Is my diff toast?

[Ehendershot]

New guy here with an issue. Last week I was on my way to work, going about 60, when all of a sudden it felt like I hit something for a brief moment before continuing on. Then the truck started making a terrible noise and I pulled over. At first I had thought I blew a headgasket or something because of the loss of power and the sound (I've had my vintage Honda twin blow a head gasket and sound/feel similar when running on one cylinder). But the truck was idling normally and revved fine. It all looked normal. I could smell something hot towards the rear of the truck but it quickly faded so I though maybe I had a rear brake seize for a second and then release. As soon as I started out, it sounded terrible again, so I limped it to a gas station to get me off the highway (with the gas station only being about 1/3 of a mile or less away. When I got to the stop light right before it, smoke was pouring from the back of the truck. At the gas station I saw the rear diff cover was completely covered in fluid and had a small drip. Had it towed home.

Fast forward to this weekend when I opened it up. I approximated that maybe 1/2 a cup of diff fluid came out. There was some silvery specks in the oil so obviously something let loose, and I found small chunks in the bottom of the case. I'm guessing at minimum I smoked the bearings, but I also need to inspect the ring gear and clutch pack more closely. Someone has been in the diff previously because the huge amounts of blue RTV that held it on made it interesting to get the cover off, plus the bolts came out with RTV on the ends.

Is it worth trying to rebuild the diff, or is it cheaper to just buy a low mileage used one? I have looked at the axle chart and I am also weighing my options on replacing it. Not sure what to go with. Local yard says they have one with 100K on it but a open diff and 9" brakes instead of 10". Would that make a huge difference? I would normally take my time on this but it's my daily and I'm borrowing a buddy's ranger until I can get this fixed. Never done diff work before so I'm completely in the dark.

Truck is a 98 B3000 cab plus with 4x4, auto trans and F7 rear diff (7.5" 4.10 with limited slip) 204K miles on the clock.

 

[rusty ol ranger]

Go to the junkyard and buy a whole axle. Youll be further ahead. Yours sounds like its pretty well cooked

 

[sgtsandman]

X2. It will be easier to swap the whole axle and probably cheaper. I would try to match what you have.

 

[Ehendershot]

That's the direction I think I'm headed. How difficult of a job is it? From looking under there, it seems pretty straightforward with disconnecting the suspension, brake lines and brake. Just curious as to the amount of time it might take. A friend was wondering if I could pull the driveshaft and diff out of the pumpkin and run in 4x4 until I get a new rear.

I also was looking at the axle info page and it looks like other fords came with similar axles. An aerostar looks like it could have the same ring gear and ratio with L/S and more capacity. Are the axles any different if the ratios and such match up? Wasn't sure if lengths were different or if I went from a 7.5 to an 8.8 with the same ratio I would have issues.

 

[rusty ol ranger]

That's the direction I think I'm headed. How difficult of a job is it? From looking under there, it seems pretty straightforward with disconnecting the suspension, brake lines and brake. Just curious as to the amount of time it might take. A friend was wondering if I could pull the driveshaft and diff out of the pumpkin and run in 4x4 until I get a new rear.

I also was looking at the axle info page and it looks like other fords came with similar axles. An aerostar looks like it could have the same ring gear and ratio with L/S and more capacity. Are the axles any different if the ratios and such match up? Wasn't sure if lengths were different or if I went from a 7.5 to an 8.8 with the same ratio I would have issues.

Aerostar is coil sprung. Plus i think wider....but not sure on the width.

No you cant pull the diff and just run 4x4...itd be hard on tht front drivetrain 1st off and second off you have C clip axle shafts.

Thirdly....time to change a rear end is directly related to how rusty shit is. Its not hard to do though....brake line fitting, driveshaft, leaf spring u bolts....should roll right out.

 

[MikeG]

It's work to yank an axle out, everything is always rusted in place. It's work to set up a diff, just different work. You'd have to pull everything out of that rear to see what can be salvaged, and what's been destroyed by the shrapnel.

I thought that 9" drums were standard on 7.5s and 10 inch on 8.8s, if you have 10" drums on there now, sounds like someone monkeyed with it (well you know that anyway).

A 7.5" rear should handle whatever the 3.0 could deal out, unless someone beat it like it owed the money.

I'd probably go the junkyard route myself, make sure you have lots of jackstands, and an impact wrench.

 

[Dirtman]

Here you go...

 

[Roert42]

I've done rebuilds on 8.8s before, I would say you could do one in a weekend if you had all the parts and tools, but it does take some more special tools to do everything by the book. When I did my first one I used all new parts and had to buy some tools (Dial indicator, bearing puller, bearing press, in/lb torque wrench, blah blah blah) and it would have been cheaper to buy a completely rebuild axle delivered, plus it took me like four months of working on it on the weekends.

So in my experience, swapping a used axle in from the junk yard would probably be done for WAY less money and time then a rebuild. Could do it in a day unless something got real fubar.

 

[sgtsandman]

If you are curious about what all goes into a differential rebuild. Check out ETCG1 or Eric the Car Guy (Same guy but I can't remember which channel did the videos). He does a full rebuild on a 8.8 in about 3 videos. It can be very frustrating and time consuming unless you are doing something that has to be rebuilt. Like installing locker, limited slip differential, or changing to gears that don't come factory in the axle.

 

[Eddo Rogue]

Sell the truck to a mechanic. Buy another one. You might save money, but will definitely save time and strenuous labor.

 

[adsm08]

A friend was wondering if I could pull the driveshaft and diff out of the pumpkin and run in 4x4 until I get a new rear.

You absolutely cannot do this. There are C-clips inside that hook into the side gears and engage a land on the end of the axle shaft. If you have drum brakes (you have drum brakes) on a Ford axle these clips are the only thing that keep your axle shaft, brake drum, and wheel from just walking away the first time you go around a corner.

 

[sheep herder]

these clips are the only thing that keep your axle shaft, brake drum, and wheel from just walking away the first time you go around a corner.

That's always exciting.

 

[Dirtman]

Wheels are stupid.

 

[Ehendershot]

I found a local yard that already has a 7.5" 4.10 pulled with 100K miles for $200. The only thing is that it is open diff instead of limited slip. Any serious downsides from going with something like that? There's the obvious "one-tire fire" when in 2wd, but any other serious downsides?

 

[scotts90ranger]

That's about the only downside, I wish mine was limited slip...

As long as the replacement is from a '93 to '09 it should be straight forward, $200 plus some brake fluid and gear oil isn't too bad to get a rig going anymore...