The Ford Barn - View Single Post

Seth Swoboda · 10-14-2025, 04:15 PM

[QUOTE=34fordy;2417160][QUOTE=Seth Swoboda; Then change the transmission to a 15 tooth input shaft and a 29 tooth cluster. When you're done go drive your truck 70 mph.

Hey Seth, Please explain the results and experience of the above swap.[/QUOTE]

You say the top speed is 50 mph. Is this all it will give you or are you saying at 50 mph the engine RPM's are very high? I've had a '39 half ton pickup up to 70 mph with a 3.78 rear end gear and it had more.

I guess we need to know more. If 50 is it with the throttle wide open, you might have other problems.

My experience with the swap is pretty straight forward. Go fast with a lower engine RPM. Does the swap add MPH, no. My engine is capable of going "fast". My end goal was to lower the RPM's at 60-70 mph so that the drive was more comfortable. The swap for me is not complicated as I've done it many times. It is certainly less involved than going to a T5 transmission and an open drive line. Plus there is no butchery involved. It is simply swapping gears that Ford offered.

10-14-2025, 04:15 PM	#24
Seth Swoboda Senior Member Join Date: May 2010 Location: Southern Illinois Posts: 4,213	Re: Rear Diff Swap [QUOTE=34fordy;2417160][QUOTE=Seth Swoboda; Then change the transmission to a 15 tooth input shaft and a 29 tooth cluster. When you're done go drive your truck 70 mph. Hey Seth, Please explain the results and experience of the above swap.[/QUOTE] You say the top speed is 50 mph. Is this all it will give you or are you saying at 50 mph the engine RPM's are very high? I've had a '39 half ton pickup up to 70 mph with a 3.78 rear end gear and it had more. I guess we need to know more. If 50 is it with the throttle wide open, you might have other problems. My experience with the swap is pretty straight forward. Go fast with a lower engine RPM. Does the swap add MPH, no. My engine is capable of going "fast". My end goal was to lower the RPM's at 60-70 mph so that the drive was more comfortable. The swap for me is not complicated as I've done it many times. It is certainly less involved than going to a T5 transmission and an open drive line. Plus there is no butchery involved. It is simply swapping gears that Ford offered.