I have an '86 Aerostar with the 2.3l 4, and 5-speed stick. It's a great little truck, and I plan on keeping it.
The bearings inside the pumpkin are starting to make a lot of noise, so I've been checking out my options. I can have it rebuilt for $615, or I can get a used one installed for around $400. I'm not rich, so the $400 option is attractive, but on the other hand, I don't know if there's any way to really make certain a used rear end is in good shape.
Opinions?

 

Most rear end noise on these units is usually the front pinion bearing. The rest of the rear end is pretty much bulletproof - unless it has been taken apart down previously. If you do an internet search, you can find trouble shooting guides for rear end noise to differentiate pinion noise from ring/pinion wear, u-joint wear and/or rear bearing noises (sometimes mistaken for rear end noise). Did your quote of $619 break out what item(s) would be replaced?

 

I'm in the process right now of having my rear end exchanged. When my '94 got totaled, I salvaged many major components, including my rear end, most because it had axle saver bearings installed only a short while before the van got hit. My '97 just lost a wheel bearing, and the pinion bearing is a little loose too. So our solution is going to be to use the axle off my '94. The only downside is the '97 is a limited slip, the '94 is not. Not the end of the world, but the limited slip is nice. Exchanging the rear end is not for the faint of heart, many of the bolts will seize into the bushings after years of corrosion.

 

If salt is used on the roads in Missoula, Khan is right: the bolts aren't fun to remove.

I've changed three diffs in my five various-year Aeros, and on the Left Coast, where salt is rarely used, it's not too bad of a job. Junkyards get around $100 for a diff.

Because you have the lowest-torque engine ever offered in the Aero, I'm surprised that you have much wear, but the manual trans is harder on all driveline components than the automatic.

If it was me, I'd play Junkyard Roulette and install a used one. If you are at all mechanically inclined, or (better yet) have access to one or more friends who can be bribed in to helping or doing the job, it's a low-tech job to replace.

I always replace the oil in the diff while it's out. The plastic diff cover is "supposed" to be replaced every time it's taken off, but that's BS. If you clean it very well, it'll seal using RTV silicone just fine.

If you buy the used diff with the brakes still attached, and there's no evidence of axle seal leakage, you don't need to change the axle seals. Do check the brake wheel cylinders for leakage though: peel back each of the four boots and if you find "wet" under them, replace that wheel cylinder. Wheel cylinders almost never can be reliably rebuilt, because unless it's straight-on seal failure, the leak is caused by rust/pitting of the cylinder, and unlike an engine cylinder, you can't hone out the pitting. New seal on pitted bore (even a honed bore) will quickly wear out the new seal, and it'll leak again in a year. I gave up rebuilding wheel cylinders 30 years ago, just buy new ones (unless you're working on an antique, and then I have the old cylinders bored & sleeved).

Again, it's a low-tech job that just requires a jack, jack stands, breaker bar, sockets, brake fluid and a lot of muscle. You'll have to bleed the brakes when you're done. You may want to budget to replace the rear brake hose (goes from chassis to the diff). Watch out to not drop your u-joint caps on that old van, as they're not captive, and as soon as you loosen the rear u-joint u-bolts, the caps want to fall off and drop in the dirt and have their needle bearings disappear. You have been warned!

Splurge and use synthetic rear axle oil when you replace the oil. I know, it's expensive, but you *will* get better cold-weather performance, which you can really feel in Missoula weather with that little four-banger.

Oh, one more thing: you must obtain a replacement diff from an Aerostar (not a Ranger or Explorer, because the mountings are different) and it must be no newer than 1989. In 1990, the differential went from using a yoke to a companion flange. A 1990-on diff won't work with your driveshaft, unless you change the driveshaft too. So, if all you can get is a newer diff, be certain to buy the driveshaft that matches it.

[I just moved -- temporarily, for six months -- from the Puget Sound area to the Denver area. We overnighted in Missoula, and it sure is a beautiful town, in a gorgeous location.]

 

pinpoint the noise if you can. jack up both rear tires and safey block the rig.
spin the tires and listen for noise.
can also be the rear axle bearings, they get very noisy when they wear out. seen them with rollers even dropped out and gone. the bearing ride directly on the axle shaft as inner race.

definitely drop the rear end cover and examine the lube for any metal cuttings fines. listen to the gears while someone turns an axle

check your drive shaft u joint bearings also, they fail and feed lots of noise into that big boom box van interior.
if they look old and dry, replace. better than being broken down on the road and at the mercy of road repair vulture shops.

wrap the axle mount bolts, shock bolts and others in long rags soaked in PB Blaster or kerosene for several days.
soak everyday
wire brush the exposed threads, then smear the exposed threads in moly grease just before air impact tool removal.
may have to use heat. propane or MAP torch enough

drive the van over a plastic tarp to save crawling around in dirt and makes small parts much easier to find. many of the small parts on the Aero are unique and unobtainium except maybe at a junke yard emporium.

Al,
you seeing many Aero AWDs in Colorado?, used to be lots of them there because of the sking and snow. last few trips I haven't seen one

gotta make the drive up the river to Estes Park and then over the 11000 ft pass in Rocky Mountain State Park while you're there. from Denver best to go W on I70 then take the Winter Park road into Winter Park and on to Grand Lake to the S. entrance to the park, then over the pass to Estes Park and back thru to S of Ft Collins.

 

I've been here just over a week, and have seen several driving around. Everyone drives so much faster here than I'm used to; it's like driving in SoCal, only a bit less agrressive.

The JY has six They're dying off, getting kinda old.

We're planning on doing a lot of weekend trips this summer. Been to Boulder Falls already, though it's not much to look at, compared to Silver Falls in Ore., Multnomah Falls, or near my town, Snoqualmie Falls.

But our dog liked to play in the stream, and as long as the dog's happy . . .