Modena's progress update

[Aussie Mike]

Originally Posted by SVO 050

I have been changing the reverse switch in my Tremek and looked at the Mal Wood site for info on the box.
I read in the Tremek installation info that you should not try to shift gears above 6400 rpm??
Anyone seen this detail and can explain why?
Cheers
SVO

The job of a synchro in the gearbox is to match speeds between gears so that when the next gear is selected it will slot in easily. It means us ham-fisted drivers can easily select a gear without having to double clutch and spin the box up to match gear speeds.

The synchro is a kind of conical clutch between each gear where one cone is forced inside another cone. They were once brass on steel but now they have organic facings like a Kevlar and carbon fiber. The issue is these clutches like any clutch can only transmit so much power. The can only cope up to a point with the loads to spin gears up and down from high RPMs.

6400RPM is probably the manufacturers recommendation for the limit of what the synchros can cope with.

Interesting fact: The cone clutch design was used as the main clutch in many early automobiles. Clutches were faced with leather or cork. Often the clutch pedal had to be pushed down to force the cone into it's socket and transmit engine power to the trans.

Racing gearboxes like in V8 supercars or F1 don't have synchros. They have dog rings on the gears. These are rings with a hard step on them. As the gear is moved across on it's shaft the edges of the steps on the dog rings collide with a bang, the gears speeds are matched instantly and the gear slots in. Very harsh and only works when shifting hard. Gear speeds need to be matched carefully on downshifts (double clutching etc). Not much good for driving down to the shops but they cope with big HP and high RPM shifting.

Cheers