Clark 5 speed change out discussion

[nchorsepower]

I have a 69 crew cab High Boy. Ive heard that Clark produced some 5 speeds with overdrive in heavy trucks and have some questions. Is there any info on the swap? What kind of donor would have one or where could one be found with usable gear ratios? I imagine the 360-390 flywheel would be ok with the right pilot bearing. What about the bell housing, clutch, pressure plate, throw out lever, output yoke and spedo cable? I would like to start gathering up the parts and do it when I do a body off restoration.

[averagef250]

Medium duty trucks of the 60's and 70's used millions of Clark 5 speeds. A Handful of those transmissions were overdrive. The 280VO's were the overdrive version that would have been era correct to come behind an FE. The medium duty trucks used bellhousing mounts and front engine mounts- The bellhousing is entirely different from the pickup stuff and so is the flywheel. FT flywheels are external balance, while 360/390 FE's are not and 410/428 are different balance. So you need the whole shebang or to make a lot of custom parts.

IMO, if you want a medium duty overdrive tranny get an Eaton Fuller. You can't beat the availability or parts support, ratio tunability. Just damn good transmissions. There are umpty million different fullers out there most being direct drive and BIG, but they are current model transmissions, built in America better than anything made way back. You probably want a smaller one and synchros with your gas engine so you want an FSO-5XXX (Fuller Synchro Overdrive 5 speed) or why stop at 5? Go for the win with the always swap-popular FSO-6406 overdrive synchro 6 speed. You need a 5 or 6 series fuller to fit under a pickup cab.

These things don't bolt together. Some/lots of machining required. The trans would definitely outclass any FE you could hang on the front of it though.

[nchorsepower]

I'll look into it but Carol Shelby, Richard Petty and I find a lot of class in FE powered vehicles.

[averagef250]

I'll look into it but Carol Shelby, Richard Petty and I find a lot of class in FE powered vehicles.

Wow! That's awesome!

[nchorsepower]

I did some poking around and found a lot of people putting Fullers in diesel trucks. Used prices were not bad as were rebuilt. If the input shaft is longer, making a bell housing adapter would be pretty easy for a fabricator if only a clutch disc, pressure plate, and throw out bearing could be found.

[averagef250]

BTW, My "outclass the FE" statement referred to the idea that pretty much all american made car/light truck engines are built to be as cheap to produce as possible with the only requirements being the engines last long enough to make the owner satisfied and there are parts available to keep the engines on the road for a decade or two. The FE's were no exception to this. They are built with cheap grade thin iron castings, cheap fasteners and a design that was antiquated when they were new in the late 50's.

The medium duty Fuller transmission is quite a bit different. They were built cheap or made just to sell. They were made specifically to hold up to full rated torque day in and day out for tenfold the lifespan of a light pickup transmission.

I don't have anything against FE's, quite the opposite, I like them a lot, but just pointing out the irony of going through all the work of putting such a transmission behind an old gas engine.