Made the swap from the NP435 to the ZF5, using the same mechanical linkage - had to grind down a few areas of the bellhousing area to make room for the linkage, but it went in just fine. I used the same setup for the linkage for the 435 behind the '70 429, so I know the geometry worked just fine.

I used a FE flywheel and had it redrilled and neutral balanced, a new Sachs HD stock-replacement pressure plate and clutch disc, throwout bearing, and pilot bearing. I had to hunt for the clutch fork, and when installed on the pivot ball inside the bell, the length of the clutch fork was suspect - the half-circle end of the fork didn't seat directly against the throwout bearing, but seemed to engage properly when moved. There was about 1/4" - 1/2" between the throwout bearing and inside of the clutch fork, but the fingers of the clutch fork made it work properly. Though I was a little apprehensive about this, I continued on.

Everything else went in just fine. When I started the truck for the first time (which was awesome - the Powermaster mini starter mated to the new flywheel/clutch setup gave it a late-model sounding start), it started right up, no vibrations, no goofy scary noises - so far, so good.

Then I came cross two issues:

The clutch pedal felt awful - not the weight of it, but the engagement. hard to describe, but it felt like an arthritic knee joint - very difficult, then a 'pop' to get it over the hump followed by smooth pedal feel. This appeared to be the exact clutch engagement point - adjustment of the clutch linkage would change the depth the pedal had to be depressed, but this arthritic hump feel changed with the adjustment and mirrored the engagement point of the clutch.

Second, since the inspection cover over the tranny was still off, I could actually hear the clutch engagement point when pressing the clutch. Awful sound - sounded like sandpaper or static on the fly when the clutch disc was at the point of slipping. This sound was at the exact engagement point of the clutch, which was at the exact pedal depth of the arthritic popping feeling. Even slowly and carefully depressing the pedal to get the truck moving resulted in extremely jerky starting to get the truck moving.

Any ideads? I guess my main questions are 1) is that clutch fork supposed to be right up against the throwout bearing (as it was with the 435) or was there a small gap between it and the bearing (the ZF5 unit is a 1987)? Could this be the culprit to the bad engagement point? 2) Is that clutch disc sound just the new clutch being broken in, and I was only hearing it so loudly because there was no sound deadener between me and the unit?

Hopefully its a quick fix - can't wait to get back on the road. And before any of you ask why I went from the 435 to the ZF5 - the truck isn't a hardcore crawler, and I want to drive on the freeway every now and then.

 

when using a zf tranny. need to use a hydraulic flywheel. its about .200 thicker than a standard FE or older flywheel. the feeling or popping your talking about is probably the throw out bearing on the end of the throwout bearing shaft on the tranny. its traveling to far forward on end of guide. need the proper flywheel for this application. also your spline contact might be wrong due to the thinner flywheel. recently went through this with a 400 ford. need a thicker flywheel for my application. got to many project at the moment and will have this problem solved hopefully soon with custom flywheel about .250 thicker. good luck.