Gearbox Oil

[Nifter]

I realise that this topic may have previously been done to death but with the demise of Blatchat I was after some advice.

I have a standard 5 speed T9 gearbox which has recently started making an unpleasant graunching noise when changing from 4th to 3rd. I suspect it's a synchro problem, unexpected with only 3000 miles and 4 years old, but before I go to the hassle of a gearbox refresh I wanted to investigate different oils.

Many people seem to advocate Redline but there doesn't seem much consensus on exactly which oil to use. Having said that I'm totally open to suggestion based upon others experiences.

Any thoughts would be gratefully received.

Dave

[V7SLR]

Use any good quality 75W/90 GL4, it's what the box was designed to use.

[DCL]

I've found Redline MTL (and MT90 in other boxes) does restore the the effectiveness of the synchro and gear change. But it does it at a cost - and that cost is a higher wear rate of the synchro cones and maybe other parts too. If you analyse the oil when it is removed, you will see wear rates are higher than other oils. On a newish box, like yours, it is worth trying it for at least one oil change then reverting back to a normal GL4 (or GL5, if specified) of the correct grade. I found this aided the running-in process and the synchro remained improved.

All IMHO of course!

Edited by DCL on Saturday 25th October 11:27

[downsman]

One thing worth checking is if the clutch is releasing fully. I had a couple of grunchy gearchanges on a long run recently and adjusting the clutch pedal stop by 5mm cured it

[Nifter]

Thanks for the advice guys, I'll most likely give one of the Redline oils a go and see how I get on.

On the clutch front I only get this problem changing into 3rd - would a dodgy clutch not cause problems with all gears?

[k20erham]

Hi blip the throttle as you leave 4th for 3rd, letting the clutch up briefly as you do, like heeling and toeing better still if you can perfect that, the synchro's wear because they have to bring the next ratio up to or down to speed, the proccess above does exactly that, it will slow the wear rate down and stop the noise, which is actual the engagement teeth on the next gear and selector ring ( so both of them are wearing too)

[Nifter]

If only I weren't incredibly bad at heel and toe! I keep working at it though...

[downsman]

It probably isn't the clutch, but strangely, once moving, I only noticed the problem changing between 3rd and 4th. I did get a bit of graunching going into reverse though which is what made me think of the clutch.

Keep practicing heel and toe, it is one of the great things about driving when you get it spot on