Hello I'm Nick I have a 2003 fx4 with 285k miles this is my second one I love them I'm i n Michigan I was driving home from work rear end was smoking and clunking really hard I'm guessing fluid leaked out haven't really looked at damage yet but was wondering if anyone could tell me what gears I have and if anyone know where I could pick up a cheep rear axle any info would be great thanks

 

Check your parking break first. If you left it on it will smoke happened to me before. There is a axle code on your door where the gvwr is an you can google the code to figure out yours gear ratio. You can also look at the tag that's bolted to the rear axle pan

 

The wasnt brakes it was the pumpkin smoking.

 

I think the fx4's are on 3.73 gears.

As stated above, check your axle code. Here are a list of axle codes and their translation into gear ratios.


19 — 3.55 non-limited slip (Econoline, F-150)
18 — 3.08 non-limited slip (F-150)
H9 — 3.55 limited slip (F-150, F-250)
B6 — 3.73 limited slip (F-150, F-250)

 

3.73 was an option on the Fx4, so will be either 3.55 or 3.73 (3.08 not an option). I believe the LS was stock on either rear, so will be a H9 or B9.

As for where to get a rear axle, craigslist or junk yard. If you have a 3.73 it will be much harder to find, they are not very common.

 

I would just rebuild the rearend if you plan on keeping for any amount of time.

 

The re build was 1200 so I was looking at a cheaper route of course it happens after vacation kinda looking at a new truck with not so many miles being I pile miles on about 3700-4600 a month runs great other than that and the stupid exaust leak where y pipe bolts to manifold you say on door tag it will have axle code

 

I've replaced the rear diff on every truck I've owned. Two were f150s. Have you noticed any noise coming from the rear prior to the smoke and clunking? Either way. 1200 to have it rebuilt is more than it would cost for a salvage rear end. On my. 01 5.4 screw I started getting the hum grind and would get bad on turns . I bought a rear end from a salvage for $600. They often come with one year warranty. My 04 started sounding bad. Think the pinion bearing was going out. Looked into rebuilding and such. It seemed easier and more cost effective to get a full rear axle / diff assembly from a junkyard / salvage yard . Got my 9.75 axle 3.73 gear for $900. And had a buddy help me swap it out... Really not that big of a deal. Hardest part is dealing with brakes. Off/on/bleed. And jacking the truck up off the ground. It's quite a simple process. Don't know about your area, but 3 73 is not that hard to come by. Def more expensive than 3.55. But you can find one online , and have it shipped if need be. Think it cost me $100 to have my. 3 73 shipped about 250 miles.
Def want to figure out what the cause was so you can avoid reoccurring issues. I ran a diff dry once. But it didn't smoke . It just broke. .
Good luck with your situation

 

Yeah. There's an axle code on the door tag. But won't tell you your gears. Just crawl under your truck and on the back side of pumpkin there's two tags. One tells you what oil to use, other will say axle and gear ratio. Like 9.75 3.73 .......

 

he's right. I've seen 1 with the B6 rest are H9s or open rear ends.