I have a 1988 supercab f-150 2 wheel drive 5 speed manual transmission 4.9 L I want to replace the transmission with one from a 1987 4 speed manual transmission long wheel base two wheel drive same engine size - do the differentials have the same gear ratio? are the drive shaft lengths different for each transmission
You have the truck…
Most 5-speeds, the 5th gear is overdrive…So if you do this, it will be like driving your 5-speed in 4th gear all the time…A custom made driveshaft with the correct length and yoke may have to be made up…The clutch disc may have different center splines…Do your homework…
I think there is fuel injection on this truck, right? Fule injection means engine computer. Engine computer means matching sensors are necessary. Unless you have the ENTIRE 1987 truck, wiring harness, engine computer and all - its going to be a pain to get that automatic to work. I wouldnt be worrying so much about gear ratios as the transmission not shifting because of a transmission speed sensor not being connected to the computer.
Its not just the transmission and gear box I would be wondering about - what about the electronicly controlled engine? If you need to reprogram it - I am not even sure it is possible.
That being said - I am not firmiliar with the older 4 speeds - and they may be able to operate completely independantly - all functions controlled internally with the transmission fluid.
You may want to check into this as well.
Yes, you can do this w/o concern of rear axle ratios, electronics, etc. The 4-speed is a Borg-Warner with a removable bell housing. The major difference is that the 4 speed has a clutch fork w/ external slave cylinder…you’ll have to take those as well. Drive-shaft length difference is minimal but probably required.