Jump to content
SAU Community

Gearbox Making Odd Noise At Idle

TiTAN
 Share

Recommended Posts

TiTAN Grand Master

TiTAN

Posted
Posted

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?

Link to comment
https://www.sau.com.au/forums/topic/394714-gearbox-making-odd-noise-at-idle/
Share on other sites
Birds Grand Master

Birds

Posted
Posted

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

Posted
  • Author
Posted

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

Posted
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

Posted
  • Author
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...

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

Posted
  • Author
Posted

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...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • MBS206
      Duncan's V37.......race car?

      By MBS206 · Posted

      Ahhh, I need the whole head unit. I definitely needed to roll back through and review your setup, ha ha! Neat setup they have going on. I just need a full double din head unit. But I want good and responsive. I might have to review what the likes of pioneer have out these days.
    • albyz34gt
      34 de+t conversion using s2 stagea automatic transmission, engine harness and ecu

      By albyz34gt · Posted

      Ok so after much research and talking with knowledgeable people I've got my turbo conversion done and it's all running great other than 1 small issue.  Car has remained auto with the na auto and tcm, I've used a stagea ecu with. NIstune board and everything is great other than my gear selection on the dash. It illuminates park, reverse, neutral, 3rd and 2nd. But nothing drive or what gear your in when you pop it into tiptronic.  I'm sure there is may e 1 wire in the ecu plug I need to move to rectify this. Dose anyone here have any ideas?   Cheers guys
    • Duncan
      R32 GTS (RB20DE) Injectors Replacement

      By Duncan · Posted

      Sorry I haven't been following all the detail, so you may have tried this. Does it idle with the tiniest bit of throttle you can add? You've mentioned the IACV, does it have an AAC valve and have you adjusted it at all (ie, screw the idle adjust screw all the way in, then back it out a couple of turns until idle is stable)?
    • GabsReDeal
      R32 GTS (RB20DE) Injectors Replacement

      By GabsReDeal · Posted

      My bad, I unplugged the one underlined in red instead of yellow before. With the car started, after unplugging the IACV (the one underlined in yellow), it idled at around 400/500 for 3 seconds before stalling. Attempting to start the car without the IACV will not start the car.   It does stutter and sputter for around 5 seconds before dying. However, immediately after starting it, you can already hear some slight sputters from the exhaust.   It won't start with the AFM unplugged. If it is when the car has already started, it stalls in a few seconds.   Yesterday, I did take some logs using Nistune of 3 scenarios. Car idling till it stalls Car idling and unplugging the IACV Car idling and removing the AFM I also have some previous logs of when the Car is idling till it stalls and when driving and it cuts. I am not really knowledgeable enough to understand what to look for. After every test, car idles rougher and rougher, until I have to stop. It will be fine the day after.
    • GTSBoy
      Wheel Sizes & Offsets For Skylines

      By GTSBoy · Posted

      There is no difference between a 17x8 and an 18x8. The total diameter of the tyre needs to remain +/- the same (so you don't mess up the gearing, speedo reading, and clearance when turning front wheels..... so you just need to use a lower profile tyre on th 18 than you do on the 17. /rocket surgery.
×
×
  • Create New...