Triumph GT6 gearbox noises

[philmcgrath]

Hi all. My first forum post since joining in April 2015.

I have an early roadster SWB (no doors) that was built out of a Triumph MkIII GT6 of 1971 vintage. The gearbox (non-overdrive) has developed some low-pitched whirring and rumbling which is worse when the box is cold, eases quite a bit when warmed up and disappears when the clutch is pressed down. In all other respects the gearbox is good. All four gears have excellent synchro, reverse isn't too noisy, no other issues. I am not hard on the gearbox, feeding the power in and not racing up through the gears. It's fitted with a very torquey 2.5 engine so doesn't need to change gear too often or rev high.

I replaced the oil with some fresh Castrol GL-4 EP80/90 and filtered the old oil to see what was in it. Not much in the way of metal, just a few tiny shiny grains. Nothing of note on the magnetic drain plug either.

Anyone have any similar experiences? I suspect a bearing or the needle rollers are on the way out. The box will clearly need to be overhauled at some stage but I am wondering whether I can keep driving until the winter months.

Any guidance will be much appreciated.

[dbazdavies]

Re: Triumph GT6 gearbox noises

Sounds like a main bearing - is it noisy when you coast along ?? you could try a spoonful of graphite powder - works sometimes !!

[philmcgrath]

Re: Triumph GT6 gearbox noises

It doesn't sound rough when coasting. Seems to be only when stationary but hard to tell. Layshaft bearing?

[listerjp2]

Re: Triumph GT6 gearbox noises

Thrust bearing maybe.

Cheaper option.

Adrian

[greyV8pete]

Re: Triumph GT6 gearbox noises

Strange that it is quieter when warm. I would expect it to be the other way around. Not familiar with that box but for whirring noise I would also suspect layshaft bearings and for rumbling maybe first motion shaft bearing. No noise with clutch pressed down and car travelling at road speed indicates one or the other, or both!

I would keep listening for a few journeys and enjoy the rest of the Summer while it lasts. Obviously if it suddenly gets much worse then it needs fixing asap. Peter.

[philmcgrath]

Re: Triumph GT6 gearbox noises

Thanks for the tips. I'll keep motoring and listening out. Assuming it keeps going until the winter (no roof!!) I can then face the aggro of overhauling the box. Not looking forward to it though. Has to be engine out. Then it probably makes sense to fit an exchange unit.

[b_caswell]

Re: Triumph GT6 gearbox noises

If it sounds noisy without the hood it must be noisier than mine and most probably the input bearing on the spigot shaft followed by the needle roller on the nose of the main shaft closely followed by the lay shaft needle bearings. It is possible to rebuild the box without any special tools but would depend how much wear there is on the bearing surfaces that are part of the shafts and lay gear.

[philmcgrath]

Re: Triumph GT6 gearbox noises

Quick update on the gearbox. The noise got a bit worse so I took it off the road. Managed to pick up a really used good engine crane locally off Gumtree. Thanks to Ben for the loan of a lifting eye and the engine/gearbox were out in a day and the box is now at a reconditioner in Falmouth together with a Rimmer rebuild kit. Fingers crossed there are no nasty surprises when box is stripped. The oil didn't contain any swarf or random bits and the gearbox was working perfectly before so I'm hoping the parts in the kit will do the trick.

It's a pity the Mk 1 chassis didn't have a removable gearbox crossmember which would make the job much simpler.