Sup. I changed my rear differential to my truck 4x4 3.5 ecoboost. After changing it, the wheels were skipping when I was backing up to take it for a test drive. Everything was don’t correct. Now I will say I accidentally bought a different gear ratio. Same pinion and ring. But the gear ratio I put in the rear was a 3.75 while the factory was 3.55. So I don’t know if that have something to do with the skipping. Because the front differential is still a 3.55 ratio but I don’t use my 4x4. What is the cause?

 

 

It was not broken until you fixed it correctly, that was the cause.

 

DId you use the correct fluid? 3.75 gears should be filled with maple syrup - the real stuff, not Log Cabin.

 

Maple syrup has many uses most of us don't know about. Vasil Pospisil, a Canadian professional tennis player, was seen drinking mple syrup during a match.

 

If the 4x4 ever kicks in it won't be good. Hopefully you have a manual 4x4 switch. Are you sure the rear end you put in has no issues?

If you switched the rear end, you should have done the front as well. Hope you get it sorted out.

 

 

Did you change the gear lube? Is it possible you need some limited slip additive?

 

You missed the part where he said he has axles with two different ratios now. Allegedly. If true, that’s a big problem.

 

Gear lube? What is that? There was some thick grease mixed with sawdust in the unit when I took it apart, so I just scooped the old back up and packed it in the new gear set.