Grinding / Rumbling Sound from ZF320 Gearbox

[Willslutton]

Hi all, I’ve bought an E36 328i that I manual swapped and been having a bit of a nightmare with.

Once the car was swapped there was a grinding sound that was more predominantly in 5th gear but showed in 4th and 3rd as well, showing up between 2-3k rpm’s. I recently got the car on a lift and can now hear a rumbling/grinding from the rear or the gearbox / front of the driveshaft.

I firstly thought that this was a gearbox problem and have swapped out for another box but the problem still persists.

If anyone has any knowledge of this problem it’d be much appreciated

[bmwdirtracer]

Well, if it's not the gearbox, given the location, it must surely be the driveshaft. Use a stethoscope, car on a lift, and listen to the CSB bracket. I'd highly recommend that you do not replace just the CSB, but replace the driveshaft with a quality remanufactured unit. If the CSB is dead, so are the u-joints.

[Willslutton]

I have done some more looking and think I must of become very unlucky with multiple poor ZF's.

I disconnected the driveshaft and ran it and could still hear the rumbling that is in the video below (did not video with no driveshaft as exhaust was also off).

Has anyone had these symptoms appear with their ZF's or gearboxes? Rebuild or replace?

Thanks

[BimmerBreaker]

I would look at whatever else was shared between the two repairs... Clutch, flywheel, pressure plate?

[pbonsalb]

I assume it is not as simple as the shift selector rod being upside down and not clearing the flex disk. Transmission mounts any more than slightly stiffer than stock can also cause problems as can significantly stiffer than stock motor mounts. 2 bad ZF320 trans are possible but my guess is unlikely unless you bought them from someone with a turbo E36….

[Willslutton]

Feeling stupid as I forgot to mention this before. When swapped the car had a new lightweight flywheel, 80A poly mounts (engine + trans) and heavy clutch installed (M3 I believe) as the old clutch and dual mass flywheel were quite worn out.

I have checked the selector rod and all clearance issues with heat shields etc, and all seem to be fine.

After some more digging and diving I did find a video on YouTube that has a similar sound and is claimed to be just "noise" that the gearbox produces.



I now understand that the Light flywheel does not dampen noise and could possibly be behind the rumbling/grinding while it is in the air, but still doesn't explain the intermittent grinding when driving as said in the first post.

Seeing an old thread also mentioned that someone believed the grinding to be their differential travelling through and sounding like its coming from the gearbox (thread was not resolved). I have drained the fluid and all seems to be well so feeling quite lost at this point???

Thanks for the help so far

[pbonsalb]

Lightweight flywheel can transmit a lot of gearbox sounds. Raising the idle speed in the tune helps a little. 80A should not cause unpleasantness for motor or trans mounts. Any stiffer on the trans mounts will.

[bmwdirtracer]

I just finished doing a bunch of work including con-rod bearings, clutch and flywheel ....and polyurethane trans mounts, on an E92 M3. All were owner supplied, but flywheel was Luk, clutch was a relined brand new Luk/Sachs, by South Bend. When I finished, and drove the car, I was horrified. At 2500+ rpm, the car vibrated terribly. Out of all the work I'd done, only one thing was easily reversible: the trans mounts. I swapped them back to the old stock ones, and the car was magnificent again.

I'd mention that I've tried poly mounts (both engine and trans) on many of my own race cars, and friend's race / street cars, in the past, and they have always yielded terrible results. Besides shaking the car badly, they usually break very soon. I was reminded once again why I despise them, but happy to return the car to the owner with no terrible vibrations, and the bling bling green poly pieces in a box.

EDIT: All my M-cars have had lightweight flywheels. The sound this imparts occurs in neutral, and I'm absolutely fine with that; I think of it like a happy gearbox chuckle.

[Willslutton]

Thought I'd make a reply to this now as it has been a while and have finally got some updates.

I changed the transmission mounts back to oem (new parts) and while it did make the sound slightly better, it is still very present.

I have since also gotten a 3.15LSD for it and that has not changed nor solved the issue (as I had seen in some other threads that the diff noise was travelling through the drivetrain).

So for now I guess its back to the drawing board until I can be bothered getting the gearbox out again and inspecting all the other new installed parts. I have a thought that the pilot bearing could be the incorrect size, although if it was I would've thought the sound would have gotten worse and the gearbox could have grenaded itself by now. Another thought would be the driveshaft (unlikely) or it could just be some harmonics that I'm going to have to live with.