Re: please help me rear end
I am no expert- but I do know that an 8.8 ring gear will not fit into a 7.5 rear end. The carrier is larger as well. It either fits or it doesn't.
Suggestion: Installing a ring gear assembly into an axle is a precision process that requires specific tolerances to avoid harsh noise and extreme wear. Do not take this to any mechanic. Take it to someone you trust- or specifically someone who has done an upgrade before.
A 4.10 will fit- but will require a different style of carrier pin- or slight grinding of the carrier pin to clear the teeth on the install. To see the shape to grind, look up carrier pins for the 7.5 and you will see the difference needed for the 4.10 gears. Maybe this is where the guy is having problems.