Trac Lok rear end oil

[Bill73Ragtop]

Just posting an experience I recently had with my Trac Loc rear end. Two years ago I had new clutches installed and a basic overall performed on my 3.25 Trac Lok rear end. It had been sitting for about 10 yrs and was slipping when I removed it.

We soaked the clutches in synthetic oil (75W-90) prior to the rebuild and installed the same grade with limited slip additive to fill the rear end. From the very beginning it groaned, moaned, popped and skipped. If I did a series of figure eights in a parking lot it would quiet down and run smooth for about 2 miles. After about 700 miles, it never improved, in fact it was getting worse.

A month ago I pulled out the center section to drain the oil and check for any debris (such as pieces of fiber clutch disk) found it was clean so re-installed using conventional rear end oil (90W - 140W) with 8 oz of limited slip additive. As I backed the car out of the garage, the difference was already apparent. Within one mile the unit was performing perfectly.

I've since learned from several other local folks that they have never had good luck with synthetic in the older style clutch units.

BTW, I also have a 69 vert with an Eaton Tru-Trac which uses the synthetic (75w - 90) with no problems whatsoever.

 

[CZ-75]

Good to know. I'm having my rear end swapped out as I type. I'm using a "kit" from Jegs that comes with synthetic gear oil.

So far, my swap has been quite the odysey... Found cracked brake pads which had to be ordered (1 day down). Then, found a bad wheel bearing (another day), then the pinion retaining clip broke (3rd day down the drain).

 

[MotoArts]

My '98 Expedition with the 9.75" rear came with synthetic.

Was dead quiet up till 100K miles, and the trac lock still worked just fine (if not TOO good). It was almost as if it got tighter with age. Drained and refilled (the still clean stock sauce) with Lucas synth and the additive @ 125K.

Didn't change a thing no matter the temp.

Sold it that way.

 

[mach1000]

I used the GM posi rear end additive in mine. Before adding the additive it would catch and pop and lock going around just the slightest corner. I never used synthetic gear oil though.