Rear Differential Leak?

[srisitt]

Looks like the ranger I’m working on has a leak in the rear differential. Heard this could be an expensive fix. Any advice on diagnosing what is causing the leak/what to repair?

 

[RonD]

Ford didn't use gaskets on the cover so it will leak eventually
No not expensive to fix

Just drain it by loosening the bolts then clean the surfaces and reinstall using RTV or there are 3rd party gaskets now for most Ford differentials

Also check the Vent hose, if it gets clogged pressure can build up inside and push the oil out
Bugs like to build nests in the end of the tube if the small filter has come off

Vent hose is top of axle tube on left side of photo

 

[Uncle Gump]

It kinda looks like the cover is leaking for sure... I would look at the pinion seal also. A leak there will blow back and make it look like the bottom of the cover is leaking. If the bottom of the diff is covered in lube up to the pinion flange... you will need a pinion seal too.

 

[srisitt]

Thanks for the help! I removed the vent hose and it was definitely clogged. Could not even blow air through it at first. Filter was missing. The fitting looked good. I inspected the differential around the pinion flange. This chassis was pretty dirty, lots of mud build up, so it was hard to tell what was ordinary grime and what wasn't underneath the differential. I did notice some caked up residue on the chassis up above the flange. Its gummy and smells like grease. Seems like it would make sense for lube to spray up there if the pinion seal blew.

Top side of the same part of the chassis. Originally I figured this was applied here intentionally to dampen between the frame and chassis like the tar pads around the bed mounts, but this could be leaked lube/mud build up too.

I haven't driven this truck much. I'm thinking I might want to drive it around more to see if there is anything else in the drive train that might need attention. That way I'm only tearing into it/replacing gaskets once. For now I might just put a new filter on the vent hose, clean up the diff, add fluid, put the bed back on and see what happens. Should be able to confirm the pinion seal leak that way. I assume if there was enough pressure to push oil out of the cover, the liquid gasket is probably compromised, so I will likely have to replace that soon.

 

[RonD]

Yes, as you drive the axle oil gets warm and expands, like any liquid does, vent allows expansion with 0 pressure, clogged vent means internal pressure builds up, do this over and over and leaks will start, and yes, now that they have, they won't stop even with clean vent hose

 

[srisitt]

Yes, as you drive the axle oil gets warm and expands, like any liquid does, vent allows expansion with 0 pressure, clogged vent means internal pressure builds up, do this over and over and leaks will start, and yes, now that they have, they won't stop even with clean vent hose

That makes sense. I guess the thing to do then will be to replace the cover gasket and vent filter now and then the pinion seal later if I need to. I’m concerned with the caked up stuff on the chassis, would you say that’s an indicator the pinion seal blew? Can’t think of anywhere else that could come from. edit: could also be grease from driveshaft/u joint.

 

[RonD]

In my opinion.................

Drain and Clean up differential, change the oil and gasket, also new vent hose filter

Wait to see if pinion seal is leaking, you can drain and reuse the new oil if it is, so no wasted time or money

Pinion seal is alot more work, to get ring and pinion set back up again, usually

 

[Dirtman]

I agree with ron, just do the cover for now. But as a side note ADSM turned me onto this new permatex green sealant made just for diff covers and gear oil. I use to use regular black but aparently the new green is awesome. Had several other mechanics tell me that.

 

[Uncle Gump]

Not doubting ADSM at all... But I have a bunch of faith in ultra black. Not sure I've even seen the green stuff.

 

[Dirtman]

I've always used ultra black as well and never had an issue. The green is new and costs the same but made JUST for gear oil. In the grand scheme of things it probably doesn't matter but adsm wasn't the only one who said the green stuff holds up better on diff covers.

 

[srisitt]

I ordered a hard gasket from rock city, those any good? Can I use it with sealant?

 

[Dirtman]

Use one or the other. Never both.

 

[projectRanger93]

I ordered a hard gasket from rock city, those any good? Can I use it with sealant?

I just did my differential flush not too long ago. I ordered my gasket from AutoZone, but i've seen it on RockAuto for cheaper. Hope you verified whether you have the 7.5" or 8.8". The flush itself was easy, i followed a youtube video. Make sure to torque the bolts back to spec.