Gear ratio

[tom'sB2B]

Is there a way to determine the gear ratio for an axle?.say between a 4.10, 3.54 and a 3.73. I picked-up a axle from a 52 desoto today and I am planning to do a swap. This is all new to me and I am wondering how I can figure out what I have. The guy I got it from didn't know and I didn't see the car that it came out of. Is there a tooth count or something?

thanks for the help

Tom

[Dodgeb4ya]

Clean the differential gear case on the lower side and you will find a slightly raised flat 1-2" square pad area with the ratio stamped into that pad. You really have to clean it well to bare metal and look closely-you will see the ratio.

[Merle Coggins]

Also, after you pull out the diff it'll be stamped into the ring gear. It'll be easier to read but harder to get to.

[Phil Martin]

My dodge with fluid drive has 3:73 desoto would probably be the same if fluid drive.

[Dennis_MN]

Some where out on the internet were instructions for counting turns.

assuming that the differential is out of the car and sitting on your kids wagon as mine was, put a wheel nut on one stud and have it pointing up. Then turn the drive pinion where the drive shaft goes, just one turn of 360 degrees. Count how many turns the axle nut made. If it turned exactly 4 times the ration is 4.00. If it turned 3.5 turns you have a 3.5 ratio. good luck.

Dennis

[Merle Coggins]

  Dennis_MN said:

Some where out on the internet were instructions for counting turns.

assuming that the differential is out of the car and sitting on your kids wagon as mine was, put a wheel nut on one stud and have it pointing up. Then turn the drive pinion where the drive shaft goes, just one turn of 360 degrees. Count how many turns the axle nut made. If it turned exactly 4 times the ration is 4.00. If it turned 3.5 turns you have a 3.5 ratio. good luck.

Dennis

Be careful with that method. Both hubs need to be turning equally for a proper test. Otherwise you have to account for the gear reduction within the differential side and cross gears.

Use 2 people, one at each wheel hub, and rotate them equally one revolution and count the revolutions of the input yolk. 4 (and a bit) rotations will most likely be a 4.10 diff, around 3 3/4 revolutions would indicate a 3.73 diff,... I think you get the picture now.

Merle

[tom'sB2B]

Thank you for all the help

I did some searching and found a stamp which says 3.54.

I wonder if that will be a good gear ratio for my B2B? I was thinking I had a 3.73.

Tom

[Merle Coggins]

What's your local terrain? If you are in hill country you may find the 3.54 makes climing the steep hills more difficult in high gear. If you're in the plains area it would probably be perfect. I've been happy with my 3.73 gears, but others have been happy with their 3.54's too.

What have you got to loose? Throw it in there and give it a try.

Merle

[oldmopar]

My 52 suburban has a 3.9 and driving 55-60 is not a problem. My B1d has either a 4.3 or 4.8 hard to read the number but should still do 50 - 55 once its on the road

[tom'sB2B]

yeah, what the hell. I will put it in and see what happens. It can't be any worse than what I have in it now. Its all a learning experience.