1998 K1500 - Whining

AceMI · January 3, 2014

Hello guys,

I picked up a '98 K1500 3 door to bomb around in and use around the shop. 200k miles on the odo - still in great shape though. I've already done a ton to it: inner/outer tie rods, pitman arm, idler arm, steering gear, p/s pump and lines, flushed all the fluids, etc.

It still has an issue that is ever so slightly life ruining. Between 40 and 50mph, under SLIGHT / coasting acceleration and around 1300-1500rpm, there is a loud whining. Letting off the accelerator or pushing it harder makes the noise completely disappear. Putting it in neutral also makes it disappear. Coasting / cruising between 40 and 50 produces the mood killer noise and it's definitely coming towards the rear of the vehicle.

The rear diff looked fine, no excessive wear. Wheel bearings seem ok.

Wondering if anyone else has come across this? I don't like to solve problems by just throwing parts at it, but I can only imagine it to be a center bearing or u joint? Any other thoughts?

Thanks!

As an aside, the p/s pump I replaced was a reman'd ac/delco that already has the EVO bypass fitting on. I noticed the steering is noticeably (though not painfully) heavier than with the original EVO valve. Anyone else noticed that? I scheduled an alignment for next week given all the front end work I did, I suspect that has something to do with it too.

1997SierraSLT · January 3, 2014

My 98' GMC K1500 with 160,000 miles on it whines a bit as well under same scenario. I've never researched it thoroughly, but it definitely sounds like it's coming from the rear differential when there is no load on it.

I'm going to assume it's just gradual wear of the pinion/ring gear. The truck drives great and limited slip differential works fine. Not worth my time to throw money at it.

Under normal load, the pinion drives the ring gear going down the road. As soon as you let off the gas pedal, the opposite occurs. The ring gear now drives the pinion gear.

JBK · January 3, 2014

I have a 1995 K2500 4x4, I also had a whine that was driving me crazy. I could not figure it out and swore I had a bad bearing in the rear axle, I just knew the sound was coming from the rear of the vehicle. I took a mechanic for a ride with me, he also heard the noise but could not pin point it. He suggested I replace both universal joints on the drive shaft which I did but still had the noise, I then thought maybe I had a bad rear even thought the truck only had about 50,000 miles on it.Then I took another mechanic from my local GMC dealer for a ride, he immediately picked up on the noise and said it's in the "right front axle". I put the truck in the shop and he replace the bearing on the end of the right front axle shaft and no more whine!! It's amazing the way sound can travel thru the drivetrain, Myself and a couple of other people swore the noise was coming from the rear axle when in fact it was coming from the front. The whine would drive me crazy when driving around 40 mph, it was such a relief to no longer have the noise.

AceMI · January 4, 2014

Thanks for the replies, guys.

scw1991 - what you describe makes perfect sense, thanks. Under acceleration, it's perfectly quiet. Under no acceleration at 40-50mph, it's also quiet. There's that sweet spot with very light throttle, which unfortunately, is where I spend the most of my time it seems, with very light throttle where it whines like my last newborn. If I had to better explain it based on what you've said, I would say it's the transition between the pinion driving the ring gear and vice versa.

JBK - that's interesting! Now that you mention it, I used to have a Grand Am that I would have sworn had a howling coming from the rear, but it was a front wheel bearing. The difference was, it was more prevelant when turning the wheel one way or another and was pretty consistent. Was your axle bearing noisy under only light acceleration while coasting between 40-50mph?

I'm starting to fear the ring and pinion.

1997SierraSLT · January 4, 2014

yup.....it's definitely a sweet spot at that speed range under no acceleration. I've been in cars with wheel bearings going out and it's quite the low pitch growling sound and just continues to get louder and louder over time. sort of like the sound made when disc brake pads wear into the rotors.

JBK · January 4, 2014

My whine seemed to "come & go" at times, but with the one mechanic we even tried locking in the four wheel drive and it was still there. Under acceleration or coasting didn't make any difference. I think that around 40 mph it was more noticeable because that's a "sweet spot" with my truck in that you don't have much motor, exhaust, or tire noise to cover up the whine so I heard it more at that speed. I know it drove me crazy until we found out the problem.

charleszalan · January 7, 2014

Mine at ordinary load, the pinion drives the ring apparatus going in the future. As soon as you let off the gas pedal, the inverse happens. The ring rigging now drives the pinion gear.