I am going to run manual front disc rear drum on my 69 camaro. Can anybody tell me what year and make of car to get the master cylinder from. Part numbers would be the most help. I am going to have to get it from a local autozone and it looks like they will have to order it, so, I want to make sure I am getting the right one. This question is probably best directed towards David, but if anyone has any input feel free to respond.
Thanks,

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Jason Renschler
Gilbert, AZ
1968 Camaro - 350 4-speed
1969 Camaro - 350 4-speed

Look for a 1" bore MC for a 67 with manual brakes. that was the only year it was an option.
If you don't find one, look for a Vette master cyl, which should be 1".

Some have used a 1 1/8" bore power brake MC on a manual application. The pedal travel will be reduced, but pedal effort would be higher by 30 lbs or so.
Very high pedal pressures are required for Manual disc brakes. Use a good carbon metallic pad to help it out.
David

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Check my web page for First Gen Camaro suspension info:
David's Motorsports page (http://ourworld.compuserve.com/homepages/David_Pozzi/)
First Gen Suspension Page (http://ourworld.compuserve.com/homepages/David_Pozzi/first_gen_suspension.htm)
67 RS 327 original owner. 69 Camaro Vintage Racer, 65 Lola T-70 Chev SB Can-Am Vintage Racer

David,
Will the pedal pressure be about the same as manual drum?

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Jason Renschler
Gilbert, AZ
1968 Camaro - 350 4-speed
1969 Camaro - 350 4-speed

David, does the choice of rotor size have any influence on the MC bore requirement?

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Rick Dorion
69 RS Conv,355,M20,4.10's and I don't worry about stone chips ( yet ).

One other option for you would be to go with a MC with a smaller diameter bore so pedal pressure is reduced. I am using a manual MC off a 75 or so Malibu with 6 cyl motor in my Nova because it has a 15/16" bore. Most people don't think they are manual brakes because the pedal is pretty darn easy to push. I also don't have excessive pedal travel, it is very nice. I'm running stock 11" disks up front and 11" drums in the rear, so that helps.

The size of the rotor does matter some as far as feel, but not which MC is needed. The larger the rotor, the further from the hub the braking force will be, so it gets better leverage. This means it takes less pressure to do the same amount of braking. You can liken it to using a short handled wrench versus using a breaker bar... for the same amount of inout you put on the handle, much more torque is applied to the bolt using the long breaker bar.

Hope that helps,
Bill C.


Good luck,
Bill C.


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Bill C.
Colorado Springs, CO

68 Camaro... someday!
71 Chevelle SS
70 Nova

Bill C explained it pretty well.
A larger diameter rotor will help with the leverage.
For example, a vette has an 11.75 OD rotor compared to a 11" for a stock Camaro.
A heavier engine or air conditioning will add to the pedal effort required to lock a wheel.

The variables for pedal effort are:
Pedal ratio (6 to 1 easier than 5 to 1)
MC bore size (1" easier than 1 1/8")
Rotor dia (12" easier than 11")
Caliper piston bore dia (3.25" easier than 2 15/16")
Tire diameter (24" easier than 26")
Tire traction coefficient (.8 easier than .9)
Road conditions (wet easier than dry)
Weight of car (light easier than heavy)
Brake pad friction coefficient (.4 easier than .3)

Some "extra info":

Larger caliper pad size does not neccessarily improve brake pad friction coefficient. A pad twice the size would not have twice the friction because PSI load on the pad would be cut in half, there would be no change.

I have set up a calculation for disc brake effort. It is not totally proven however. I need real world data to verify if it is right.

The calculation is:
Brake pedal effort x pedal ratio X MC bore in sq inches= line pressure psi.
Line pressure X caliper piston bore*(see note below) in sq inch = pad force X pad coeficient divided by rotor mean radius in inches = rotor torque in inch pounds.
Rotor torque in inch pounds divided by wheel radius in inches = torque at tire tread in lbs.
Tire traction coeficient X weight on tire = lbs required to lock front wheel.

You have reached the system limit when wheel force developed exceeds lbs required to lock wheel.
I hope I got the above calculation right, I did it from memory.

* For any caliper you only use one side of the caliper for the piston area calculations, ignore the other side.
If a differential bore caliper, add the area of all bores of one side and use that.

To lock a front wheel on a SB camaro with .9 traction coefficient tires:

BORE = PEDAL EFFORT TO LOCK FRONT WHEEL
15/16" = 97 lbs
1" = 110 lbs
1 1/8"= 140 lbs
While these may go up or down with tire traction and weight or tire height changes, they are good for comparison of pedal effort.
They are on the high side because I used a high tire coeficient of .9 G this would be a very good tire like a Corvette would have.

Power disc brakes usually don't require over fifty pounds to lock a wheel.
Guys who are big don't complain much about pedal effort, but many others do (like me).

I don't have a good way to predict drum brake pedal effort. This is because they are self energizing, the front shoe pushes on the rear shoe, jamming it into the drum. There ARE drum systems that are not self energizing, used usually on the front of big trucks.

Self energizing drum brakes are very sensitive to lining fade. A small change in lining friction due to heat is multiplied by the system and you really notice it.
I think fairly cool manual drums are pretty close to 50-60 lbs to lock a wheel. But when extremely hot, pedal effort can go over the 140 figure and higher!

Discs can increase effort due to heat fade too, but it is a much smaller change.

If anyone can contribute more info on drum brake effort, please do.
David


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Check my web page for First Gen Camaro suspension info:
David's Motorsports page (http://ourworld.compuserve.com/homepages/David_Pozzi/)
First Gen Suspension Page (http://ourworld.compuserve.com/homepages/David_Pozzi/first_gen_suspension.htm)
67 RS 327 original owner. 69 Camaro Vintage Racer, 65 Lola T-70 Chev SB Can-Am Vintage Racer

[This message has been edited by davidpozzi (edited 03-30-2002).]

[This message has been edited by davidpozzi (edited 03-30-2002).]

I purchased a manual disc brake master from NAPA for my 69 some years ago. It was sold under the "UNITED" Brake parts catalog.
Not sure if it still is listed though.

Have you auto parts store look up the master cylinder in the Autospeciality Catalog. These are new master cylinders but it may be in the 1970 style. I bought one for a 68 camaro. Mine cost fifty six dollars.

Well, I finally found what I was looking for. A 1967 chevelle listed a master cylinder for "manual disc". It is the same dual bail round style as the 69 camaro would of had. My local Checker auto lists it for $26.99 with a $5.00 core. Part # for those interested is R11372.
Hope this info helps you guys as much as it did me.


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Jason Renschler
Gilbert, AZ
1968 Camaro - 350 4-speed
1969 Camaro - 350 4-speed