brake distribution block help

[aslanefe 333]

44 minutes ago, danno said:

I tried jamming on the brakes years ago on wet asphalt.  The rear brakes locked up, I could not get the front to do it.  Again, my system is all factory except for a new master cylinder. I am the 3rd owner of the car since new, I bought it in 1982 with  60,000 miles on it, so I am pretty sure it is all factory stuff.    I have tried at least 3 masters, even a brand new one from Ford. I did put a new kit in the proportioning valve a year ago, but the results seem to be the same, although I have not tried locking them up again.  I still wonder.  Maybe it is time to put a pressure gauge on the wheels, as suggested? 

What kind of pads do you have on the front?

[barnett468 418]

13 hours ago, aslanefe said:

I did not say tires affect how prop valve works, prop valve does not care about tires or piston diameter, it just limits the fluid pressure applied by the master cylinder.  If you have bold hard tires on the back and soft sticky tires on the front with factory prop valve, which tires lock first, front or back? How about sticky tires on the back, bold on the front, which ones will lock first?

1. ummm...yes, you did.

" I believe, with modern better gripping tires, the original prop valve is not working right..."

2. I know how brakes work.

[signorc 31]

13 hours ago, barnett468 said:

Here are the answers......

what year is your car? 69 convt

did you install a disc brake pedal? yes

exactly what brake booster is it?  wouldn't know. came in kit from ssbc. see attached pics

what engine? 302

does it have a rough idle like it has a big cam. no

is the booster working? yes

did you check the booster for leaks? don't know how

does it require a lot of force on the brake pedal to do a moderately fast stop and feel like there is no power brakes? it brakes well enough to pass inspection and it feels  as thought the booster is working

did you check the clearance between the booster rod and the master cyl piston? This is my first step!  can i assume i gotta go with trial and error to get the distance correct?

did you install the same size rear wheel cylinders that you took out? I didn't know there was more than one choice.  I'm assuming so

do you have a disc brake master cylinder? I'm assuming only because it came with the conversion kit from ssbc

about how far does your brake pedal travel once it just barely begins to engage the brakes, 1",  2", 3", 4" ? 1 inch

not worrying about the fact that you can not lock the brakes up, does it at least stop well enough that it is safe to drive or do you have to use 2 feet on the brake pedal and pray it will stop in time?  It stops with 1 foot.  I'd like it to stop quicker in case of an unforeseen circumstance thats all 

Thanks for all your ideas!

 

 

 

 

 

 

[barnett468 418]

You're very welcome. I know this can be extremely frustrating, especially when parts are not easy to locate and may be quite expensive.

Did you use silicon brake fluid?

Does your pedal very slowly continue moving towards the floor when you hold your foot on the brakes. if it does, there is a small leak.

Does your pedal travel slightly less if you hit the brakes 3 times in a row within 2 or 3 seconds? . if it does there is air in the lines.

Did you install new front lines? . old brake lines can swell internally which can restrict the amount of fluid going to the brakes. we had this problem on a couple cars but it is rare.

 

If there are no problems with the brakes, my first thought is that you need a bigger brake booster or dual diaphragm type, or a master cylinder with a smaller piston. the bigger brake booster will not change the amount of pedal travel it has but it will require less force on the pedal to stop. one problem this may create is that your brakes can become a little too sensitive because they operate over such a small range of just 1".

If the pedal really does operate over just 1" of travel, it would be my preference to use a master with a smaller piston. The issue with this obviously is that you need to remove the master then measure the bore size. You can do this without removing the piston, but the hard part can be finding a replacement oem type master with a smaller piston than yours but I can help you with that.

There are aftermarket masters that may be smaller,  Wilwood makes some. It is also possible that brakes with different material would work better but unless you know what material yours are, it is hard to know if others would be better or not, however, ssbc most likely gave you generic pads, and if this is the case, there are pads that will be more effective. one of these pads is called "green stuff" mfg'd by EBC and they are very popular for street cars. Another popular pad mfg is Hawk. They also make several different materials for various apps.

 

BRAKE BOOSTER ROD TO MASTER CYLINDER CLEARANCE.

0.15" is the most common clearance used but it can be very hard to measure this.

 

BRAKE PEDAL MODIFICATION

Another possibility you can try is to relocate the pin on the brake pedal that the rod attaches to. I have done this numerous times. Look at the angle of the brake rod on the pedal. If it is parallel to the ground or it runs uphill as it goes to the booster, you can relocate it around 10 mm higher. Since it may be hard to get parts for this car in Italy, this may be one of your better options. This would increase the distance the pedal travels and reduce the amount of force required on the pedal to stop. This mod would make a moerate change, not a big change and will have the same affect as changing to a master with a slightly smaller diameter. If it still does not stop to your satisfaction, I would probably try different front brake pads first but they rotors sound be sanded clean to remove old brake pad material first then the new pads need to be broken in properly to achieve maximum effectiveness.

[signorc 31]

5 hours ago, barnett468 said:

You're very welcome. I know this can be extremely frustrating, especially when parts are not easy to locate and may be quite expensive.

Did you use silicon brake fluid?

Does your pedal very slowly continue moving towards the floor when you hold your foot on the brakes. if it does, there is a small leak.

Does your pedal travel slightly less if you hit the brakes 3 times in a row within 2 or 3 seconds? . if it does there is air in the lines.

Did you install new front lines? . old brake lines can swell internally which can restrict the amount of fluid going to the brakes. we had this problem on a couple cars but it is rare.

 

If there are no problems with the brakes, my first thought is that you need a bigger brake booster or dual diaphragm type, or a master cylinder with a smaller piston. the bigger brake booster will not change the amount of pedal travel it has but it will require less force on the pedal to stop. one problem this may create is that your brakes can become a little too sensitive because they operate over such a small range of just 1".

If the pedal really does operate over just 1" of travel, it would be my preference to use a master with a smaller piston. The issue with this obviously is that you need to remove the master then measure the bore size. You can do this without removing the piston, but the hard part can be finding a replacement oem type master with a smaller piston than yours but I can help you with that.

There are aftermarket masters that may be smaller,  Wilwood makes some. It is also possible that brakes with different material would work better but unless you know what material yours are, it is hard to know if others would be better or not, however, ssbc most likely gave you generic pads, and if this is the case, there are pads that will be more effective. one of these pads is called "green stuff" mfg'd by EBC and they are very popular for street cars. Another popular pad mfg is Hawk. They also make several different materials for various apps.

 

BRAKE BOOSTER ROD TO MASTER CYLINDER CLEARANCE.

0.15" is the most common clearance used but it can be very hard to measure this.

 

BRAKE PEDAL MODIFICATION

Another possibility you can try is to relocate the pin on the brake pedal that the rod attaches to. I have done this numerous times. Look at the angle of the brake rod on the pedal. If it is parallel to the ground or it runs uphill as it goes to the booster, you can relocate it around 10 mm higher. Since it may be hard to get parts for this car in Italy, this may be one of your better options. This would increase the distance the pedal travels and reduce the amount of force required on the pedal to stop. This mod would make a moerate change, not a big change and will have the same affect as changing to a master with a slightly smaller diameter. If it still does not stop to your satisfaction, I would probably try different front brake pads first but they rotors sound be sanded clean to remove old brake pad material first then the new pads need to be broken in properly to achieve maximum effectiveness.

Give me till Monday to try to modify the rod (I have a wife and 2 small kids I gotta acknowledge every so often lol) .  i just installed new Raysbestos pads. rotors had done 300 miles with the old squeaky pads which i just replaced. did not use silicone fluid (i like the old fashion stuff).  the pedal does not go down after i brake.   i did install new front lines. pedal travels the same once hit 2-3 times. as a matter of fact after hitting the brake 3 times, the stopping distance gets longer (due to heating I'm assuming).

One thing at a time........ let me adjust the booster rod and we'll see what happens. Ciao!

[barnett468 418]

ok, xlnt.

[1969_Mach1 333]

I don't have much to add other than the brake booster looks odd for a 1969 or 1970 Mustang.  It looks like a single diaphragm instead of the Bendix dual diaphragm brake booster found on 1969 and 1970 Mustangs.

[aslanefe 333]

19 hours ago, barnett468 said:

1. ummm...yes, you did.

" I believe, with modern better gripping tires, the original prop valve is not working right..."

2. I know how brakes work.

Not working right does not mean how it works is changed. Put sticky tires, pads with better friction coefficient, bigger disks etc, your brake bias is going to change, to change the bias back to how you want, you are going to need a different prop valve that works right for your changes,  a valve with proper rate and knee point for your current combination.

[barnett468 418]

28 minutes ago, aslanefe said:

Not working right does not mean how it works is changed. Put sticky tires, pads with better friction coefficient, bigger disks etc, your brake bias is going to change, to change the bias back to how you want, you are going to need a different prop valve that works right for your changes,  a valve with proper rate and knee point for your current combination.

that is a more clear explanation of what you were previously trying to say

[danno 128]

This post is giving me ideas.  I do not want to hijack it with my problems, so I will start my on subject ( if I still need it ) in May when I start driving my car again.  But this is giving me ideas and filling in details.   Thanks 

[aslanefe 333]

5 hours ago, danno said:

This post is giving me ideas.  I do not want to hijack it with my problems, so I will start my on subject ( if I still need it ) in May when I start driving my car again.  But this is giving me ideas and filling in details.   Thanks 

Danno, tried to send you a link that has good info but looks like your inbox is full.