Differential Repairs

Good Morning To All,

I spent some time performing an unscheduled axle removal (UAR) this weekend. I have worn out differential gears shafts and spool. Therefore I will be replacing the differential. Pole Cat was originally an open rear end and I intend to make it a limited slip.

So for a street machine I am leaving the 3.00 drive pinion and ring gear in there (great shape) what recommendations on differentials can you give me? Searching this site and then the interweb it looks like Moser, Eaton, Detroit Locker, Track Lock and Ford Racing seem to be the choices.

What are the good and bad on these. Ford Racing appeals to me for a couple of things, price and the Blue Oval.

Is one better with turning than another?

I have emailed an old timer engineer at the Ford Sterling Axle plant to see if he has any interesting comments. If he does I will report them here.

BTW its a 69 XR7 with a 390 and c6

Thanks in advance.

Detroit True Trac is my recommendation. Helical gear driven posi, no clutches (and so no friction modifier lube additive required).

Detroit Locker is said to be less than smooth in turns and makes noise, this is what I have read/heard, never ran one and do not intend to (Royce likes them and will say they are no trouble).

Just curious, is the rear 28 spline or 31 spline?

28 splines Bob, what do you have in Isabel?

28 spline and Detroit True Trac limited slip.

Detroit Lockers made in the past 35 years make zero noise, unless you have one of the H series lockers used by dirt track and road racers. They are great in turns, you hear nothing. Link to utterly silent and bulletproof Detroit Locker:


I installed one in my green GT-E 21 years ago. It has withstood countless burnouts, drag strip passes, and close to 30,000 miles on the street. Two transmissions, three sets of tires, same bulletproof differential. No need to use oil additives, and no need to replace worn out clutches, ever.

The Detroit Locker I had in a Camaro back in high school did ratchet during turns. That being said it would hook up and took a LOT of punishment (4500 rpm launches, etc.). It actually never failed from the abuse of 17 yr old me, so that is saying quite alot about its durability. The only other thing I noticed is it wasn’t gentle if you were trying to come around a corner hard (read fish tailing, and having to be on top of it in the correction dept). Don’t know about the true trac personally, but have heard very good things.

Just a word of caution: sometimes when something is described as having an abrupt or hard lockup/unlock, it may be better suited for racing than a street car.

We (Eaton) pretty much own the market except for some of the race applications. Detroit also is owed by Eaton as we bought them out a few years ago and kept their name for marketing. For your application go with the Eaton Tru Track like Bob is running and I also have one in the road race Cougar. Very reliable especially on the street. You won’t have any issues with that unit.


Where are those Detroit Lockers made?

That’s good to know as I am also in the market for a limited slip.

Depends on the unit. They go down different lines at different plants all round the world. For the true trac unit the gears are forged and machine either in Belmont Iowa or Kearny Nedraska. I don’t know what plants the rest of the components come from. I believe the Tru trac unit is assembled in Taiwan. I’m not part of that division but I do some instrumentation work for the differential group.