Annoying vibration during deceleration

[westslope]

At the end of July I had my mechanic switch out almost the entire exhaust system from the manifolds back. The catalytic converter and 02 sensor were relatively recent and not replaced.

 

Everything worked fine except the new system produced a very annoying vibration during deceleration in 3rd and 5th going down hills that I could not only hear but feel with my feet. The vibration also caused the rear door plastic paneling to hum.

 

The first potential culprit was identified as pipe that was too close to the gas tank. That was fixed. It improved the situation but did not solve it. Some other silly cosmetic attempts were made to fix the noise, e.g., replace the muffler, something I NEVER asked for. The new muffler worked just fine. I assumed, perhaps incorrectly, that it was the way the new muffler/exhaust system was attached to the '93 pathie that caused the annoying vibrations.

 

Thoughts? Anybody else experience this problem? Any suggestions on how to reduce chassis vibration during abrupt decelerations?

 

I can probably fix the annoying hum in the rear plastic panel with plastic putty or similar.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Precise1]

It sounds like you have resonance for one reason or another. First, I would make sure it is well anchored but with vibration mounts (not hard anchored). Second, make sure that it isn't contacting when the load on the drive train, ie the motor/tranny moves sideways due to damaged/aged mounts and it is enough to push the exhaust against something. Third, dance around a bonfire naked wearing a goat's head while chanting "Nissan... Nissan".

 

B

[Tungsten]

Check that mount by the muffler. If the muffler is placed too tight against the hanger then you will have to lower the hanger to release some tension.

[westslope]

Thanks B.

 

Tungsten: The mechanic changed out a hanger for one with more rubber Saturday morning. Did not reduce the 'resonance'.

 

 

 

 

I'm not in a position to work on this myself, no hoist being the first obstacle. So I guess I should make the rounds of other muffler shops and perhaps the local Nissan dealer.

 

 

 

 

 

 

 

 

[Tungsten]

You can do that. The exhaust needs a little slack to not vibrate. I built an entire system by myself so I know all about it. Make sure that the exhaust system goes straight and is not forced into any spots. The other spot that I would check is by the transmission cross member mounts. Just after the Y pipe take a look at how close that exhaust pipe gets. I had to shave about a 1/4 inch off there so that my 2.5" pipe fit. Sometimes they are not bent around properly and will cause a disaster with vibrations.

Edited October 17, 2011 by Tungsten

[westslope]

Tungsten: I believe we examined the clearance around pipe near the transmission cross member mounts when it was up on the hoist Saturday morning. It looked fine.

 

However, from my untrained layperson's eyes I wasn't so sure about the tiny clearance between the muffler and some metal near the gas tank.

 

A buddy suggested that deteriorating engine mounts could cause the vibration or that the universal joints are wearing out. I thought universal joints usually exhibited symptoms that were correlated with specific speed ranges.

[adamzan]

Engine mounts is a good possibility. My exhaust is nice and tight and there are no vibrations (at least from the exhaust). I would also check the transmission mount and the universal joints. What I do is take the drive shaft off and try to move the joints in every possible direction to check for binding. To check for play put the transmission in neutral and put the parking brake on so you can move the drive shaft a bit. Grab it and try to move it and check for lateral play in the joints.

[Tungsten]

I was just thinking it was hanger related because he said it happened after the new exhaust system.

[qatcool]

Have you finally identify that the problem is the U - joint? coz. mine is having a vibration during deceleration, as if you are using engine brakes. but i dont have it if i applied the brakes./

[westslope]

I was just thinking it was hanger related because he said it happened after the new exhaust system.

Good analysis!

 

UPDATE: It appears that the problem has been fixed though I have yet to test the the vehicle on the highway in 5th gear. I can no longer reproduce the annoying vibration and resulting noise when decelerating in 3rd gear.

 

 

A Midas Muffler shop in South Surrey, British Columbia diagnosed the problem as insufficient play in the exhaust system. The shop charged me $200 to remove an exhaust hanger and replace it with a custom-welded part that was closer to the stock specification.

 

The assistant manager reported that he had seen this often. Mechanics that simply didn't know or lacked experience.

 

 

 

 

Question: Do I inform my mechanic of the goods news? And if so, how?

 

 

 

 

Otherwise, thankfully, I don't have to..... " dance around a bonfire naked wearing a goat's head while chanting "Nissan... Nissan". "

 

 

 

 

 

[Kingman]

$200 to remove an exhaust hanger and replace it with a custom-welded part that was closer to the stock specification.

 

 

Good you got the problem fixed, but damn that's expensive!

[Tungsten]

 

A Midas Muffler shop in South Surrey, British Columbia diagnosed the problem as insufficient play in the exhaust system. The shop charged me $200 to remove an exhaust hanger and replace it with a custom-welded part that was closer to the stock specification.

 

 

Yes, that's the one problem I also ran into building my system. This is why I was 100% sure that's what it was. I had it up too tight against the frame but when I modified the hanger a little bit it sat nearly perfect and did not shake the truck. $200 is a bit steep for that mod but that's Midas... I guess they spent more time looking for a way to modify the hanger.

[Precise1]

Question: Do I inform my mechanic of the goods news? And if so, how?

 

 

Otherwise, thankfully, I don't have to..... " dance around a bonfire naked wearing a goat's head while chanting "Nissan... Nissan". "

Of course you do. Just tell him you had someone else look at it and that they were able to determine... It is not insuling him, it is educating him and unless he is a fool, that is the way he will take it.

 

Don't be so quick to avoid the pagan method of mechanics, it can be rather... exhilarating.

Besides, it's not like I told you to slaughter a chicken...

 

B

[westslope]

Precise1: I sent the shop owner an e-mail explaining how I had resolved the problem. He responded by offering to pay for half. I haven't replied to his offer yet. I should probably accept.

 

Frankly, what I want him to do is put the vehicle up on the hoist and look at what the Midas shop did.