Okay, I have seen some great advice from several guys like AxRacer, and NumberDummy, on gear ratios. Does anyone have a chart or formula, so I could see the compound ratio if I changed the rear end in a truck and then later changed the transmission? I am still looking for a truck. I want to start with a 4 speed and change the rear end to a high ratio, and then change to a 5 speed at a later date. This truck is going to be a driver, not a hauler, so I need speed and smooth ride more than stump pulling power. I also want a 300 six eventually, so I am trying to figure out how to work all this out so I don't waste money along the way. Any help on a compound ratio formula would be helpful.

 

I am not sure what a compound ratio formula is but whenever I have gearing questions I go to the Richmond Gear Calculators site and play around with everything there and record my data. I start with a particular gear gear, then change around the tire size and high gear tranny ratio, then I change the rear gear and see how they compare. If you do this on some kind of spreadsheet it sounds like that's what you're looking for.

 

When you say that you want a 5-speed at a later date, I assume that you mean with a 5th gear overdrive and what you really want to know is what your effective final drive ratio would be in OD for any given rear axle ratio. That's easy! Just multiply the OD ratio by the axle ratio and you've got it. For ex.: My truck is going to have a ZF 5-speed with a .80:1 OD ratio and 3.73:1 gears in the axles. .8*3.73 = 2.98

 

Blue oval, Thanks that is what I am looking for. With that information I can calculate what the truck has now for gears, and see what changing to this gear set or that gear set will do to it. I am not really interested in putting a Car 5 speed in my truck primarily because most of the shifters come off the side or too far back. If I can stick with Truck trannys then I am pretty sure there is less work to install them.

 

Glad to help. If you're wanting to stick with a truck transmission with a 300(and you listed a couple good reasons for doing so), then your best choices are the ZF S5-42/S5-47 heavy duty 5-speed available in '87-'96 F-250 and larger trucks and the M5OD light duty 5-speed available in the full size Bronco and F-150. The M5OD has a reputation for being weak and needing frequent rebuilds. If you keep it serviced and shift her nice, it should be fine in a cruiser, though. The ZF is a good, stout transmission and many M5OD owners swap a ZF into their trucks when the M5OD goes out. I just tore the ZF that's going into my '52 down for a maintenance rebuild this afternoon. It'll be interesting to see how it fits in the truck, but my initial rough measurements say that the shifter will be almost exactly where the old 4-speed shifter was. I'll be wedging it and a 351W in this winter. Watch this space for details!

 

Hi Broom!

Here, use this one.

You have to enter the transmission gear ratios (which you can vary at will or to suit different transmissions) you have to enter a rear end ratio (which you can also vary) but most important, is you have to accurately measure you rear wheel roll out distance - one revolution. This chart is RIGHT on the money of you do.

http://www.et-studios.com/motorsports/gears/gears.html


Good luck.

 

Julie,

Thanks a ton, that is exactly what I have been wanting to do. This shows me what I get now with a 4 speed, and I can play with different combos to see if what I want to do is even possible. Thanks again.