Diagnosing rear differential

06 f150, 200k miles.

Started a light whine about 5k miles ago, barely noticeable. Changed fluid around 3k ago, noticed no major issues inside, magnet and bottom of case didnt have above average junk.
On my way back from TX, it was noticeably louder, and would make a deeper whine on downshifts (I was pulling a trailer back). Is this thing salvageable, or should I swap out the whole deal for a used unit? I dont have much experience with these things, never took one apart.

Here's a video showing the backlash just shifting from reverse to drive.

https://youtu.be/IiUS00OnwuI

When you changed the fluid did you put any additive in ? The rear takes 75/14 and I always put in friction modifier as well. It could be salvageable. take the diff cover off and check the gears and look for discoloration and funky wear patterns. also look at the axle bearings as well.
Could be the axle bearings going south on you. With the wheels off , take the rotors off and check how much play is in the axles also look for signs of leaks.
With 200k and if you aren't comfortable pulling the guts out a used unit probably would be best. Also you should have an idea of how much millage is on the used unit.
Now from my experience getting used units you will probably need to swap over all your brake stuff- the backing plates unbolt as a unit-you may have to swap out the emergency brake shoes. And you might have to replace the axle and pinion seals. Now the pinion seal is tricky, after you replace the seal and you put the yoke back on ( its the part that the rear u joint goes into)
you have to be careful not to over tighten the nut otherwise you wipe out the pinion bearing.

It got plenty of LS additive and synthetic oil.

I will try to dismantle it as much as I can tomorrow, but will leave the diff cover in place so I can actually get to work for now. I will pull driveshaft first and check there, then head to wheels/brakes/seals. The amount of backlash alone makes me lean away from axle bearings. I can "rock" the truck going down the road and do not notice a change in pitch. Only throttle input changes the sound.

It?s definitely salvageable at this point. I mean a new ring and pinion and a handful of bearings and the whole thing will be brand new.

I?d see what the brand new parts cost versus the cost of a used axle assembly and decide which way is the best bang for your buck.

If you haven?t dealt with this kind of repair before you may be better off letting someone with some experience do it. Nothing worse than brand new parts that weren?t installed correctly and are noisier than the worn out parts that they replaced.

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Originally Posted by 00tec

It got plenty of LS additive and synthetic oil.

I will try to dismantle it as much as I can tomorrow, but will leave the diff cover in place so I can actually get to work for now. I will pull driveshaft first and check there, then head to wheels/brakes/seals. The amount of backlash alone makes me lean away from axle bearings. I can "rock" the truck going down the road and do not notice a change in pitch. Only throttle input changes the sound.

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Yea if there's a lot of backlash that would point to ring and pinion. Like ray said, still salvageable and I don't think the parts are overly expensive. Hardest thing will be setting it up, getting the proper shims for the lash and preload for the pinion bearing. If you have access to the tools and the shop manual shouldn't be to hard to do. You could probably u tube it.

Likely the pinion bearing. Salvageable but I'd recommend you take it to a shop. Setting up gears is not easy and it takes a lot of time even for an experienced person.

I'm looking at $400 in parts to rebuild, another $175 if it needs ring and pinion. Plus labor- I have some tools, but do not have the special tool to get the clutches out of the LSD or a dial gauge to set backlash. Plus $60ish in fluids

Used unit is probably gonna be $300-$400, plus fluids.

If you're in need of a good shop, Bill at Western Drivetrain knows his stuff and is fair on pricing. He's on the east end of Aurora.

Link below has some pictures and the story of rebuilding a Ford 8.8 diff on a Crown Victoria. I have never rebuilt a differential personally, but I know you need special tools to do the job right.

https://www.crownvic.net/ubbthreads/...2557964&page=1

First quote for rebuild was $1762. Happens to be more than a new one from autozone

That seems a little steep on shop time if your material cost was accurate... but I've never rebuilt one by myself so I maybe I wouldn't know.

His pricing on parts was about 50% higher than the parts I priced (I did not go for the cheapest stuff either)

That is crazy expensive, shouldn't be more than $1000 top.

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Originally Posted by 00tec

First quote for rebuild was $1762. Happens to be more than a new one from autozone

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Ouch. That is on the high side. Best off getting new at that point.

Called the local mechanic in Bennett too, he referred me to the same place I got the first quote from. Going to call one more shop tomorrow and see what their input is. If the price isnt significantly better, I'll just go pick up a used one from the yard and cross my fingers.

That seems really high...

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Originally Posted by Irving

That seems really high...

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It was $1495 if they didnt replace the limited slip clutches

I know its out of your way but Im going to suggest Active Transmission in Arvada. I wholly trust Jeff to be honest & his prices have always been fair & I've never had a single issue with the work they've done on any of my trucks. (That alone is amazing)

http://activetransmission.com

Second quote: $1000 without gears, $1350 if gears are needed.
3rd quote: close to the same.

Those seems more reasonable than the first estimate if you're going to go the rebuilt route.

Thanks for updating, could be handy for folks to have a point of reference.

Found a used unit with half the mileage of my truck for $550. Going that route. Avoids other expenses such as rental.

Sounds like the best deal so far.

This thread is bumming me out since I'm thinking about changing gears in either my current off-road truck, or the next one, and I didn't think it'd cost this much.

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Originally Posted by Irving

Sounds like the best deal so far.

This thread is bumming me out since I'm thinking about changing gears in either my current off-road truck, or the next one, and I didn't think it'd cost this much.

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4x4's and gears, never a cheap repair or replacement.

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Originally Posted by Irving

Sounds like the best deal so far.

This thread is bumming me out since I'm thinking about changing gears in either my current off-road truck, or the next one, and I didn't think it'd cost this much.

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Its what stopped me from a 2" lift with 33s on the burb. Front and rear diffs wouls need to be done.

Suburban doesn't have enough power to take the mild tire size increase?

Seems like 33's is the cap on most off-road type vehicles before you really start having to modify stuff. I heard newer full size trucks can fit 37's now.

My Amigo could handle 33's but I'd really have to regear, especially since it's an auto (and a crappy one at that). But I'm thinking of selling it and getting something a bit bigger and possibly going even larger on the next thing. If it were only like $500 an axle, I'd go ahead and re-gear and get some lockers (not included in the $500), but if it's going to be $1,000-$1,500 just to regear each axle, then I might as well pick a platform and go hog wild from the get go.

Probably could but the calculation I did said I would need to go from 3.75 to 4.11 to keep engine rpm the same. So fuel economy would go from 14 to 16 average to crap.

Local dude swapped 31s on his Mini Cooper to make a rally car. Left gearing the same and went from 30 to 18 mpg or something like that. Car looks awsome but milage sucks.

Ahh yeah, mine is already at 4:30, but a much weaker motor so going from 30.5's to 33's is probably less of a jump for me than you.

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Originally Posted by Great-Kazoo

4x4's and gears, never a cheap repair or replacement.

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Yup, I?ve decked out several rigs, from Jeeps, to Tacoma?s, and even a 72 Scout II, and despite lifting and adding larger tires to all of them, I?ve not once re-geared, not because I didn?t want to, but because it was too cost prohibitive, I just dealt with the sluggish acceleration and crappy gas mileage.