"Large" GM calipers VS. "Small" (metric)

[SinistrV6]

I appears that I'm gonna have to change over from the large (early Camaro) caliper to the late Camaro (metric) so they won't rub the air bags at full lock.

Either that or buy an aftermarket setup from Baer or Wilwood. Big Buck$.

Is there much difference in the stopping ability of the two calipers? Anyone have experience with both?

This is in my '36 Chevy w/ Fatman's MII cross member and 10.75" Camaro rotors.  I realize I'll have to change caliper brackets.
--
Richard

1936 Chevy Standard Sedan (Buick Grand National powered!!)
2003 Chevy Avalanche - Black WBH
2003 Chevy TrailBlazer - also black
1987 Buick GN (sold as rolling chassis)
1986 Buick GN (stolen 4/99)

[Bob Paulin]

I appears that I'm gonna have to change over from the large (early Camaro) caliper to the late Camaro (metric) so they won't rub the air bags at full lock.

Either that or buy an aftermarket setup from Baer or Wilwood. Big Buck$.

Is there much difference in the stopping ability of the two calipers? Anyone have experience with both?

This is in my '36 Chevy w/ Fatman's MII cross member and 10.75" Camaro rotors.  I realize I'll have to change caliper brackets.
--
Richard

Richard:

Have you actually looked to see if the later Camaro calipers will fit the earlier spindle? Don't forget the later Camaros utilized a modified strut suspension.

We tried to help an oval-tracker install the later Camaro, aluminum rear calipers, but he ended up using the so-called "Metric" calipers from the 108" intermediate car.

The "big" GM caliper has a 2-15/16" piston while the so-called "Metric" caliper from the 108" intermediate chassis has a 2-1/2" piston.

What's the difference?

The "Big" piston has a surface area of 6.777-inches while the "Metric" has a surface area of 4.908-inches.

So, 100 pounds of brake system hydraulic pressure creates 677.7 pounds of force with the "big" caliper and 490.8 pounds of force with the "Metric."

Now, there are some "Metric" calipers available through some oval-track parts dealers that have been bored out to 2-3/4- inches....resulting in 5.939 square inches of surface area, and 593.9 pounds of force for 100 pounds of hydraulic pressure.

These modified "Metric" calipers are selling for around $70 each.

I just built a couple for the car I built for my cousin. I also installed phenolic pistons which seem to help a bit with the heat problems associated with racing.

If you are now marginal on braking with the "big" calipers, going down in size is probably not a good idea....and, you probably should be considering multi-piston racing calipers such as Wilwood, etc.

But, the modified "Metrics may be a reasonable compromise for you if the car isn't a tank.

Bob Paulin

[wayfarer]

Before you use the metric calipers, read this:

Brake question - today must be the day



Apparently, the '78 monte carlo calipers are the same size and provide much better performance with the master cylinders we all use on our cars.  I'm switching out my metric calipers ASAP.

[SinistrV6]

Wow!  You guys really know your stuff!

After my original post I found out that I don't have the "large" calipers, but rather, the "Metric" ('85 Camaro according to receipts) calipers.

I don't know how well the brakes work since the car has never been finished (someone else's abandoned project).  

I saw some of the "modified" Metric calipers on a racing parts site while searching for info on all this.  That may be a good option.  
Anyone have any idea what the correct M/C would be for the calipers that need a "quick take-up" M/C?  Why not the factory Camaro M/C that was part of the factory system?  Or will the plastic reservoirs not survive under the car?  Maybe MP Brakes can steer me to the correct one to work with this setup and my '01 Explorer rear w/discs....

There's no telling how many people out there are having this problem and just decided to "live with it" (not acceptable to me)!  All safety equipment has to be in perfect working order or it WILL NOT leave the driveway.  I don't want to waste money, but I'll spend what's neccessary to have good brakes.

[Bob Paulin]

Okay....here's some additional notes I found from one time when I was working out some brakes for a customer.

First of all, you'll have to figure what your own pedal ratio is. A higher numeric ratio - 4:1 versus 3:1 for example - will result in more input force at the Master Cylinder for a given amount of force against the brake pedal.

Since there are so many possibilities, I won't even go there, but here's some Master Cylinder info.


Master cylinder size - piston area in square inches - pressure developed from 100 pounds of input force at the MC piston (not on the brake pedal).

3/4" - .441 Sq. In. - 226.757 p.s.i.
7/8" - .601 Sq. In. - 166.384 p.s.i.
1" - .785 Sq. In. - 127.388 p.s.i.

Now, here is the actual force output of the different calipers resulting  from 100 pounds of force input at the MC piston. It is often called "mechanical advantage" when discussing hydraulics.

2-15/16 caliper (6.777 Sq. In.)

3/4" MC = 1536.372 lbs.
7/8" MC = 1127.734 lbs.
1" MC = 863.308 lbs.


2-3/4" caliper (5.939 Sq. In.)

3/4" MC = 1346.710 lbs.
7/8" MC = 988.184 lbs.
1" MC = 756.557 lbs.

2-1/2" caliper (4.908 Sq. In.)

3/4" MC = 1112.923 lbs.
7/8" MC = 816.637 lbs.
1" MC = 625.220 lbs.


A 2-1/2-inch caliper actually puts out MORE braking force with a 3/4-inch Master Cylinder than a 2-15/16-inch caliper does with a 1" Master, and nearly as much as a 2-15/16-inch caliper driven by a 7/8-inch Master.

So, you see, it is actually possible to INCREASE braking force using smaller calipers.

You also need to factor-in brake fluid volume movement with various calipers and masters.

A 3/4-inch master cylinder piston will need to move further than a 1-inch master to move a given caliper piston the same distance....

....and a bigger caliper piston will require a given master cylinder piston  to move further in order to move it the same distance as a smaller caliper piston.

The "fun" part is coming up with the right combination to give a desired braking force with an acceptable pedal "feel" and movement.

Bob Paulin


P.S. Hey Fat Cat!!!

If you wanna' somehow combine the two sets of calculations I have given in this thread and file them in the Tech section for future reference, that's fine with me.

It'll save me from having to post it again, and somebody may find it helpful if they run across it while surfing through the Tech area.

B.P.