Triumph Repair: Gearbox Noise, shaft bearings, clutch release

Question
Hi there Howard, I know that you don't usually deal with GT6 but i assume the problem im having would apply to Spitfire's. When the gearbox is in neutral there's a harsh sound coming from the gearbox, this disappears when the clutch is depressed. I've Drained and refilled the gearbox with oil but the noise is still there. The engine and box have only just been installed in the car so have not been run properly for a number of years. Any ideas? Thanks in advance Jamie  

Answer
Hi Jamie,
When you shift into neutral and the clutch out, The input shaft, the laygear and every gear in the box is rotating except the reverse idler. You can narrow the noise down to a more specific area by doing some driving tests. However, there are no problems that can be repaired outside of the box. The only thing that can make noise outside of the box is the clutch release bearing. To test that all you have to do is to run the engine in neutral as you have and lightly put your foot on the clutch peddle. If you can make the noise go away with light peddle pressure, then it is most likely just a clutch release bearing problem.

For the driving test you can just note when the noise is most pronounced. Run in 1st gear up a grade at a steady speed and go down the grade at a steady speed and run on level ground at a steady speed. Do this in each gear and log when the noise is most pronounced. Keep in mind that 4th gear is direct drive meaning all the gears (except reverse idler) are turning but none are under any load.
When you are in 1st, 2nd or 3rd the 1st motion shaft (input shaft) gear is turning the laygear which in turn is turning the main shaft (output shaft)by way of either the 1st, 2nd or 3rd gear on the mainshaft. This applies a load to the 1st motion shaft and bearing and the lay gear with it's bearings and to the mainshaft which applies a load on the small bearing in the end of the 1st motion shaft that supports the front end of the main shaft and loads the rear main shaft bearings too.
So you can see that there are many possibles for noise. The good part is that the noise maker is easily identified when closely inspected when disassembled.
When you go into or have someone go into the gearbox, you should replace all the syncros and all of the bearings and the "noise maker" if it is not one of the bearings that will be replaced anyway.
You should also read my tech tip on my web site "how to make a straight stick gearbox last" http://mg-tri-jag.net/tech4.htm
I hope this helps,
Howard