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."

Anyone?

Nissan has a habit of fixing a problem by using slightly less prone to fail parts. I wouldn't be surprised that they 'toughened' up the 5th gear synchro a few times and it's still shitty. That's what happened with the steering lock. They had four revisions before removing it completely in 2012 and later US models. Rev D is the version to be installed via the recall notice, but it had known failures on this forum long before the recall was even issued.

I have a late model 2011 FWIW. 5th and 6th gear synchros both started showing signs of wear under 20K miles. I've just tried to avoid stressing them for the past 40K miles (I'm over 60K now).

When you say they are showing signs of wear, what are you referring to specifically? Grinding?

Yes, grinding. I can grind 5th and 6th gear on demand shifting normally. But with a little bit of patience it does not grind at all - I just hold it at the gate for a moment while the engine RPMs drop.

It's still unacceptable Nissan can't build a transmission that doesn't grind

My first to 2nd gear can be a little stiff when cold but after that i have no problems.

I feel shifting slower is better for the synchros. I don't feel that fast shifting every gear is necessarily better for the transmission.

Of course slower shifting is going to cause less wear on the synchros. Assuming proper shift timing. I don't think anyone here said that fast shifting is better for the transmission.

My only comment is that fast shifting, when done properly, should not wear out the synchros significantly faster unless you're just ripping through the gears every time you drive. If you drive mostly with casual, patient shifting, then the occasional fast shift at high RPMs should not be causing excessive wear on your synchros.

The synchros are crap in 5th and 6th. I had my tranny completely replaced under warranty about 5k miles ago. I really think it's either you get good ones or you don't. Nissan really has a knack of having issues like this with their cars.

No issues with the new tranny but it only has 5k miles on it. Oh and I added 250hp/tq since then so I wouldn't blame the tranny if it craps out on me. :rofl2:

So... sort of stupid question to ask and it's in line with my OCD about my car...

A while back I swear I was having the same issues as the OP in terms of the SRM acting funny when sometimes up shifting into 5th gear from 4th. I now understand it was driver error as I was hitting the gate of 4th very slightly on my way to 5th.

However, for a period of about 2 weeks I was trying to replicate the issue by up shifting from 4th - 5th between 4-5k rpm continuously all the time, during my commute, during my spirited driving, etc. I must have done a few hundred of these upshifts in that RPM range. However, I was very careful about these upshifts and never shifted hard or too fast. I would go up from 4th, pushed the shifter to the right and up into 5th - I never once diagonally up shifted and always kind of eased it into 5th during these up shifts.

It remains smooth as butter but I can't help but ponder if that did any damage to the synchro but continuously up shifting or if I accelerated any kind of wear. Again, it shifts great for the record.

If you don't experience any grinding now and it's smooth, I can't imagine you didn't anything that accelerated wear. I think it's as simple as that

Don't drive around with the weight of your hand or arm constantly resting on the shift lever.

I hear ya...It's just an uneasy feeling knowing that I possibly accelerated wear on that synchro from the higher rpm (4-5k) shifting

I never heard of this. I thought once the shifter is locked into gear then it wouldn't matter

I have a 12 with about 56k miles on it and I had my transmission replaced twice, one for 5th gear and the other for 6th gear. The first time I fought with shop foreman the second time they just put it in there. I'm a senior tech (at lexus so noises bug me a lot) and I was not about to have him tell me its normal lol it happened in 10k-12k mile intervals If i remember right the first one was around 12k and the next one around 22k. I drive the same as I have then and the third transmission has been fine, and recently I've experienced random sticking csc and clutch slippage issues (after shifting to second at times the pedal doesn't come up all the way like as if it looses pressure and the rpms just go to red line and burnt clutch smell comes right after and the pedal is very soft and then it regains pressure. They already bled it and put in gtr fluid as if it would magically solve everything.) Also the way I found my synchros failing was either shifting from 5th to 6th and 6th to 5th.

Google "resting hand on shifter" and lots of info will come up. It was one of the first things I was taught when I starting driving manuals 25 years ago and Im pretty sure it still holds true with todays manuals.

So high RPM shifting isn't really bad for the synchros so long as they are executed with care by not slamming the gear and fast shifting and basically just easing into next gear. I searched about this online and it seems really only 3 things are bad for synchros:

- Skip shifting
- Fast shifting
- Hard shifting

The fact that the 4th to 5th up shift remains smooth even at high RPMs probably means I didn't do too much damage or caused any major addtl wear

Firmly move the shifter into the next gear, but do not rush or force it. Even when I drive fast, I still shift smoothly and don't try to rush the shifts, and I do not powershift. I leave that crap to the drag racers on Youtube.

Im pretty paranoid about this especially cause its hard to source replacement syncros. I shift slow (just hold it at the gate and wait for it to fall in) on upshifts, and on most downshifts I let SRM help me to do a double clutch downshift. I have to double clutch my little ford ranger with 255k miles or it wont go into gear and big rigs for work....so I get a LOT of practice.

I wish i could source out synchros also.... my G is currently stuck in 5th gear awaiting the replacement transmission.... this sucks...

I've seen kits with syncros and bearings for about a grand on various websites. Also there is a complete new transmission for sale in the marketplace right now I believe.

Pretty sure Z1 sells new 6MTs for under $2K. If bearings and synchros cost $1K plus rebuild labor, there's no question in my mind that a whole new transmission is the better option.

And yes, there is a brand new 6MT posted up for $1500 local pick up in the FS section (I believe local is CA).

I think it's a little cheaper than that since he has a G and its not rev matching. The G tranny is slightly cheaper since it doesn't rev match.

I think you're right ($1800ish IIRC). So even better :tup:

Sounds about right. I looked into it before I turboed the car just to see worse case what it would cost if it failed.

Does Level 10 or anyone offer upgrade services for the 6MT?