Preserving transmission synchros
 

Hey guys,

Whatever manual car I've had has had their related online forums that have a lot of topics on synchros going bad, usually 3rd and 5th gear. On these forums it seems the 5th gear synchros aren't that durable either. I currently have a 2014 Nismo but my previous 350z had a 5th gear synchro issue and it happened first upon a simple downshift from 6th to 5th - from that point on, it would grind every now and then.

So I'm curious, is there an inherent design flaw in the Z transmission, where, over time, the synchros will just start to fail? Is there a reason it's more prevalent in 5th gear rather than 2nd or 4th? Even if the driver is very careful about shifting, is synchro failure still inevitable?

Are there any best practices to preserve the synchros in this car that involve driving habits or maintenance? My car is covered till 2021/100k miles but I'd still like to avoid any problems if I could.

Be gentle with your gear changes especially when ever switching 1st and 2nd gears. A non defective syncro can last you hundreds of thousands of miles if you don't be aggressive with your gear changes all the time. Oh and follow the mfg. maintenance recommendations.

Are high rpm (5-6k rpm) gear shifts necessarily bad so long as I don't bang into the gear and ease my way into the gates?

Do you mean shifting slowly? Mine becomes clunky when I shift slow in low rpm and very smooth when I shift quickly in high rpm. Am I actually doing more harm going slow?

I use to grind 1st - 2nd every time no matter how slow I shifted. I switched to Redline and I don't grind at all. I find that the Z seems to like slower shifts, or rather unforced into the shift gate.

not sure if your 350Z was an isolated issue or not, but usually the first plan of action is to try different tranny oil. my G is 04 and while it was tight in the early days, no issue with grinding. honestly i dont think ive ever grinded the gears on my G over the 10yrs.

hell, i grind my 2.5 yr old honda fit more than my G and Z total years combined (15yrs total) :icon17:

I feel like the synchros are pretty shitty in the Z. Sometimes it just acts like a unsynchronized transmission. I skip gears pretty regularly and have found that you just have to be patient with it. I like to shift from 3rd or 4th directly to 6th gear when I'm accelerating to merge onto the highway, but I have to hang out at the 6th gear gate waiting for the engine to slow down to match drivetrain speed. If I don't, it will grind, guaranteed.

All that being said, I hardly ever grind the gears. When I was still learning the vehicle, I had 1-2 grind a couple of times, but those were 100% my fault. And after about 20K miles, I started getting the grind going from 4th to 6th too quickly. Nothing I couldn't control with some practice and basic adjustments to my driving habits. I've been running Redline since 15K miles, also.

Is high rpm shifting necessarily bad for synchros even if it was done carefully and gently (not slamming gears and letting the shifter slide into place)?

I would say there is nothing gentle about my high RPM shifting. But if done properly, the excess wear is minimized. Hard shifting at high RPMs is always going to wear on the synchros more than normal, casual shifting. But it shouldn't significantly decrease the life of the synchros unless you just do it all the time or do it improperly.

Even though I clearly have some synchros that are wearing as indicated by my grinding when upshifting from 4th to 6th, I have never experienced grinding on a hard sequential shift at high RPMs.

What do you guys consider rpm high for shifting in this car? I've been driving stick for many years and with my past cars I would shift around 2.5k (6k-ish redline). With this car, because of the 7500 rpm redline, I find myself shifting higher... around 3.5 - 4k rpm. Is this bad for the synchros? Again, I'm gently shifting and not forcing the shifter... I just let it ease it's way into gear nice and slow, no fast shifts here.

To me, high RPM shifting is 5.5k+ with this car.

:iagree:

This car likes higher RPMs than most MT cars I have experience with. I find myself casually shifting as high as 4K RPMs on occasion. 5K and up is high RPMs.

The Z's transmission comes kind of stiff when you first get it. With some time it will loosen up and be smooth, especially with some redline in it. I like to agree on one thing. The Z with the stock clutch and flywheel takes a little bit longer to rev DOWN when UPSHIFTING gears to match the next gears rpm. I hear you can have faster down revs with a lightweight flywheel. Most likely a performance clutch would help and also more stiff motor and tranny mounts. Not sure about any side effects. Some people complain they hear noise or something with a lighter flywheel.

In regard to a base transmission without Synchro Rev match

Shifting gears while the clutch isn't completely disengaged will cause wear and tear on the syncros. Like I preached before, its better to go to the floor with the pedal when shifting, especially if you are a newer manual driver. Better safe than sorry IMO. Yes, we all know the true engagement point is about halfway down on the pedal and not the floor... but if the clutch is even slightly still pressed up against the flywheel during a shift, its going to transmit that torque throughout the transmission, and eventually you'll be saying "can't find it, grind it".

You'll be fine, quick drastic changes do the most harm. High rpms put a lot of stress on everything, not just your transmission. But, plenty of people track this car getting it close to or at redline often under high load and still have their engine running fine for years now. You can change the fluid the Redline MT-85 or similar if you want the added piece of mind or feel you have similar issues to what people described above.

http://www.the370z.com/diy-section-d...il-change.html

Any truth to upgraded 5th gear synchros?
 

Came across 2 posts mentioning Nissan upgraded the 5th gear synchros in the later model Zs. Is this true?

http://www.the370z.com/1556425-post14.html

http://www.the370z.com/1884615-post10.html
"Well known that the Z has crappy synchros.

They toughened up the 5th gear synchro in mid10 and again in early 11. By all measures the mid11s seem to have dramatically better 5th gear behavior."