Ford C4 Advice Needed

Pony Pilot · 11-04-2014, 09:23 PM

I recently replaced my 383 Cleveland stroker in my SST Mustang with a 438 stroker. HP increase is in the 100 hp region. I re-used the C4 behind the 383 with the 438. The shifts were solid when it was behind the 383, but now with the 438 I had to increase the shift points 500 RPM and have a 600 to 800 RPM spike before the 2-3 shift. Usually, I would conclude that I had excess clearance in the clutch pack, which was true when I removed it and checked with feeler gauges. But, when I put in a fresh rebuilt unit with 6 discs vice the five in the previous trans, I still had the same RPM flare-up. I have built my own trans for years, and .010 per disc clearance has always served me well. I called two well-known trans aftermarket companies with one telling me this is a valve body issue and the other saying it's still excess clutch pack clearance. Has anyone else out there encountered this? If so, what's the fix? Thanks in advance for any help.

Just for background, these trans have 6-pinion planetaries, Alto red clutches, Kolene steels, Kevlar bands, PA Pro-Shift servos, and hardened input shafts.

11-04-2014, 09:23 PM	#1
Pony Pilot Junior Member Join Date: Aug 2012 Posts: 25 Likes: 0 Liked 0 Times in 0 Posts	Ford C4 Advice Needed I recently replaced my 383 Cleveland stroker in my SST Mustang with a 438 stroker. HP increase is in the 100 hp region. I re-used the C4 behind the 383 with the 438. The shifts were solid when it was behind the 383, but now with the 438 I had to increase the shift points 500 RPM and have a 600 to 800 RPM spike before the 2-3 shift. Usually, I would conclude that I had excess clearance in the clutch pack, which was true when I removed it and checked with feeler gauges. But, when I put in a fresh rebuilt unit with 6 discs vice the five in the previous trans, I still had the same RPM flare-up. I have built my own trans for years, and .010 per disc clearance has always served me well. I called two well-known trans aftermarket companies with one telling me this is a valve body issue and the other saying it's still excess clutch pack clearance. Has anyone else out there encountered this? If so, what's the fix? Thanks in advance for any help. Just for background, these trans have 6-pinion planetaries, Alto red clutches, Kolene steels, Kevlar bands, PA Pro-Shift servos, and hardened input shafts.