Brake advice?

[PSYCHO]

Afternoon all I'm in need of some advice on my rear brake issues.
Here is some background info, FFR kit which supplies all the braking components from a 99/04 mustang twin piston front and single piston rear calipers with standard non slotted rotors. I have installed a 7" dual diaphragm booster fitted with a XB master cylinder with an in built prop valve.

Here's the issue the pedal requires a lot of pressure to stop the car and only at the bottom of the pedal does the front end want to lock up. After testing/bedding in the brakes they feel weak and almost non assisted by the booster . I have had the bosster rebuilt and the master cylinder stainless steel sleeved I have replaced the pads for softer ones and tested again now the car dips the front end a little better but still requires a lot of pressure. After the brake checks the front rotors are really hot but the rears feel cool, I have fitted a aftermarket prop valve and wound it all the way on and off but no change I have checked the vacuum on the booster and that's up in the 20s so I am now at a complete loss. Any help or recommendations would be appreciated thank you

Regards Psycho

[Rob. Smith]

It's been a long time but I had some dramas with the proportioning valve on a 73 mustang. After a lot of headaches I found that it was worn out. not sealing properly etc. Got it rebuilt by a "brake expert" and it was useless. The apprentice had had a go and put it together all wrong. You can buy new replacements now. Check that first.

[Bender]

Hi psycho. A propotioning valve is just like a tap that restricts the flow. You need to have too much flow/pressure before you can use a proportioning valve to restrict it back. It cannot create flow/pressure it can only restrict it. In some of those early pbr cylinders they had a shuttle valve that operated a switch/light if you had a failure in one system. Its a nylon switch that screws in the side or bottom of the master cyl. Pending on the model. This switch needs to be removed while bleeding the brakes. The shuttle valve will move towards the system that is being bled. ( lowest pressure)(Front or rear) if the switch is still installed while bleeding. 2 things can happen. 1 the shuttle can be held by the switch in one direction resticting the flow. 2 sometimes the switch gets damaged. ie bent. If the master cyl has a switch. I would unscrew it. You may hear and feel a click as you remove it. That will be the shuttle being released.After bleeding the system. Pump the pedal a few times to centralise the shuttle vavle then re install the switch. Hope this helps. If you have more questions, maybe add a photo to make sure its the master cyl I think it is. One other thing I would check is the master cyl bore diameter. I think there was different sizes for the drum brake and 4 wheel disc brake models. This will effect the master cyl to caliper ratio. Regards Bender

[Zedn]

Is the pedal easy to push down with the rear bleed nipple open? I wonder if there is a blockage in the rear line or stuck pads.

[PSYCHO]

Originally Posted by Rob. Smith

It's been a long time but I had some dramas with the proportioning valve on a 73 mustang. After a lot of headaches I found that it was worn out. not sealing properly etc. Got it rebuilt by a "brake expert" and it was useless. The apprentice had had a go and put it together all wrong. You can buy new replacements now. Check that first.

Thanks Rob
The built in prop valve has been reconditioned by the brake shop along with the master cylinder which they pressed in a new bore sleeve which so far hasn't made much difference so I have fitted a second external prop valve unfortunately still no change but thank you for the advice mate👍

Regards Rob

[Gav]

Why did you use a XB master cylinder?
Was it recommended by someone?

[PSYCHO]

Originally Posted by Zedn

Is the pedal easy to push down with the rear bleed nipple open? I wonder if there is a blockage in the rear line or stuck pads.

Thanks Zedn
I have had both rear callipers off the discs and pumped the pedal and I could see the pads close the gaps and stay there then reset them and refit them to the discs. I then pumped them again and could see them apply pressure to the discs it just seems to not apply enough pressure under drive. Thank you for the advice I will keep looking.
Regards Rob👍

[PSYCHO]

Originally Posted by Gav

Why did you use a XB master cylinder?
Was it recommended by someone?

Hi Gav
It was just the idea I had at the time and the fact that I already had a 7" booster which is the only size I can use due to space restriction. Is there something else you would suggest for the master mate I'm always up for ideas.

Cheers Rob👍

[Gav]

The problem that you have is that you need to match the master with the calipers.
It sounds like the front calipers are not getting enough fluid (cylinder too small) and the tears are doing most of the work.
Try ringing racebrakes, hoppers stoppers or a reputable brake shop near you, tell them what you have and let them make a recommendation.
Personally, Howard from race brakes ph 03 96877222 is fantastic to deal with.

[PSYCHO]

Originally Posted by Bender

Hi psycho. A propotioning valve is just like a tap that restricts the flow. You need to have too much flow/pressure before you can use a proportioning valve to restrict it back. It cannot create flow/pressure it can only restrict it. In some of those early pbr cylinders they had a shuttle valve that operated a switch/light if you had a failure in one system. Its a nylon switch that screws in the side or bottom of the master cyl. Pending on the model. This switch needs to be removed while bleeding the brakes. The shuttle valve will move towards the system that is being bled. ( lowest pressure)(Front or rear) if the switch is still installed while bleeding. 2 things can happen. 1 the shuttle can be held by the switch in one direction resticting the flow. 2 sometimes the switch gets damaged. ie bent. If the master cyl has a switch. I would unscrew it. You may hear and feel a click as you remove it. That will be the shuttle being released.After bleeding the system. Pump the pedal a few times to centralise the shuttle vavle then re install the switch. Hope this helps. If you have more questions, maybe add a photo to make sure its the master cyl I think it is. One other thing I would check is the master cyl bore diameter. I think there was different sizes for the drum brake and 4 wheel disc brake models. This will effect the master cyl to caliper ratio. Regards Bender

Thanks Bender
Awesome info in your post mate yes it is the PBR master with the nylon brake switch and I didn't remove it when I bench bled the MC as for the bore ratio it has had a stainless steel sleeve pressed into it when rebuilt to suit disc disc system, I will remove the switch and re bleed the system and try it again I will definitely let you know how I go thanks again mate👍
Regards Rob

[PSYCHO]

Originally Posted by Gav

The problem that you have is that you need to match the master with the calipers.
It sounds like the front calipers are not getting enough fluid (cylinder too small) and the tears are doing most of the work.
Try ringing racebrakes, hoppers stoppers or a reputable brake shop near you, tell them what you have and let them make a recommendation.
Personally, Howard from race brakes ph 03 96877222 is fantastic to deal with.

Thanks for the recommendation I will give them a call Monday
I thought that a 1" bore from a large falcon would of had enough pressure to activate a standard brake setup from a fox body mustang but I will check
Cheers Gav👍

[Jaydee]

Another way to test the booster. Apply the brakes with the engine of, then start the engine and the pedal should go down a little bit further.
JD

[Treeve]

Think of it like gears on a mountain bike - small gear at the back and big at the front is hard to push down on the pedal. Try a smaller size on the master. It’s not about how much fluid you move it’s about the pressures you generate in the circuit.

[PSYCHO]

Originally Posted by Jaydee

Another way to test the booster. Apply the brakes with the engine of, then start the engine and the pedal should go down a little bit further.
JD

Thanks Jaydee I have tested that out and had the booster rebuilt just in case I have tried a single diaphragm and then a dual diaphragm booster but unfortunately no change thanks for the suggestion mate

Regards Rob👍

[PSYCHO]

Originally Posted by Treeve

Think of it like gears on a mountain bike - small gear at the back and big at the front is hard to push down on the pedal. Try a smaller size on the master. It’s not about how much fluid you move it’s about the pressures you generate in the circuit.

Thanks Treeve that makes perfect sense mate I will look into that once I try out what Bender has suggested cheers mate

Regards Rob👍

[Zedn]

Originally Posted by PSYCHO

Thanks Treeve that makes perfect sense mate I will look into that once I try out what Bender has suggested cheers mate

Regards Rob👍

Whats your pedal from? Maybe its too short?

[Zedn]

Just had a look at the FFR website. I see they supply a willwood pedal assembly and master cylinders with the complete kit. Why not just email them and ask what master cylinder(s) they provide and then check that with the measurement of the one you have?

[PSYCHO]

Originally Posted by Zedn

Just had a look at the FFR website. I see they supply a willwood pedal assembly and master cylinders with the complete kit. Why not just email them and ask what master cylinder(s) they provide and then check that with the measurement of the one you have?

G'day Zedn yes they have supplied a willwood pedal assembly but they only supply 2 under dash reverse facing 1" master cylinders which I decided to use one for the clutch instead and the pedal is normal length if anything it could be a bit shorter lol. I have weakened after trying out what Bender suggested but to no avail so I have taken it to the brake shop to see what they can come up with fingers crossed🤞

Thanks for the suggestion mate🤙

[Gav]

I have the standard mustang brakes on my coupe.
FFR supplied a 3/4” mc for the front and 5/8” for the rear.
What do you have?

[Zedn]

Originally Posted by PSYCHO

G'day Zedn yes they have supplied a willwood pedal assembly but they only supply 2 under dash reverse facing 1" master cylinders which I decided to use one for the clutch instead and the pedal is normal length if anything it could be a bit shorter lol. I have weakened after trying out what Bender suggested but to no avail so I have taken it to the brake shop to see what they can come up with fingers crossed🤞

Thanks for the suggestion mate🤙

Do they supply a dual master cylinder set up with balance bar?