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  July 7, 2010 8:37 a.m. ClemSparks SuperDork

  Hey all,

  1986 Volvo 740 TurboWagon with 5 speed.

  So my engine is up and going after a headgasket replacement.
  

  Now, as expected, I am figuring out all the other stuff that needs attention.

  The subject of the post is a road-speed (not engine speed) dependent growling noise. I originally though "wheel bearing" but now I'm not sure. First off, the noise sounds like it's coming from somewhere in or around the front of the transmission (hard to explain how we know/think these things...we just do). Secondly, it doesn't seem to change/worsen when I turn. It doesn't start to show up audibly until around 40 miles per hour. It seems to be a little louder while accellerating, but it is there even coasting on the highway with the clutch depressed and/or the transmission in neutral.

  I'm just checking to see if anyone knows of any common failure points that this could be. I'm hoping it's not transmission-internal. And maybe I shouldn't be ruling out the wheel bearings yet.

  I'd really think it was something like noisy gears in the rearend, but it's definitely not coming from back there.

  Thanks,
  Clem

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  July 7, 2010 7:56 p.m. EvanR New Reader

  Driveshaft carrier bearing. All these cars used a 2-piece driveshaft. Your symptoms have occurred in thousands of these cars, and replacing the carrier bearing is the fix.

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  July 7, 2010 8:50 p.m. Junkyard_Dog HalfDork

  EvanR wrote:

  Driveshaft carrier bearing. All these cars used a 2-piece driveshaft. Your symptoms have occurred in thousands of these cars, and replacing the carrier bearing is the fix.

  What he said. FCP Groton seems to have the best prices. I used a press to do mine.

  Also don't rule out tires if the car has sat for a good long while.

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  July 7, 2010 11:26 p.m. Streetwiseguy Reader

  Driveshaft center bearing is definitely a good place to start. Warning- there are 3 different sizes, with no apparent logic to what car got what size. Drop the center of the shaft, and if you can measure the shaft diameter ( the I.D. of the bearing), that will tell you whether its a 6007, 6008 or 6009 bearing. You will probably need the matching rubber support as well.

  Those cars also have greased rear wheel bearings as well- inner and outer seals keep the diff oil in the diff, and the dirt out. Get the inner seals, pull the axles, clean and repack is a good idea every decade or so.

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  July 8, 2010 8:27 a.m. ClemSparks SuperDork

  Cool!

  Thanks folks. This possibility had crossed my mind. I'm glad to hear it's probably the issue.

  While it doesn't sound like that's where the noise is coming from, it won't surprise me at all if that's the culprit.

  Much appreciated!

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  July 11, 2010 6:40 p.m. ClemSparks SuperDork

  All right...who wants to tell me how to get this bearing replaced?

  Do I take the driveshaft out, then apart at the center u-joint and then get the center bearing off?

  I'm not sure, and I don't have a manual. Also...who's got the deal on a manual?

  Thanks!
  Clem

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  July 11, 2010 7:34 p.m. Junkyard_Dog HalfDork

  Haynes manuals are pretty good. Mine is packed up somewhere since I just moved. I removed the shaft and used a press on the center bearing and mount.

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  July 12, 2010 9:21 a.m. ClemSparks SuperDork

  I'll start by getting the driveshaft out. I haven't looked to see how the two halves come apart to be able to press the bearing off yet, but I'll assume it will be evedent when I get it all out (and/or have a closer look).

  Thanks,
  Clem

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  July 12, 2010 5:33 p.m. Evan_R New Reader

  It will be so evident that it will fall apart on you if you're not careful. It it a splined connection, and the driveshaft is factory balanced.

  Make SURE you index it somehow before taking it apart. If you don't put it back together EXACTLY how it came apart, it will never be balanced again.

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  July 13, 2010 8:16 a.m. ClemSparks SuperDork

  Cool, thanks!

  I've decided that I should get the rear up on jackstands and run it up to speed to confirm that the noise is coming from the center bearing. Before putting the car down for a few days (have to remove the driveshaft to measure it so I know what part to order, order the part, get the part, put it on the driveshaft, put it back together, etc) I'd like to be sure I'm chasing the right tail.

  I just found the brickboard FAQ...pretty cool!

  Thanks again,
  Clem

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  July 15, 2010 3:15 p.m. ClemSparks SuperDork

  Here's what I did a couple evenings ago:

  Jack up the rear and put it on jackstands.
  Start the car and run it through the gears.
  Listen for noise.

  I DID hear some noise that sounded similar but at a MUCH lower volume than it is on the highway.

  When on the highway, this will happen in any gear. It is LOUDER when under load, and quieter when I get off the gas and/or put it in neutral. It is very much still there, however even if it's in neutral.

  So, I'm a bit concerned that it is something in the transmission causing this noise, since it seems to be load-dependent. Does that make sense?

  Can anyone confirm if the driveshaft center bearing noise can be load-dependent?

  I'm pretty good about hearing where the sound is coming from and feeling this stuff telepathically, typically. I'm not completely sure, but it really doesn't feel like it's coming from the center bearing.
  

  My next step is to drain and refill the gearbox to see if it makes any difference. If it is the gearbox, I fear the damage has been done already anyway.

  Thanks,
  Clem

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  Aug. 8, 2010 11:44 p.m. mondobravo

  In reply to ClemSparks:

  Clem,

  I could have written your post word for word ... already drained and put new gear fluid in the gearbox. I have the identical M46 w/ Overdrive. It made no difference to the road noise whatsoever. I also thought wheelbearing, but after reading the posts above am inclined to believe it is the D/S Centre bearing. My main reason for thinking so beyond what has already been written is that I had no problem before having my clutch replaced by a couple of local good ol' boys. I strongly suspect they messed something up pulling the shaft while doing the clutch job. I would be really po'd if it turns out they didn't index the shaft and spline! Hope this helps.

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