49 f1 PU T5

melisahe

melisahe

Senior Member
current project 49 f1. Thinking of putting in a T5 transmission to gain highway speed (70mph). Will I be able to cruse at 70 with my flathead and the T5? How feasible is it? Will I need frame modification? Thanks for any input. I did a thread search and got no results. Truck currently has original four speed.
 
Unlike the guy above me, I’ll try to be more helpful. Yes it’s possible to go 70 in overdrive. What rear gear ratio do you have/want. You will need to cut the crossmember as the T5 is longer. Many people sell adapter kits for Flathead to T5
 
Frontal area is always going to be an issue, but not really anything you can do about it. RPM with a given combination of OD gear ratio, rear axle ratio and tire size is easy to calculate. If it was me, I would want to keep the RPM high enough at cruse speeds to not load the engine, but this can be very subjective.
 
The truck has the original rear end at present. I have a ford 9 inch out of a 78 ford. I don't want to go radicle, Just don't want to do 45-50. Maybe keep original rear end?.
 
My '38 has a T5 and 3:54 banjo rear end. 70mph is no problem but its noisy. I don't know about frame modification but you may also have to change the driveshaft. If you are planning to go that fast you will also want to make sure that the front end is in good shape and that the brakes are up to snuff.
 
Thank you for the replys. The truck with have new brakes all the way around and I'll be changing any front end part that looks suspect. Many test drives and power stops to make sure all is OK .
 
melisahe said:
current project 49 f1. Thinking of putting in a T5 transmission to gain highway speed (70mph). Will I be able to cruse at 70 with my flathead and the T5? How feasible is it? Will I need frame modification? Thanks for any input. I did a thread search and got no results. Truck currently has original four speed.
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Yes, it will work fine, but keep in mind, with a stock engine and the wind resistance of a truck, you only have about 90 to 100 hp so at 70 even with ideal gearing, your gas mileage is going to suffer.

Yes, you will need to do some modification to the frame and driveshaft.
 
My 48 F1 was a 3 speed. Had to cut the center out of the rear cross member and brace it back to the new cross member I fabricated as the brake and clutch pedals mount to the original cross member. Had to shorten the drive shaft and be sure it was correctly aligned. Bought a kit from Cornhusker. It made the bolt up part easy as everything you will need is in the kit. Was the swap easy? No. Was it worth it. Oh my YES. Mine has 3.78 gears and cruises at 60 - 65 all the time.
 
There's an adapter out there that cost only 160 dollars and allows the T5 to bolt to the stock Passenger bell housing and uses the stock clutch linkage. But I don't think a stock engine can handle 70 mph. It just doesn't have the power for extended running.
 
I replaced the 4 speed in the Tonner with a 49 Merc 3 Speed O/D trans behind a 239 CI engine and a set of 4.11 gears driving 30” Michelin M/S tires on the Tonner and it cruises nicely at 60-65 MPH. The sweet spot for me is closer to 60 MPH where you feel like you can enjoy the ride with less concern about the vintage brakes and steering. I’d say go for it you won’t regret it.
 
melisahe said:
The truck has the original rear end at present. I have a ford 9 inch out of a 78 ford. I don't want to go radicle, Just don't want to do 45-50. Maybe keep original rear end?.
Click to expand...

If you go with a T5, you can probably keep your stock rear. 9 inch rear from 57-72 F100 are the easiest to swap in as they are the same width and spring perches are in the right spot. 78 ford rear is 3” too wide if it’s out of a truck.
 
I thought the 4-speed used a different cross member but after looking in the parts
book I see it only shows one cross member for the F1.


Bob
 
The stock 239 engine in good tune only produces aprox, 80 HP less fan and generator load. This is at 3200 rpm. AS noted in jWL's book. Dull exhaust doesn't improve it much. Advertised Horsepower numbers are the figment of the sales department imagination
 
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