V8 Clutch in Model A: Something is not right

[lyleknievel]

note on the second picture I removed the nut that was originally on that side, backed out the screw, and added a nut on the other side (which may or may not end up as the final configuration -- but at least this way I would not drive the fingers into the clutch disk, all other things being equal)

[Rob Doe]

Lyle, what is the status of your project? Any luck?

[Kurt in NJ]

get a disc that is the proper thickness, then no modifications are needed

[lyleknievel]

The measurement from the flywheel plane to the pressure plate plane (with no clutch disk installed) is ~ 0.140". I got a friend to measure the same dimension on his V8 pressure plate and it was 5/16 (0.313). I called Bratton's and the person measured one off the shelf and it was 0.185". And so if I take the bratton's measurement, that is still 0.045" more than the one I have. And the design of the fingers give about 5:1 ratio on movement of the throwout bearing to movement of the plate...which means my throwout bearing would have to move 0.225" farther towards the engine to get the same release of the clutch. And so this is enough to explain why the fingers were having interference with the clutch disk.
Bottom Line -- I think the V8 Pressure Plate Assembly that I have is not right.
Bratton's agreed to exchange it for a new one, but I have already had this one balanced to the flywheel and so I am inclined to just shim the pressure plate out from the flywheel using some precision washers. I have not started that process yet, but that is what I plan to do at this point.

[Flathead]

It works.

[Rob Doe]

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lyle: you might benefit from this Youtube video:

Balance your Model A flywheel at Home!

The portion of interest starts at ~ 14 minutes in. George mentions the relationship of the range of pedal movement as it relates to the range of the pressure plate finger movements. He is discussing the stock Model A setup, but it applies to the non stock, customization of using a modified flywheel dimension along with a V8 pressure plate.

I've read that the collar on the end of the pedal shaft is not the sole player in the travel of the clutch pedal. A senior guru stated that the upper floorboard had a role in limiting that travel. I believe this is true of our coupe's functioning and a friend's coupe with a stock setup. Without the floorboard, the pedal goes all the way to the firewall metal. This may be further than with the upper board installed. Just a thought.

Our coupe's functioning, with new Bratton's clutch disc measuring ~.375-.380 thickness with the used V8 pressure plate required additional free play at the top of the pedal to work correctly. When I had it at 3/4" free play, I had the same result that you had, and I could watch it happening via the inspection window.

I'll be interested in your experiment moving the pressure plate farther away from the flywheel. I suspect that you will simply diminish the pressure that the pressure plate exerts on the clutch disc when the pedal is at the top of its range. A stock setup exerts 1200 pounds.

I don't have enough experience to speak with any authority, but in IMHO, I'm thinking that the proper operation of your setup will require a proper adjustment of the free play. In other words setting the max forward position of the throw out bearing in the correct position of the min and max travel of the pressure plate fingers.

I'll be learning with you as you report your findings. Luck to ya.

[Rob Doe]

lyle: where'd ya go, any progress?