Master Cylinder guidance please

[Ian Hunter]

I have the standard Mustang brake master cylinder as supplied by Breeze: Breeze Automotive Factory Five Racing

It works just fine, but the predal pressure is too high and with not enough feel, which (particularly on the track) gives little confidence. I have changed to EBC brake pads which has helped.

I am looking to fit a remote servo, but my potential supplier has suggested that the master cylinder bore at 7/8" is too large.

Does anyone know of another master cylinder with a smaller bore that would be directly interchangeable?

Many thanks

Ian

[MikeKelly]

Originally Posted by Ian Hunter

Does anyone know of another master cylinder with a smaller bore that would be directly interchangeable?

To answer that question, no, maybe someone else does.

My question: Has the brake pedal you're using been modified to provide at least 6:1 mechanical leverage?

And here's some interesting reading while you're thinking about brakes:

Brake bias concern and a warning for safety


Mike

[Ian Hunter]

I don't have any proportioning valve installed anywhere and on track have yet to lock a wheel - I am happy with the distribution (I thought!) its just the pressure and lack of feel.

I am interested that you mentioned modifying the pedal - I have stock Mustang clutch and brake pedals using their original pivot points - I don't remember seeing a need to modify anything - should I have done?

My brake supplier suggested a new pedal box, but I reckon I would have to take the body off to change it, bearing in mind various mods had to be done in our rhd conversion as the Mustang pedal unit wouldn't fit - it isn't straight as I remember! Worse, the fuseboard sits under the pedal box, just to make it even more difficult!

One of the threads you pointed me to used a Mitsubishi master cylinder - anyone else done that and know what model it came from?

Many thanks

Ian

[MikeKelly]

I can't help you on the Mitsubishi MC, maybe someone else will jump in.

Regarding the brake pedal:

A lot of people here use (one of) the (various) Mustang pedal box(s), and the power brake pedal is far more common than the manual brake pedal (I'm not sure I've ever even seen a manual brake pedal or stock manual brakes in a late model Mustang). Anyway, the power brake pedals are usually about 4:1 mechanical leverage, while manual brakes require more like 6:1.

Most of the "help - brake problem" threads seem to come from having used an unmodified power brake pedal without a booster. It's a well known issue, the FFR build manual mentions it specifically (use a booster, or modify the pedal to 6:1).

So, here are a couple of links that go into further detail about the brake pedal mod.

brake pedal mod

Brake Pedal Modification

HTH,

Mike

[Ian Hunter]

Mike

That's definitely worth investigating!!

My Breeze description says the one I bought has been modified, but I will double check!

Breeze Automotive Factory Five Racing

Thanks for that!

Hopefully someone will pipe up with a master cylinder!

Best regards

Ian

[OPEN ROAD]

In past threads on this subject I believe 1984 jeep m/c was mentioned. look into the archives under the roadster or ask an expert forums - Gordon Levy or Richard Oben.......but that pedal mod might be all you need.

[Cone Basher]

I have the 84 jeep master cylinder on my Coupe which is 15/16. I have 13 inch front brakes and spindles (straight leg) from the Mustang Cobra with a brake upgrade for the rears from Richard Oben, also Mustang Cobra items for the IRS. My pedal box is the Mustang item with the brake pedal mod with the adjustable push rod from Whitbys. I installed Hawk HP+ pads on the rear of my car and the pedal effort is very high compared to power brakes but they work fine once once I got used to the higher effort. Perhaps a brake pad swap might help.
HTH
CB

[ehodger]

I have pretty much the same set up as Cone Basher right down to the Hawk pads the only exception is I am using the 94 cobra master cyl. also 13/16". High pedal effort but it would put you through the windshield without seat belts. You need to modify your pedal.

[h82crash]

Originally Posted by Ian Hunter

Mike


My Breeze description says the one I bought has been modified, but I will double check!

Breeze Automotive Factory Five Racing



Best regards

Ian

The photo of that Breeze pedal does not appear to be modified. If you going with manual brakes, the mod is a must. The links above show it. I made mine even closer by 1/2".

[Ian Hunter]

I managed to get some "under car" time over the weekend and checked the car over in advance of my Track Day next week.

I took a tape measure into the footwell and reckon my brake pedal is 30 cm long from the centre of the pivot point at the top to the centre of the pedal pad at the bottom. The master cylinder rod pivot is 6 cm from the top, giving me a 5 to 1 ratio as close as I can guess.

The master cylinder rod is currently a perfect 90 degrees to the pedal. If I move the master cylinder rod pivot up 1 cm, I will get 6 to 1 as a ratio, but lose my perfect 90 degree angle.

Is this a problem? Or is it just worth it?

Best regards

Ian

[Cone Basher]

Ian: The brake pedal mod does not move the pushrod up, it lowers the upper pivot point and that creates the leverage. If memory serves me correct my mustang pedal box came with two holes to be used as pivot points you want the bolt for the pivot point in the lower of the two holes on each side. I cut a section 1.5 in (I think, memory again), out of my brake pedal between the pivot point and the push rod and had it welded on, this lowers the upper pivot but maintains the correct anglefor the push rod. I suggest you use the google link below and enter brake pedal mod and you should find lots of info there;
HTH
CB

[CraigS]

If you decide that you need to do the pedal mod spend a long time under the pedal box looking at how it could be done. I did mine in the car (left hand drive) and it was not fun but definately worth it. Apparantly there is some variation as to whether the head of the bolt is on the left side or if the nut is on the left side. this can make a big difference in how hard it is to get apart. on mine, I ended up cutting a hole in the aluminum to allow the head of the bolt to pass through to allow enough movement to remove it.
I just looked at the Breeze link and it specifically states that the pedal is modified so I definately trust that it is.
Another option might be to go to a vacuum power brakes setup like this.
Whitby Motorcars
That would get your overall effort down which would help w/ feel.
See this thread for a comment about the PB results
Whitby's power brake install