[projo198]

I believe the door jam stickers only say what count spline is needed. Mine is an '09 so simply having a transmission temp gauge doesn't tell me anything.

The only identifying factor I can find on the drivetrain is what is left of a sticker on the rear differential. I can't post pics here, but the part # listed is 43001 ZX41A.

I can't find this on the internet, it only says it is a discontinued part. Any ideas?

 

[SuperTighty5.6]

Pretty sure its stamped on the rearend or axle somewhere or if you're doing 70mph and at 2k rpm you have 3.36 gear ratio.

 

[projo198]

Can't find any stampings that would identify it, and I don't have stock size tires.

 

[OnTheWrongSide]

Is it apart already? The crown wheel will have the ratio stamped into it. Or you could just count the teeth on it and the pinion.

 

[projo198]

Is it apart already? The crown wheel will have the ratio stamped into it. Or you could just count the teeth on it and the pinion.

Not yet, but it sounds like that's my only solid option. Just haven't had time and wanted to have a replacement ordered or on hand to do it all at once.

 

[CL 8 2WD]

I believe the door jam stickers only say what count spline is needed. Mine is an '09 so simply having a transmission temp gauge doesn't tell me anything.

The only identifying factor I can find on the drivetrain is what is left of a sticker on the rear differential. I can't post pics here, but the part # listed is 43001 ZX41A.

I can't find this on the internet, it only says it is a discontinued part. Any ideas?

get the rear tires off the ground (jack stands) block the front tires so the truck doesn't move.
chalk a white line on the driveshaft and one on the tire, turn the driveshaft and watch the chalk mark on the tire count how many times the driveshaft go's around per one complete rotation of the tire. 3.36 means the driveshaft does 3.36 rotations per one rotation of the tire (stock size tire)

 

[IMADOGMAN]

get the rear tires off the ground (jack stands) block the front tires so the truck doesn't move.
chalk a white line on the driveshaft and one on the tire, turn the driveshaft and watch the chalk mark on the tire count how many times the driveshaft go's around per one complete rotation of the tire. 3.36 means the driveshaft does 3.36 rotations per one rotation of the tire (stock size tire)

https://www.youtube.com/watch?v=yubcxmidj5g

It doesn't matter what diameter the tire is if you are checking it off of the ground. One rotation of a small tire is equal to one rotation of a big tire. If you have 44" tires on the axle, it will still turn one time :wink:
Also, the video says that the ratio is engine/tire. This is only correct if you are in a 1:1 transmission ratio. He should have said, 3.90 turns of the DRIVESHAFT to one turn of the tire.

You could also do the math by comparing your larger tire circumference to the stock circumference, and determine what your RPM should be at 70MPH with the bigger tire.

 

[projo198]

Thanks guys. I can't run the truck with the front dif in right now, but I will try the chalk idea when I get back into town. Seems pretty straightforward.

And if anyone knows where to get an affordable front dif or a rebuild in the Kansas City area let me know!!!

Thanks much!

 

[dubyam]

Unless you've installed a speedo correction device, you won't have to worry about the tire size. RPM and oem speedo are inextricably linked until you install a device to correct for a different tire size.

Now, beyond that, you my have already seen the ratio, you just didn't know it. You said you looked at the sticker on the rear diff? If that's the sticker on the rear snout, look for the number 3.357 or 3.359. Can't remember which it is, but that indicates the 3.36 ratio. You may also see something like 2.938 or some such, which would indicate the 2.94 ratio.