2joejoe2

Drive Train Noise on decel

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Hey Guys.....I need your help again. 

 

A couple weeks ago I had an issue with a bad pressure plate strap that caused a pretty bad engine vibration.  Thanks to Toby for helping me find that issue. I replaced the pressure plate and the clutch friction disk. and now the vibration is gone.....yay! 

 

Well now I have a different issue. When decelerating I get a vibrating howling noise its even there when car is under very light load....the noise is definitely  coming from the tunnel area . I  can make the noise come and go by playing with the throttle. The noise goes away when the clutch is pressed.  I have  thoroughly checked the exhaust to make sure it is not rubbing the car anywhere. 

 

I am worried that it could be a bad pilot bearing I did not replace that when I replaced the clutch.....however I checked it by putting the alignment tool into it and it seemed to spin smoothly....It was very stupid of me not to replace it

I am also worried that it could be a bad trans input bearing.....maybe the bad pressure plate caused the trans input bearing to fail??? ...........I hope not!!! 

The Drive shaft and center bearing are only a year old so, I doubt that it could be that.

Maybe rear end....but this noise was not there before the bad pressure plate issue.   

 

Thoughts? 

 

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It is not the pilot bearing, the only time it spins is when the clutch is disengaged and the flywheel and clutch disc are turning at different speeds.  Is the noise there in 4h gear?  If it is, it is not the input or front counter shaft bearing (this is because the 4th gear is actually just a locked main shaft so there is no side load on any of the bearings in the transmission in 4th gear)  If the noise is there even in 4th gear it is possible that it is a Pinion bearing in the differential or even the pinion gear.  Does the noise change depending on speed or does it change depending on speed AND what gear you are in?  If it is strictly speed related and does not change in pitch depending on what gear you are in it has to be something from the drive shaft rearward.  If it changes depending on what gear you are in it has to be something from the Guibo forward. 

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forgot to mention it is a getrag 245 5 speed swap. 

 

The noise is there in 2nd 3rd and 4th, I can not confirm if it is there in 5th.............the noise seems to be depending on speed of vehicle not the gear. 

 

I am also getting a clicking noise from my dif when I change directions...........maybe that is related to this issue. 

 

Diff is a E21 3.91 lsd 

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My guess is a differential problem.  the "clicking" noise is usually a CV Joint that is badly worn.  Drain the oil out of the diff and look at it,  if there is a lot of metal stuck to the drain plug magnet you should pull the back cover off the diff and have a look at the gears. 

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I have this exact same issue in my 1975.  Sounds great through the gears, but the minute you are off the throttle, Pinion bearing whine in the differential.  Seeing yours is a E21 3.91 LSD, better to repair than replace.

 

Mark92131

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On 8/4/2016 at 10:19 AM, 2joejoe2 said:

Hey Guys.....I need your help again. 

 

A couple weeks ago I had an issue with a bad pressure plate strap that caused a pretty bad engine vibration.  Thanks to Toby for helping me find that issue. I replaced the pressure plate and the clutch friction disk. and now the vibration is gone.....yay! 

 

Well now I have a different issue. When decelerating I get a vibrating howling noise its even there when car is under very light load....the noise is definitely  coming from the tunnel area . I  can make the noise come and go by playing with the throttle. The noise goes away when the clutch is pressed.  I have  thoroughly checked the exhaust to make sure it is not rubbing the car anywhere. 

 

I am worried that it could be a bad pilot bearing I did not replace that when I replaced the clutch.....however I checked it by putting the alignment tool into it and it seemed to spin smoothly....It was very stupid of me not to replace it

I am also worried that it could be a bad trans input bearing.....maybe the bad pressure plate caused the trans input bearing to fail??? ...........I hope not!!! 

The Drive shaft and center bearing are only a year old so, I doubt that it could be that.

Maybe rear end....but this noise was not there before the bad pressure plate issue.   

 

Thoughts? 

 

 

It might be best to attempt duplicating the noise with the rear wheels elevated or removed.  Posting the sound or a video might also be helpful.

 

At the risk of belaboring the obvious, some noise can easily be explained by low or improper lubricant.  Although I am not suggesting this is the case, a "dry" transmission or differential is unlikely to remain quiet for long.:huh:

 

The fact that you seem to localize the sound to the tunnel, causes me to first consider the transmission.  This includes the input shaft bearing but from experience, the layshaft bearing below the input is also a likely culprit.  When it develops enough wear, the sound can be strongest at idle  -  diminish with the clutch engaged, and depending upon harmonics, be evident at low speeds.  If anything, check for metal debris at any magnetic fill or drain plugs.  Wear at one area often leads to advanced wear elsewhere.    Although changing lube is probably a short term fix, it could mitigate things, if,  for example, your present lube viscosity is a tad too thin to work with out-of-tolerance (worn) parts.

 

The differential (pinion bearing) is certainly a noise making candidate - and the sound could be significant enough to resonate throughout the chassis, but generally, differential noise/failure is fairly obvious to most drivers as coming from the rear (in a rear axle drive).  Others seem to think you have a limited slip which is stouter than the open version.  If you had the latter, they have a habit of spyder gears seeking freedom, which often entails noise on deceleration followed by a loud "boom" and a clunkity-clunk to the pits or nearest roadside. 

Edited by avoirdupois

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Take out the bottom seat pad in back, and try again.

 

If it gets noticably louder, it's very likely the diff.

 

hth

 

t

 

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Hey Guys,  I have not had much time to diagnose the issue. But I did notice this today. I can only hear the noise in  2nd 3rd and 4rth  when  the RPMs are between 2500 and 3500. any lower or higher the noise is not there.  Say I am in third decelerating and the noise is there. If I shift to 4th the noise goes away unless I am in the above mentioned RPM band.........maybe that means if the diff is driving the motor not very hard (less than 2500 rpm) its not enough load to cause the noise and if the diff is driving the motor hard ( above 3500) its loaded too much to cause noise 

 

I will try toby's Idea of pulling out the rear seat before I drive home today. 

 

also If the pinion is lose should I be able to get some movement on the diff input shaft? 

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