I had a concersation witha friend the other day about weather or not changing gears in a syncro box without the clutch does any damage.

Looking around on the next there is equal arguments on both sides, and both make sense.

I have a bad habit of doing it in my pootrol since I drive trucks regularly with dog boxes, and I grew up driving the farm hacks that didnt have the clutch still working correclty.

Assumeing that you dont crunch gears and mtch revs etc, is there any extra wear and tear on the box?
Some say the syncros wear out faster, some say its fine. I dunno?

Opinions people?

If you can match the revs correctly, then there will be no problem at all, but if you can't, then don't.

The synchro is simply a form of brake that is applied to the rotating gear that you are about to select. It uses spring pressure to push a brass ring with a conical face against a matching & highly polished steel cone on the gear in question.

The idea is to either slow down or speed up the gear that is attached to the input shaft [via the cluster in most instances] This 'synchronises' the rotating speeds of the two parts that are to be connected via a dog clutch arrangement. It's the rotating mass of the cluster, the input shaft & the clutch disc that bust be slowed or accelerated, but if you don't touch the clutch, & you don't get the revs right, then that little synchro brake is trying to change the speed of the flywheel & the whole bloody engine too.

It doesn't take Einstein to figure out that this part is seriously overloaded & will wear quickly if the driver gets it wrong, but the driver with a gentle touch & a measure of patience in allowing the engine to slow, or rev up, will get a great deal of satisfaction as it just snicks into engagement with the most gentle pressure on the lever & no grinding noises from the box. It's an art.

OK thanks for that Dodgeman.

That was the line of thought that I had. I was sure that it didnt do anything bad as long as you get it right. Ie no crunching, no forcing etc, and it just effortsly slips in and out of gear.

Like you said though its an art, and I find syncro boxes harder to do it to then a dog box.
ironically, I usually do it when I am feeling lazy, and as such probally dont do it very well. Lucky for me that nissan make gearboxes that are indestructable!


thanks again for the easy and accurate advice from this forum.

You're welcome.

In reality, the synchro tries to adjust the speed of both the input shaft as well as the output shaft at the same time, but the output shaft is connected to the driveshaft, diff, wheels, & these are connected to as much as several tons of vehicle, so the output shaft side of things becomes the unstopable force while the much lighter cluster/input shaft/clutch disc are the items that are effectively 'synchronised'

It's all easy enough to grasp when you think of it.