Spraybar Mod For Gearbox And 3Rd Gear?

[R32 TT]

Hi guys,

Has anyone fitted an electric oil pump and cooler to their GTR gearbox? And/or have you done any mods to the return to direct oil directly at 3rd gear?

Everyone knows GTR boxes tend to break 3rd gear (most common). I happened to pull down my PPG box to fix a simple syncro issue on first gear and we noted wear on third gear.. no wear on other gears.

PPG have looked it and seem to think its lack of oiling.

I am running Motul 75W140 - so a good oil and yes it was 'full'.

It was suggested that with a hard launch, gear oil moves to the back of the gearbox, engulfing 1st and 2nd gear, but leaving 3rd with little on it.. by the time you do get into 3rd, there may not be sufficient oil to protect. And then of course you spend more time in 3rd than the previous two gears... hence wear on the teeth.

So perhaps - all these broken 3rd gears are partly because over time the gears get worn due to lack of lubrication.. then one day you give it some hard accel and bam 3rd gear breaks. Most people assume the gear was not strong enough - but perhaps it was prematurely weakened?

I note plenty of mods for thing like Porsche 915 boxes, rally cars etc that introduce spray bars to spray oil directly onto the gears for this very reason. And of course cooling the oil onto the gears doesn't hurt either.

I'm about to design something up to do this - but before I reinvent the wheel - has anyone done this kind of mod?

thoughts?

[tricstar]

Wow Matt. Very interesting.

[jiffo]

I think your spray bar lube plan has merit for bearing lube and cooling if heat is removed via a suitable external cooler.

But having seen older style sugar mill gearing (transmitting over 1,000,000 ft lbs torque) tear teeth from pinions/bull gears, always fitted with lube spray bars, and to hear that lube crack out from the meshing gears with the noise of a 30/30………If it's not designed for the torque, lube can't stop the damage.

I may be wrong but typically in my 5 speed RWD cars, 1st and 2nd simply couldn't be loaded with the available hp due to wheel spin. Even 3rd would break away as the engine reached the peak power band.

Perhaps a GTR is simply reaching that traction grip point in 3rd and as such the box must then cope with the full power.

4th was direct and so the strongest gear in the box.

[MrStabby]

Hmm, from http://www.sau.com.au/forums/topic/414977-gearbox-oil-level-question/#entry6655671

"I'm getting it rebuilt at Award gearbox and diff, they will replace everything with new and do a internal mod to help with the oil feed to the front" - I wonder if that is related.

Would be nice to know which oils have a good boundary anti-wear additive pack (eg high levels of zinc and phosphorus) which is all 3rd gear would be left with if the oil has sloshed to the back. I couldnt find an oil analysis for Motul 75-140, but here's one for Redline MT-90 which has way higher zinc and phosphorus than the "universal averages", but i'd imagine there is a lot of cheap crap oil making up those averages. It would be interesting to see how the Motul compares as another high end oil.

[R32 TT]

Thanks Jiffo - that does make sense.

now we've had a closer look at the gears some opinions are that the oil shear just couldn't cope. Perhaps this was because it was under-lubricated, or perhaps simply the oil could not take it.

I just realised that I did not note in my first post the box originally ran Castrol 75W90 Syntrax in it for the first 200kms of 'hard kms' or so - and only recently was running Motul 75W140. The question might be that perhaps the lighter oil couldn't withstand it, and perhaps the damage was done then..

Either way - its interesting its only on 3rd - and your explanation could be a valid one.

Cooling the oil onto third just might give the extra 10% it needs to avoid shear though... we won't know until we try I guess.

[R32 TT]

Thanks Adam,

I might give Award a call and see what their thoughts are on it..

I've always run Redline Shockproof in my stock box.. PPG recommend the Motul 75W140 though - but as above - can't now be 100% certain that was the oil in it when the damage was done.