grinding noise

pokemon · 10-17-2001, 08:53 AM

Hi,
My 68 912 makes grinding noises (metal to metal contact alike) when driving. As soon as I push the clutch pedal the noise is gone. Smooth coasting. Release the clutch pedal and the grinding is back.
The gearbox was already checked a few years ago by a reputed gearbox/engine rebuilder. No problem found. The half-axles were replaced a month ago. The originals were worn. TIP: I used secondhand VW 1303S ones. They fitted perfectly and only costed 25$ a piece. With the half-axles out I checked the wheel bearings and they sounded smooth. Is this good enough for a wheel bearingtest? Can they still make noise under load?
Anybody having solved this one before?
Thanks,

WFBowen · WFBowen's Garage

If you have the car running and in neutral, do these noises occur while pressing/releasing clutch pedal?

Rich Lambert · Rich Lambert's Garage

Sounds like the throw-out bearing. Was it replaced when the transmission was checked?

Rich

pokemon · 10-19-2001, 06:02 AM

I just did another test drive.
There are no grinding noises in neutral and below 20mph. Coasting down from 4000rpm in third gear seems to produce most noise. Also it seems the grinding noise gets worse after 5-10 miles driving when the engine become warm.
The throw-out bearing was checked by hand, it did spin smoothly.
The gearbox has fresh castrol EPX90 oil. For the engine I use 20W50. Got 3 bar pressure.
Can you make something out if this?
Regards,

WFBowen · WFBowen's Garage

Did you replace the halfshafts because of this noise? Did anything change?
If you're absolutely sure about the bearings (wheel & t/out) I'd double check the fit of the halfshafts-clearances are absolutely critical (i.e. distance from transaxle to carrier/hub.) You might also check for a loose flywheel/pres.plate, but that's a stab in the dark. Do make sure you get this fixed, as problems like this have a way of working their way "upstream" quickly & you don't want to destroy a gearbox. My best guess is the trans if everything else checks out.

pokemon · 10-19-2001, 11:13 PM

The halfshafts were checked because of the noise. They were bad. When I wiggled the joints I could feel mechanical resistance points at random. Replacing them didn't solve this grinding noise though.
The flywheel and resurfaced pressure plate were torqued to Maestro specifications and loctited. The pressure plate was renewed at the same time. The old one had pretty bad grooves. The wheelbearing are OK although I'd like a second opinion on this. I'm gonna contact the gearbox rebuilder and make a testdrive in his presence. I'm curious to see what he has to say.
Regards,

john walker's workshop · 10-20-2001, 09:57 AM

sounds like the ring and pinion are eating themselves up. the drainplug magnet should have a lot of particulate in it if that's the case, along with metallic looking gear oil.

pokemon · 10-21-2001, 12:03 AM

Two years ago when I opened the gearbox myself and found the ring and pinion teeth contact surface was spread over the WHOLE teeth surface. The complete surface was shiny. I read an article about this topic that stated the contact patches should be located in the middle of the teeth with a rectangular shaped surface with round-off corners.
Adjusting ring and pinions is above my abilities which was the reason why I send to the box to the rebuilder's workshop.
With the box open I also found some brass particles in the oil which came from the speedo meter drive wheel. It's supported in a brass bush at one side. This bush was worn. There were no steel like (white and shiny) particles in the oil then.
Thanks so far for sharing your ideas and experiences,