1973 P-400, a 2-ton truck chassis with a van body on top. It's got a 300 Heavy Duty six (HD exhaust, steel gears, tricycle motor mounts) and a 4-speed NP435 with a driveline brake. Current clutch is good but I'm getting my ducks in a row for the possibility of replacing the RMS. RockAuto lists "lever type" and "diaphragm type" as options; what's the difference? Mine is hydraulic if that matters, with the clutch master cylinder apparently the same as a 66 F250's brake master.

 

Ok, the lever type typically consist of 3 levers on the pressure plat...very effective but it takes a bit more leg strength as compared to the diaphragm type which has "fingers' all the way around the pressure plate (typically about 12 or so). A good local clutch rebuilder is best to purchase from.....in most cases they have access to the same or better components, have direct experience with the vehicle you specifically have, have direct knowledge of general drivetrain/chassis issues, are faster and cheaper than most of the oem replacement units.

 

Any way to tell what's in there now? Clutch pedal effort is reasonably light and should stay that way; the seat is not very supportive for heavy leg action.

Clutch rebuilder? I was thinking more along the lines of eBay or RockAuto. The latter shows me Luk 07027, but for something this old I prefer to verify parts catalogs' info. They don't even list a '73 P400; I've been selecting a P350 and so far most parts have been correct.

 

1965/66 F100/250 Master Cylinder is C5TZ-2140-A

1968 P350/400 from serial number C70,001 is C1TT-7A542-B as is 1969/72 and some 1973/77 P350/400's.

But there's two other possibles for 1973/77 (I need the number off the original), but they're not the same as any brake master cylinder!

What you have is a P400 "rolling chassis" with an aftermarket body mounted on it.

 

When mine failed, nobody had a "1973 P-400 clutch master cylinder" (or P-350). I read the casting numbers on mine to an older gentleman at a local truck shop who knew older medium Fords, and got a call back saying his microfiche crossreferenced that number (Bendix?) to the brake master of a '66 F250. Well, that was not only available but in stock at O'Reilly's - whose underpaid teenagers had no clue what was going on - and it was identical, down to the casting numbers that were different from the O'Reilly's part number and didn't appear anywhere except on the part itself. Looks like this:



C1TT-7A542-B looks way different and seems to mount with a two-bolt side bracket that is absent on my rig:

 

I know what the brake master cylinder looks like, I passed out dozens at the parts counter and owned a 1965 F100 with the same one for 44 years.

But no truck of any year with a clutch master cylinder used a brake master cylinder.

So, a previous owner changed it.

Brake master cylinder is basic part number 2140 .. Clutch master cylinder is basic part number 7A542

See 7A542 in parts catalog pic.

 

PN might be different but the first entry in the P-series list - C1TT-7A542-A - looks just like the 66 F250 brake master. Oh hmm... images search for that PN shows both types I have pictured above, though mostly the first, so I'm not sure. I'll read casting numbers tomorrow.

This rig is so old and been through so many hamfists that it's no surprise something's been modified. But what's surprising is that this modification is so clean I never noticed, in contrast to the rest of the previous owners' hackjobs.

Bill, penny for your thoughts on the clutch itself? Were clutches in the heaviest applications of the 300/NP435 different from those in lighter rigs with the same engine and trans? Does the tricycle mount configuration have anything to do with clutch fitment (bellhousing shape, I don't know...)?