Mike Frye

OK,

This is probably a stupid question, but has anyone considered running the automatic without the pinch bolt on the flex plate collar?

I've seen a couple of these up close and on both, the issue isn't the fact that the pinch bolt doesn't hold, it's that it holds after it creeps forward. The twisting pressure on the flexplate is a result of the torsional stress caused by the crankshaft turning the flex plate and the flex plate turning the drive shaft. This stress is taken up by the flex plate, but the problem with the stock setup is that the bolt doesn't hold the pinch collar tightly enough and the collar 'winds up' and creeps forward over time. I guess it moves under rapid acceleration, but then doesn't move back because the load in the other direction is only supplied by the 'flex' of the plate.

If the pinch bolt weren't there, wouldn't the collar just move forward and back on the splines of the drive shaft without any issue (and without pushing or pulling on the crank shaft)?

It might require some re-working of the design (maybe stack two flex plates like leaf springs or something) but I think then you'd be working with the natural stresses of the car rather than against them.

Just a thought. (Donning flame suit)

AO

Why not just pin it?

Mike Frye

Not sure I follow you here. If it were pinned then the push and pull caused by the flex from the shaft would be directly applied to the crank, wouldn't it?

Tony

First time you "goosed" it i imagine you would strip the splines clean off either the shaft or the collar.

Big Dave

Something has to secure the pinch collar to the torque tube. Wouldn't it be prone to spinning inside the pinch collar without clamping pressure? I assume a pin would solve that (at least in theory).

Mike Frye

That's what I was wondering. Maybe the slot in the pinch collar can be closed up so that it doesn't expand, but in some way that would allow it to slide fore and aft enough to return it to where it needs to be without pushing or pulling on the crank shaft.


Isn't the inside of the transmission basically just gears and cogs driving each other? What's the difference here?

killav

The best explanation I have read on this I will recount as follows.

Lay down a wet towel. Twist the towel in opposite directions and the towel gets shorter. Untwist, and the towel returns to its original length. This is what happens when you excelerate briskly I assume. This twisting action pulls the solid shaft inside the torque tube away from the flex plate little by little over time. The rear pinch bolt rides in a notch on the torque tube shaft, so there is no where for the back section to give. The front flex plate can only flex back so far, and then has to give somewhere, which is at the front pinch collar connection. This ratcheting action starts to push on the flex plate more and more over time.

I have no idea if this is what actually happens, but it made sense to me at the time.

Also, I think that the splines would be stripped in short order if the female portion of the front clamp was not tight. I think it would spread open under load and just chew up the threads on the torque tube shaft or clamping collar.

killav

I think your on to something Mike with welding up the slits that are in the pinch collar. Why woulnd't this work?

Tony

Go ahead and try this stuff guys! You wont know until you try

Mike Frye

Dude, I have a 5-speed, you couldn't pay me to drive an auto. I'm just throwing it out there.

Bill Ball

W/o the bolt, the shaft will strip the splines. Pinning weakens the shaft. I think Constatine did a lot of these experiments when he developed his clamp, although it was already well know that you can't run with a loose/missing bolt.

Mike Frye

You see, I was right. It was a stupid question.

AO

I can't imagine that a small divet for a set screw would weaken it by much, but then I drive a 5-speed!

Bill Ball

I don't think a small divot for a set screw would do anything good or bad. Maybe Constantine should jump in. He has numbers on the amount of clamping force needed to resist movement. It would probably snap a small set screw.

Bill Ball

No, it's a hard question. I believe there are only 3 procedures that have decent support. 1. Circlip an early style shaft. 2. Constantine's clamp. 3. Red (permanent) Loctite. And even these could generate a good debate.