Clutch Pedal Clearance

[4.6 litre]

Guys,

Below is a photo of my pedal box installation. As you can see the clutch pedal hits the original 3/4" chassis square tube before full clutch extension. I intent to cut the 3/4" square chassis tube. I have welded a back up 3/4" tube to the original chassis bar for support. Can anyone tell me how much I should cut the original 3/4" chassis bar to allow full extension of the clutch pedal.

Thanks for your advice,

Damien

[CraigS]

There have been two good threads on this recently w/ very good pictures.

[karlos]

A couple photos for you showing the clutch pedal travel stop-to-stop. The first is with the pedal out (clutch engaged); the second is with the pedal in (clutch disengaged). Looks to me like 1" to 1-1/4" would be sufficient.

pedal_out.jpg

pedal_in.jpg

[RRussellTx]

Karlo's,
That's a very helpful comparison. What clutch setup did you end up going with that requires this amount of travel? I have a max of a little over 1-1/4" available (depending on pedal placement) and I'm hoping to avoid a chassis modification but I'm afraid I'll have to do something eventually.

[karlos]

The photos show the maximum travel possible based on where the clutch quadrant hits the stops on the top of the pedalbox. The stops are currently adjusted to maximize the amount of travel, so 1-1/4" or so should be enough regardless of how the clutch is eventually adjusted. This is for the Wilwood pedalbox, which is what I have and what the OP's picture clearly shows. Also note that 1-1/4" at the location shown corresponds to about 5" of travel at the footpad on the end of the clutch pedal.

I don't actually have my engine/trans installed in the car yet, so I'm not sure how much travel I'll eventually need. Probably less the the full 5", which of course means less than the full 1-1/4" at the crossmember. But as I mentioned, if the OP removes about 1-1/4" from the crossmember then he should be covered for all eventualities.

Final note: rather than tweak the crossmember I simply notched the clutch pedal as shown below. Before I did I looked at how this would affect the pedal's section properties. The modification shown results in about a 10% loss in the moment of inertia (small change because most of the "I" is derived from the tall vertical web), and this leads to a roughly equivalent increase in the stress level at the notch. The modest increase in stress level combined with the fact that this location is loaded in compression (meaning no cycle life or fatigue issues to worry about) tells me that the pedal can withstand this just fine. I'd be less inclined to do this on the previous version of the Wilwood pedalbox where the quadrant was offset from the centerline of the pedal, as this creates a nasty torque/twist that does not exist in the updated design. Also note the importance of using a large blend radius at the beginning and end of the notch to reduce stress concentrations associated with abrupt changes in section.

Opinions vary as to whether it's better to notch the frame or the pedal. Not trying to defend/support one or the other, just providing info that can be used to make an informed decision.




pedal_w_notch_1.jpg

pedal_w_notch_2.jpg