RED MX5

This is one of the problems people complain about but that I've never seen. Until tonight I've wondered why, but I think R11 and Mikes256 hit the nail on the head. When the car is cold, or in casual driving, each shift is a three step process. 1) Shift into neutral. 2) Engage the synchros until ... 3) the car happily shifts into the next gear. When the engine is cold, this results in a rather leisurely shift, because the synchros respond slowly in the thick/cold oil, but there is never a grind or crunch. The "trick" (if it can be called that) is to put just enough pressure on the shift lever to cause the synchros to start bringing the gears up to speed. This is easier to feel with the RP shifter, but can be felt well enough with the stock shifter. If you get the pressure just right, the car will drop into gear perfectly even when cold.

Once the transmission and engine are warmed up a "normal" shift should result in the clutch engaging just as the engine speed falls to match the road speed in the new gear. This results in a shift that is is extremely smooth and easy on the entire car. For speed shifts, going back to the three step shift is fastest, and allows you to get the clutch fully engaged BEFORE the engine speed drops to road speed. This allows the inertia of the flywheel to solicit a nice chirp from the rear tires.

Anyway, if you get a crunch, you've beaten the synchros for some reason. They're a little slow when the transmission is cold, so you have to be patient. Rev matching during a double clutch will work too, but it's not good to be in a hurry while the lubricants are still cold.

DiamondDave2005

I had tried a few different shift points before, from 3,000 RPM to 5,000 RPM. I was always careful with shifting into 2nd, never speed shifting with a cold transmission, but I crunched anyway.

I grew up driving stick, so it's not like I'm not used to shifting.

Race Miata's suggestion sounds interesting, but it's one of those things I'd need to see demonstrated before trying it myself. After all these years, I'm so used to making sure the clutch is all the way in before shifting, it'll be hard to change

R11

That's it in a nutshell. Pull it into neutral maintaining just the right amount of pressure and let the tranny tell you when it's ready to proceed from there. When it's cold, I'd say "leisurely" is a pretty good description alright. I think the transmission/syncros on the S are optimized for light shifting at full operating temps, which entails the tradeoff in the cold. After mostly being able to shift almost normally during the summers, I have to force myself to consciously slow down as the temps drop in the fall and the tranny starts "talking back" to me .


ron

spa-zz

Umm, no.

The crunch comes from the splines engaging before the syncros have had time to do their job. The syncros do not create the crunch sound.

R11

What I meant is this particular issue is not gear on gear grinding.


ron

RED MX5

I don't mean to be critical of anyone's driving skills or experience. When there is a "crunch" it is due to what we use to call "beating the synchros." As far as I'm aware, it can only be caused by one of two things. Either it's a weak synchro or it's a driver rushing the synchros. Since not everyone has the problems I don't see how it could be a design flaw; I suspect that some of the crunching is due to weak synchros in some cars, and some of it is no doubt due to drivers rushing the shifts a little. If there is anything else that can cause grinding/crunching I'm not aware of it.

Anyone know of any other possible causes?

dolebludger

I have read about the 1 to 2 shifting problem on this board many times, and only felt a very minor "crunch" a couple of times in over four years of ownership. My 62nd birthday present from my wife was a Voodoo knob, which lowers the shift shaft distance for supposedly a faster shift. This should make things worse, right? Well not here. It's just snick, snick, snick. And it also takes the "vagueness" out of that 6 to 4 shift. I can't explain how a supposedly FASTER shifting mechanism makes this situation better, but maybe somebody can.

Thanks,
Richard

spa-zz

It increases the effort due to the shorter length. This naturally keeps you from putting less force on the syncros. I doubt the shift is faster. It's more likely slower due to that increased effort.

dolebludger

Strangely, the Voodoo knob does not result in greater shift effort for me. It could just be my own physical build, and the fact that the Voodoo allows me to attack the shift better. And yes, for me it is faster. Just as fast as "snick."

Thanks,
Richard

spa-zz

Interesting. Too high speed of the shift is one of the main reasons for the crunch. If you're shifting faster, I would expect more crunching. You have one of the better gear boxes, I think.