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Exhaust noise after Prothane Poly Tranny and Motor Mounts...

This is a discussion on Exhaust noise after Prothane Poly Tranny and Motor Mounts... within the External Engine forums, part of the LSx Technical Help Section category; So I replaced the tranny mount and immediately got a lot of exhaust noise and vibration. Everything was louder. I ...

  1. #1
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    2001 WS6 Pontiac Trans Am

    Talking Exhaust noise after Prothane Poly Tranny and Motor Mounts...

    So I replaced the tranny mount and immediately got a lot of exhaust noise and vibration. Everything was louder. I thought after the motor mounts were installed that the noise would go away, but it didn't. It did fix the motor and stick shift from bouncing around. My question is, did the mounts change the angle of everything(exhaust system, pipes, rear end angle, driveshaft)? If so what can I change or look for? BTW motor mounts sucked to change out... probably be easier with the right tools... hehe.

    Also keep getting a bad O2 sensor 1st one on the driver side. I've switched out the sensor and the cats(magnaflow) are only like a year old... still keep getting the error code. Is there something else that could cause it or am I gonna have to send the cat back in for warranty replacement?

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    Member WS6SP33D's Avatar
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    Yes anytime you replace the old worn mounts with brand new ones it is going to change the angles height of the motor and trans. Also can you tell where the noise is coming from? And what code is the o2 sensor throwing?

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    The reoccurring code is P0420. I haven't pinpointed the noise exactly as it seem to be everywhere, knocking and being loud as if there were a leak or something. Is the height difference going to affect the exhaust and the pinion angle... I really don't wanna replace the rear again... ugh.

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    Member WS6SP33D's Avatar
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    p0420 I believe that is Catalyst System Efficiency Below Threshold (clogged, dirty or blocked cat) Even with the cats been as new as you say there is still a chance of restrictions. Also Yes the angles have changed but to the better not to the worse. It will have no effect on you pinion other than putting it back close to it's original/factory angle.

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    I assume you went with a poly replacement? The poly trans mount on our car lasted all of two weeks before I yanked it and put a stocker back on. Some of the poly mounts seem to cause issues. Whether it is changing the angle of the driveshaft, the density of the material, or what, I am not certain.

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    Yeah, I went with the Prothane Poly Motor and Tranny set. It seems they are doing what they are supposed to but the exhaust noise is noticeable. If I am going 70 seventy and let off the gas it is real loud. Not sure if it is banging against the car or if something has came loose.

    What can I do about the clogged cat? Taking it off and mailing it back would be such a pain.

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    Member My00Z28's Avatar
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    IMO ditch the Poly trans mount! i have poly motor mounts and love them went to the poly trans mount and when to the track and felt like my car was going to shake its self apart... removed it on the 3rd day with it and now its just collecting dust in a cabinet ....

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    Also I meant to note that this car is a daily driver, I don't do any track stuff... the car has had too many problems to race.

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    Member My00Z28's Avatar
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    well driving on the street was horrible also like you stated it felt like my drive shaft angles were off installed old mount and it was perfect again ill never do a poly trans mount again unless someone can guarantee it would be as bad as the last!

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    its short but its skinny. jiveass's Avatar
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    i guess im a lucky guy.....i installed poly engine and trans mounts and i dont have an issue...sure..i "feel" more of the engine running, but thats not really considered a problem to me.....i got the firmness that i want.

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    The poly's are fine and fixed the issues that they were supposed to fix(engine doesn't vibrate, shifter doesn't bounce around). The problem is the exhaust... is there a problem area to look for where it may need to be adjusted or a place where it could be knocking on something?

    Also on the cats, is there a way to clean or unclog them? I switched the O2 sensor with a working one and got the same result so I know it's not the sensor.

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    Senior Member kenro23's Avatar
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    Mine was rubbing when i would get on it so i took it to the exhaust shop and they added another rubber hanger where the noise was coming from (right below drivers seat) and i havent had that issue since. Seemed to just stiffen it up more.
    Suspension: Lower control arms (Spohn), Drive shaft safety loop, Torque arm (Edlebrock), Strut tower brace, Panhard Bar (BMR)

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    Senior Member kenro23's Avatar
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    I also have poly motor/trans mounts and notice a small shake at idle but nothing to the point that i wanna change it.

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    Senior Member JayTA98's Avatar
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    is the noise happing at idle too? or it is more noticible when you are driving? I had the trany poly mount and got rid of it. My whole dash and center console vibrated very hard. The poly mount I had was higher than the stocker and it changed the angle of the driveshaft causing vibration. There is thread about some members grinding off a portion of the mount and getting good results. I will suggest if you have the stock mount to re install it and see if it goes away. The noise could be exhaust but it could your driveshaft vibrating too. Do you see the exhaust close to any part of the body?
    Last edited by JayTA98; 11-12-2011 at 01:58 PM.

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    At this point I'm going to take it to the exhaust shop like kenro23 did. I had the exhaust worked on before when it sounded like this and it was an easy fix. It sounds like the exhaust is banging up on the bottom of the car especially when I'm on the interstate. At idle I can tell the noise is there but it isn't as bad as when I stomp the gas. The prothane polys don't have the tabs that the Energy Sus. has that people are grinding off. Prothanes are pretty much bolt on as far as the tranny goes... no extra plates or anything. Hopefully, when I take it in the issue will be solved. I will update when I find out.

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    Senior Member INMY01TA's Avatar
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    I'm using stock motor mounts but the poly tranny mount. Immediaetely after installing it I noticed increased exhaust noise/vibratiom. I lived with it and don't even notice it now. I believe the mount softens a bit over time.

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    So it's been a while since I've updated this post but I am still having problems with the vibration. It is a thumping/knocking sound like something is hitting the the bottom of the car. It's slightly noticeable at idle but when I drive thumping sound gets louder. I took it back to the exhaust shop and they found nothing banging on the floorboard. I had so much work on this car since last time(new clutch, new stock aluminum drive shaft, new ac Compressor, new motive 4.10 gears, new back tires...) and thought that vibration would go away with all of that. When I installed the motor mounts that's when it all started... is it possible that the engine is not balanced on the mounts or it raised the engine to where something is banging on the body? I'm tempted to just take it to a shop and put the stock ones back in. It's just the knocking sound that is insane. The slight vibration of the poly doesn't bother me so much as whatever is banging around.

  18. #18
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    Welcome back! I scanned back through this thread since it was from 2 years ago. How about the torque arm mount on the side of the transmission?

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    I've replaced the torque arm mount too with the poly version and was the first poly upgrade I had done. That stopped the issue I had where the back end was sliding back and forth when I would stop or take off. I haven't checked it in a while though...

  20. #20
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    I did get the codes to go away by changing out the densos for bosch's in the front and the O2 simulators in the back.

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