06 LGT 5MT transmission decel rattle - Video included

I know there are a few other threads right now relating to trans noises/rattles, but after reading through those I've found mine doesn't quite match up to what's described in them.

 

I have a decel rattle in my 5MT that been going on for a while now. I can't remember exactly when it started, but I'm thinking it was around the same time as my clutch swap because that was the last time I had everything under the car disassembled.

 

Video of the noise can be found here:

http://youtu.be/SV2r9p_84Jc

 

You can hear me accelerating slightly, with the noise happening after the gas pedal is released and the vehicle is coasting down under engine braking. This noise always occurs between 2-3k RPM, and as soon as the slightest amount of throttle is added, the noise stops. The noise is coming directly from the gear shift area, and happens in all gears. The video was taken in 3rd gear around 40 MPH.

 

My first thought is a loose heat shield, but I have checked and re-checked and found no witness marks or loose shields. I will be doing engine mounts this weekend, so I will be checking all the shields again. Since it's associated with decel, I'm wondering if the powertrain is pitching under ending braking, causing something to rattle. I would expect this at a wider RPM range if this is the case.

 

I have an Exedy Stage 1 and SMFW installed right now. While this is not a LWFW, could this noise be clutch/flywheel chatter usually associated with aftermarket clutches?

 

My other thought (hope) would be the center differential bearings, because those can be replaced relatively easily. To me, this rattle does not sound like a bearing noise issue, so I'm doubting that one.

 

The final option (trans related) would be some form of internal issue in the gear box itself, but I would think that would cause noise at other RPMs and during acceleration. I would also think it would be more bearing noise than a rattle noise.

 

Clutch operation is smooth, and the TOB is very quiet. Other than this noise, there are no other issues with the trans. It shifts just fine without grinding, and there are no other noises beside a little gear whine in 1st and 2nd, which it's always had.

 

I would love to get the thoughts/opinions of those on the forum here with more experience diagnosing trans issues than I have. Thanks!

My 05 LGT sounds just about the same with an aftermarket clutch installed. NO driveability problems but noisy when off the throttle at certain RPMs.

 

I think this is a well known "non-issue" issue.

Not an expert but here are things I think it is NOT:

 

1) "heat shield" - doesn't sound like that

2) "clutch/flywheel chatter" - that's only happens on engagement

3) "bearing noise" - I also don't think it sounds like a bearing

 

Diff or trans noise? Well, if it happens in "all gears" it's probably not one gear or synchro. RPMs will probably drop to quickly to to tell, but does it make the same noise with the clutch in or tranny popped out of gear? I'm guessing the front diff. Have you tried changing trans fluid yet?

 

J

Spent the day in the garage swapping engine mounts, trans mount, and trans cross-member bushings with Group N parts. I am confident the noise is NOT a heat shield, because they are all tight and well clear of the powertrain.

 

MaStaMooN - I hope your right on this being a normal "non-issue" issue. The Group N stuff makes the noise more noticeable, along with other powertrain noises, but it's not objectionable.

 

I also changed the transmission fluid, since it's got about 30k miles on it. I had Extra-S in there and it came out surprisingly clean, with no shimmer to the oil or excess gunk on the drain plug indicating an internal problem. Replaced it with Motul 300 and Redline Lightweight Shockproof in a 3 to 1 ratio. We'll see how that performs.

Usually a dual mass flywheel is used to combat issues such as this.

My transmission makes the noise. Nothing is wrong with it. It's made the noes for awhile.

New fluid did not make any difference to this noise. Improved shifting a little bit and cut down on some of the gear whine in 1st and 2nd, but that's about it.

 

Unless the performance of the trans starts to decrease, I'm going to ignore this rattle.

 

On the plus side, the Group N stuff really helps with the on-power shifting. The powertrain is much better controlled now.

Any stiffer bushing will make the decel noise louder. Get used to it.

 

Next time you go down a big hill, put the tranny in neutral clutch out and listen for noise. If you hear tires and wind noise only don't worry.

 

I had decel noise since Sept 07 when I went to a LWFW. Now with Cobb rear diff cradle bushings its even louder. But coasting down hill all is quiet.

Any stiffer bushing will make the decel noise louder. Get used to it.

 

Next time you go down a big hill, put the tranny in neutral clutch out and listen for noise. If you hear tires and wind noise only don't worry.

 

I had decel noise since Sept 07 when I went to a LWFW. Now with Cobb rear diff cradle bushings its even louder. But coasting down hill all is quiet.

 

I was completely expecting additional noise from the stiffer bushings.

 

I'll give the down-hill thing a try when I get a chance. Thanks to everyone for the input.

Don't know if you saw this in other threads, but I went through the same search for the rattle a few years ago with my LGT and with a previous Impreza RS........The techs just couldn't find it (All on warranty) but after checking a lot of 'net info it turned out to be slightly loose springs in the clutch face........ Not "loose" just not as tight as supposed to be,,,,,

http://i23.photobucket.com/albums/b375/RM-RS/clutch-fig6_zpsd07a6a39.jpg

That could definitely be an option, but I'm not going to go through the hassle of checking. The clutch is basically new, so I don't plan to change it any time soon.

I don't blame you......If it is those springs it will not do any harm at all....just a little deceleration rattle.....both mine were new too, so since they were on warranty I had them replaced......No warranty and I would have just lived with the rattle.

What brand of clutch did you have this happen on?

Both were OEM stock clutches ... hence the warranty replacement.

Ah, makes sense. Thanks for the info.

I've got a little bit of an update here. I replaced my crank pulley two weekends ago with Grimmspeed's lightweight option and this rattle seems to have decreased significantly. The stock crank pulley looked fine, with no signs of wear or indication of impending doom. I will note that driving under load at lower RPMs is definitely smoother now than it used to be (such as cruising at 40 mph in 5th gear), so maybe this is linked to the rattle getting better.

 

Or something finally broke, even though it still drives fine. Or something fixed itself, which would mean my LGT is magic. Who knows - I'm happy.

Interesting...grimmspeed crank pulley...

 

I have noticed after all these years that when I apply the brakes like normal, the decel noise goes away. By normal I mean not just touching the brakes but like your trying to slow down a bit.

 

Again, I have no noise when coasting in neutral, at any speed.

I also have zero noise when coasting in neutral. Mine happens when coasting in gear, between 2k and 2.5k RPMs, even if I'm on the brakes a little. There's just less of the noise now.

I wonder how the LWCP effects the driveline noise. Just saying... I realy have no idea why that would make a difference. If it works, it works.

Change the mass of a system, and you change it's resonant frequency and amplitude.

 

40 MPH in 5th gear? Holy lugging city Batman!

Change the mass of a system, and you change it's resonant frequency and amplitude.

 

40 MPH in 5th gear? Holy lugging city Batman!

 

Okay, maybe it's not exactly 40 MPH in 5th gear, but the point was I can cruise at a lower speed in a higher gear than I could before without lugging the engine.

 

I'm certain it has to do with system resonance. Given the LWCP and Group N mounts all kind of new noises show up while some go away. The Legacy likes to shake things up...

I used to be able to drive my wagon in 5th at 40mph. I can drive the Spec at low speed in 6th. Stock FW

 

Since the wagon got a LWFW, 45 in 5th is about the slowest it can go.

I have the same problem on my 98 subaru legacy gt just started today. Smh drives find n all but I let goes gas there's goes a loud rattle smh I hit the gas it goes away I serviced everything else and was just about to start trans work and drive train work and this happened now I don't want to waste any maintenance money until I find out this issues I've been told it the transmission bearings on the inside idk looking for more input thanks

I've also heard it could be the outrigger what ever that is I'm just looking for someone to explain this problem better