I think the fingers of the clutch pressure plate do more to push the
slave
rod back (by pushing the throwout bearing/sleeve back and thus the
clutch fork which turns the clutch fork shaft which moves the shaft
lever which pushes the slave rod back) than the push rod return spring
does. That spring simply finishes the job that the fingers on the
pressure plate did. The push rod return spring pulls on the clutch fork
lever enough so that the TO bearing is pulled away from the clutch those
last few millimeters and keeps it from spinning when the clutch pedal is
out.
My TR6 didn't have the push rod return spring as factory equipment. My
PO's mechanic had made one for it however, and he said it was done to
pull the throwout bearing away from the clutch when the clutch pedal is
out so that it would not have to be spinning more than necessary.
So my conclusion is that since the clutches for the 4A and the 6 are so
similar that the push rod return spring was a nice wear out prevention
measure for the TO bearings and not a necessary part to push the slave
rod back. Hopefully that answers one of your questions...it's not a
necessity. I always thought the 6 was the first model to come
out of the factory without them, but I could be wrong about that.
Unless some mechanic didn't replace them I would expect models before
that to have them, but the list will have to weigh in on that one cause
I don't know.
Why it was left off by the factory on the 6's, can only be answered by
the factory although some believe that the cost saving guru's at Triumph
may have had something to do with it. And the cynics among us might
argue that there just weren't enough TO bearings being sold as
replacement parts because they were lasting too long and some way needed
to be found to make them wear out sooner so they left off the push rod
return spring (which killed two birds with one stone...less cost
initially and more revenue from replacement TO bearings). Designed
obsolescence I believe it's called. But I find THAT hard to believe
because if they were that clever then they might still be in business.
Dimensions of the spring that was on my 6 are, 3 1/4 overall length, 2
inches of that is spring the rest is the hooks, 1/2 is the diameter of
the spring part. I'm sure this isn't what came from the factory but it
worked on my 6 until the adjustable bolt/clevis broke and I replaced it
with the standard slave rod.
You can make a little plate (3/4 inch x 1 inch) with a big hole for the
bolt that holds the slave cylinder to the tranny housing and a little
hole for the spring.
Bud
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