Ok, I need some help. My 53' has a flathead, 3spd w/o overdrive, and stock rearend. Trying to figure out RPM's since I dont have a tach. Motor runs great but want to not abuse it on the highway. What is a safe speed at say 3k rpm's? At 65, it sounds like it wound pretty tight.
Standard Transmission—3.90-1 (39-10). Overdrive Transmission—4.10-1 (41-10).Fordomatic Transmission—3.31-1 (43-13) If you can find an axle from a Fordomatic car youll get pretty good mileage but you may have to slip the clutch a bit to get going from a dead stop. A **** from a V8 Maverick or Granada will fit with minor modifications and maybe a better variety of ratios.
Here's a formula for figuring it out. You need to plug in your tire diameter. mph X 336.1524 X final drive ratio ÷ tire diameter I had a '53 like yours, also no tach, 390 ****. I didn't feel comfortable driving it much over 60 for long distances. You might want to consider getting an OD transmission. The OD reduces rpms at a given speed by about 30%. They bolt right in with no modifications needed, except for maybe drilling the firewall for the OD cable and kickdown switch. The T-86 with R10 OD is all you need for a flathead.
The T-86 was the Borg Warner 3 speed Ford used in light duty applications from 1949 thru the late '50s/early '60s. The R10 is the OD unit. It wasn't an aftermarket piece, the OD is integral with the main transmission. The trans is the same as yours but with some internal and external parts to make the OD work. The external dimensions and mounting points are the same as yours which is why they are a bolt in conversion. They were usually installed on the ***embly line, but dealers could install on customer request. They show up regularly on that auction site and other places like craigslist. http://www.ebay.com/itm/Ford-Borg-W...r_Truck_Parts_Accessories&hash=item4ad3e6c4fa The picture is of a T-85 with OD; the T-86 looks similar but is smaller.
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