I have a late year 50 F1, 3.92 gears, Which is the best tranny- 2 to choose from, C4 OD, Three speed with OD, partial to manual. Have access to pre 72 rear, 3.73? any help appreciated. Want as low RPMS as possible, running a stroked Flathead.

 

What engine?

 

running a stroked Flathead.

 

mid 80's S10 T5. w/flathead conversion kit. Best bang for your buck. No C4 had OD, and the 3sp. manual w/OD lacks a low enough 1st gear for the flathead. Just my two cents, though.

 

Here is a site with some info on the certain T5 transmissions Havi is talking about: T5 Transmisison Swap

Here is a RPM calculator I use to figure out what rpms I'll be pushing with my setup. I use the last calculator on the bottom of the page so i can manually enter the third member gear ratios and trans ratios. Hope this helps!
Engine RPM Calculator

What cubic inch are you going with stroking wise with your flathead?

 

merc. crank .60 over, 3/4 cam. builder says around 170hp, about 266 ci. I bought a c-4-aod from speedway with the conversion kit for the flatty.

 

Just a little confused-- the three speed with od came out of a 53 merc. with flathead, so should it not work? Just asking.

 

Welcome to FTE!

 

The AOD trans has an over drive ratio of .67 which helps out a lot on the highway cruising at 70-75mph with the low geared rear end. Plus the low gears in the rear end to help out on take off. Best of both worlds.

 

Just a note about the '53 OD tranny - I tried to put one out of a '52 in my F-1. It should be the same tranny that you are considering. The clutch linkage is completely different and would require extensive fabrication to make it work with the OE pedal assembly. I endded up rigging a cable, but it was not easy. The other problem was the F-1's transmission crossmember. The OD solenoid wants to sit smack dab in the middle of the crossmember and requires extensive crossmember mods or a new crossmember.

That part, unfortunately, will be an issue no matter what transmission you use. The bulk and design of the original transmission crossmember will get in the way of anything other than one of the original transmissions. You need to be careful with the transmission crossmember, though. Part of the reason it's so bulky is that it's the only one between the front crossmember and the one under the middle of the bed. It attaches to the top and bottom of the frame rails and keeps them in alignment. Any replacement or modification needs to maintain that function and not just hold up the transmission or you'll have problems with the rails twisting.

If you're runnng a flatty, you're partial to a manual, and you're not interested in hacking the crossmember up, then my advice would be to use one of the original transmissions and swap the rear out to a '57-'72 9-inch with about a 3.25 gear. That should give you plenty of get up and go and keep the highway RPM's at a comfortable level. If you're willing to rebuild the crossmember and fab clutch linkage, skip the vintage OD and go with the S-10 T-5 that Havi mentioned along with the original rear axle. It requires the same mods to put in, but you get a lot more bang for your buck. The extra gear really helps the little flatmotor stay in it's powerband and get the truck moving in a hurry. If you're going to go to all that work, you might as well get the most benenfit for time you'll have to invest.

 

speaking of tranny questions and not trying to hijack the thread but right now i have a 250 with a C4 and plan on going with a 289 with the C4. what will it be like on the highway, hopefully it wont sound like a grenade getting ready to go off...lol

 

post delete

 

Don't worry what it sounds like. We, as a society, have become spoiled with regards to noise levels in cars. We want them to be all quiet and plush, and that's what we've been given from all the manufacturers over the last 25 years. So when we get into an older rig, even one from the 60's, where it was common for engines to turn 3000 rpm's on the highway, we cringe and think it's going to blow up. Build your new engine for the application it's going to be in, and it'll live forever.

 

Goofing off today and put 30 miles on the truck. I'm still happy with my choice of BW T-19 with the same basic gearing as the T-5 minus the 5th gear. @ 2000 RPM I'm running 50 MPH.

 

Don't worry about it. Had a 289 in an early Bronco with 4.56 gears and a 3 speed. With decent mufflers, sound was not too bad. Nomally cruised on the freeways at 3400 to 3800 rpm. Tire and wind noise was worse than engine noise.