T5 Gearbox Oil - KCK RE44 Pro-Shift PAO Manual Transmission ATF

"What oil goes in a T5?" is the question we get asked more than any other. The answer is ATF, not gear oil. A World Class T5 runs its synchros, needle bearings and thrust washers around a thin, friction-modified automatic transmission fluid. Fill one with 75W90 and you get a notchy shift into second until the box warms up, and a gearbox that never quite feels right.

We wrote the full explanation here - why a manual gearbox wants automatic fluid, the four wrong answers you will hear on the forums, how to fill it, and how often.

There is a very direct reason for that. The OEM blocker rings in a World Class T5, first through fourth, are lined with the same friction material used on automatic transmission clutch plates - fifth was the only brass ring in the box. The friction surfaces inside a T5 are automatic transmission friction surfaces, so ATF is not a workaround, it is what the gearbox was built around.

KCK RE44 is a full synthetic PAO and ester based ATF, hot blended in Australia, built specifically for manual gearboxes and transfer cases that specify ATF rather than for automatics. That distinction matters. A generic Dexron clone is formulated around a torque converter and clutch packs. It is not formulated around blocker rings taking repeated shock loads at 6,000 rpm.

TREMEC is named on the bottle, alongside LENCO, G-Force, Hollinger, Quaife and aftermarket sequential boxes. This is not an automatic fluid being talked up for manual use after the fact - it was formulated for gearboxes like yours from the start.

Why it suits a T5

• The right friction package - tuned to grab against synchro lining material rather than slip past it, which is what gives you a crisp change instead of a cold notch into second
• Shear stable - holds its film under repeated hard changes instead of thinning out
• No GL-5 extreme pressure additives - nothing to attack the brass fifth synchro or the bushes
• Thermal stability - a T5 in a track car gets genuinely hot, and fluid life is usually what gives up first
• Suits carbon lined synchros too - if you have fitted a carbon synchro kit, ATF is still the correct fluid

The 2.5 litre does a T5 in one bottle

You fill a T5 to the level plug, not to a measured volume, and 2.5 litres gets there. One bottle, one gearbox, nothing left over.

That is a genuine improvement on the fluid this replaces. The Dexron III ATF everyone used to recommend only came in 4 litre bottles, so every T5 service left you with well over a litre sitting on the shelf that you paid for and will never use. If you are doing a full rebuild and want fluid in hand for the next service as well, the 5 litre is the better buy per litre.

Ordering more than 10 litres

Our online freight rate covers up to four 2.5 litre bottles or two 5 litre bottles per order. Above that the checkout will not offer a shipping option, because larger consignments need to be quoted individually.

If you need more than that - a workshop stocking up, or a club buy - get in touch and we will sort out a freight price for you. Perth customers can also select collection in person at checkout and pick up from the workshop.

If you are topping up regularly

Fluid is not the fix for a leak. The rear output shaft seal and the front input shaft seal are the two usual culprits on a T5, and both are cheap next to the labour of pulling the box out twice. Worth replacing while the tailshaft is already out.

Not just gearboxes

KCK also rate RE44 for high-load transfer cases, and for drag, circuit, rally, off-road and 4WD use. If you have a transfer case that calls for ATF and lives a hard life, the same reasoning applies.