63 F85 Cutlass

Im currently looking for a clutch. I've been looking and asking around and was wondering what opinions on this board were between the Borg & Beck 3 finger style pressure plates and the Diaphram style pressure plates.

From what ive heard the Borg & Beck style is a firmer feeling engagement and the diaphram style has more of a gradual feel, but i've had a hard time with finding consistant feedback on which offer better reliability, as well as performance strengths/weaknesses compared to eachother.

-Ryan

Rickman48

Clutches have come a long way in the past few years, and all the manufacturers will say theirs is the best!
After my experience with the B+B, I'd be trying the diaphram at this point - they're currenty being used on the 600+HP Vette, without any problems!
I attribute my knee surgury to the B+B I had in a '56 Chevy, 40 yrs. ago! My wife couldn't push it down with both feet!

joe_padavano

I've used the Borg and Beck style and frankly today I'll only use Centerforce diaphragm clutches.

Run to Rund

A diaphragm pressure plate used a formed flat-type spring called a Belleville spring. Its pressure curve is a Bell curve vs. distance the fingers are depressed. Thus, it is stiffest as installed with a proper thickness disk. It is easier to hold down when released fully as the spring is away from the stiffest shape. It is reminiscent of a kid's toy cricket. Its advantages are cost, needing less fork travel, the fingers need little clearance to the release bearing, ease of operation (pedal effort vs. clamp load). It seems like about a 7:1 lever ratio with the advantage of the bell curve clamp load (less effort to hold it down where the spring is away from its designed stiff spot). While a Belleville spring can be heated and then re-tempered for more plate load (or less), the process is difficult and risky. The spring may crack then or later. The change in pressure is hard to predict and duplicate exactly.

The Borg and Beck and Long styles use coil springs for clamp load. The Long uses forged fingers and has a triangular, 6 bolt hold down pattern. The Borg and Beck uses a six bolt symmetrical hold down pattern, and three stamped steel fingers. Coil springs get stiffer the more you push the pedal down. Upon installation, the springs are compressed more than they were as installed, and stiffer yet as the pedal is depressed. There is no "over-center" spot where it gets easier to hold the pedal down, it just gets harder and harder. Long lever ratio is 5.5 and B&B is 6:1. You need more travel at the fork because the fingers can come out to their "rest" position with rpm and you don't want them to touch the release bearing and wear it out. Old style release bearings are not intended for constant spinning like newer hydraulically operated bearings. You want at least 1/4" clearance fromt he bearing to the fingers after installation with the engine off. Advantages to the B&B include ease of customizing plate load by a smaller clutch shop by selecting different springs and disk thickness, smooth, predictable plate load, slightly quicker release characteristics, and no chance of getting the spring "over center" during a shift if the pedal is depressed more than needed. Some of us remember diaphragm clutch pedals "sticking to the floor" because the spring went so far from its max pressure point that it stayed there from centrifugal force, again like a kid's cricket toy that is easily held "popped."

Modern racing adjustable clutches are based on the Long design because the fingers can have counterweights attached and the pressure plates can be set up for external adjustment of the springs length or clamp load. While B&B can be adjustable, they don't use counterweights. They can have rollers installed between the "hat" and the finger. With rpm the rollers press outward between the finger and hat, adding clamp load. This arrangement is less reliable and consistent than counterweights. Centerforce adds counterweights between the multiple fingers of a belleville spring, and they work fairly well.

In summary, for street and street/strip with a conventional disk such as organic facing, the diaphragm is fine. Stock clutch pedal geometry gives plenty of fork travel with the proper length ball stud for the flywheel, etc. in use. For racing, the B&B allows more clutch tuning especially with brass or iron ceramic facings that may need different pressures to hold yet not grab too quickly, breaking drivetrain parts. I change the leverage of the pedal by heating and bending the tab for the upper rod to get more travel at the fork. This further increases pedal effort beyond the increase from using the B&B pressure plate, but I somewhat alleviate that because I use less clamp load, enough to keep the ceramic disk from slipping but not more than needed so I will get a bit of slippage on clutch release to (hopefully) prevents drivetrain breakage.

citcapp

Great information as I am installing a stick setup in my 48 and have been wondering which way to go. TKO 600 with a 500+ hp 455 3:50 9" ford rear end. Street car with some strip use for fun. This is what makes this forum great.

My442

Me too.