Grinding noise when selecting gears but gears select ok

[b3nson]

Hi guys! Just wanted to get some opinions as it's really annoying me!
My Triumph Dolomit Sprint, 4 speed manual with overdrive.
Gears select perfectly hot or cold, clutch biting point is great.
New braided clutch hoses fitted, problem still similar.
Basically:
After a longish run (over 1 1/2hrs at speed) and in warmer ambient temperatures sometimes (and not always) when you got to select gears (mainly 1st or reverse but sometimes other gears) the gearbox grinds as soon as you put it in gear with the clutch pedal depressed. The gear still selects ok and as soon as you take up drive/get to the biting point the noise goes away and the car drives 100% ok.
Any ideas?

[Imperial]

I'D start checking your gearbox oil level, and when did it last get changed?

[kevins]

So does it crunch as you put it in gear or still make the noise if you sit there with the clutch depressed and it in reverse or 1st?

If it is the former the clutch is probably dragging a little which is not usually enough to turn the gears but with the lower resistance of hot thin oil does.

[b3nson]

Apr 24, 2017 11:39:28 GMT kevins said:

So does it crunch as you put it in gear or still make the noise if you sit there with the clutch depressed and it in reverse or 1st?

If it is the former the clutch is probably dragging a little which is not usually enough to turn the gears but with the lower resistance of hot thin oil does.

The second one, noise starts as soon as it's in gear and continues until drive is taken up. Can't feel anything odd through the gearstick (no extra resistance etc).

Gearbox oil level is spot on, although has not been completed flushed and changed for a while.

[nomad]

I guess it can happen when the car is at a standstill (as you mention reverse)
If it's making the noise when it's in gear and the clutch is pressed but the car is stationary, it has to be something before the gearbox (the front shaft out of gearbox can't be turning when the car is in gear and not moving)

Maybe the clutch release bearing or the spigot bearing in the end of the crankshaft ??

[jikovron]

Imo as Nomad points out thats akin to a worn/dry spigot bearing noise where the input shaft end OD essentially is walking up the ID of the bush and falling back/batting about at high frequency in a similar way that a curse word old plastic pram wheel behaves, ive had that attention grabbing noise with 4 cars thus far mainly where ive hurriedly and subsequently badly turned a spigot bearing just to get it running.

Excessively worn thrust bearings on the crank might do similar if they are totalled and allowing mechanical contact elsewhere, easily checked via crank pulley axial play.

[b3nson]

Apr 25, 2017 11:14:16 GMT jikovron said:

Imo as Nomad points out thats akin to a worn/dry spigot bearing noise where the input shaft end OD essentially is walking up the ID of the bush and falling back/batting about at high frequency in a similar way that a curse word old plastic pram wheel behaves, ive had that attention grabbing noise with 4 cars thus far mainly where ive hurriedly and subsequently badly turned a spigot bearing just to get it running.

Excessively worn thrust bearings on the crank might do similar if they are totalled and allowing mechanical contact elsewhere, easily checked via crank pulley axial play.

This would make sense as far as noise is concerned, but why would this happen only after a long journey and not from cold?

[jikovron]

Potentially temp having an effect on oil viscosity which possibly could reduce the harmonic threshold of the input shaft or indeed thermal expansion of the spigot bush and crankshaft.
One thing i remember with my skoda was that the noise manifested itself if i rolled the car down a slope in gear to bump start it, the dolomite however only did it while stationary