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M3 Noise

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  • M3 Noise

    Well, I'm a newB, but I've had my M3 (88, Alpine, 75K) for a few weeks now. It had hardly been run the last few years prior to my purchase, but it's the most fun I've had in a car since my teenage years!

    After putting 1000 miles on the car, it has developed a knocking noise that seems to come from the transmission area. It starts at about 3200 rpm, gets louder on slight acceleration and disappears on deceleration. It doesn't vary with rpm, and rattles in regular cycles. The cycles don't increase or decrease with rpm. It occurs in every gear, and is only apparent once the car comes to operating temperature. Holding the Turner short shifter tightly doesn't make any difference. If the engine is revved up to 4000 rpm at a standstill, it doesn't make the noise. A/C on or off doesn't make a difference. The previous owner recently changed the transmission and differential with Redline MTL. The car has no leaks (amazing!) Engine oil level is fine.

    About the same time this started, the tachometer started skipping. Rather than increasing smoothly with rpm's, it increases smoothly until about 3200 rpm (about when the knocking starts) then jumps up in stairstep fashion with rpm. In other words, it stops at 3200 rpm, then jumps to 3500, etc. as rpm's increase. Is there anything that could relate a transmission noise (assuming it's really coming from the transmission) with the tachometer? I've read most tach problems are related to dead batteries in the SI board but thought this was interesting. It may just be coincidental.

    I've already searched the archives on the this and other sites and can't find anything that sounds like this. The regular cyclic nature of the noise seems unique and is very annoying. My biggest concern was rod knock, but since it doesn't vary with rpm and goes away on deceleration, that seems unlikely. I'd appreciate any advice. Thanks, Drew

  • #2
    Does the noise change when you have the clutch in or out? Rev in Neutral with the clutch in and then the same with the clutch out. That should determine if it's coming from the trans or engine.
    Several E30 M3's.

    More than I need but not as many as I want....

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    • #3
      Remove & check the two sensors in the transmission bellhousing (drivers side)... try switching to Redline Shockproof gear oil it worked better for me for shifting difficulty.
      Rich!

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      • #4
        Could be the trans internally.

        Check the Guibo for disintegration.

        m

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        • #5
          M3 Noise Update

          When the car is not moving, the noise does not occur, whether the clutch is in or out. I only occurs when the car is moving, but doesn't vary with speed or rpm.

          << Check the two sensors in the bellhousing>> I think I see the two sensors from the engine bay driver's side. What are they called and what do they do? If I know the part names, maybe I can find a procedure for removing and checking them. I'm a passable mechanic but haven't worked on these cars before.

          <> I don't know what was in the trans or diff before, but the PO put in MTL just before I purchased the car. I was going to try changing the trans to MT90 as it's a little more viscous at higher temps, but was concerned about making it more difficult to shift with a thicker oil. How does Shockproof (Lightweight?) compare to MT90? I also was going to change the differential oil to Redline 75W90NS as that's closest to what the manual recommends. It's a GL5 oil, MTL is GL4. (I've read about a billion oil combinations other members use, let's not restart that thread!)

          The guibo was installed backwards when I got the car. It's since been properly installed and looked fine, but I did wonder if reversing it would cause it to disintegrate. I'll check.

          Thanks for the advice, guys. This is really helpful. Drew

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          • #6
            ...
            Last edited by justin11572; 07-15-2009, 10:38 AM.

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            • #7
              "The guibo was installed backwards..." -- are you sure you don't mean the center support bearing was installed backwards? AFAIK there's no "front" and "back" to the guibo ("flex disk"). I had the same thought as Mmark -- a failing guibo can allow the driveshaft to move around and vibrate. The fact that you're getting the noise only while the car is moving suggests something in the drivetrain.

              Dunno about the tach issue, though. That shouldn't be related to a drivetrain problem.
              The day ain't over yet....

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              • #8
                Could be a long shot, but have you inspected the carrier bearing?
                What sets the e30 apart is that it set the precedent, the benchmark, for every "M" car since... - Top Gear

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                • #9
                  Perhaps the guibo was installed in the wrong position, rotation-wise.

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                  • #10
                    As suggested check the Guibo. But also look at the shift linkage. If the Guibo is coming apart it could/will hit the shift linkage depending on how bad it is.

                    Also as suggested check the carrier bearing. I think they are supposed to be slightly loaded when fastened in the car.

                    While you are under there, exhaust down checking the carrier bearing, also check the drive shaft universal joints. It maybe worth it to pull the drive shaft and check the range of motion on each u-joint. Pay attention to any bind points or play. also check the center section where the driv shaft can telescope. There is a large nut that has a rubber insert. I am not sure the spec on how tight that should be when the drive shaft is in the car.

                    Tach jump could be worn gears in the cluster?!? Someone else will have to confirm that. Or a contact, board ground issue?!?

                    I apologize if I repeated anyone elses suggestions. Just shooting from the top.

                    Good luck

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