I think my differential needs a rebuild, it's developed a clunk when turning, jacked it up pushed and pulled slides about 3/16. Has anyone done a rebuild on 3.73 rear? What kit should I get?

 

The axle shafts are supposed to slide in and out a little bit. I would do some more diagnosis before tearing apart the differential.

 

I'm trying to track down this clunk, it showed up a few weeks after I put in a clutch. Everything seems tight underneath, drive shaft,trans mounts, unless it's the transmission itself or transfer case. It's a suttel cluck that shows up randumly. I've had vehical 9 months don't know a lot about whats been done to it.

 

You say a "clunk when turning".... is that the rear diff turning? .. or when driving and turning the vehicle? Not alot of info here... what slides in and out 3/16"? Rear axles dont move anywhere near that much, maybe 1/64".

Most common "clunk" is likely the front axle/u-joints which can be heard when turning the vehicle.
Have you checked the lug nuts?

 

I haven't checked up front, felt like it's in the rear area. As for the3/16 I jacked up the rear to look at suspension, brakes, that's when I noticed I could pull axel3/16. An update: bronco2 broke down, the drive shaft turns differential doesn't move the wheels something in there finally stopped working. Do you know if 97 explorer 8 inch rear end will fit under a 90 b2, would mods be difficult?

 

If I remember correctly, Bronco IIs have the leaf springs mounted to the top of the axle. Explorers have the leafs go under the axle, so you would have to cut off the old spring perches and weld new perches to the top of the axle. You'd also need to weld on new shock mounts. Drive shaft flange may or may not be different, I'm not sure. 95+ Explorer axles have disc brakes, so you'd have to modify the parking brake cables to get them to work.

 

I appreciate everyones help. I wish I would of pulled the Diff.cover to look, but my son drove it and it broke down. It's the differential, drive shaft turns but truck doesn't move much, just a clunk,clunk,clunk. Towing it home tomorrow. Don't know enough about differential rebuilds to try, so I'll find a used one. Does anyone know the pro's and con's of 3.73 rears verse 4.10? Mine has 3.73, I found a rear same year with 4.10 gears.

 

Doing the fab work to replace the rear axle would be easy enough but... whats the gearing???... you probably would have to swap out both diffs.

I would pull the cover off and see what went wrong, maybe just a broken axle shaft or something else easy to fix.

 

Front gear ratio MUST be the same as the rear ratio if you ever want to use 4wd. If you're going to change to a different ratio in the rear, you must change the front gear ratio too. 4.10s will help the truck accelerate faster and be more fun to drive around town, but the engine will be spinning at a higher RPM when you're on the highway and may make gas mileage go down a little. But 4.10 isn't a huge jump from 3.73 so there shouldn't be THAT much difference in acceleration or gas mileage.

 

You cant have 3.73 in front and 4.10 in the rear... you need to find out exactly what broke. The 4.10 rear may or may not have the parts you need to fix the 3.73.

Diffs are not hard to rebuild but you do need to pay close attention to clearances and shim accordingly.

 

Thanks for the education on differentials, I never would of thought the front and back diffs. would have to be the same, but that makes sense. I'll probably do a axel swap with another 3.73, I'm not changing the front, I'll let you know what I find when I crack the diff. open.

 

You can get the rear end out of a ranger instead of the Explorer, then you will not have to weld on the housing. my Bronco ii has 93 ranger 8.8 read end and the front end Dana 35. I got a front drive shaft out of a 94 explorer and had to get it cut down so it would fit in the rear of my bronco ii.

 

I'm pretty sure up front a D28, should I stay with 7.5? Does it matter if it's an 8.8? This truck is mostly going to be on the road, I've thought of swapping the rear just for strength and the transmission. I read some about the 7.5 diff. my tag on the differential says it's a 3SL7375 I know that a L means limited/slip what's a SL mean?

 

You can upgrade to an 8.8, but I don't think you'll really see any benefit if you're mostly on the road. The 7.5 should be more than adequate. Check out this link to see if you have a limited slip or not:
Ford 7.5 & 8.8 Inch Axle Tag & Door Codes

 

I think you would complicate what is normally a very simple and effective design, unless you intend to build a dedicated off road truck where you would benefit from the larger diffs. I have two early B2s and Im not nice to them but they seem pretty tough on and off road, hauling trailers on hunting trips, whatever and wherever. Busted diffs are not a common problem so unless you want a rock crawler I wouldnt suggest anything but a stock diff.