Rear Axle Ratio

[dakotajeep]

Guys,

I just put a different axle in my rig. The driveshaft spun 3.5 times to make the tire turn twice.

If my calculations are right that should mean I have 3.55 gears.

But when I just went out and drove my truck the speedometer still read inaccurately off the same amount that the 4.10's did. (This truck came with 3.55's stock but was changed to 4.10 by the previous owner)

This doesn't make any sense to me. Please help.

Thad

 

[bghnkinf350]

Absolute 100% best way to find the axle ratio is to pull the cover. The gear count should be stamped on the ring gear. It would be the perfect excuse to change the gear oil on the new axle too!

 

[dakotajeep]

Yeah, I am just procrastinating the inevitable.

 

[franklin2]

What are you using as a speed reference?

 

[MUDKICKR]

gear ratio would be 3.55 to tire turning once, not twice. mark the driveshaft with a line and then while turning the driveshaft count how many times it turns for the tire once.

 

[bghnkinf350]

Make sure you block the other wheel if it is an open diff.

 

[dakotajeep]

What are you using as a speed reference?

GPS and comparing that to the speedometer. Basically, I assumed that since I put the same gears in it the it was originally made with (3.55's) that now the speedometer would be accurate or close. Its still the same as with the 4.10's.

 

[dakotajeep]

gear ratio would be 3.55 to tire turning once, not twice. mark the driveshaft with a line and then while turning the driveshaft count how many times it turns for the tire once.

With one tire on the ground and the other in the air, if I turn the wheel once the drive shaft spins less than twice.

Maybe because its an open diff?

Thad

 

[jhnlennon]

With one tire on the ground and the other in the air, if I turn the wheel once the drive shaft spins less than twice.

Actually doing it that way, a half turn of the driveshaft=1, so 2 turns complete would roughly be a 4.11. 3.55 would be a little over 1.5 turns of the driveshaft to 1 complete revolution of the tire. Sounds like you do indeed have 3.55's.

 

[benton]

what about the stamp on the axle housing?

 

[dakotajeep]

what about the stamp on the axle housing?

Yeah, I spent tons of time with a wire wheel without finding the anything....rust has prevailed.

THad