I spent a bunch of time in the past year searching for info on the 8.8 and 9 inch rears in order to compare and decide what I wanted to do in my car. I had a lot of trouble finding weight comparisons, actually I never did find the information. I was told repeatedly that the 9 inch was heavier and the gears transferred power less efficiently, but no exact numbers. So, I have a few rear ends at the moment and I decided to weigh and measure them. I have to say the results surprised me.
The weights are with axles but with no fluid or brakes.
Trac-loc 8.8 from Fox Mustang (was in an '85 but the tag gives a build date of April '87) weighs 155 pounds. It measured 59.5 inches from end to end of the axles.
Small bearing 25 spline 9 inch open diff from a '67 Mustang (not original to car but fit properly with original wheels) weighs 149 pounds. It measured 61 inches from end to end of the axles. I did not think the 9 inch would be lighter!
Not a fair comparison, because it's quite a bit longer, but I also have a big bearing 31 spline 9 inch open diff rear from a '79 F150. It weighs 192 pounds. It measured 71.5 inches end to end of the axles. I believe that a big bearing 9 inch rear would be significantly heavier than a small bearing unit, even if the two were the same length.
I have an 8 inch rear end in my convertible currently. When I get around to pulling it, I'll add the info.
I hope this is useful to someone.
The weights are with axles but with no fluid or brakes.
Trac-loc 8.8 from Fox Mustang (was in an '85 but the tag gives a build date of April '87) weighs 155 pounds. It measured 59.5 inches from end to end of the axles.
Small bearing 25 spline 9 inch open diff from a '67 Mustang (not original to car but fit properly with original wheels) weighs 149 pounds. It measured 61 inches from end to end of the axles. I did not think the 9 inch would be lighter!
Not a fair comparison, because it's quite a bit longer, but I also have a big bearing 31 spline 9 inch open diff rear from a '79 F150. It weighs 192 pounds. It measured 71.5 inches end to end of the axles. I believe that a big bearing 9 inch rear would be significantly heavier than a small bearing unit, even if the two were the same length.
I have an 8 inch rear end in my convertible currently. When I get around to pulling it, I'll add the info.
I hope this is useful to someone.