gt6123 Posted June 11, 2018 Report Share Posted June 11, 2018 Hi, I have a mk3 gt6 and I am having problems with the gearbox. When in neutral with the engine running there is a rumbling noise from the gearbox (like a thrust bearing noise) and when I press down on the clutch pedal the noise goes away. Also when driving, 1st, 2nd and 3rd gears are noisy, sounds like the gearbox on a rally car with straight cut gears and 4th gear is fine with no noise at all. Any help will be appreciated. Link to comment Share on other sites More sharing options...
NonMember Posted June 11, 2018 Report Share Posted June 11, 2018 Possibly silly question - have you checked the oil level? The idle rumble that goes when the clutch is pressed could just be the release bearing, but it might also be the off-load version of the noise when you're driving. In 4th gear, the input and main shafts are directly coupled, so none of the gears has any load on it. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 11, 2018 Report Share Posted June 11, 2018 The common denominator here sounds like the layshaft bearings are in trouble or the mainshaft spigot has died Both are under load in 123 but not loaded in 4th Do check you have oil up to level an empty box makes some alarming noises Pete Link to comment Share on other sites More sharing options...
gt6123 Posted June 14, 2018 Author Report Share Posted June 14, 2018 On 11/06/2018 at 8:36 PM, NonMember said: Possibly silly question - have you checked the oil level? The idle rumble that goes when the clutch is pressed could just be the release bearing, but it might also be the off-load version of the noise when you're driving. In 4th gear, the input and main shafts are directly coupled, so none of the gears has any load on it. When I bought the gt6 the gearbox was out of the car and I was told it had been rebuilt, so a couple of years ago I filled the gearbox with oil and installed a full new clutch kit, and then when I started the engine and heard the noise I got a bit disheartened and parked it up! until now. So yes I done the oil but 2 years ago! so I will have to check the level In case its dropped. Link to comment Share on other sites More sharing options...
gt6123 Posted June 14, 2018 Author Report Share Posted June 14, 2018 On 11/06/2018 at 9:05 PM, Pete Lewis said: The common denominator here sounds like the layshaft bearings are in trouble or the mainshaft spigot has died Both are under load in 123 but not loaded in 4th Do check you have oil up to level an empty box makes some alarming noises Pete I have a feeling you could be right about the layshaft bearing, but I am hoping not! as I don't really want to remove the gearbox after fitting it. Is it possible to remove the engine and gearbox together? without having to remove the fibreglass gearbox tunnel? as fitting the tunnel, centre console, sound deadening and carpets was a pig of a job which I never want to do again! Link to comment Share on other sites More sharing options...
Gully Posted June 14, 2018 Report Share Posted June 14, 2018 I've never tried it, but I suspect even if you pull the engine and gearbox as a unit you'll need to take the tunnel out - or at the very least the H frame and carpets to release the gear lever gaiter. I also seem to recall the gearbox mounts are accessed from above (inside the tunnel), then there's the simpler access to the prop shaft bolts... Stripping out the interior and tunnel takes me around an hour (inc,using the radio) - but I had more practice than wanted a couple of years ago! Always takes longer to reinstall though. Gully Link to comment Share on other sites More sharing options...
dougbgt6 Posted June 14, 2018 Report Share Posted June 14, 2018 Gully's right the tunnel has to come off to get the engine plus gearbox out. Engine out is a much bigger job than just taking the gearbox out. Did you cut a hole in the tunnel for gearbox oil top up? a tricky job from underneath. Doug Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 14, 2018 Report Share Posted June 14, 2018 Yes its an inside job realy, you cant undo the prop or tail gearbox mount from underneath its tunneling again i fear. Pete Link to comment Share on other sites More sharing options...
Cookie Posted June 15, 2018 Report Share Posted June 15, 2018 Certainly sounds like layshaft bearings. Nine times out of ten the layshaft itself will need replacing as well as the needle rollers and if it's be been left too long the inside of the layshaft cluster may have worn which means either a replacement cluster or some machining to bore out and sleeve the bearing faces inside the worn cluster. Link to comment Share on other sites More sharing options...
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