Reply
 
Thread Tools Display Modes
Old 05-22-2018, 10:52 PM   #1
Junior Member
 
Join Date: Mar 2018
Posts: 18
How does one PROVE the axle ratio of a used truck?

Hey all. Currently, we have a little 22 foot TT and looking to upgrade our TV with an eye towards our *next* camper (10,000 or less, fully loaded) We have our eye on a 2012 Ram 2500 5.7, crew cab, 4x4 LB The dealer says it has a 3:73 axle however according to the VIN at this site below, it has a 4:10 This COULD represent up to a 3000# difference in max tow ratings, according to the 2012 Trailer Life Towing Guide

https://www.dodge.com/webselfservice/dodge/index.html


One question I have is, which to believe? (the VIN!?) but also...if you had absolutely NO idea, how would one determine exactly which rear diff he actually has?
__________________

gorgerax is offline   Reply With Quote
Old 05-22-2018, 10:57 PM   #2
Junior Member
 
Join Date: May 2018
Posts: 7
Quote:
Originally Posted by gorgerax View Post
Hey all. Currently, we have a little 22 foot TT and looking to upgrade our TV with an eye towards our *next* camper (10,000 or less, fully loaded) We have our eye on a 2012 Ram 2500 5.7, crew cab, 4x4 LB The dealer says it has a 3:73 axle however according to the VIN at this site it has a 4:10 This COULD represent up to a 3000# difference in max tow ratings, according to the 2012 Trailer Life Towing Guide

https://www.dodge.com/webselfservice/dodge/index.html
file:///C:/Users/gorge/Downloads/2012_towing_guide_lo_res.pdf

One question I have is, which to believe? (the VIN!?) but also...if you had absolutely NO idea, how would one determine exactly which rear diff he actually has?

There should be a tag on the axle that says the ratio, or gives you a BOM number (bill of materials) that you can look up.
__________________

nick1236 is offline   Reply With Quote
Old 05-22-2018, 11:02 PM   #3
Senior Member
 
Cypressloser's Avatar
 
Join Date: May 2014
Location: Alberta - East of the Rockies, West of the Rest
Posts: 1,296
That's a good question, I had my truck custom built and only the build sheet and the window sticker are correct. All the web services return false information in one way or another.
Having said this, the max tow rating is not a number that's written in stone or legally binding AFAIK, but shouldn't be ignored either.
__________________
Almighty 2018 RAM 5500 Laramie CC
Fulltiminig in our Riverstone Legacy 38RE, 960 Watt Solar, 6x6 Volt Battery Bank, Freedom SW 3012 Inv/Charger
Cypressloser is offline   Reply With Quote
Old 05-22-2018, 11:08 PM   #4
Senior Member
 
DieselDrax's Avatar
 
Join Date: Feb 2018
Posts: 718
The Dodge URL you used pulls the equipment listing as the truck was built. Believe that over what anyone else tells you.
__________________
2017 GMC Canyon - CCLB, 4x4, 2.8L Duramax, ARE Z-series shell
2013 Shamrock 21SS
DieselDrax is offline   Reply With Quote
Old 05-22-2018, 11:16 PM   #5
Senior Member
 
Join Date: May 2015
Posts: 141
How does one PROVE the axle ratio of a used truck?

What you could do is jack the rear end up on the truck, make a mark on the drive shaft and a mark on one rear tire.
On the tire, rotate the tire 1 full revolution and count how many times the drive shaft turns past the mark you made on the shaft, this is your axel ratio.
For example. 1 full rotation of one rear tire equals 3.73 turns of the drive shaft.

You may have to put the auto trans in neutral when you do this so the drive shaft turns.
cfiowa is offline   Reply With Quote
Old 05-23-2018, 04:39 AM   #6
Senior Member
 
Join Date: Jun 2017
Posts: 220
What was just stated by cfiowa is the old school but as long as you donít get distracted very reliable
moose074 is offline   Reply With Quote
Old 05-23-2018, 05:17 AM   #7
Senior Member
 
Join Date: Jul 2010
Location: Waynesville
Posts: 13,158
Quote:
Originally Posted by moose074 View Post
What was just stated by cfiowa is the old school but as long as you donít get distracted very reliable
Old school or not he is correct,It's "Simple Math"! But since it is a "Used Truck" if they have also Changed the "Tire Size" all bets are off in regards to "Tow Rating"! Youroo!!
__________________
youroo is online now   Reply With Quote
Old 05-23-2018, 05:18 AM   #8
Mod free 5er
 
Join Date: Mar 2008
Location: Concord, NC
Posts: 24,485
Quote:
Originally Posted by cfiowa View Post
What you could do is jack the rear end up on the truck, make a mark on the drive shaft and a mark on one rear tire.
On the tire, rotate the tire 1 full revolution and count how many times the drive shaft turns past the mark you made on the shaft, this is your axel ratio.
For example. 1 full rotation of one rear tire equals 3.73 turns of the drive shaft.

You may have to put the auto trans in neutral when you do this so the drive shaft turns.
If you are unsure whether you have a Posi Rear or not

Be sure to use jack stands under the axle for safety precaution***
Jack both wheels off the ground and turn one wheel.
•If the opposite wheel turns the same direction or doesn't turn at all, then the rear axle is posi or limited slip.
•If the opposite wheel turns the opposite direction, then it's probably an open rear axle (non-posi).

Determining a Rear Axle Ratio of a Non-Posi Rear
1.Jack one wheel off the ground, put the transmission in neutral and take the parking break off. ***Be sure to use jack stands under the axle for safety precaution***
2.Mark the wheel and the drive shaft with chalk or masking tape.
3.Turn the wheel TWO revolutions and count the number of driveshaft turns.
4.The number of driveshaft rotations will help you determine your rear axle ratio. For example, if it turned 3 and a half times, it's a 3.50:1 ratio. If it turned 4 and a quarter times, it's a 4.25:1 ratio.
__________________
OldCoot is online now   Reply With Quote
Old 05-23-2018, 05:28 AM   #9
Mod free 5er
 
Join Date: Mar 2008
Location: Concord, NC
Posts: 24,485
Quote:
Originally Posted by moose074 View Post
What was just stated by cfiowa is the old school but as long as you donít get distracted very reliable
Only correct if it is a limited slip/posi rear end. Not correct if it is an Open rear end.
__________________
OldCoot is online now   Reply With Quote
Old 05-23-2018, 05:43 AM   #10
Senior Member
 
Join Date: Aug 2015
Location: Garner, NC
Posts: 689
Quote:
Originally Posted by cfiowa View Post
What you could do is jack the rear end up on the truck, make a mark on the drive shaft and a mark on one rear tire.
On the tire, rotate the tire 1 full revolution and count how many times the drive shaft turns past the mark you made on the shaft, this is your axel ratio.
For example. 1 full rotation of one rear tire equals 3.73 turns of the drive shaft.

You may have to put the auto trans in neutral when you do this so the drive shaft turns.
What he said.
__________________

__________________
2017 Ford F450 Lariat 6.7L
2016 Vengeance Touring Edition 40D12

Former Forest River Campers:
2004 Puma 30FQSS
2010 Sabre 31QBDS
2014 Work & Play 30WRS
KFX450RXC is offline   Reply With Quote
Reply

Tags
axle, truck

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



» Featured Campgrounds

Reviews provided by




ForestRiverForums.com is not in any way associated with Forest River, Inc. or its associated RV manufacturing divisions.


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 12:25 PM.