .005 each is just .80 cc
Loose wheel bearings will knock back the pistons, sometimes pretty good, er,bad.....If the pistons are knocked back just .005, not very much, but that would double the volume required.I like to run a bit of extra clearance in my wheel bearings, specifically for knock back.The pads last waaaay longer, and it can't be bad for fuel-mileage.
rmchrgr
Skate And Destroy
Thanks AJ.
I thought about the pads but came to the conclusion that was not the issue. The pads are what came in the kit and were bedded in properly. They are a cold compound.
During the course of trying to get the car to stop better, I replaced the distribution block from a drum/drum to a disc/drum which helped a bunch with stopping power, the drum/drum did not have the proper bias. Still wasn't great though so I took out the prop valve in the rear line which also helped some but it never got to the point I wanted.
Like I mentioned, I had a Line Lock and it NEVER held, even with forceful pumping. It was plumbed correctly, I know for a fact so that wasn't the issue and it led me to the fact that there was just not enough pressure being generated.
In my search for answers, there was also the pedal ratio aspect. I think the OE drum pedal was not the right ratio. Hard to piece together this stuff with all these factors involved, you have to pay attention to every single component.
I thought about the pads but came to the conclusion that was not the issue. The pads are what came in the kit and were bedded in properly. They are a cold compound.
During the course of trying to get the car to stop better, I replaced the distribution block from a drum/drum to a disc/drum which helped a bunch with stopping power, the drum/drum did not have the proper bias. Still wasn't great though so I took out the prop valve in the rear line which also helped some but it never got to the point I wanted.
Like I mentioned, I had a Line Lock and it NEVER held, even with forceful pumping. It was plumbed correctly, I know for a fact so that wasn't the issue and it led me to the fact that there was just not enough pressure being generated.
In my search for answers, there was also the pedal ratio aspect. I think the OE drum pedal was not the right ratio. Hard to piece together this stuff with all these factors involved, you have to pay attention to every single component.
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