I have a few reasons to believe my truck has been gear swapped. I've asked Ford what gears it came with, they say 3.73. The rear diff says 73ls on it. However, the way it runs compared to my old excursion is huge. I thought mostly that was due to the weight difference, but the RPMs seem a bit different than what I remember; so I decided to check it out.



According to Engine RPM Calculator (and other calculators) with 0.71 od ratio, 65mph, 32 inch tires (it does have 33s but the speedo has not been calibrated for that) and 4.30 gears, it looks like the rpms are supposed to be 2084, which looks right. At 75mph (didn't take a pic), it's just under 2500 rpm, which also comes out...

My question is, is there any foolproof way I can tell the gears? Anything I can read/datalog with the sct x3 programmer? Or for those of you using torque android app, any way I can read any PID or anything? Or can i just make a calculation between obd2 mph, trans gear ratio and rpm?

Any other ways I can tell with a certainty what gears I have in the truck?

 

I have 265/75/16's (30inch) and Im at about 2 grand going 65 in 5th.. no clue what gears i have though.

 

Maybe its not shifting into overdrive with 3.73's making it seem like 4.10's?

 

it's definitely in od, it comes out of it if I push the button.


265s are 32" I believe, not 30".

 

Hm... i just measured em today cause i was looking what i could stuff in there after a leveling kit and the tape said 30

 

it won't be perfectly round with all the weight on it; and the thread adds a bit of diameter/radius variation between new and well worn...

 

Good point. Damn so i could totally fit 35's on my truck after i level her

 

I was able to do that on an 04 f150 with just a 2.5" leveling kit in the front. It looked like what should have come factory on that thing...

 

Thats what im aiming for. OEM+, how it shoulda looked from the factory, with some attitude to it.
My tires look like they should be on a fricken 2wd ranger. Theyre so small for my truck.

 

I have 315/75/16 (34.7") tall, with a 2.8" levelling kit, I did have to space out my bumper 5/8" and pull the inner fender wells back at the rear of the well and secure with cable ties, but no rubbing now. Every truck will be a little different, I'm also running 10" wide wheels which was the main reason for bumper spacing. With my stock wheels and 305's I had no rubbing.

 

Jack the rear tires off the ground. Put truck in neutral. Put a chalk mark on the bottom side of the tire. Put mark on drive shaft. Have someone turn the tire one full turn and count how many times the drive shaft turns. This will get you close enough.

 

Your speedometer and tach look about the same as mine, with 32 inch tires and 3.73 gears. 2000 RPM is about 65 MPH.

 

Are you sure it's 65? I remember being at 2100 rpm at 75 in the excursion... which according to the calculator comes out right on the money...

 

My 4.30 geared truck turns 2100 rpm @ 60mph. Stock 235/85/16 tires.

 

Im at 2000rpm at 65mph. And i know that i have either 3.73 or 4.10 gears. On "32inch" tires