8.5" 28 Spline Detroit Locker VS. GM 3 Series Posi for 80s Build

by relic7680 Sat Sep 14, 2024 6:37 pm

I am wanting to get a posi or locker unit for the 8.5" 28 spline 10 bolt rear in my '76 GMC Sprint. The car is being built as a period mid 80s street machine and will have a 3.42:1 ratio with 275/60R15 rear tires. It already has Yukon 28 spline replacement axles and a freshly built TH350 is in front of it. The car WILL have a 425-450hp 406 small block (currently a mild 9:1 355).

I am considering some 3 series GM posi units on ebay here:
https://www.ebay.com/itm/235263577331
https://www.ebay.com/itm/154649352539
The second listing proclaims to be a stronger design.

I am also considering Detroit Locker part # 187C149A, which sells new from Summit for $1000+. Was a Detroit Locker for my 10 bolt available back in the 80s? How many guys were running them on the street? What are the pros and cons of this setup versus the GM posi units?

I am honestly not very knowledgeable on this topic, though I have done some research. Any help from guys who were running this stuff back in the day would be very appreciated.

by bracketchev1221 Sat Sep 14, 2024 11:13 pm

In the 80’s there was the gm/eaton posi or the Detroit locker. The locker was noisy and rough. But it was stronger and didn’t slip. You could get a higher spring pressure Eaton that would be fine for anything you throw at it on the street.

by Iggy Thu Sep 19, 2024 9:04 pm

I have always been a fan of the Eaton clutch type posi over the GM unit for street use, and Detroit Lockers for off-road (off pavement) use. The Detroit Locker can be noisy in turns and is a negative in snow (we had to drive our cars all year back then due to being dirt poor). The G80 is typically a truck GovLoc and is a stay away from for anything more powerful than a 305 2BBL with single exhaust and pellet type catalytic converter - they are referred to by most as a GovBomb because any additional power will make them explode on a burnout.

This is the Eaton Unit I have used in the past https://www.summitracing.com/parts/etn-19557-010 and helped a friend put one in his '55 Belair with a 1973 Nova rear end - his 383 makes similar power to what you are looking at and he is not easy on his care at all! An Eaton TrurTrack is another good option.

by Sponsored content

8.5" 28 Spline Detroit Locker VS. GM 3 Series Posi for 80s Build

8.5" 28 Spline Detroit Locker VS. GM 3 Series Posi for 80s Build

Re: 8.5" 28 Spline Detroit Locker VS. GM 3 Series Posi for 80s Build

Re: 8.5" 28 Spline Detroit Locker VS. GM 3 Series Posi for 80s Build

Re: 8.5" 28 Spline Detroit Locker VS. GM 3 Series Posi for 80s Build