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#1
10-24-2005, 09:12 PM
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drivetrain hum / whine
Until yesterday, I had a vibration at 65 mph and above. After reading up on the subject, I suspected the flex discs and center bearing. Turns out the front flex disc had a crack between two of the bolt holes, and the center support was dried out, weak and cracked. I replaced both parts, put it back together, and went for a test drive. Now, no vibration at all even up to 90 mph. However, starting at about 60 mph there is a hum or whine. It gets louder when I hit the gas. Any ideas? I tried to mark and realign the driveshafts as best I could, but maybe I was off by one tooth on the spline...would this cause the noise?
Rich Mayer 82 500 SL 
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#2
10-24-2005, 11:10 PM
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i t might
be the diff. probably was there before but masked by the other sounds.
tom w
__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.  [SIGPIC]..I also have a 427 Cobra replica with an aluminum chassis.
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#3
10-25-2005, 07:26 AM
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thanks for the response. the noise is loud enough that I doubt the earlier vibration could have masked it. regarding the diff, is the diff. flange supposed to line up with the trans flange in any way or are they independent? I am just wondering if I rotated one or the other by 1/3 while the driveshafts were out. would that make a difference? also, is it possible that the whine could be caused by overtightening the flange bolts on both ends or the bolts for the center bearing carrier? I tightened everything by the book, but they seemed not to be very tight, so i gave them an extra turn.
Does anyone know for sure what the sound would be like if the driveshafts were not properly aligned? Rich Mayer 82 500 SL
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#4
10-25-2005, 07:52 AM
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Could it be motor and tranny mounts letting the parts sit off center enough to cause the noise?
I had a hum at 60 in my Subaru that I couldn't track until it was put on a rack (4 jackstands actually but that's not what I can suggest  ) and driven. Stethescope wasn't needed.
__________________
82 300D....went to MB heaven 90 350 SDL....excercising con rods
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#5
10-25-2005, 10:44 AM
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motor and trans mounts are new, and the car now drives very smoothly at high speed.
Rich Mayer 82 500 SL
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#6
10-25-2005, 11:10 AM
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Quote:
Regards, Bruno
__________________
_ 1992 300TE 160 kmiles Last edited by Bruno_300TE; 10-25-2005 at 10:24 PM.
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#8
10-25-2005, 05:23 PM
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OK, Bruno, you got me interested there...of course, I did not have a torque wrench when I tightened that one. I tightened it pretty snugly with large adjustable pliers. Are you saying that it is supposed to move some as the driveshafts turn? Now that I think of it, this large nut was very loose when I dis-assembled the driveshafts. In fact, I removed it by hand. Why would the driveshafts need to move forward/aft as rpm's increase?
As to the engine and trans mounts, I replaced them all before this episode even started. All of my rubber was original when I bought the car from hot, dry Texas a few years ago. I have systematically replaced a lot of rubber. Before I did the mounts, the engine was in contact with the steering box, causing some noise problems there. Replacing the rubber has made an incredible difference in how the car runs and handles. PS I just went out and removed the forward drive shaft and flex disc to see if the shafts were aligned. It seems that they were correct. Rich Mayer 82 500 SL Last edited by diqmayer; 10-25-2005 at 05:25 PM. Reason: add content
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