Svscott

Hi, this is my first post here and I'm looking for some help diagnosing a horrible squeal coming from my 2003 Express 3500 extended van that had about 160,000 miles. It started fairly suddenly after the van sat for a month or so, and makes a loud semi constant squeal sound when I back up a hill. I can back up gently on flat ground with no sound and in forward, it seems fine. Aside from when backing up hill, I can make the sound by power braking in reverse with a foot on gas and one on brake. When i crawled under, it sounds like the squeal is coming from the pinion seal area when the driveshaft rotates a few degrees under load. It squeaks as it loads then again when it unloads.
I was at first hoping the sound was the E brake shoes dragging because of badly rusted out backer plates and a rusted cable so I started with replacing the backer plates and all e brake parts. No dice, but I noticed a leaking right axle seal so I replaced seals on both sides while I had the Dana 60 axles removed. After that didn't fix the issue, I just replaced the rear U joint that was a little stiff and checked the other 2 u joints, which seem to be ok, but it is still making the sound.

pomerlo

Have you check the belt and idler pulleys ?

An easy check could be to temporarily take the belt off and try to reproduce the sound if it can be done within a minute or so..
Note the belt routing before remove it. Or get the diagram on the web.

Kael

Quick check if it's the pinion, spray some silicon lubricate around the base of the diff pinion, trying to get into the bearing area (not forcefully). If that quiets it for a bit, you know where the problem is.

Mine squeaks a little in reverse at idle, nothing in forward. Haven't chased exactly why, but it's definitely the pinion bearing area. Didn't do it when I bought it (with 300,000), one of those things.

Already checked the diff fluid and level, right?

Svscott

The sound is definitely coming from under the van at the rear u joint or more likely, the pinion since I just put in a new Moog U joint.

Svscott

I'll spray a bunch of lube around the pinion seal area and see if that quiets it down for awhile. When doing the rear brake backer plates a week ago, I found the passenger side emergency brake assembly was wet and oily so I just replaced both axle seals, rear diff cover, and put in new fluid.... "pouring" (more like doing CPR on the bottle) a gallon of gear oil into the differential while laying on my back was a heck of a workout.

Svscott

I had Firestone look into the squeal today while they were putting my studded tires on and doing an alignment and they confirmed the sound seemed to be from the pinion seal area but offered no solution. I stopped by a local transmission specialist and he test drove and listened then said he thought it was the brakes or suspension. I assured him the sound was coming from the diff or driveshaft and he recommended silicone spray or WD40 around the driveshaft connection.
I bought a can of Fluid Film and sprayed a bunch into the gap for the little shield around the pinion seal. The noise is gone, at least for now. I don't think running the van as is will grenade the differential or driveshaft so I'll just wait for the issue to come back before addressing it further.

Next, I've got to tackle my terribly rusted out rocker panels.