Originally Posted by DaveFab

Anyone who's spoken to us will know that gearboxes have been an issue for us for a while now. It's a known weak point in the mx5's drivetrain, once you're over a certain torque figure gearboxes, even the 6 speed variety, become a disposable item. Fun as it is to drive a car back from a track day with most of the teeth rattling around in the casing (it's not fun) the novelty of changing gearboxes had well and truly worn off for us.

There are many theories why the gearboxes don't last and the reason we find most believable is high torque causing excess friction, leading to high temperatures. We believe the high temperatures introduce two problems.

1. The fluid starts to break down and loose its integrity. The film strength of good quality gearbox fluid is such that there is no metal to metal contact when the gears mesh, as soon as the fluid breaks down the teeth touch, friction and therefore temperature increases and a vicious circle begins.

2. The second problem is the casing itself. As the temperatures increase the alloy casing beings to expand and flex, this would only be by a tiny amount but it is possible that it's enough to allow the gear mesh contact patch to change or to effect a bearing or two. It's telling that it's generally 4th gear that lets go, as this is the gerear canoet furthest from the supporting bearings.

Anyway - the outcome of all of this theorising was that we decided reducing gearbox fluid temperatures wouldn't be a bad thing. Keep the fluid within its operating temperature and it will retain its properties, the housing keeps its tolerances and all should be well.

With the kit designed and high quality components sourced we fitted it ready for Germany. A dedicated oil pump draws the fluid from the drain plug on the 'box through a super fine filter before sending it on to the cooler core. It then re-enters the gearbox via the fill point. We designed a special bracket so the core can be installed out of the way of stones and speedbumps. A second bracket secures a Spal fan to the core, this means it doesn't need to be positioned directly in airflow - giving even more mounting options. Both the pump and the fan are triggered by a temperature switch, so it's a real set and forget system, exactly what you want on track.

The gearbox cooler works. Never have we had a gearbox in the car that can go more than 15 minutes on track without starting to feel notchy. With the cooler we comfortably drove to the ring, did 40 laps, then drove home and the shift still feels great.

Originally Posted by allofit

Several years ago a British fabrication company called DaveFab built an EFR 6258 powered NA at 20psi & ran it around the Nurburgring for 40 laps without munching their 6 speed box.



Serxio of OneLapHeroes drove the car for 5 back-to-back flying laps of the Nurburgring before it developed a misfire and melted a piston through.

Originally Posted by technicalninja

Thanks Tran!
Put's it in a whole different perspective when you get the whole story.
Cooling the gear box IS a good idea.
Sourcing from the drain is fine but I'd want my feed back into the box into a pipe with spray nozzles at each gear.
Sort of like the piston squinters in a BP

Originally Posted by allofit

I think 35 laps of the Nurburgring in the hands of even moderately talented drivers, putting down "365hp/330ftlb at the flywheel at 20psi" would qualify as a test of the gearbox cooler? .

Originally Posted by allofit

Is there anybody here running a gearbox cooler?