Test for mis-matched axle ratio

[TJBaker57]

I frequent a lot of GMT360 related internet sites. Yes, that includes the old or as I call it the ancestral site, TV, and several Facebook groups.

Lately I have encountered a number of users who have newly purchased GMT360 and have reported wheels binding when in 4WD. Reading their descriptions led me to the suspicion that they had axle ratio mismatches. In the past week there have 2 confirmations of this. I made a short video for a method I concocted to test for this condition. Additionally I made 2 others showing how I would identify an axle ratio. (Actually, I have a custom Torque PID to display rear axle ratio). There isn't much, if any, talking in the videos but details are in the descriptions. You would need to go to the Youtube site to see the text in the descriptions.

I ~think~ I have everything right. Your thoughts?

 

[budwich]

this is the result of "differential replacement"??? IF so, does this cause any issue with the transfer case if it is always run in 2W. Very sad that the seller didn't notify the buy of the "situation".

 

[TJBaker57]

this is the result of "differential replacement"??? IF so, does this cause any issue with the transfer case if it is always run in 2W. Very sad that the seller didn't notify the buy of the "situation".

Yes, as stated previously these are mostly newly acquired vehicles for the posters who are now trying to diagnose their 4WD troubles. . These are cases where a previous owner has replaced a differential and not matched the axle ratio. In some cases the vehicle has changed hands several times and more than one recent owner was unaware of the issue, not having tried to use the 4WD.

As you surmised, this is generally not an issue if one doesn't engage the 4WD. If the rear is the incorrect ratio the speedometer will be off by about 5 or even 10 mph at 60 mph. I also wonder of implications with the ABS and or stability systems when the sensed speeds for the rear wheels will be incorrect.

I came up with this simple test to make it easy for these new owners to check for the mismatch before they throw money at encoders, TCCMs, and front axle splined disconnects.