Clutch Parts Identification

Do you know what kind of clutch set-up you have in your Big Healey? Do you know what are the correct replacement pans to order to overhaul your clutch? Well, a good friend of mine recently needed a “sanity check” to help identify the clutch parts found in his 3000 MK II BT7 center shifter so he could order the correct replacements. For many of us, we don’t know the complete history of our cars clutch maintenance and that was the case with his car. And since clutch and transmission swaps are possible between the Austin-Healey models, and the fitting of incorrect parts over time is also a possibility, being able to identify what you have and what you will need becomes very important when renewing the clutch mechanicals. Since a real enthusiast never throws anything away (and must hide it all from the “significant other”), out to my used parts bin I went to collect clutch sets. I was able to come up with the three basic complete stock sets which are pictured here.

First let’s take a look at the accompanying photograph and briefly describe what it contains. The clutch sets are arrayed in three columns with 100 and 100-6 sets in the right column, early 3000 sets in the middle, and the late 3000 set on the left. In the picture, each pressure plate type is represented twice at the bottom of the column, once pressure plate side up and once release bearing side up. (Yes, I do have a lot of old rusty parts!) You will note the similarities between the two single dry plate type pressure plates (marked “SDP” in the photo) in the center and on the right contrasted with the uniqueness of the diaphragm spring type (marked “DS” in the photo) on the left. The three types of flywheels appear next going up the column after each type’s pressure plates. And on the top of each column you will find the clutch discs for each type of flywheel/clutch plate set-up. The two distinct 100 and 100-6 clutch discs are in the top right column where the BN1 disc is on the very top and the one that fits the BN2, BN4, and BN6 cars is below it. Now armed with a guide to the photograph, let’s review some rules about Big Healey clutches.

Flywheels

There are just three types of Big Healey flywheels to which mount a corresponding pressure plate. All flywheels have the same outside diameter as the ring gear used by the starter is the same on all Big Healey’s. However, their shape, clutch disc bearing surface diameter, and number of pressure plate locating dowels vary between the three basic types. The picture included here represent stock, unmodified flywheels. The flywheel used on 100 and 100-6 engines is the heaviest of the lot with a large

flange at the circumference within which the pressure plate mounts. Since machine work may have been done in the past to lighten this massive flywheel.This flange may have been cut away on your car leaving any number of patterns based on the machinist’s craftiness at the time. The 3000 MK I and MK II flywheel is a flat plate to which is attached the ring gear. The later 3000 flywheel has a small machined step in the outer circumference near the ring gear attachment, probably where the factory lightened the flywheel a little bit more than the previous 3000 flywheel. In fact, I have seen 100 flywheels that looked very similar to the late 3000 fly wheel due to machining. So further detective work is needed for a positive ID if your flywheel does not match the stock one.

Pressure Plates

All 100 and 100 6 models use the same 9″ single dry plate type pressure plate which measures 9 3/8″ across the plate surface diameter. 3000s through MK II BJ7 Engine 29F4878 use a 10″ single dry plate type which measures 10 and 1/4″ across its plate surface diameter. Later 3000s use a 9 1/2″ diaphragm spring plate which measures 9 5/8″ across it’s plate surface diameter. As for fly wheels, the same tape measure across the clutch disc mating surface diameter pattern left over from the old disc, should yield the same numbers. For further I.D., count the number of locating dowels on the flywheel. The earlier fly wheels have just two dowels to locate the single dry plate type of pressure plate. The late flywheel has three dowels to locate the diaphragm spring plate.

Clutch Discs

There are four types of clutch discs. The 100 BN1 has a unique clutch disc due to it’s 3 speed transmission’s 1st motion shaft being a smaller diameter than the larger size used on all later Big Healey gearboxes. This disc measures 9 3/8″ in diameter. The other three clutch discs correspond exactly to their pressure plate/flywheel counterparts. All 100 BN2 and 100-6 models measure 9 3/8″ across the disc surface diameter. 3000’s through MK II BJ7 Engine 29F4878 use a 10″ clutch disc which measures 10 1/4″ across it’s surface diameter. Later 3000’s use a 9 1/2″ disc which measures 9 5/8″across it’s surface diameter. Just in case you don’t get an expected measurement on your clutch disc for your diaphragm type pressure plate, don’t panic! A 9″ clutch disc will interchange with the 9’/2″ disc and the “wrong” one could have been put into your car some time in the past. If this has happened to you, opt for the larger disc when replacing.

Throw-Out Bearings

There originally were five types of release bearings used throughout the Big Healey production run. This part is unique to each style of transmission bell housing. If you know the factory part number of your transmission’s bell housing, then you will know exactly which release bearing to order (provided all the clutch parts inside are stock If you do not have the correct release bearing for your type of transmission, you may experience vibration, poor clutch action with only partial disengagement, or maybe even no action at all. Each release bearing is designed specifically for the clutch actuating geometry unique to its corresponding bell housing.

The 100 BN1 3-speed has a one-piece transmission case with the bell housing cast as a pan of thc entire case and can be identified as such. The Moss part number for this transmission’s release bearing is #595-020. All following bell housings arc cast separate from the transmission case and will have their pan numbers cast into the driver side of the bell housing or stamped into the top flange of the casing (BJ8 only). The 100 BN2 bell housing is part number IB 3703 and further identifiable by it’s mechanical clutch linkage. It uses #501-022 for its release bearing. All later bell housings have a hydraulic clutch actuation mechanism and will have a clutch slave cylinder attached to the passenger side of the bell housing. The 100-6 bell housing is AEC 3067 and uses the same release bearing as the BN2, #501-022. The 3000 BN7/BT7 for all side shift transmissions is AEC 3534. With the introduction of the centershift transmission for both the BN7 and BT7 up to BJ7 Engine (29F4878 (or French Engine 29FF149), the bell housing part number is AEC 3559. All3000 transmissions up to this change point use the same release bearing, #501-020. And the last bell housing for the remaining BJ7’s and all BJ8’s will have pan number 22B 172 or. as superseded, 22B 237. This late bell housing uses #501-032 for it’s release bearing.

As it turns out, the BN2 and 100-6′ release bearings are essentially the same even though they have different factory part numbers and have been combined into a single listing in the Moss catalog. So that makes just four types of release bearings currently available today.

Mix and Match (Not!)

Needless to say, you should not mix and match clutch components. But, be aware, you or others before to you may have interchanged complete (or partially complete) clutch set-ups. If this is the case or you plan to replace the 10″ clutch in your 3000 MK II center shifter with a BJ8 clutch 9,/z” set-up to get thc easier clutch pedal feel from the diaphragm spring type pressure plate, be sure you do so in complete sets that include the corresponding flywheel, pressure plate, clutch disc, bell housing, and correct release bearing for the new set-up.

And since this particular changeover has become quite common, you can see why my friend wanted that “sanity check”. I hope this will help you to identify exactly the parts you need prior to ordering. It’s a lot of work to replace a Big Healey clutch and it’s always nice to get it right the first time!

By Ron Phillips, Healey Association of Southern California