Old Ford Banjo Ratios

The stock gearing on my 41 Ford Banjo rear is 4.11, correct? If I move to 3.54 gears at the rear, and leave the trans alone, does this represent a 14% OD at top gear? My math is this:

3.54 / 4.11 = .86

and

1 - .86 = .14

By switching to a 3.54 ratio at the rear, the input shaft (driveline) spins 3.54 times per one revolution of the rear wheels, correct?

Sorry for a bone headed question, but this rear end ratio stuff has always confused me.



Mike

 

Math looks good to me. The rear gear may be a 3.78. Look on the rib on the bottom of the case below the torque tube flange. Might have to s****e but it should give you the tooth count.

 

Thanks Andy.

I understand that you get the gear ratio numbers (like 4.11) by dividing the ring gear tooth count by the input shaft tooth count. Like 9 teeth on the input shaft and 37 teeth on the ring gear gives 37/9 = 4.11.

So if I can figure out the ring gear tooth count, what is the input shaft tooth count so I can do the math.

Thanks,

Mike

 

IF........no one has changed it......you can tell by the speedometer drive

A 18T is 3.54
A 19T is a 3.78
A 20T or 21T is a 4.11

 

Also, what Andy is saying is that the tooth counts are stamped on the case near the lower rib--same IF applies, of course. Most '41's would have had 3.78 originally.

 

Thanks all,

I'll do some poking around and see what I can find.

Mike

 

I looked on the front/bottom of the banjo and saw these numbers:

9 - 34

34 / 9 = 3.78.

Thanks for the help. The HAMB sure is quick.

Mike

 

A 3.54 is only .23 from a 3.78.

65 mph with a 29 inch tall tire is

3.78 = 2847 RPMs
3.54 = 2666 RPMs

That's a lot of expense and trouble for less than 200 RPMs change

 

[ QUOTE ]



A 3.54 is only .23 from a 3.78.

65 mph with a 29 inch tall tire is

3.78 = 2847 RPMs
3.54 = 2666 RPMs

That's a lot of expense and trouble for less than 200 RPMs change




[/ QUOTE ]

I hear ya. I'm just working out my options at this point.

I have a 50 Flathead with 50 trans and o/d to drop into my 41 PU, but there's gonna be a lot of mods to the K member if I'm to get that trans in there.

I also own an open drive line 47 truck trans, which would make the engine swap way easy. Then my only options are to play with the banjo gearing if I want some sort of OD in top gear.

Mike

 

bvmike,

do you have the open drive rear to go with the truck ******? if so you should keep in mind that if you use the pick-up open drive rear that only pick-up open drive rear gears will work with it. car gears won't fit. and the last i knew no one was making open drive gears. so you're pretty much going to have to stick with whatever open drive gears come in your rear.

if you don't have the pick-up open drive rear then you'll be converting a closed rear to open rear. you can use the kit from speedway or hotrod works The Hot Rod Works or you can use the way Smokey described banjo conversion .

prolly unnecessary info (stuff that you already knew), but i like to take every opportunity to get folks to look at smokey's conversion thread. one of the best posts ever, in my opinion. too bad the pic isn't there anymore. the post is in tech o'matic, though.