IRS Question

[Bad Moose]

What I've got is a rear cover leaking on my rear axle. It happens to be and IRS. First stupid question is, do I have to pull the entire assembly to reaseal the rear cover? Second stupid question is, what fluid do I use. It does have a locker in it, so I'm assuming a friction modifier also.

I think I know the answer to the first, but hoping for the best. On the second I honestly don't know either of the answers.

[CraigS]

Admittedly I haven't done this but.. I think you can remove the diff mounting bolts, push the diff far enough forward to get the rear mount out from between the ears on the frame, and go from there. I 'think'. For oil I use Mobil1 80-90 w/o any modifier. I will send this to a friend who has done exactly what you need to do to get him to chime in here w/ his experience.

[rich grsc]

Just drain the oil in a clean container and reuse it. It has at least a 60,000 mile life.

[Bad Moose]

I would but it has been leaking for a bit, so I'll need to add more and don't know what is currently in it. I know I can ask but I'm also not a fan of reusing fluids. Gear oil is cheap imo and I don't want to redo anything that could of been prevented.

JMHO

[mikeinatlanta]

Make sure it is actually a clutch type limited slip before adding modifier.

[phileas_fogg]

I had the exact same problem you describe. In my case, I had already installed my axles and together CraigS and I had completed the rear end alignment; I sure didn’t want to take the entire rear suspension apart. If you haven’t installed the axles, I recommend removing the pumpkin (assuming it wasn’t a bear to get installed; this depends on the diff cover). It just makes things easier. Also, you will want the gas tank out of the way as well.

I removed the mounting bolts and slid the pumpkin as far forward as I could while simultaneously tipping the front end upward. I used some rope around the axles and the nose to keep the differential from moving around. Next I removed the plug and drained the gear oil into some clear glass jars for reuse. Note that I knew there were no contaminants in the differential. Also note that you'll be throwing these jars away; there's no cleaning up gear oil and friction modifier. After getting as much fluid out as I could through the drain, I removed the cover bolts & cover; that allowed me to drain the remaining fluid. I finished the draining process up by mopping up the dregs with a shop towel.

After the fluid was drained, I tilted the front of the pumpkin downward to keep residual oil from dripping where it shouldn't, cleaned the cover and differential mating surfaces with acetone a couple of times, and let everything dry out. I applied a 1/4” bead of “The Right Stuff” gasket maker - no paper gasket - to the differential and carefully replaced the cover. I torqued the cover bolts to spec (20-22 foot pounds), slid the pumpkin back into position and bolted it down.

I use Red Line 75W140 gear oil (https://www.amazon.com/gp/product/B0006HKN6S?psc=1&redirect=true&ref_=oh_aui_detailpage_o02_s00) and Ford M-19546-A12 Differential friction modifier (https://www.amazon.com/gp/product/B003TPGELM?psc=1&redirect=true&ref_=oh_aui_detailpage_o06_s01).

Once the repair is complete, you can expect to find a drop or two of gear oil at the bottom of the pumpkin for a couple of days. After a week it's gone. My guess is that while filling the pumpkin some oil slipped down the plastic fill hose and onto the metal. It takes a while for this oil to move to the bottom of the pumpkin where it collects into a drop that make you think the gasket didn’t “take”. After a week or two of worrying, I’d wiped all the oil off and I’ve been dry ever since.

There are pictures in post #200 of my build log (http://www.ffcars.com/forums/17-factory-five-roadsters/508121-phileas_fogg-s-mk-4-roadster-build-2.html).


John

[Bob Cowan]

Yes, you can. Just slide it forward a couple of inches and you can remove the rear cover. You'll have to disconnect the drive shaft, but you don't need to remove the axles.

As for oil, it depends on what you're doing with it. For general street use, you don't need a really heavy oil, a 75W-80 will work just fine. If you're road racing, then go with something a little heavier, like a 75W-90. I would not recommend a heavy duty oil like 85W-140 - unless you're towing a camper.

https://www.bobistheoilguy.com/wp-content/uploads/2011/03/visc.jpg

Road racing creates a lot of heat in the differential. For that, I recommend - and use - a true synthetic fluid. For anything else, a decent dino oil will be just fine, and half the money.

You said it has a "locker", what do you mean by that? It's uncommon to find a true locker in an 8.8 street diff. Most are limited slip. The factory limited slips use a clutch pack. But aftermarket diffs like the Torsen TruTrak do not. Anything with a clutch pack needs a friction modifier. The other diffs don't need a friction modifier, but it won't hurt anything to use some. So, if you're not sure, use the friction modifier. Some gear oils - like Royal Purple - already have the friction modifier in it.