Heres my problem. I was driving home and I was about a mile or two away when my truck started violently shaking. Then some smoke started pouring out of the back end so I pulled over. A friend was right behind me so we took a look. We discovered that the rear differential was on fire. Luckily we had some water to put it out right away. My friend knows quite a bit about trucks and he thinks that the differential was leaking grease and that the bad exhaust was blowing right on it, so it started a fire on the differential and then in it and burned every visible amount of grease. I then limped it home, which I don't know if that was good or bad, but I needed to get it somewhere else. He thinks that the differential is probably shot and that since there was no grease, in it, the gears were just grinding together and there could possibly be metal shavings inside it. The shaking also caused the driveshaft to almost fall off from conection with the differential. How bad does this sound? Would it be that tough or expensive to fix? I know I'm just hoping for the best, but if I added more differential grease and fixed the leak, would that make it better or worse? Please respond or send any other info or helpful advice to jmeyer10(No Email Addresses In Posts!) Thanks for your time. - Jeff

 

Jeff ,
Where was the leak ? If the driveshaft was wobbling then the pinion gear / bearings are likely toast ? Only way to assess the damage is to remove the cover of the diff and have a look . You may have been able to save it had you not driven it . The only places on the rear diff you could of had a leak was the pinion seal, axle seals or the rear cover was leaking , I doubt the vent could have sprayed enough gear lube to ignite it . What caused the fire was the gear lube being slung out of the rear diff and landing on the hot exhaust . I seriously doubt you have anything left to save . If the leak was bad enough that you lost the majority of the gear lube ( pre fire ) then you probably did a lot of the gear damage prior to it failing , which may have been why it failed . Its history now ...only way to find out how bad it is is to remove the rear cover , Good Luck .
Paul

 

Thanks Paul, I think the leak was where the driveshaft goes into the differential, I'm not sure what thats called, I don't know a whole lot about trucks yet. I think the leak was so bad that the grease was everywhere and the *****ty exhaust which I was just about to replace was blowing right on the grease and got so hot it ignited the fire. I'll take your advice about taking a look inside the differential, I was going to probably do this eventually I'm just so pissed and scared about how bad it is. Now that I pretty much know for sure its toast, do you have any idea how much it would cost to get this repaired/replaced? Or if it would be feasible to try and repair it with a used piece, if a couple of my buddies that know something about trucks helped me? Those are my last questions, if you could please answer them to the best of your knowledge, that would be great. Thanks for your time. - Jeff

 

Jeff ,
First off , Have a look inside and see whats going on . Rear diff work requires the proper preloads on the pinion bearing . The pinion and ring gears have to match tooth contact patterns to ensure proper meshing / contact of the two gears . There are bearings , gears that you have to consider may be damaged due to the lack of lubrication . Unless you have the tools and expertise to do an overhaul , I suggest you let a pro handle it . It wont be cheap , but its better than doing it twice in the event it wasnt repaired correctly the first time . Some folks install aftermarket rear diff gears . Best option is to price what needs to be replaced from Ford and a few other aftermarket sources and decide what is best for you . A hint ...often times pinion seal leaks are caused from the vent hose from the rear diff becoming plugged , the pressure buildup forces the fluid out the next best escape and thats the pinion seal ( Pinion shaft is what the driveshaft bolts to in laymans terms ) If the vent remains plugged , eventually you will lose a considerable amount of gear lube . Post back if you have any other questions .
Paul

 

Jeff:
Probably your cheapest, though not easiest, solution would be to hit several "automotive dismantling and recycling centers" and just buy a complete used rear axle assembly, with or without brakes (your option), and simply swap it in.
Your truck's axle type could be an 8.8 or a 9-inch--if it has a detachable sheet metal cover plate at the rear held on by ten bolts, it is an 8.8, which is what Ford currently uses.
Try and find one with the same ratio you now have, probably a 3.08 or 3.55.
You can find the axle ratio on the mylar sticker on your driver's side door jamb. Post the code here and I'll decipher it for you.
With your driveshaft wobbling around, you probably ought to slap in new J-joints, too.
Eddie

 

Thanks Eddie. I'm at college right now, so I can't look at the door jam and the sticker on the truck. But I can give you all the other info about the truck and maybe that could help. It's a 1981 F-150 Custom, "Explorer", has a 300 6 cyl. and the VIN is 1FTDF15EXBUA62575. I think it has the 9.0 axle, but I'm not sure about the ratio, which you we're going to try and figure out for me. How much do you think a used good condition rearend would cost from a junk/salvage yard? Would it be that tough to remove and then install the new one? Also, how much do you think it would cost to have it all done by a repair shop? I know you can't give an exact estimate, but if you could at least give a ballpark estimate, because I don't have the slightest clue about it. Thanks a lot.

 

It's a good old Ford 9 inch... And for the record, it took a slurpee and a Dr. Pepper to put it out.

 

Yes, thank you run8. And let the final record show, it was not water, but slurpee and Dr. Pepper that put out my rear end fire. That right there is reason enough to carry a fire extinguisher in your car. So its a 9 inch, but do you know what the ratio is for the rear end???

 

Jeez, fire extinguishers are expensive. A Slurpee and a DP are pretty cost effective fire fighting tools.

I can't translate the axle ratio from the VIN; you are going to have to blow off finals or something to get me this vital piece of information off your door "jamb".

Eddie

 

Sorry, Mr. Meyer, but I'd have to get near the rear end when it's NOT in flames to determine the ratio!

(Did I just "flame" him??)

Run 8

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