Transmission Ratios?

J

jeepguy1948

Well-known member
I'm going to put a Mitchell transmission in my 28 RPU. I would like to get some feedback about stock ratio vs the 15% higher 1st & 2nd. I'm planning to get an overdrive from them a little farther down the road. Motor has high compression head,, Weber carb, header, fsi ignition, so it has more poop than a stocker. I do not know for sure what diff ratio I have either and with a closed driveline I don't know how to figure that out either. Being a truck it likely started out with a 4:10 but that could easily have been changed (my truck is actually going 40 miles an hour when the speedo says 35. Plus or minus a bit).Thanks
 
Over the years these speedo's have become very inaccurate. Mine reads slower than the actually speed, 40mph is actually 45 mph and 50 mph is really 57 mph.

There are many threads on figuring out the actual get ratio in search.
 
Are you hauling firewood or loads to the dump? Do you live in Florida where the highest grade is the overpass over the interstate? If you live in a flat area and don't haul heavy loads then go for the higher ratio gearbox.

To measure your rear end ratio, jack up one rear wheel. Put a chalk mark on the tire. Take the plugs out. Put the transmission in high gear. Hand crank the engine over and count the number of engine revolutions for 20 revolutions of the wheel. Divide that number by 10 and that is your answer. For instance if the engine has to revolve 41 times then the ratio is 4.1 or 4.11 to be more exact. If the engine revolves 38 turns then the ratio is 3.78. If you don't have a helper then you can use a large mirror to watch the tire. There will be a math exam on why this works tomorrow.
 
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Stock A's have a 1st gear that is quite low, and 2nd is close in ratio to 1st but a big ratio change into 3rd. So it would be similar to installing a V8 trans, I think you would like it.
 
'28 RPU said:
I do not know for sure what diff ratio I have either and with a closed driveline I don't know how to figure that out either.
Click to expand...

Easy way to determine ratio. Pull the fill plug, mark a tooth and count the ring gear teeth. 3.78's = 34 teeth, 4.11's = 37 teeth.
 
I just recently put a 36 Ford v8 transmission in my A using one of clings adapters. It has the same gear ratios as the B transmission. The gear spacing is an enormous improvement and makes the car more comfortable to drive around the moderns in town. I also have a Mitchell od, 5.5 head, B distributor and single 97 on a Burns intake. Although not the most correct A that I've owned it has become the most pleasant to drive.
 
With an engine like you describe and assuming you won't be hauling heavy loads in your P/U, I think a higher diff ratio is quite in order. 3.54 certainly, 3.27, maybe. I have no experience with the 3.27 ratio.
I drag a heavy load behind my A when towing with an engine that sounds similar to yours. I have a Mitchell gearbox (higher 1st and 2nd gears) and O/D in that car with a 3.78 rear end. I do 50mph all day, every day, literally for weeks at a time. The gearbox has the higher 1st and 2nd gears but I still find high second a very useful combination. In other cars with standard gear spacing, it is even more useful because of the wide gap between 2nd and 3rd gears.
The fitting of later gearboxes like you guys do is not much of an option here. All of the adapters I have seen have been designed for LHD cars and it is illegal to cut the chassis. I suspect the designers forgot there is any such thing as RHD cars.
If you are driving a solo car, I'd go with the higher ratio 1st and 2nd and get the O/D in there asap or try a higher diff ratio. The choice is yours.
 
Synchro909 said:
With an engine like you describe and assuming you won't be hauling heavy loads in your P/U, I think a higher diff ratio is quite in order. 3.54 certainly, 3.27, maybe. I have no experience with the 3.27 ratio.
I drag a heavy load behind my A when towing with an engine that sounds similar to yours. I have a Mitchell gearbox (higher 1st and 2nd gears) and O/D in that car with a 3.78 rear end. I do 50mph all day, every day, literally for weeks at a time. The gearbox has the higher 1st and 2nd gears but I still find high second a very useful combination. In other cars with standard gear spacing, it is even more useful because of the wide gap between 2nd and 3rd gears.
The fitting of later gearboxes like you guys do is not much of an option here. All of the adapters I have seen have been designed for LHD cars and it is illegal to cut the chassis. I suspect the designers forgot there is any such thing as RHD cars.
If you are driving a solo car, I'd go with the higher ratio 1st and 2nd and get the O/D in there asap or try a higher diff ratio. The choice is yours.
Click to expand...

If you check his website you will see that Clings does make a pedal setup for the righthand drive cars. His stuff is quality components.
 
Synchro909 said:
With an engine like you describe and assuming you won't be hauling heavy loads in your P/U, I think a higher diff ratio is quite in order. 3.54 certainly, 3.27, maybe. I have no experience with the 3.27 ratio.
I drag a heavy load behind my A when towing with an engine that sounds similar to yours. I have a Mitchell gearbox (higher 1st and 2nd gears) and O/D in that car with a 3.78 rear end. I do 50mph all day, every day, literally for weeks at a time. The gearbox has the higher 1st and 2nd gears but I still find high second a very useful combination. In other cars with standard gear spacing, it is even more useful because of the wide gap between 2nd and 3rd gears.
The fitting of later gearboxes like you guys do is not much of an option here. All of the adapters I have seen have been designed for LHD cars and it is illegal to cut the chassis. I suspect the designers forgot there is any such thing as RHD cars.
If you are driving a solo car, I'd go with the higher ratio 1st and 2nd and get the O/D in there asap or try a higher diff ratio. The choice is yours.
Click to expand...

If you check his website you will see that Clings does make a pedal setup for the righthand drive cars. His stuff is quality components.
 
Colonial coupe said:
If you check his website you will see that Clings does make a pedal setup for the righthand drive cars. His stuff is quality components.
Click to expand...

That's good to know but it is only a first step. Getting one here is another and finding a good gearbox (trustworthy seller) and then getting that here are another thing.
Thanks for the info and I am aware of his high quality.
 
I tried a 3.27 rear in my speedster for awhile. It was great on the highway, but terrible getting away from a stop light. I replaced it with a quick change, the best of both worlds!
 
I'm a big fan of ordering the Mitchell synchro transmission with the stock 1st gear, 15% higher 2nd gear and using a 3.54 rear end ratio. That puts second gear almost exactly between 1st and 3rd in terms of RPM's to speed, and gives you easy 55 MPH. The 15% higher second gear ratio with the 3.54 rear is awful close to the 2nd +OD with stock rear ratio.
 
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