transmission strength: 48 ford

Hey Guys,

I've been looking at options for transmissions behind a SBC in a 1948 ford coupe.

The results I have come across after scowering the hamb via multiple searches are an automatic, which seems to require quite a bit of floor and cross member modification. not to mention spliting the front wishbone<--possibly you can just lower the wishbone mount but i have yet to see mention of that option.

the next option is a t5 manual transmission, which requires not so much cross memember or floor hacking but a decent amount of parts hunting. finding a v8 model transmission and then a s-10 model for the tail shaft so the shifter isnt nearly under the front seat from what i can gather.

the third option, what many would consider the tradition route i suppose, is to use the one thats in it.

ive seen quite a few posts mentioning running the ever popular 39 ford trans behind overhead valve motors so i would like to ***ume that a 48 3 speed would be up to the task but ive been wrong before. it does see to be the easiest way to get back on the road though.

so im currious, how much grunt with a 48 ford 3 speed take? for sake of conversation the one in my mind is currently bolted to a stock flathead 6, the 226 H series i believe.

is this something that your going to have to baby? or with a 250hp sbc itll be just fine as long as your not being a total ***.

i figure theyve lasted this long and were put in all sorts of things over the years even from the factory so its not hard to believe that itd be fine. but itd also be belivable that anything over the weezing thunder of a flathead will crack it.

does anyone know or have a good idea of what this gearbox would hold up to realisticly?


sub question: sbc+stock 3 speed<-of the flat6 variety+ stock 3:54 or 3:70 something rear even if it wont break are you going to run out of gear and be stuck with something that wont let you run 70mph down the road?

just figured i hadnt seen a lot on discussing the actual strength in these swaps so i thought id put it out there.

thanks in advance.

timm

 

I don't think the 40-48 Ford transmissions were ever noted for their ability to hold up under loads of torque and horsepower.

 

We built a '48 years ago...actually my first introduction into old cars when I was 8. It went through a handful of variations over the next 15 years, but the last variation was a 400 SBC with the original 3 speed. We ran it like that for probably 7 or 8 years until it was sold. It survived me driving it during my teenage years, doing burnouts even though I knew better. It would actually light them up taking off in second gear since the ratios were so low.

 

All the internal parts are pretty much Identical to a 39 box, so I doubt they are any stronger than those even.Maybe the case is a little stroger, but I dont know.
the issue is how you drive it. if you only mash the pedal from rolling, and dont rush your shifts (hard with a column change anyway)it will last some time, how long depends on how well it has been rebuilt, and how gentle you drive.

Top gear is 1:1 on these trans, so should be easy to use an online ratio calculator to determine cruising RPMS at different speeds, just need rear end ratio and tyre diameter.

Id try it, with the thought that maybe you have to go stronger if it doesnt hold up. its probably the cheapest,easiest swap anyway, the others require converting to open drive, and possibly a diff change which all adds up..so give it a go!

 

I'd skip the power-shifts and launch style starts. Otherwise just keep the trans well lubed and listen to her once in a while.

 

thank you for all the info thus far, i realy apreciate it!

any links to information on how to properly keep this transmission lubed and taken care of? i havn't ever messed with a transmission of this vintage.

 

If you are going to use the original diff, get a truck 4-speed from approx '87 can be adapted to the torque tube, then everything else fits as the original. have one in my 48 Ford with the flathead all gears are syncro 4th is od. about 28% used now for 2yr and about 6000miles. the trucks had 6's or 302's. cost me about 3g's to buy but think it is well worth it Laurie

 

Sheesh! Nobody does this the easy way. I use late-'60s fullsize Ford 3-speed top loaders. They can be shifted with the '42-'48 column shift linkage, or converted to floor shift. NOT SIDE LINKAGE! REAL FLOOR SHIFT! Jeep 3-speed toploader tower shifter, big cane stick. All 3 gears forward are synchro, and the gears inside are 20% WIDER than Cad-LaSalle! Big block Fords don't bust 'em, so small Chevies aren't about to.
Chevy bellhousing is re-sized for the front bearing support, Chevy throwout bearing and fork, Chevy pressure plate with Ford disc, plus trans case is small enough that it fits between the crossmember with little t*******.
Tailshaft of the Ford ****** can be used with open drive, 8" or 9" rear.
Trans could be converted to torque tube rear (with '48 Ford rear mount, but tailshaft has to be chopped off and resplined, and a rear bearing fitted. (some machine work, but it can be done)