Lotus Elan and Lotus Elan Plus 2 Forums

20 miles ago a knocking noise that varies in speed started in gearbox area -
This noise is present in all gears and if clutch pedal is depressed - knocking noise stops.

I disconnected drive shaft and ran engine / gearbox to eliminate driveshaft etc and same knocking phenomenon detailed above still exists.

I had suggestions from input shaft bearing to the release bearing.

Trying to get idea prior to pulling it all apart

Any thoughts gentlemen?

Thank you
John

If noise is the same frequency in all gears this would suggest a fault on the input side, first motion shaft or laygear problem.
FWIW

Yes same frequency though noise speeds up with vehicle speed.

It was your comment that you disconnected the drive shaft that prompted the thought of engine speed related not road speed.

Blocker rings?

What does it do when in neutral? You said noise stops when the clutch is so if in neutral it still makes noise with clutch out then I'd bet something under the housing (release bearing or clutch). If quiet in neutral with clutch in and out then I'd bet on something in the gearbox. Either way, engine out to resolve.

I'd guess you've got a broken tooth off the input shaft gear or its mating gear on the laygear (cluster gear), except you said the sound happens even in 4th gear.

Roger

SENC wrote:What does it do when in neutral? You said noise stops when the clutch is so if in neutral it still makes noise with clutch out then I'd bet something under the housing (release bearing or clutch). If quiet in neutral with clutch in and out then I'd bet on something in the gearbox. Either way, engine out to resolve.

Throwout bearings work only when the clutch is depressed, otherwise the input shaft spins at the same speed as the flywheel.

Input shaft bearings tend to howl when worn. I agree that thumping sounds like a missing tooth somewhere, but curiously if it's shaft speed the cycle is going to be at least 1,000 times a minute.

There isn't much in there that can thump without breaking stuff. I'm sure you'll figure it out when it comes apart.

denicholls2 wrote:

SENC wrote:What does it do when in neutral? You said noise stops when the clutch is so if in neutral it still makes noise with clutch out then I'd bet something under the housing (release bearing or clutch). If quiet in neutral with clutch in and out then I'd bet on something in the gearbox. Either way, engine out to resolve.

Throwout bearings work only when the clutch is depressed, otherwise the input shaft spins at the same speed as the flywheel.

Agree, but wondering what would happen if one of the clips broke or came loose - might act normally when clutch depressed (for a while) but be loose enough to clang around when the clutch isn't depressed?

I have seen coil springs from the clutch plate or arms from the pressure plate diaphragm spring break and fall out and then thump as they get hit occasionally by the moving parts as they sit in the bottom of the bell housing.

cheers
Rohan

Test number 1:

Whilst stationary put the transmission in gear and depress the clutch pedal. Under this condition the transmission is eliminated as everything inside has stopped spinning from input shaft rearward.

Test number 2:

Whilst stationary put the transmission in neutral and don't press the clutch pedal. Under this condition the release arm is unloaded and free and the gears inside the transmission are all turning but not transmitting drive nor of course is the mainshaft turning.

Test number 3:

Have a poke around with an inspection camera through the bellhousing release arm aperture and see what things look like.

The clutch appears fully intact and no debris was present in bellhousing

rgh0 wrote:I have seen coil springs from the clutch plate or arms from the pressure plate diaphragm spring break and fall out and then thump as they get hit occasionally by the moving parts as they sit in the bottom of the bell housing.

cheers
Rohan

What type of throw out bearing do you have. Flat or round face?

Well , I dismantled the gearbox - nothing is looking out of place - all gears are in good shape as are bearings ! Took clutch pressure plate and disk off and these look a ok too !
Only thing I can think of is the release bearing - but there is No Knocking noise in neutral, so I can?t think the release bearing is slapping the pressure plate (and I see no witness marks on the pressure plate diaphragm.

As well as the release bearing arm, release bearing pivot pin and release bearing clips check the engine crankshaft for excessive end float - the action of the release bearing on the clutch diaphragm spring will temporarily eliminate the slack and quieten any noise. The crankshaft thrust bearings may be worn or have been installed the wrong way around. Also check the flywheel pressure plate and flywheel to crankshaft attachment bolts to ensure they are correctly torqued.