Technical question on caliper clamping force
 

Below is a pic of a rebuilt 4-piston caliper for a 1995 Toyota 4Runner that looks as beefy as a 993TT caliper. Knowing the guys at the parts wholesaler/runner business below me, I got it for $33.

it's heavier than a 993TT caliper, but not by that much. Not saying I want to start plugging these onto 911's, but it got me thinking about the performance of this caliper vs. a Porsche one of about the same size.

how do you measure the clamping force or efficiency of such things as calipers?

http://forums.pelicanparts.com/uploa...1197340124.jpg

Clamping force is simply a function of piston sizes. If the pistons were the same size as that of a 993TT caliper, the clamping force exerted would be the same (assuming the same pedal pressure and master cylinder size). Smaller pistons exert less force, larger pistons exert more.

That looks like an iron caliper. It will be much heavier than the equivalent Porsche part.

-Andy

Shaun,
Interesting question. Like you, I have been trying to come up with a more cost effective solution to the expensive Brembo calipers. I would tend to agree that the Toyota caliper appears to be Cast Iron would be significantly heavier. I'll weigh one of my 964 calipers tonight, which is roughly the same size, so we can use as a reference.

BTW, I am also surprised about how beefy those calipers are. Very impressive.

Like someone mention before, clamping force is a factor of piston size and hydraulic pressure from the MC. I bet that Bill V could shed some light on this for us.

Noel

Shaun,
I was thinking along the same lines when I replaced the calipers on my Tacoma. 4 pistons, fixed caliper, $50.00 seemed like a winner. Unsprung weight is up there of course, but these calipers will stop a 4500 lb truck and tow weight of 5000 lbs. I'll bet we need $1500 of adapters to bolt on a $50 part.

thanks Jonathan, good to know.

Noel, please post if you have a chance to weigh your 964 calipers. I'll weigh one of these today. Yes, it's cast iron, but doesn't feel that heavy compared to 993TT calipers I've picked up before.

LJP, $1500 worth of adaptors AND custom hats and rotors! :D

The great thing about my new (to me) 4Runner is that it has the extensive, and expensive, rust lightening option. Just look at this lower front A-arm...light as a feather (most of the underside is gone) as well as the anti-roll bar drop mount, etc.

http://forums.pelicanparts.com/uploa...1197382654.jpg

WOW, I remember you telling me about that A-Arm. Unbelievable. I'm glad you caught this before a failure on the road...

Yup, you really have to see this thing in person Noel to appreciate that it was one pothole away from disaster. And with the roads here in Boston...:(

I'm replacing every component save for the steering knuckle and 4WD hubs in the front suspension.

klauke correctly described the idea as far as hydraulics go. otyher issues are related to the stiffness of the components and materials.

Here are some weights
993 n/a front caliper w/o pad 7.50
993 n/a front pad I&O 2.40
993 n/a rear caliper w/o pad 6.00
993 n/a rear pad I&O 1.70
front 993 304x32 16.00
rear 993RS 299x24 12.00
rear 993RS 322x28 18.20
front 993tt 322x32 20.50
4x12mmx77mm caliper bolts 0.75
Big Red caliper 8.30
993RS caliper 8.00
993tt (wet) 8.25
911rear rotor 13.10
911 front rotor 10.75

993RS total front 26.50
993RS total rear 26.20

993 total front 24.00
993 total rear 21.00

thanks Bill.

these weigh 12 pounds without pads. pistons are about 50mm give or take 5mm.

964 Calipers are 6 lbs each sans pads. I just weighed them.

That's correct. The 964 f/r & 944t f/r are all essentially the same caliper as the 993 n/a rear caliper. small body, 4 piston, axial mount. There are differences in piston size and throat width. a caliper pad set will weigh ~1.7#

Piston sizes?

??

Sorry Bill, I was hoping you had the piston sizes of 964-993TT calipers.

I guess in the end this is all mental masturbation given how heavy these calipers are, but hard to believe they are only $75 on the street vs. megabuck Brembos.

I will say that NA cars up through 89, 911 brakes are are very inexpensive compared to other parts and perform to a very high level.

All of the brake specs for '72 -98 are here