My neighbor and I are going to the Seattle RV show tomorrow. He is mildly interested in getting his first RV in the near future, perhaps a tent trailer. Naturally, I'm trying to set the hook..It looks like his truck is rated between #7300 and #9300 depending on what what gearing he has. Is there an easy way to determine what diff he has?Thanks,Scott

Used, so the previous owner(s) may have changed out the diff gearsetBest and easiest is to tie a length of string to the U-Joint. Choose the one pointing straight down and roll the vehicle until it is pointing straight downRoll the vehicle one tire rev. Use the valve stem as a markerThen count the whole number of string turns. That will the the whole number...3 turns means 3.4 or 3.7...4 turns means 4.1, etcThen the fraction of a turn will be the rest of the diff ratioRemove the string (have to say this, as assumed they would in past posts and got some PMs yelling at me that I should have said that)

Thx Ben. Yeah, I know we could figure it out but I was hoping the actual number is posted someplace, like it is on Ram's.The truck is bone stock and doesn't have a ton of miles. I think we can safely assume it's orig.

you Can do it without the string, just eyeball the U-JointIsn’t a 2,000 lb rating difference worth it ?

Other than RVers who changes rear end ratios? And darn few of us.

find the axle code on the door jamb sticker and then google it.Here is mine.. It's a 13, but even my 97 had this same tag, just not the same code...Mitch

2005 F150 tow rating | Good Sam Community

blt2ski
Moderator
Feb 07, 2020
Lwiddis wrote:
Other than RVers who changes rear end ratios? And darn few of us.

If the rig was used by an offroader, lifted, taller tires. A VERY common practice. RV folks, more common to upgrade the truck per say.

I really doubt Scott's friend has a different Ra ratio than what it came with.

Marty
2manytoyz
Explorer
Feb 06, 2020
You can use the online VIN decoder. This is what was recommended on a Ford forum for retrieving the axle ratio:

http://www.etis.ford.com/vehicleSelection.do
LanceRKeys
Explorer
Feb 06, 2020
While your at it, good time to go ahead and change the diff fluid.
Adam_H
Explorer
Feb 06, 2020
There should be a tag on the rear diff cover. Most F150s of that year range came with a 3.55 or 3.73 gear ratio. Metal tag bolted to the diff cover will read:
3 55 = 3.55 ratio (duh)
3L55 = 3.55 locker
3 73 = You get the idea......
The odds of someone changing the gear ratio are slim.... The odds of that tag not going back on after a diff service are greater but most never service the rear axle.
Payload sticker is in the door jam and most are around 1500-1700 lbs.
ScottG
Nomad
Feb 06, 2020
BenK wrote:
Scott

Morning reading...funny coincidence...came across this for you

https://nasaspeed.news/toolshed-engineer/how-to-determine-what-gear-ratios-you-actually-have/?amp

So all it takes is a NASA engineer to figure out this stuff! :B
BenK
Explorer
Feb 06, 2020
Scott

Morning reading...funny coincidence...came across this for you

https://nasaspeed.news/toolshed-engineer/how-to-determine-what-gear-ratios-you-actually-have/?amp
ScottG
Nomad
Feb 06, 2020
Perfect, thanks Mitch.

Scott
MitchF150
Explorer III
Feb 06, 2020
find the axle code on the door jamb sticker and then google it.

Here is mine.. It's a 13, but even my 97 had this same tag, just not the same code...

Mitch
Lwiddis
Explorer II
Feb 06, 2020
Other than RVers who changes rear end ratios? And darn few of us.
BenK
Explorer
Feb 06, 2020
you Can do it without the string, just eyeball the U-Joint

Isn’t a 2,000 lb rating difference worth it ?