LF Rear Diff Fill Plug Tips & Tricks

[19Walt93]

I'd tap on it a few times with a hammer like has been suggested, soak it a couple of times, and get it out even if I had to heat it- though I never have had to heat one in 50+ years. I would also get an actual 3/8 square male socket so you don't break an extension off trying to get it out, the hole the ball lives in weakens the end of the tool. When Fairmonts came out Ford was using water as a coolant for tapping the rear fill hole and then screwing the plugs in while it was still wet and hot so the plugs rotted in place. After twisting off two 3/8 to 1/2 adapters I bought a 3/8 male square socket for 1/2 drive. If you install a fill plug in the rear cover, how do you decided where to locate it? Too low and the rear bearings may fail, too high and it will blow lube out the vent.

 

[JohnnyO]

A homemade 50/50 mix of ATF and acetone in a spray bottle is the best penetrating oil there is. Let it sit overnight, hit it again, and after a while use a 3/8" breaker bar on it, not a socket wrench. Should come out okay, the rust probably doesn't go past the first one or two threads.
Just mix a small batch of it, it doesn't keep because the acetone will evaporate.

 

[adsm08]

I'd cook that if you can. It isn't needed, but it helps. What you really need is a bigger ratchet.

I've only had to head two in my life. Both were worse than that, with the inside of the hole starting to flake away, making it hard to get good depth, or a good bite at the edges.

I'd also replace it. I usually replace them any time I have one out. Those plugs are cheap enough.

 

[Otis413]

I'm also a fan of adding a fill hole to the cover, I'v did a couple of them using the small bung from a 55 gal oil drum, there's always a few laying around where I work. (in the pic., I wish I'd pit it about an inch lower.)

 

[Snoranger]

Worst case scenario... pull the wheel speed sensor and fill it through the top.

 

[HenryMac]

Ugh.. Those castings sure do get attacked by road salt. When I lived in Ohio I used a posi out of a '68 Impala for my '31 Ford Model A Sedan. I bet I spent 20 hours air chiseling and sandblasting it to get it down to sound metal.

The rear differential housing on our '69 Camaro that's been in Colorado it's entire life has only minimal surface rust.. no rust herpes whatsoever.

 

[sheliable]

woooohoooo!!!

Soaked in in PB Blaster two or three different times. A little heat and she came right out. Tightened first.

 

[Dirtman]

Awesome... well except for the look of that gear oil.

 

[JMF661]

Its yucky.

 

[sheliable]

Baby steps.

 

[MikeG]

Looks like maybe some water got in there with the gear oil.... I had it come out of my early bronco front diff, looking like jelly, with water at the bottom. No telling how long it had been like that.

Anyway, congrats on a step in the right direction

 

[Rick W]

Just an afterthought for the next guy: I agree with tapping on it, but I don’t know if anybody mentioned using a 3/8 extension inserted, and tapping on that. Also, the afterthought, is when one is frozen in that hard, from the chemical Oxidation reaction of rusting, the metals can actually slightly fuse. If you just force them in One Direction, they can gauld together and the bits of rust act like a grit to prevent slippage. The point is, after tapping on it, work the wrench back-and-forth, only a tiny bit out each time, until the plug moves very freely. This will crush the tiny bits of rust, and also prevents the gaulding if there is any metal fusion.

 

[lil_Blue_Ford]

I have only had one absolutely refuse and I didn’t try heat, but a breaker bar didn’t do the trick and neither did a 1,100 ft/lb impact. That one got a plug welded in the cover above the fill line and I just measured out the correct amount of gear oil when I filled it

 

[racsan]

I bought a summit girdle cover for my 8.8 (that was in the ‘93) just because it had a fill plug on the cover, still have it. When I retired that truck I swapped the composite cover back. If the fuel tank wasnt in the way you could get a 1/2 air impact in there with a 3/8 adapter and use that. What I ended up doing was using a 3/8 breaker bar and a hydraulic bottle jack. It worked but the breaker bar isnt quite straight anymore.

 

[Jazzer]

If you put anti-seize on the outer half of the threads of the new plug, you won’t have to worry about it next time. Easy peasy.

Jazzer