Hey guys!

These disk brake questions sure seem popular in this forum! Here is my turn at getting some help!

The brakes on my Super Bee are absolutely terrible. I can not lock the brakes under any circumstances.

I have bled and rebled the brakes (pump method, gravity, MityVac) and there does not appear to be any air trapped in the lines. I pulled the master off and re-bench bled it, and there are no air bubbles coming out. No leaks in the lines that I can tell.

I have seen Feets' great "Brake Math" thread... I even built a Google spreadsheet for doing the calculations for me, but Im just not sure how to tell if anything is mismatched, even with the numbers that the spreadsheet spits out at me.

Here is a rundown of things that I think are related to braking on my car.

69 Super Bee
Manual brakes
Wilwood 1" master cylinder
Wilwood 10.75" front rotor
Wilwood Dynalite front calipers - 4 x 1.75" pistons (4.8 square inches)
Dr Diff 10.7" rear rotor
Dr Diff Ford caliper... ??? piston?
Stock manual pedal approx 7:1 ratio

* 17x8 front wheels
* 18x10 rear wheels

Here are the numbers that I get for my front brakes from the Math post.

1" Master Cylinder piston area - .79 square inches
Front caliper piston area - 4.8 square inches
Master cylinder pressure @ 100 lbs leg force- 891.27 psi
Effective radius of rotor - 4.94 square inches
Brake torque - 3528.26
Pad movelent @ 1" - 0.0058

Does anything here sound completely mismatched? I know that the front brakes are positively tiny these days, but I would have thought that they should be big enough to stop the car a few times in a hurry.

Any help is greatly appreciated!

You can try a 15/16" bore master cylinder and a pair of aggressive brake pads for the front (Wilwood # 15E-6096K).

I had a beeotch of a time with my 4 wheel disc brakes earlier this year. I tried several master cylinders, proportioning/combination valves and I even tried different front calipers.
It all started when I wanted to shed some weight and ditch the power brakes for a manual setup. I tried 3 different bore size manual master cylinders and they all resulted in hard pedal with zero ability to safely stop the car. I threw in the towel and went back to the power booster and added a vacuum storage can.
I'm not one to give up on a problem. I still think that the answer is out there but I just got tired of messing with it all.

Not a big fan of the Wilwood master, IMHO I'd swap it out with a factory piece, either a Fenco pn#1523 or Cardone 101523 (Autozone, CarQuest, most parts stores), or napa NAPA TruStop line 10-1523, Summit Racing.com pn# 100-101523...this master has a 1.031 bore, large fluid capacity and proper stroke for a 7:1 pedal ratio....for a manual disc brake system

No mention of whether or not your using a distribution block/ proportioning valve etc,


For your combo, I'd recommend, no proportioning valve, you could use a stock drum/drum distribution block, but remove the residual valve located in the rear line 69 and down factory disc/drum cars, if the car was previously disc/drum (no mention of the cars former factory equip.) if the car was previously drum/drum the distribution valve is fine,...although IMHO I'd eliminate any factory DV/PV I'd tee the front lines directly of the master, and plumb the rear line directly off the master, and test the system (with 2000 psi hyd gauges) to see what the bias/pressure specs are, and determine if you need an adjustable pressure valve in the rear line

Mike

There are a couple different causes for something like this. Before we can even speculate we need to know what the pedal is doing.
Is it hard and not moving far or soft and squishing to the floor?
If you keep bleeding them looking for an answer it tells me you've got a soft pedal.
Assuming that's the case, what kind of calipers do you have out back? I had a never ending soft pedal after a brake swap and it turned out to be a tiny bit of air in the rear calipers. I had already bled the brakes numerous times and never got any air. A close examination showed the rear calipers were mounted in such a way that a tiny bit of air could be trapped. I had to pull them off the mounts, hold them at a funky angle so the bleeder was absolutely the highest point, and gravity bleed them for a few seconds.
That's all it took.
Yeah, I was a wee bit irritated with myself.

Hey Guys!

Thanks for the help so far guys! :-)

I see that Dr Diff is saying to use a smaller master, and Dayclona is saying to use a larger one.

I do think that using the Wilwood master was a bit of a mistake as it has been quite the pain in the butt. Having said that, it cost enough money that I dont want to just toss it in the trash to try another master, unless Im positive that doing that will cure my troubles.

OK, some answers to some questions:

- This was originally a 4-wheel drum car.

- I am using stock unmodified distribution block.

- Have a prop-valve sitting on the shelf, but it currently is not plumbed in. Previously I ran the Wilwood disks and a stock Master with the stock rear drums and I used the PV then.

- Pedal is not soft... it just doesnt seem to stop quick enough no matter hard I push on it. I wouldn't really call it terribly hard as it does move some. JCC is correct, I am simply bleeding the brakes because I feel I should be doing something to correct the issue.

- Car with me it it weighs somewhere in the 3700-3800 lbs range. Aluminum everything on the engine, aluminum rad, wilwood disks all took a decent amount of weight off, but those large forged wheels added some back on!

- Tires are Falken Azenis RT-615Ks... 245-45-17 and 295-40-18. Awesome sticky tire by the way!!!

- Pads are unknown compound... stock Wilwood on front and whatever Dr Diff sent in his kit for the rears.

Thanks for the help guys!

I'd look at a smaller MC.

You need a smaller bore master cylinder to increase the line pressure and aggressive front pads to help compensate for the small diameter front rotors.

Of course, you really need much larger brakes for a nose heavy muscle car with large wheels and sticky tires.

Hey guys!

Ok... So I need a new master. Is there a readily available 15/16" master? I have a 2-bolt adapter for the Wilwood master cylinder.

I also have an adjustable pushrod that adjusts to be only as long as a stock pushrod or shorter... Will that be useable with the stock style MC, or would it need to be longer to compensate for the adapter?

Thanks for the help!

You can buy a 15/16" bore 4-hole iron master cylinder from any auto parts store, but as far as I know, I'm the only source for a manual brake, 15/16" bore aluminum master.

If you are running an AR Engineering MC adapter, you do not need to alter the length of your manual brake push-rod.

Hey DrDiff... I don't believe it's an AR adapter... It came in a kit I got from Magnum Force. I guess that the difference would be the thickness? What is the thickness of the ARadapter so I could measure mine and see if it would work.

How much for the 15/16"master from you?

Thanks a lot, I really appreciate the help!

I don't know the thickness off the top of my head, but it is fully machined with a diamond shaped relief next to the master. It is not flat.

The complete kit runs $100. The master cylinder runs $70 separately.

The 1" MC piston is too large for manual disc brakes unless you have a very high pedal ratio. Run the .750" Wilwood MC with at least a 6-1 pedal ratio and you will have great brakes. What looks good on paper is not a substitute for experience. The paper math just gets you to a starting point.

The 15/16 MC is a pretty good fit for many common brake systems. Not too many guys have mentioned going to a 3/4" MC. That's getting fairly small and pedal travel can become excessive.

Still, if that's what works on your car, go for it.