Gearhead

TOPSIDER METHOD OF CHANGING THE DIFFERENTIAL FLUID
A quick and easy method to change your rear differential fluid is to use a marine oil-changing tool called a “Topsider”. Being a vacuum pump with a 12-quart capacity, it allows you to draw out the fluid through the differential fill hole. It does take about ½ an hour to vacuum out the viscous oil. Transfer the used oil to an old 2-liter pop bottle to make sure that you have extracted out the almost two quarts (for the 7.5” differential). This way, you will know you are ready to refill. Be sure to have a bottle pump for the fresh fluid and wrap your fill plug with Teflon tape to facilitate sealing. I also rotate my axle a little on refill to make sure the TrueTrac doesn’t have trapped air in the casing.

WHY THE TRUETRAC SHOULD HAVE THE FORD STANDARD GEAR OIL
At the installation of my Detroit TrueTrac, we used a NAPA brand of 75W-140 Gear Fluid that included Limited Slip Friction Modifier. The Friction Modifier is not needed for the TrueTrac or a standard 7.5” rear end. After the first 1,300 miles, we did a break-in change with Mobile 1 Gear Oil. Being the synthetic 75W-140 variety, we thought that it didn’t have the Friction Modifier, but indeed, it did (as discovered in comments from this forum). It is hidden in the Mobile 1 title’s “LS” designation (LS = Limited Slip). Both of these Friction-modified Gear Oils are not what Ford recommends for the standard 7.5” rear differential.
In an effort to reduce the slow-down noise that I call the “TrueTrac Shuffle”, I changed to the Ford Stock Fluid (75W-140, no friction modifier, Ford Part #XY-75W140-QL). The noise has been reduced by about 80%, and I believe it is solely due to the increased lubricity of the fluid.

esorense

Gearhead: Did you need a dial indicator to ensure your new ring/pinion was installed correctly? Or did you just use gear marking compound? I'm changing my ring/pinion to 3.45 FRPP w/ the true trac. BTW: Thanks for the tip on the gear oil. I'll be getting the stock Ford plain 'ol gear 75W-140 oil you recommended instead of the valvoline plain 'ol gear 85W-140 oil....

Eric.

Stoenr

Let me add this about using the topsider. Dont pump it up too much, it will start to cave in. Found that the hard way.

Gearhead

My mechanic Randy of Randy's Exhaust up in Marysville did the work, while I just watched. He used a backlash gauge both before he tore it apart and afterwards. The reading was the same each time. Randy also used the gear marking compound. I understand that you need to do both, because not only could you change the shims on each side of the ring, but also you can change the shims behind the pinion. The gear meshing is subject to the pinion position, and the backlash to the ring position.