Also, according to the tech guy, the smaller OHV clutch has 1800lbs of clamp force, whereas the later SOHC clutch has 2100lbs of force, so there is an improvement in load holding ability, when using the SOHC clutch in an OHV. He also confirmed that the OHV flywheel can be drilled/tapped for the SOHC pressure plate. He stated that it takes 40 grams of material removal, all one side, to cause an imbalance. Drilling the new bolt holes is nowhere near 40 grams of material removal, and they holes are spaced around the diameter, not in one spot.
After a 2nd call to AMS, it looks like drilling/tapping will not be needed. Part# 07-167 WOULD require that, as it has different bolt pattern. Part# 07-139 will bolt right up to my '93 OHV flywheel, is an oem self adjusting style, and has the larger SOHC 10.125" disc. I believe I have found the "magic" solution here. There is now no reason for anybody to buy the smaller OHV 9" clutch. You can buy AMS 07-139 from RockAuto ($161.79) and bolt it right in to your older truck. Instant clutch upgrade. While AMS doesn't do disc upgrades, they offered to put me in touch with someone who will replace some of the friction material w/ kevlar. However, I don' think I will need to do this.
Also, we spoke about early slave failure, and he agreed with my hypothesis that most of them were due to over-travel of the slave. He pointed to a blocked "compensation" port in the master as one frequent issue as well. He agreed that a 0.020 (20 thousandths) - BUT NO MORE - (unless the flywheel has been machined) flywheel shim, would help reduce the likelihood of early, over- travel induced, slave failure.
So, I am looking at AMS part# 07-139. Any thoughts, opinions, dire warnings, etc...?
The 07-167 clutch kit is for a 2001-2006 Explorer and 2001-2005 Sport Trac (and also the 2001-2010 Ranger and similar Mazda B4000). I can see why it wouldn't be a bolt-on.
The 07-139 clutch kit is the same clutch kit offered for a '98-2000 Explorer with the 4.0L OHV and the SOHC.
The smaller-diameter 07-096 kit fits both the '93-97 and '98-00 Explorers, and they all use the same slave cylinder, so it's not too surprising that the larger diameter SOHC clutch fits the smaller diameter OHV applications.
Also worth noting, these are the same as the LuK clutch part numbers, so LuK makes these parts for AMS (and lots of others).
I'd mostly be concerned about weight - if it is a whole lot heavier, that much extra weight spinning on a lower-torque, lower-horsepower, low-revving OHV engine is likely going to drop the revs quicker than it would on the higher-torque, higher-horsepower, higher-revving SOHC.
It might sound like a minor thing, but clutch weight makes a big difference - it could impact driveability to the point where it's the reason Ford or the aftermarket didn't just decide to use the SOHC clutch in the OHV rather than make two seperate parts. Even just a pound of extra weight, when spinning at thousands of RPM, plays a big role in how fast that disc assembly (and the crankshaft it's attached to) speeds up or slows down.
I'm not saying for sure that's the case - it's definitely possible that Ford just stuck with the smaller diameter clutch design for the OHV because that's what it had for the OHV prior to the SOHC and it just never dawned on anyone that the SOHC clutch could supercede the older design as a one-clutch-to-rule-them-all solution.
Heck, it could even be an overall improvement - the clutch for the 91-92's was designed way back in the late 80's prior to Explorer production in 1990. The clutch used for the '93-97's was slightly improved but still based on that. Technology leapt forward in the years after that, so a decade of progress and computer design might have produced a better-performing, smoother-operating, perhaps even lighter weight clutch. Not that clutch design changed all that much, even now, clutches are clutches, but it's just hard to say without at least some overall specs in terms of weight and (even better) comparing the two side by side.
As for the travel issue, yeah, that's probably part of it, but the problem is the proportion of how far the clutch pedal has to be pushed to get the required travel out of the slave cylinder - you can push the pedal a whole lot and only move the slave a small amount. I don't think a 0.020 flywheel spacer is going to do much about that, and it seems like spacers are only offered in 0.025/0.040/0.050 sizes for this application.
