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noise related to rolling speed, bad on deceleration, gone on acceleration


RustyShackleford
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My 2006 Outback (2.5L 5MT 130,000miles) suddenly developed a noise today.

 

1. It's a whirring noise, kinda like a playing card on a kid's bicycle spokes,

 

2. Its's sync'd with rolling speed, regardless of engine RPM or transmission/clutch position.

 

3. It's bad during deceleration (braking or coasting) and goes away under acceleration.

 

4. It came on suddenly today - from un-noticeable to "yikes, this is serious" - in less than 30 miles.

 

5. Driving, I thought maybe it was coming from one of the passenger-side wheels; wife thought it was coming from driver's side or from the center.

 

I imagine tranny/driveshaft/differential is why I used this forum. I know it doesn't sound anything like any wheel bearing failure I've ever heard, and it doesn't seem related to brakes (except deceleration causes it, but it doesn't matter if it's from braking or from coasting). I checked the transmission oil earlier today.

Edited by RustyShackleford
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Thanks for the quick reply.

If it’s regardless of gear...

It's even when coasting in neutral.

I’d be checking the front and rear ring and pinions by checking the gear oil first (or isolating the noise to the transmission or rear diff).

I don't believe it's from the rear, but I'll check tomorrow.

 

What do you mean "by checking the gear oil" ? I mentioned the level is good (or was before this started). You mean check for evidence of metal shavings on the oil stuck to the dipstick ?

 

Sounds like we're narrowing it down to the tranny pretty quick. If so, is this likely to be something worth repairing on a car this old, worth $5000 or less. I work on the car a lot, but I think tranny work (even R&R'ing a rebuilt one) is probably outside my pay grade. OTOH, I like the car and I like the idea of keeping old ones running, within reason.

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Yup, I would drain the oil from the gearbox into a pan and look for any debris. If you have access to a lift or can put it high enough on stands you could even try to reproduce the sound while listening with a stethoscope to pinpoint the sound. However a gear oil check is where I would start.

 

I suppose it’s possible for it to be a CV joint though I haven’t experienced them fail in this way. They usually show wear by clicking/binding through turns. Like you said, wheel bearings don’t typically fail in this way either (though still worth inspecting while you’re under the car). Rough noise on decel only suggests damage to the coasting contact surface of the gear teeth. The R&P is road speed and gear independent, and has distinct contact surfaces for accel and coasting, so it fits all the problem criteria.

 

Setting up a new R&P is not rocket surgery but it’s not trivial either. Some special equipment and know-how is needed. Removing and tearing down the transmission is certainly doable, and more straightforward than pulling the engine, for example. I’d say cross that bridge once the problem is identified.

Edited by Underdog
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Thanks for the replies. I am a moron. Wife fixed it - apparently a stick stuck near the driveshaft somehow. This crossed my mind, but two things made me rule it out (without actually looking under the car ;) ): the fact it started while driving on freeway and major highway, and the fact it was loud under deceleration and absent under acceleration. I still don't understand these things, especially the second. Nonethless, my apologies to anyone who spent more than a picosecond thinking about this or making a reply.
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You may want to grab the Prop shaft on either side of the carrier bearing and check for play. I little movement is normal, I'd say more then a 1/2" is more then normal.

 

My OEM shaft was replaced at 215,000 miles. I just replaced the new OEM shaft installed at that time with a shaft from The Drive Shaft Store, in CA. This one has greaseable replaceable U joints. I think I placed a link in JmP's sticky at the top of the 4th Gen forum in July of this year.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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One thing I forgot to mention: the clutch was replaced at the dealership perhaps 5-10K miles ago. I imagine they'd be more than willing to point out a driveshaft or engine/tranny mount in need of replacement. OTOH, maybe they failed to put something back right ? However, I think the mechanic was probably a cut above the stereotypical, because they also did the recall of the airbag recall, and I had a bunch of custom wiring between the stereo HU and the cubby (installed a little 3v/5v power supply up there for radar detector and sat radio, as well as input jacks for sat radio and iPod and a switch) and he put it back just right and even fixed a loose connection.
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Your Outback may be high enough so you can just slide under it and grab the shafts on either side of the carrier bearing. Just saying...It a quick easy free check.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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