Clunking under acceleration? Decel whine?

[Bushwick]

OK, a few nights ago I heard a decel whine. Figuring the tires might be getting under inflated, I checked but they were all spot on. While checking the air pressure, I went ahead and installed those 2" spring lifter blocks on the rear springs as the car was squatting a bit (about 150 pounds of equipment in the rear) and wanting the ride height OK for the snow that's coming (front struts are newer, so the car had a fairly ugly negative rake). Drove around and the whine stopped (for whatever reason) but occasionally came back, though not as loud. Seemed as though is was a central to rear whine sound, but hard to detect location. On a hunch, I decided to pop in the FWD fuse and see if the sound would persist or not, and drove 20 miles. During that time, the deceleration whine stopped completely. BUT, anything above 50% throttle was causing a clunking sound up front. Seems more prevalent under straight-line acceleration and not present during turns. It sounds similar to a CV clunk, BUT it wasn't speed consistent. Mash up a creaking wooden ship on the ocean with a CV clunk sound, and that's what I'm hearing. With forced FWD, the front end rises a lot (gearing) obviously at it's throwing the weight to the rear, which seemed to play a part in the noise, as light acceleration didn't make the noise, nor does turning.

 

 

1. What causes decel whine on these? Carrier or wheel bearing? Cold weather? Rear end fluid was replaced when the rear crossmember was done and isn't leaking. 

 

 

2. The clunking.... could it be something with the sway bar mounts? As the car is trying to squat in the rear, maybe it's lifting pressure on the sway bar C-clips or the end links are clunking?

[Fairtax4me]

High pitch or low pitch whine?

 

Clunking could be an inner CV joint on the front.

 

Squat and dive don't typically cause sway bar clunks. You migh get a creak or groan sound from the frame bushings.

 

One other thing you might want to check is the lower control arm bushings. If the fluid has leaked out of them they can clunk on heavy acceleration.

[Bushwick]

The control arm bushings are hydraulic? *sighs*. I had noticed a very small puddle of "oil" about a week ago, under the evap canister area on the driveway. It didn't smell like engine oil, or any oil I'm familiar with. Definitely not trans nor power steering, nor non oil smells like coolant. Seemed similar to cooking oil. Couldn't see where it was leaking from either. I'll bet that's where the "oil" came from. 

 

 

The "howling" sound is more inline with steep gearing whine. I put 3.73's in a 79' Mustang with an 8.8 swap, then decided to run 4.10's. I remember the 4.10's had a tinge of noise which was apparently normal. It's similar to that. Low pitch whine when coasting, immediately disappears when you push the gas pedal, returns when coasting. Last time it happened (months ago), I found my rear tires were roughly 10 psi low, filled all 4 to be identical, whine stopped. It's slightly unpredictable at this point as after I installed the rubber lifts, it wasn't as consistent.

[Fairtax4me]

Just the big bushings at the rear of the front arms. They're filled with heavy greyish silicone.

 

What kind of fluid did you put in the rear diff? Subaru recommends 80w-90. I've used 75w-90 and had good results.

75w-140 is fine for wear protection, but its so thin it doesn't cover up the noise of the hypoid gear set.

 

These diffs tend to make a bit of noise anyway, I'm tempted to say its normal and you won't ever have any trouble out of it. But if the noise bothers you make sure you have some 80-90 in there. Add some Lucas oil stabilizer if you want.

[Dj7291993]

Not sure about the whine, but while you're under the car, check the rear drive shaft u-joints.

[Bushwick]

The rear diff either has 80w 90 or 85w 90. I'm just wondering if the ring and pinion might be engaging incorrectly at times, or if something is worn and allowing the carrier to shift slightly i.e. worn spacers or failing carrier bearings? Under load it's always been quiet. But the coasting howl has me on alert. 

 

 

Well, that oil on the driveway wasn't grey. The sound is a knock....knock....creak..knock, but again only occurred with around 50% or more gas pedal. Enough to break traction and lift the front up. The rubber spring lifters in the rear are preventing full squat, so the rear is staying up more.

 

 

Suppose I'll try and run it hard w/o the FWD fuse and see if the sound up front persists. Never heard it before with AWD going. Easier to live with noisy bushings over a winter than a possible CV failure.

Edited November 12, 2014 by Bushwick

[1 Lucky Texan]

I suppose it's possible some rear strut oil made it to the ground.

[Bushwick]

The struts are dry. Actually, with the exception of a very slight leak on the passenger side valve cover, there are no other visible leaks which is always puzzling. 

 

 

Are there any other hydraulic bushings or hydraulic motor mounts up front? I remember about 5 years ago my mom's Buick LeSabre had a near identical puddle towards the center of the engine. The oil smell was unfamiliar as well. Puddle size was about the same, same color & consistency. Had no idea at the time what is was, then discovered the front motor mount ruptured (40k miles and it failed).

[Dj7291993]

Did you check the u-joints?  I've only seen them go bad on a subaru once, but they were completely destroyed.  Made a terrible clunking noise.  Thought it was the transmission hitting the tunnel at first, but it turned out to be u-joints.  They're easy to check.

 

As for the hydraulics, I don't know of any hydraulic mounts on a subaru.  The engine mounts are pretty basic, solid blocks of rubber with two pieces of steel, a stud, and an alignment dowel. Not sure what the fluid could be though. By the way, what is the car?

[Bushwick]

Haven't checked u-joints. The sound was further up in the engine compartment, and only occurred under harder acceleration with FWD forced. There's no delayed clunk when going into reverse/forward gears either. Not near the trans tunnel either. Haven't driven in a couple days, still need to see if it occurs with the rear axle engaged. Never did in the past, but the front doesn't lift anywhere as much with the rear axle active, which I think would point more towards a suspension piece or a mount somewhere. The more lift the front gets, thew harder it it'll pull on the end links, which pull on the swaybar. Thinking it's up around there.

 

 

95' Legacy wagon in the sig.

[Fairtax4me]

No fluid filled motor mounts on the 95. Check the control arm bushings. It's usually pretty obvious if they've leaked all their goo out.

[Bushwick]

Well, went back to AWD and the noise up front never occurred. So it seems to be related more to when the front was lifting excessively. Kinda funny how this thing likes to spin it's tires with forced FWD. Between the excessive weight transfer to the rear and the gearing, it doesn't take much. 

 

 

And the rear end whine has subsided once again. Sometimes it's slightly pronounced, other times it was barely audible and sounded more like normal steep gear whine.

 

 

Guess both of these issues are getting filed away for now until something breaks or gets worse.