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Gearbox Making Odd Noise At Idle

TiTAN
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TiTAN Grand Master

TiTAN

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just recently my gearbox has started making clunky noises while idling, the noise goes away if you push the clutch pedal in. it has been suggested that it could be the spigot bush but i know it has a manual one in it and not an auto/none at all.

in the same time it has locked me out of all forward gears 4 times while driving, to get it into gear again you have to completely stop the car moving, select first and it will then work fine again, someone said this could be a synchro ring jamming out of alignment?

any other ideas as to what it could be before i go to the effort of taking the gearbox out?

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Birds Grand Master

Birds

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A damaged synchro won't lock you out of all 4 gears...it can, however, lock you into a gear. A selector issue, on the other hand, can lock you out of all gears.

Locking out of all gears is usually a clutch dragging issue - input shaft is turning despite clutch pedal being depressed, meaning gears will be hard to select as if you're not touching the clutch at all. When you try to engage the gear while locked out, does it crunch or just keep you locked out? If the latter, then I'd move towards a selector issue. It CAN also be a spigot bush/bearing issue, as a jammed up spigot can also turn the input shaft making it difficult to engage a gear. Does it ever happen on first start up? If not, then it is likely heat related - hydraulic systems behave differently under cold and hot operating conditions. The next time it jams you out of gears, check your clutch fork travel under the car while someone pumps the pedal. If there is plenty of travel then it could be the pressure plate.

The clunking itself may or may not be related. It is likely a gear rollover noise, be it a loose piece of metal inside the gearbrox or a missing tooth on your input shaft/cluster. Does it change the clunking when you rev the engine in neutral, i.e. clunking sound disappears or gets louder?

Sorry for the clustered questions and thoughts, there are lots of possibilities with drivetrain issues...the trick is to diagnose it part by part, and there is a logical process for it. You need to get as much information as possible to make the best diagnosis.

TiTAN Grand Master

TiTAN

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A damaged synchro won't lock you out of all 4 gears...it can, however, lock you into a gear. A selector issue, on the other hand, can lock you out of all gears.

Locking out of all gears is usually a clutch dragging issue - input shaft is turning despite clutch pedal being depressed, meaning gears will be hard to select as if you're not touching the clutch at all. 1. When you try to engage the gear while locked out, does it crunch or just keep you locked out? If the latter, then I'd move towards a selector issue. It 2. CAN also be a spigot bush/bearing issue, as a jammed up spigot can also turn the input shaft making it difficult to engage a gear. 3. Does it ever happen on first start up? If not, then it is likely heat related - hydraulic systems behave differently under cold and hot operating conditions. The next time it jams you out of gears, check your clutch fork travel under the car while someone pumps the pedal. If there is plenty of travel then it could be the pressure plate.

The clunking itself may or may not be related. It is likely a gear rollover noise, be it a loose piece of metal inside the gearbrox or a missing tooth on your input shaft/cluster. 4. Does it change the clunking when you rev the engine in neutral, i.e. clunking sound disappears or gets louder?

Sorry for the clustered questions and thoughts, there are lots of possibilities with drivetrain issues...the trick is to diagnose it part by part, and there is a logical process for it. You need to get as much information as possible to make the best diagnosis.

1. Keeps you locked out of all the gears, no crunching it just wont let you select any at all.

2. it doesn't have any issues going in or out of gears with the clutch in normally, only on the 4 occasions that it has done that

3. it has never happened on immediate startup, the car has driven fine for a few km, then it has done it (not up to temp yet for 2 occasions but the other 2 car was at normal operating temp and had been for a bit)

4. clunking sound appears to go away during a free rev in neutral, the sound is also not there while the car is moving in gear. only while idling in neutral

Birds Grand Master

Birds

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Posted

1. Keeps you locked out of all the gears, no crunching it just wont let you select any at all.

2. it doesn't have any issues going in or out of gears with the clutch in normally, only on the 4 occasions that it has done that

3. it has never happened on immediate startup, the car has driven fine for a few km, then it has done it (not up to temp yet for 2 occasions but the other 2 car was at normal operating temp and had been for a bit)

4. clunking sound appears to go away during a free rev in neutral, the sound is also not there while the car is moving in gear. only while idling in neutral

There are still many possibilities, as to what it could be, however I'm leaning towards loose bits of metal inside your box for the clunking sound. Gears missing teeth tend to make a grinding sound that increases with RPM in neutral. Try dumping the oil and see if anything comes out...if not, then do the proper checks to rule it out as a clutch issue and start whipping out the box for a reco or second handy.

Possible that the loose metal is sporadically getting stuck in the selectors and locking you out of gears, or if the clunking issue is unrelated to the selecting gears issue, it could still be a clutch issue responsible for the latter. Hydraulic pressure doesn't change so much with the rest of the vehicle heating up, it tends to work independantly based on continued use of the clutch pedal, thus it will never happen on start up even if the engine/gearbox is warm.

It's a shame gearboxes don't have glass cases!

iseekool Veteran

iseekool

Posted
Posted

Just wondering have you changed the gearbox oil yet?

Had a simlar issue with my IS200 (partially locking me out - until you force it a little).

Change the gearbox oil - No problems...

TiTAN Grand Master

TiTAN

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Just wondering have you changed the gearbox oil yet?

Had a simlar issue with my IS200 (partially locking me out - until you force it a little).

Change the gearbox oil - No problems...

gearbox oil is 6000km old, was changed when i put the engine back in the car.

whole gearbox had a full reco about 3 years ago (~25-30,000km), all new seals, gaskets, synchros etc

TiTAN Grand Master

TiTAN

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Took the car to get checked out by a gearbox shop, they suggested it stop being driven at all after getting it up on the hoist and playing around with it, they feel its something to do with the clutch/pressure plate but cant say for sure until the box is out.

  • 1 month later...

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