Front diff fluid question

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HTownWill

HTownWill

Joined
Jun 13, 2017
Threads
5
Messages
24
Location
Houston, TX
I started my knuckle rebuild today and I ran into a problem with my front diff fluid. I went to drain my diff and pulled the drain plug and almost nothing came out. I removed the fill plug and a little more came out. The fluid was the thickness of like ketchup. From my understanding there should be like 3 quarts in there. Maybe 1 came out. I know I had at least one bad axle seal as there was a ton of grease caked on brake assembly’s and everything really. I haven’t had the truck for too long and really i was just doing this because I was pretty sure the axle seals were bad. The stuff in the knuckle looked the same as the stuff that came out the diff. I haven’t had any problems with knuckle or diff I just was doing preventative maintenance.

Can I just finish rebuilding both knuckles and put it all back together with new axle seals, wipers, bearings and whatnot? I was thinking of doing a couple of fluid changes on the diff when I get it all back together. Like change and drive a couple hundred miles and change again.

My main question is do I need to pull the diff apart? It looks like a pain in the ass. Would a couple of fluid changes rinse all that grease out sufficiently?

Thanks

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No need to pull the diff. I would give it a drain and fill though after a few trips to Lowe's.
 
I bought a panel truck years ago that had diffs packed with wheel bearing grease to hide the noise of the bad third member. Hope that's not what you have going on.
 
Check the axle breather, they tend to get clogged and when the axle cools (after heating up during use) it will pull grease from the knuckles into the axel resulting in the observed sludge. Just make sure the breather is clear (or better yet make an extended breather out of fuel line and a fuel filter), put some cheap oil in the diff, run it for a few miles then change it. Might have to change it a couple times until you get all the gunk out.
 
There is always some migration of grease from the knuckles, so the gear oil needs to be changed more often than most axles. No need to do anything fancy, a couple of short run changes will clean it up.
 
To help get the sludge out, put the drain plug, jack one side of the axle, pour some diesel or paraffin down the axle tube, half an hour later drain and repeat the other side.

As above sort the breathers, change the oil a couple of times, job done.

Regards

Dave
 
Last edited:
76FJ40 said:
I bought a panel truck years ago that had diffs packed with wheel bearing grease to hide the noise of the bad third member.
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I haven't seen this used car lot "trick" done in many years, but to quiet down noise coming from an axle they would mix saw dust with gear oil. The saw dust would take up the extra clearance between the gears and bearings, making it run quiet. Sorry to say within a 100 miles of you buying it from the used car dealer, it would start making LOTS of noise again, but now it was your problem.
 
I wouldn't use any solvent, cant get it all out, so will contaminate the new fluid. Gear oil will get enough to do the job.
 
Just fill it with gear oil, drive it 200 miles or so and get it good and warm, then drain and refill. That should rinse it well enough.
 
If your knuckles are apart already, all the hard work for pulling the diff is already done. No big deal at this point to drop the third member so you can scoop some grease out of there with your fingers, before re-sealing everything and filling with oil. :)
 
I Lean said:
If your knuckles are apart already, all the hard work for pulling the diff is already done. No big deal at this point to drop the third member so you can scoop some grease out of there with your fingers, before re-sealing everything and filling with oil. :)
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That's a good one!

In reality land, pulling the axles is about half the work. Mayyyybe two-thirds. I wouldn't pull the diffs unless necessary. A little diluted grease won't hurt a thing in the diff. It's not like someone packed it with grease, it got in there because it is mixed with oil, it will come out the drain hole just fine.
 
-Spike- said:
That's a good one!

In reality land, pulling the axles is about half the work. Mayyyybe two-thirds. I wouldn't pull the diffs unless necessary. A little diluted grease won't hurt a thing in the diff. It's not like someone packed it with grease, it got in there because it is mixed with oil, it will come out the drain hole just fine.
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I guess your "reality land" is different than mine. :rofl: Once the axle shafts are out (which I'm assuming they are, since he mentioned rebuilding knuckles and replacing axle seals), you're 4 driveshaft bolts and 10 small nuts away from pulling the third.

I'm not disagreeing with you, I probably wouldn't bother pulling it unless there was a leak. But, for peace of mind it's not that tough at this point.
 
CJF said:
Quick reminder for anyone new to fluid changes:

Pull the FILL plug FIRST, cuz there's no point pulling the drain plug till you know you can get the fill plug off.
Click to expand...


Oh yes, seen that a few times, often ended up welding bolts on the plugs to get them off.

Regards

Dave
 
I am in agreeance to pull the differential 3rd member since you already have the axleshafts out. It's a great time to go ahead and reseal the 3rd member and check the bearings and backlash of the gears also. Clean everything out with rags and brake cleaner to make sure you are starting on an even playing field.
 
fill it with seafoam and drive it around the block a couple times and let it set. drain it and laugh at the amount of crap that comes out. fill it with gear oil and drive it. drain and refill...
 
The locked front axle that I swapped in had less than a quart of thick moly goop in the differential. I just filled it with cheap gear oil, drove a few weeks, then changed it. Repeat until what drains out has the viscosity of oil instead of goop. The differential has been fine for several years since this.
 
Thanks for all the advice guys. It’s supposed to be 103 this weekend so I think I am just gonna rinse and repeat a few times with gear oil over the next couple hundred miles. I have had no problems with the diff or birfs I just knew the seals were bad as there was tons of grease leaking from the wipers. I was thinking of putting in a can of sea foam with some oil and doing an initial fill and rinse with just like 5 or 10 miles of driving to warm it up but I didn’t know if it was safe to put the sea foam in there as I doubt I would be able to get ALL of it out after draining. Going to finish the job this weekend as long as the heat doesn’t take me first.

Thanks again
 
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