Loud Banging Noise & Felt Vibration from tunnel area

[timzoy89]

Hi all,

im new to this forum, and fairly new to AWD car's.

im about at my witts end.

i have a 99 subaru legasy L "30th aniversery" 2.2L auto tranny.

the car is making a very loud and noticable banging noise/vibration comming from the tranny tunnle area (felt the strongest) but the noise sounds like its comming from the pashenger inner cv axle joint.

it dose it 100% of the time at slower speeds 0-35 mph and the most prominent when Decelerating to a stop (15 - 5 mph) it makes the nose during acceleration, turning, stright, and decelerating.

it dose not make the nose at higher speeds but will make the nose/vibration (softer) when turning at faster speeds like a highway clover (40 mph 'ish)

 

the noise basically behaves like a bad CV axle, but is making the noise and vibration of a bad U-joint.. thats why im stumped.. THE DRIVE SHAFT IS BRAND NEW, i even removed it once the noise/vibration started and had it checked by the manufracture (because it sounds like a drive shaft)

 

the only thing i can conclude is that its the front diff.

BUT I HAVE NO IDEA (im new to AWD)

[lmdew]

Put the FWD Fuse in and see is anything changes.

 

Have you drained the front diff and checked for metal?

 

Couple of easy checks that may show something.

[johnceggleston]

crawl under and shake push pull on the drive shaft to the rear.

check the universal joints and the carrier bearing, the mid point support.

 

this is further back than the CV but it sounds like it could be your problem.

Edited May 29, 2012 by johnceggleston

[timzoy89]

Put the FWD Fuse in and see is anything changes.

 

Have you drained the front diff and checked for metal?

 

Couple of easy checks that may show something.

 

I did not know that there was a fwd fuse. That's good info. I'll try that out Thank you.

[crazyman03]

I would recommend doing the drive-shaft check first - it is most likley a U-jont/bearing issue, I had the same issue.

 

Doing the FWD fuse check won't eliminate any banging/vibration issue because it wont stop the shaft from free-spinning. (it'll spin with any 4wd/AWD car because the rear diff is causing it to spin)

 

 

Also, for the record, because its appealing to have FWD on all the time to save gas, DONT leave the "FWD" fuse in. It will screw up a lot more than you want.

 

 

-Justin

[LosDiosDeVerde86]

Also, for the record, because its appealing to have FWD on all the time to save gas, DONT leave the "FWD" fuse in. It will screw up a lot more than you want.

 

 

-Justin

 

Not really sure what harm would come from leaving it in. I suppose the worst case scenario would be that the duty-c solenoid burns out because it has constant power...but to that point, it always has some kind of power going to it as the drive wheels are never 100:0.

 

In all likelihood - leaving in the FWD fuse would do nothing bad but wear down your front tire's tread because you'll be spinning from every stop.

 

Also, for the record - 2010+ doesn't have a fwd fuse.

[crazyman03]

Not really sure what harm would come from leaving it in. I suppose the worst case scenario would be that the duty-c solenoid burns out because it has constant power...but to that point, it always has some kind of power going to it as the drive wheels are never 100:0.

 

In all likelihood - leaving in the FWD fuse would do nothing bad but wear down your front tire's tread because you'll be spinning from every stop.

 

true. I was always told not to do it anyway, so i always say to not do it.

 

 

Also, for the record - 2010+ doesn't have a fwd fuse.

 

He did say it was a '99. I've seen the FWD fuse (I think) on a '00 Lego GT. not a '10

 

 

 

-Justin

[idosubaru]

if the driveshaft ujoint is that bad it should be obvious - grab it and shake it at each ujoint - if it's loose it should show movement.

 

in rare cases the ujoint is hosed but you can't tell by sharking - the ujoint can "seize" and doesn't move at all, so that's the problem. a close visual inspection of the joint should still show some wear without removing it first though, at least the ones i've seen do.

 

if the CV axle has ever been replaced with an aftermarket (any brand) then that's a high probability place to look too. aftermarket CV axles have a high rate of issues.

 

there are no issues running with the FWD fuse for any length of time you need.

[nipper]

My car does this from time to time, usually means the tranny mount is weak or bad for Blu.

 

Have it checked out as it may also be the driveshaft. You are at the right time for either or both and the driveshaft is not pretty when it fails.

Edited May 31, 2012 by nipper

[timzoy89]

The noise basically behaves like a bad CV axle, but is making the noise and vibration of a bad U-joint.. thats why im stumped.. THE DRIVE SHAFT IS BRAND NEW, i even removed it once the noise/vibration started and had it checked by the manufracture (because it sounds like a drive shaft)

 

The drive shaft is brand spanking new, even had it removed and rechecked after the noise started. Conformation was the shaft is good. Carrier is a little week but ok.

 

I'm confused, (I'm a truck guy)

Is the FWD fuse - 4 wheel drive or front wheel drive ?

I assume that it meens, front wheel drive only when the fuse is in place ?!?

And I did just replace the Pashenger cv axle (aftermarket) but only now like 2 miles on it. I've been driving the truck these last few days.

I have not even tried the fuse yet. Where is it located ? Under hood or interior panel

Edited June 1, 2012 by timzoy89

[ccrinc]

My money's on a broken/cracked flex plate. I don't have a sound, logical reason to back this up with, but it's my gut feeling, and I've learned to trust my gut feelings.

 

One question: Does it do it while not in gear? Like in neutral?

[crazyman03]

Conformation was the shaft is good. Carrier is a little week but ok.

 

Is the FWD fuse - 4 wheel drive or front wheel drive ?

..

I have not even tried the fuse yet. Where is it located ? Under hood or interior panel

 

 

The fuse is located on the passenger side "top" of engine bay closest to the weather stripping/windshield (under the hood) It has a cap that says "FWD" on it. What it will do is keep the transmission/transfer-case from engaging the rear tires.

 

Now, you can try this.. but I don't believe it will help you any simply because if it is anything related to the drive shaft, It will still make the sound simply because the drive shaft will continue to spin because the rear tires are turning= drive shaft spinning. But try it, see if it doesn't eliminate the problem.

 

 

My money's on a broken/cracked flex plate. I don't have a sound, logical reason to back this up with, but it's my gut feeling, and I've learned to trust my gut feelings.

 

iirc, a Flex plate is only on Manual transmissions? Automatics dont have this..

 

You might try taking the drive shaft off and see if it doesn't help the problem too. if it continues, it would likely be something maybe in the rear diff. area.

 

if it does stop the problem, either have your drive shaft re-balanced, or something is going on with your tranny..

 

 

 

-Justin

[ccrinc]

The fuse is located on the passenger side "top" of engine bay closest to the weather stripping/windshield (under the hood) It has a cap that says "FWD" on it. What it will do is keep the transmission/transfer-case from engaging the rear tires.

 

Now, you can try this.. but I don't believe it will help you any simply because if it is anything related to the drive shaft, It will still make the sound simply because the drive shaft will continue to spin because the rear tires are turning= drive shaft spinning. But try it, see if it doesn't eliminate the problem.

 

 

 

 

iirc, a Flex plate is only on Manual transmissions? Automatics dont have this..

 

You might try taking the drive shaft off and see if it doesn't help the problem too. if it continues, it would likely be something maybe in the rear diff. area.

 

if it does stop the problem, either have your drive shaft re-balanced, or something is going on with your tranny..

 

-Justin

 

You have it backwards: only automatics have flexplates: it's what the torque converter bolts up to. Manuals have a clutch pressure plate.

[crazyman03]

You have it backwards: only automatics have flexplates: it's what the torque converter bolts up to. Manuals have a clutch pressure plate.

 

Hmm, I thought it was Engine -> flywheel -> torque converter -> transmission..

 

oh well least i was close.. its been a while since i've been in the neighborhood.

 

 

-Justin

[nipper]

Hmm, I thought it was Engine -> flywheel -> torque converter -> transmission..

 

oh well least i was close.. its been a while since i've been in the neighborhood.

 

 

-Justin

 

Engine - flywheel (flexplate) - torque converter - transmission.

 

Basically the flex plate has the ring gear for the starter and the TQ bolts to it. They tick when they crack, and this is not what it sounds like as described.

[crazyman03]

Engine - flywheel (flexplate) - torque converter - transmission.

 

Basically the flex plate has the ring gear for the starter and the TQ bolts to it. They tick when they crack, and this is not what it sounds like as described.

 

Ah hah! I wasnt (too far) off..

 

yea, try the drive shaft idea.. might give some light..

 

 

 

-Justin

[Fairtax4me]

A broken flex plate will tend to pop or knock when the engine is under load, such as when put into gear. It can cause vibration as well, typically at low- mid range rpm, and it can prevent the engine from reaching higher rpms due to imbalance. A broken flexplate will have no correlation to wheel speed.

 

I would guess a worn/broken trans mount or possibly bad axle. Is the axle aftermarket?

 

Front Wheel Drive fuse keep the trans in FWD only while a fuse is in the holder. It's on the passenger strut tower. Small black holder with a flip cap might say FWD on top if it hasn't faded off.

 

What's the reason for having the brand new driveshaft? Obviously the old one failed in some way.

[nipper]

I havent seen one that bad in ages, last time i did it envolved transmission entrails blasted into the ground ... a Chrysler 383.

[Fairtax4me]

SBC 350. Somehow the guy forced a starter into place and it was dragging the flexplate. Said it still started and ran just fine (somehow) the noise started about 2 days after the starter replacement. I stumbled onto this while changing the transmission that died about a month later. Somehow it lasted that long without exploding. I couldn't believe how bad it was shaking.

[nipper]

SBC 350. Somehow the guy forced a starter into place and it was dragging the flexplate. Said it still started and ran just fine (somehow) the noise started about 2 days after the starter replacement. I stumbled onto this while changing the transmission that died about a month later. Somehow it lasted that long without exploding. I couldn't believe how bad it was shaking.

 

DAMN! That thing ran for 2 days ?

 

Amazing.

[Fairtax4me]

You'd think it even more amazing if you actually saw the truck!

[timzoy89]

My money's on a broken/cracked flex plate. I don't have a sound, logical reason to back this up with, but it's my gut feeling, and I've learned to trust my gut feelings.

 

One question: Does it do it while not in gear? Like in neutral?

I like your thinking. I always trust my gut first & no only while driving

 

The fuse is located on the passenger side "top" of engine bay closest to the weather stripping/windshield (under the hood) It has a cap that says "FWD" on it. What it will do is keep the transmission/transfer-case from engaging the rear tires.

 

Now, you can try this.. but I don't believe it will help you any simply because if it is anything related to the drive shaft, It will still make the sound simply because the drive shaft will continue to spin because the rear tires are turning= drive shaft spinning. But try it, see if it doesn't eliminate the problem.

-Justin

thanks justin.

 

A broken flex plate will tend to pop or knock when the engine is under load, such as when put into gear. It can cause vibration as well, typically at low- mid range rpm, and it can prevent the engine from reaching higher rpms due to imbalance. A broken flexplate will have no correlation to wheel speed.

 

I would guess a worn/broken trans mount or possibly bad axle. Is the axle aftermarket?

What's the reason for having the brand new driveshaft? Obviously the old one failed in some way.

I dont know if the axles were stock or aftermarket... i did how ever just installed a aftermarket one, but havent driven it enough yet to say if it helped or not... ( i did a circle in the subdivision and parked it for 3 days now) it was still making the noise but not as bad

 

I replaced the drive shaft because the front joint exploded, which caused damage to the shift linkage. which i temporally fixed. and it just came loose again (4 months later) which is why i havent driven it the last 3 days.

Edited June 2, 2012 by timzoy89

[johnceggleston]

while checking the shift linkage, re-check the new drive shaft install. if there was some undetected damage from the failure it could have caused something to come loose.

 

or matbe the trans mount as mentioned.

[Fairtax4me]

That opens several other possibilities. How long after the replacement of the driveshaft did this vibration begin?

[ivans imports]

front diff pinion or awd tranfer gears had one that rear diff had siezed and broke pinion when it broke it took teeth of awd tranfer gears sounded like what your explning the awd gears still worked but bang bang bang in deaqd center of car.When the front diff go's it makes noise in same place becasue the diff is linked to the rwd and the fwd trough the awd tranfer gears. take off diff end of drive shaft and make shure it turns smothly in trans end no tight spots or grinding.