Transmission swap question

[Lee]

Hi all,

Does anyone know if a 5-speed bellhousing/Tranny from a 1974 Ford cab-over (391FT) will bolt up to a 390 FE? I have a lead on one and would love to replace the NP435 in my 1970 F250 with it.

Thanks,
Lee

[ICEMAN6166]

yes the bell housing will bolt up but there are other issues to deal with.
the FT bell has the trans mounts integral and the 5 speed has no tail mount so something there must be done.
the 5 speed will bolt up where the 4 speed is but the input shaft end uses a different size pilot bushing and im not sure if it will fit into the FE crank and there is no mounting point on the back.you would have to take the tail section off the 4 speed and put it on the 5.all that is assuming the 5 speed is also a new process and the tail section would fit..
the starters are the same.

heres the big kicker, 5th gear is the same 1-1 ratio as 4th in the 4 speed, so you are only gaining another low gear as 2nd in the 5 speed is 1st in the 4 speed.has a real funky shifting pattern on them too.1st is straight down from where reverse is on the np435 and second is where first is so you have to go from 1st is on the right to 2nd all the way over on the left.
i could start out in 3rd in my f600 wrecker if i had no load.
i have some ft parts here a 4 speed ft and a 5 speed ft trans as well as 2 ft blocks, i would consider using them in an f350 or a 4x4 but there is no economy or advantage from the FT 5 speed in a f100 or f250 2wd pickup.

10 cents worth.

[averagef250]

If it's from a cabover truck you also have to deal with the guess-a-gear shift linkage.

There is really no practical way to install a cabover transmission in a conventional cab truck without replacing the top plate.

Ford used many different 5 speeds in thier heavy trucks. New process and clark made most of them. I've never seen an NP 5 speed, but I've owned several clarks. In order to run the clark you have to run the FT bellhousing. As Ice mentioned it has mounting ears that get in the way of everything and cutting them off takes alot of integrity from the bellhousing. In addition to the FT bellhousing you must also run the FT flywheel and clutch. The FT flywheel weighs twice what the FE one does and is externally balanced. You'd have to have the FT flywheel nuetral balanced to run it. To match the flywheel you must run a big truck pressure plate and clutch. The only clutches that will fit are lever style. Your left leg will get a hefty workout.

This is all in addition to completely engineering and fabricating a rear crossmember/mount system for the tranny.

About 1/2 the clarks I see from 70's era fords are the overdrive versions. As I recall the overdrive serial numbers start with "VO" or something like that.

I know this seams terrible, but a far easier near bolt in overdrive 5 speed is the one the binders used in the 70's pickups. It uses the same diameter bearing retainer as a 435 and the input shaft is the same. It gets you overdrive, but it still shifts like a 435 and parts are real hard to find for them.

[fordman]

if you cant find em grind em. or dont worry they will make them out of rubber next year.

[averagef250]

They practically are rubber anymore. Most modern design manuals use kevlar and composite synchros. Price out just synchros for an NV4500!

[ICEMAN6166]

i had a spicer 5 speed in the 97 binder rollback we had a few years ago.you have to use the clutch on them or you will trash the synchros.friend of mine had to buy a couple spendy rebuilds after his drivers did not always use the clutch when shifting.glad i found that out before we had ours.