Re: BB Clutch, Pressure Plate, Bearing Replacement

[Gary Schisler]

I used a Centerforce clutch on my 66 SB and I have not had any problems with it. This is the second Centerforce I have used in a mid-year. I had heard the same "rumor" that only GM units will work. My engine rebuilder is also a Corvette enthusiast (owns a 66 BB) and he swears that since another vendor builds these units for GM then they must also build acceptable clutchs for the aftermarket crowd. Besides, go to your local Chevy dealer, check on the price for a new "GM" clutch (which will not be GM at all) then price out an aftermarket such as Centerforce.

There are two distinct types of clutches available. One is a three finger design, which I think is a heavy duty type. This design generally gets the credit for the heavy clutch feel of many Chevys. The other is the diaphram type with many fingers running around the inner perimeter of the clutch. This has a normal clutch feel to it and is very easy to shift, even for my wife.

[Joe L.]

Re: BB Clutch, Pressure Plate, Bearing Replacement

Many of the components used on Corvettes over the years which we think of as "GM" parts were and/or are not actually manufactured by GM. As I have mentioned in the past, this is especially true of many of the Corvette's unique components since GM does not generally produce low-volume components in its own manufacturing plants. Items like clutches, however, used to be high volume, production pieces and, I believe that once upon a time, they were manufactured in GM plants. That belief is based upon two things. First, if you closely compare a GM clutch to an aftermarket unit like LUK (which I believe does manufacture the clutches for GM for C4 and C5 Corvettes) there are many dissimilarities. Of course, LUK could make the GM units differently. Second, I carefully disassembled the original clutch cover assembly from my 69 which I removed from the car years ago. On the back of the cast iron pressure plate there are GM casting marks typical of those used in GM foundries.

I do believe that the clutch disk assemblies were always manufactured by outside vendors. I have some very old and discontinued NOS GM clutch disks for 1966-72 Corvettes. The brass rivets which retain the woven facings have several different corporate insignias on them, varying by GM part numbers, which indicates that different manufacturers made different GM part numbers. One that I recall was "B&B" for Borg and Beck.

Regardless that outside vendors may actually make many of the parts that we think of as being "GM", it is important to understand that these manufacturers may very well make these parts DIFFERENTLY than they make parts which carry their own or other brand names for the aftermarket. I even can describe some information which came my way several years ago which confirmed this fact.

About 4 or 5 years ago I was at the Bloomington Show (at that time in Sprinfield). I stopped and talked with the Walker Muffler manufacturing representitive regarding Corvette mufflers. I knew that Walker had manufactured most of the GM OEM mufflers for Corvettes during at least the 53-72 period. I also knew that the 63-72 Corvette mufflers had a very unique exhaust note and I asked the rep which available Walker mufflers were manufactured exactly like the ones that they manufactured for GM, since the GM mufflers had been discontinued by that time. The rep confirmed that Walker had manufactured ALL Corvette mufflers during this period, but he also told me that there was NOT THEN and NEVER WAS an available Walker-branded muffler manufactured to the GM specs. As a matter of fact, the rep told me that Walker had about 20 muffler manufacturing plants; about half made mufflers for the OEM market and the other half made them for the aftermarket to be sold under the Walker or other brand names. The mufflers made at the OEM plants were completely different than the ones made at the aftermarket plants, even though they both might make mufflers for the exact same application. Also, the mufflers made at the OEM plants were never sold in the aftermarket and the mufflers made in the aftermarket plants were never supplied to OEM manufacturers.

I believe that you would find this situation to be true for many other parts vendors. Most have "aftermarket divisions" and "OEM divisions". The OEM divisions manufacture the parts for GM, Ford, Chrysler, etc. production line installations AND service part sales. The aftermarket divisions manufacture their own or "off-branded" REPLACEMENT parts for sale in the aftermarket.

As a matter of fact, the major auto manufacturers have their own version of REPLACEMENT-QUALITY parts sold through very competitive aftermarket channels. GM calls theirs AC-Delco; Ford calls theirs Motorcraft. Parts available through the AC-Delco parts system are not neccessarily the same as those available through the GM parts sytem, even though they may service the same application. How can you tell when the parts are the same through both systems? Very simple. Check the GM "long number" found on the box. This is a 6,7,or 8 digit number with no letters or hyphens. If these numbers are the same through AC Delco or GM dealers, then the part is exactly the same. If the numbers are different, even though they service the same application, the parts are different. Guess which one is better?