Gearbox and Clutch FAQ / troublshooting
Given so many people have problems with their gearboxes/clutches I though i'd write this up. Shoot a reply if I have missed something.
When changing gears, there is a 'crunch' / 'catching' noise for some gears only
This is most likely due to synchro wear as the synchros are failing to bring the input shaft and output shaft to the same speed so the gears can engage. If the problem isn't too serious or only happens at high RPM when shifting up/down a gear, you could either try changing your transmission fluid or trying a thinnger grade oil. Note however that this is just a temporary fix. You can reduce the effect of this by rev matching while changing gears.
When changing gears, ALL my gears 'crunch' / 'catch'
This could be due to a coupe of different factors so lets look at the more simple reasons.
1. Check your clutch fluid (or cable) and make sure it is operating properly. A clutch that isn't disengaginig properly can cause problems while shifting. Try a fluid change or tighten your clutch cable.
2. Check all your engine mounts as a moving tranny could cause problems when shifting.
3. Check your slave cylinder mount on the transmission and the master cylinder for any leaks/worn seals.
There is a whining / whirring noise when driving (gets louder as I accerate) but goes away when I put the clutch in (disengage it).
This tends to point to a worn input shaft bearing (ISB) or other bearing within the gearbox. The ISB is the most common to fail. The best way to diagnose this is to let the car idle and listen for the noise. Then put the clutch pedal in (disengage the clutch) and you will probably notice that the noise will die out. A very slight noise is OK however if it is very loud and noticable you will want to change your bearing(s) before they fail.
I get a whining / whirring noise when I put the clutch pedal in (disengage the clutch)
If you get a similar noise to the above when you disengage the clutch and have your foot on the clutch pedal, this is most likely your thrust bearing (aka throwout bearing) which is worn and needs replacing. this isn't as expensive as changing the ISB because the thrust bearing is actually outside the gearbox.
There is a squeaking or similar noise WHILE i'm operating the clutch pedal only
This shouldn't be too serious and is most likely due to a lack of lubrication where the slave cylinder piston meets the release fork OR poor lubrication of the release fork/thrust bearing. You might be able to spray some grease by removing the slave cylinder dust cover as a temporary fix.
For cable transmissions, it is the same as above but also check the clutch cable to see if it is rubbing on anything.
The clutch only seems to engage right at the top (Ie only bites right at the end before I take my foot of the clutch)
Generally, as a clutch wears out you will notice this happening as the material on the clutch disk wears. If your clutch is new/resonably new however, try giving your clutch fluid a flush and also check your slave cylinder mount to make sure it is fastened in the correct position.
My clutch fluid level has dropped but I can't see any fluid leaking?
Inspect the slave cylinder area on the transmission and check for any leaks in the engine bay. Also have a look at the slave cylinder from the cabin side. Put your head under the steering column and have a look against the firewall/carpet where the clutch pedal activates the master cylinder. If there is a leak you may have to replace your master cylinder seals (or buy a new master cylinder).
