Clutch fork welding

averagef250 · Post by **averagef250** » Wed Apr 26, 2006 4:21 pm

I'm in the final stretch of stuffing an HD NV4500 5 speed into my 70 f-250 4x4 behind a 390. I decided to run the large HD cummins 1 1/4 " input shaft transmission which doesn't seam to be a common transmission for swapping into anything other than an early cummins truck. Well, the last issue I have is coming up with something to disengage the clutch, i.e. throwout bearing and clutch fork. I'm using the factory iron FE pickup bellhousing with an A/A adapter plate. I've found that an early clark 5 speed throwout bearing fits the NV4500 1 3/4" bearing retainer perfectly. I also managed to scrounge up a clutch fork from a 1970 F-600 cab over truck with a clark 5 speed. The bearing end of the clutch fork is perfect, but the pivot and the opposite end are completely useless for a pickup bellhousing. My plan is to cut the bearing release end of the clark fork off and weld it to the stamped pickup clutch fork body, BUT something I didn't realize is that these darn clutch forks are harder than all heck. a file skips across them. SOOO... I'm a decent welder, but I've never needed to TIG weld high carbon steel before and wondering if anyone has any experience with this. If this stuff was thicker, I'd preheat it and stick weld it with 7018 or one of those crazy alloy rods they have nowadays, but it's pretty thin stuff. Anybody have experience tigging stuff like this? Thanks.

4x4_Welder · Post by **4x4_Welder** » Wed Apr 26, 2006 9:58 pm

High carbon steel/ HSS/ OSS is really easy to tig, it flows beautifully, and doesn't blow out like aluminum and alloys do. I would do a double bevel, and put another piece of 3/16" on the backside, fully welded to help support it.

averagef250 · Post by **averagef250** » Thu Apr 27, 2006 12:38 pm

So I'm worried over nothing? Just use mild steel filler? The two arms really don't lend themselves to being welded together, so it's been quite a bit of grinding to fit the two parts together tightly. The web of the forged clark arm is around 1/4" and the stamped pickup arm is the regular 3/16" unit. I'm trying for a full-pen butt weld and it should be pretty strong with the legs of the C-shaped pickup arm welding to the sides of the forged piece. Maybe I'll cut up another clutch arm for a backing piece.

4x4_Welder · Post by **4x4_Welder** » Thu Apr 27, 2006 8:41 pm

Pretty much, just use 70s filler, I'd probably use 1/16" or 3/32" since the base metal isn't very thick.