Question about locking differentials

Ok guys heres what happened: I took the old 10.25 rear end out, with a lot of miles. I found a newer model 10.25 with traction lock. I drained the grease out and refilled with 85w-90. My question is this: Since it is a locking rear end is there any special friction modifier I need to add to the diff to keep it alive a little longer?

A little story on LuluBelle my '89 f-250: Bought her for $1,000 along with:
4 new tires
4 new monroe magnum gas shocks
New GPC and glow plugs
Grille guard( cow catcher)
Headache rack
2 full tank of diesel
1 fresh oil change + another complete oil-change
100 gallon in bed tank with 12v transfer pump
New fan belts

The a/c needed changeover, but it works.... Other things ive done include:
New clutch master and slave cylinder, new brake M/C, new thermostat, and general clean up work... will post a photo soon

Depends, did you put full synthetic in?

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What's oem say?
But most everyone I've had wanted something....
Cept my arb's

mexicanjoe said:

Ok guys heres what happened: I took the old 10.25 rear end out, with a lot of miles. I found a newer model 10.25 with traction lock. I drained the grease out and refilled with 85w-90. My question is this: Since it is a locking rear end is there any special friction modifier I need to add to the diff to keep it alive a little longer?

Click to expand...

Its not a locking rear end. Its just a couple clutch packs that 'resist' one-tire-fire.

If its fresh and grippy, then friction modifier additive will calm it down. If its well-used/worn, you may get some grip back by leaving the additive out.

Drive around a bit to warm things up... then start doing tight figure 8's in a parking lot.


if awful noises start .. you might need some friction modifier

Fredrickson: what brand can I purchase and where exactly can I buy it? Im open to any comments!

Clb said:

What's oem say?
But most everyone I've had wanted something....
Cept my arb's

Click to expand...

Same here. Have both front and rear in the Jeep XJ. Noth comes close.

Ford XL-3 Friction Modifer

It's on Amazon as an example.

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What @hacked89 said.. Ford XL-3 Friction Modifier

I just stopped in at my local Ford dealership ..
walked up to the parts dept, and got two bottles.. one for the noise.. and one for just in case I needed more.

It was about $8 a bottle.

u2slow said:

Its not a locking rear end. Its just a couple clutch packs that 'resist' one-tire-fire.

If its fresh and grippy, then friction modifier additive will calm it down. If its well-used/worn, you may get some grip back by leaving the additive out.

Click to expand...

This...….I usually don't worry about additive in the trac lock......they almost never have any issue being grabby.