I must admit that I have never worked on rear end gears. I'm thinking of switching from 4:11's to 3:73 or maybe even 3:55. I'm running a zz502, th400 with 3600 stall, and a 12 bolt 4:11 posi. Street tires are about 28" tall. What kind of difference do you think I'll notice with 3:73 or 3:55? I'm thinking the car might even feel quicker with a little less gear since it has good low end torque? It might pull a little longer? Also, would it change the converter stall to a higher or lower RPM?

I'm going to have a local speed shop do the swap for me, but I want to buy the parts. All I know about my current setup is it has Richmond gears. I assume I'll have to buy ring and pinion gears and an install kit? I see there's 3 and 4 carriers. How do I know which I have? Anything else I need to get or know?

Thanks for any advice!

What differential do you have? Is it an Eaton, Auburn or other? You must find out what you have before getting any other parts. If you have an Eaton then all you have to do is look at the casting number on the case. EDB30140 is a 3 series and EDB30174 is a 4 series.

I'm not sure. I'll have to pull the cover and check it out. If I still can't figure it out I'll post some pics of it. I won't have the car home from it's winter resting place for about another week, but I'll post what I find then.