I think I need a new master cylinder which brand?

[Shaunp]

You dont have residual pressure valve any where do you?

[lukep6470]

Yep rear goes to the small reservoir and the two front go to the large reservoir. As I understand it the P6258A is suitable for disc/disc.

[hybrid]

Does it go to a distribution block after the master? That's often where the valve is.



The cylindrical part on the end of the block is the residual valve I think.

[Shaunp]

If I recall my 67 had it in line with the rears, but after the block.

[lukep6470]

No the pipes go straight to the calipers. I'm starting to think these GM style boosters don't work with the PBR kit. The other problem is the setup is very close to the inner fender. I don't think I could get anything bigger than an 8" booster in the engine bay.

[Shaunp]

No the pipes go straight to the calipers. I'm starting to think these GM style boosters don't work with the PBR kit. The other problem is the setup is very close to the inner fender. I don't think I could get anything bigger than an 8" booster in the engine bay.

The valve would be in the rears circuit. As long as the booster rod allows the master piston to come all the way back it will be fine.

[Nuts]

Just a thought, are you using a power brake pedal?

[lukep6470]

Now that you mention it, no. I have put a return spring on the pedal though.

Isn't there a circuit in the booster that is supposed to release the pressure when you take your foot of the pedal? It's like that circuit isn't working properly.

[Nuts]

Your problem could be as simple as the pedal. Check out steves site.

http://www.mustangsteve.com/fyi_brakepe ... edals.html

[lukep6470]

Well hello there!!

Scott Drake adjustable manual pushrod

So I don't think my firewall is right. I have to lift the pushrod up to fit it on the brake pedal. I think the angle is what is causing the binding of the booster. Remember my car has had a RHD conversion so I don't think things line up like they used to. This will lower the lug for the pushrod thus making it more in line with the booster.

[hybrid]

The manual pedals connect higher up the pedal for more pressure. The power pedals connect lower down the pedal.

[lukep6470]

OK so that kit lines up the pushrod with the booster perfectly. The brakes can lock up on dry tarmac if you really mean it.

The pedal is still not returning properly. I've now worked out it is fine when the car is cold and the booster starts binding once everything gets hot. I think the piston in the back of the booster is heating up and binding once it expands a bit. I've put some grease on the piston to see if that sorts it.

[lukep6470]

I've now replaced the 7" double diaphragm booster with an 8" double diaphragm on the weekend. It seems to have a stronger return spring than the 7" units and is a slightly different design.

I've only driven it 30 miles now but the brakes now feel like they should. They are a lot more responsive and the pedal is returning properly. They're not as grabby as the Mrs Suzuki but they do feel like brakes from a modern car. I won't call this fixed until I've put a couple of hundred miles on this booster but it is sooo much better.