Major 1-3 Shifting issues after Synchrotech Carbon Synchro upgrade
 

Fellas!

last week I installed the carbon fiber synchronizer rings by Synchrotech in a spare transmission I ordered On The Line.

I rebuilt it the new unit and installed the carbon synchro rings in place of the old ones. Although I did wreck a few parts in the process and had to take apart my current cars transmission to cannibalize some parts off of it (mostly 6th gear and the bellhousing)

I put the unit back in place and filled it with Lucas Oil 75W-90, link here:

https://lucasoil.com/products/gear-o...hetic-gear-oil

It worked fairly solid for the first two days and now it is plagued with problems with the shifting. Second gear lockout has been made worse and I often find that third will also be unwilling to move as well

I made sure to bleed/flush the clutch fluid with fresh DOT-3 and adjust the clutch for the best travel to ensure the clutch isn't dragging

Right now my thoughts are that the synchro rings were low quality, the oil is improper and isn't being pushed out properly by the synchros, something has worked loose, or the driveline and engine mounts are in need of being replaced

Thoughts? Comments/concerns? I am officially at a loss. I thought this upgrade would help the transmission, not hinder it

Are you using the stock clutch?

EDIT: and why upgrade? Where you have shift issues before changing out the synchros?

I also have synchrotech synchros installed, but frankly didn't feel much difference shifting wise just from them. It's other bits, eg. oil, or clutch, that affected shifting feel more. Imho these synchros might be less for feel, more for longer lasting.

Assuming that synchros were replaced and gearbox reassembled properly, what i'd check:
1) gearbox oil level. Twin MT gearboxes have worse shifting both if over & underfilled. As way to set level is by fillport, worth ensuring car is level, when changing gearbox oil.
2) if lockout was properly adjusted properly and tightened properly and hasn't come loose/moved
3) clutch drag. What is 'best travel' mentioned by you? Does it include some dead travel? Sometimes slight clutch drag might be harder to detect, yet still affect shifting when actually driving. Saw enough cases of overdone clutch pedal travel adjustment mods, "fixed" by reverting it for some extent.
4) from self tried oils had best shifting feel experience with Redline MTL 75W80 + stiffer trans support mount and trans shifter bushing (these will add some NVH though in lower gears with audible gearwhine).

Imho (2.) & (3.) more probable by description of it, & (3.) is easiest to check/adjust. Not sure if any issue might be with oil, as you reported normal shifting during first weeks. For example this post describes very similar symptoms.

Of course it's all assuming that there were no issues with reassembling gearbox and mounting it back. No clue on possible glitches with something done incorrectly. I doubt faults in synchros themselves, imho some glitch in work is more probable.

Clutch and pressure plate is the Exedy Stage 1 Available for this car. Flywheel is stock. I upgraded because I bought the car used, and soon after I got it (bought at 60K km) it started to develop a grind in second gear that soon progressed into a guaranteed grind into 1-3 and sometimes sporadically 4-6. The gearbox would literally grind into 1-3 regardless of shifting style, clutch adjustment, timing, trans oil temperature. It was horrible. I have owned several used manual cars over the years that had that and I know from experience if you let it continue, you eventually lose those gears altogether.


I am pretty sure I nailed it down when I was assembling the car but I live in the land of frost heaves and pot holes and level ground is hard to find. I tried my best to level the car when i was reassembling the car but it is worth investigating

I had another look at the lockout last night and moved it over another 1/16" to the left to give it more room on the 1-2 side.I installed it right next to the shifter in first and second. It maybe helped? But the car was already warm by that point so it warrants more investigating. But I did add more room to the shifter on 1-2

According to me, best clutch adjustment is based on this video from Jacks Transmissions that was posted on the internet ages ago

https://youtu.be/vYJxQyjIhUw

I actually found a shop in town that sells the Motul 300 oil everyone on here raves about. It is expensive, but it might be worth picking up. Some time ago, I put in the Energy Suspension rear shifter bushing, MTEC springs, and cusco shift carrier bushings as well to try and improve the shifting much earlier in my ownership of the car. Stiffening up the rest of the mounts and bushings in this car might have to be the next step

I followed the directions based on the rebuild by Verus Engineering. A lot of the parts only go 'one way' so its hard to put something in the wrong spot, but not impossible if you weren't paying attention. I mention the synchros though, because when I received them, the carbon "fish scale" pattern that exists on them had a few high points on the ends of the scales. only a couple synchros had this, and it was only one high point. Do I think that the synchros are actually the problem? Well no. But the fact that there was some slight defects does make me wonder about their overall quality. But with that said I'm going to recheck my work in a few places and make sure. Next on the list is recheck the gear oil and ensure that the quantity is correct. I will have another gear oil waiting just in case. But that will be the last new fluid I put in. I'll have resigned myself to the fact that oil won't fix anything. I've used a lot

Motul 300 was improvement in feel over OE oil (most oils i tried were improvement. in addition to OE, i had tried mentioned Motul, Synchrotech MTF, but Redline MTL subjectively seemed best). Good bit of Motul 300 is it conforming both GL4 & GL5 standards, as in it can be used also in our torsen diff.
Still, imho lockout misposition or slight clutch drag is more probable causes for hard to engage gears then oil. And why do you need whole new oil volume if it's just to inspect level and add or drain slight bit? Current oil isn't there for long mileage, just since synchro installment job? At most i'd inspect if there are no metal shavings in it.

I'd suggest you buy a new transmission ..... before you drive yourself crazy - :iono:

Do carbon synchros have a bed in period?

If they do have a break-in period. I have found no mention of that anywhere on the internet. On the advice of churchx I did have another look at the reverse lockout plate and I believe it to now be adjusted to where it should be. I don't however believe my issues to be clutch drag related. One advantage of the new transmission is that it has a lot more gear whine than the original unit did. I can physically hear the transmission wind down when the clutch is pressed. And I also raised the back wheels off the ground and checked again and they don't turn in gear

With the lockout plate adjusted, and the clutch not dragging, I had another look at the trans fluid. It was quite full. I'd reckon another 100-200ml overfilled. Like WHOOPS! So far it is behaving acceptably. I'll give it another couple days to a week before I will know if it worked. Took about that long for the problems to begin showing up in the first place

LOL I actually found a new transmission on eBay for around $600 CAD shipped. That eBay trans was the unit I rebuilt with new synchros and put in my car. Came from LKQ on The Ebay. This one had as many miles as the one in my car did. According to the service records, my car had its transmission replaced at 40K km and was at 66k km before I replaced it with the eBay unit that had 27K km on it

more gear whine is 90% probably due stiffer bushings. I had more SC like audible gear whine in lower gears when i changed just those with everything rest stock back then, including oil, synchros and so on.
"I put in the Energy Suspension rear shifter bushing, MTEC springs, and cusco shift carrier bushings as well to try and improve the shifting much earlier in my ownership of the car. Stiffening up the rest of the mounts and bushings in this car might have to be the next step"
- put these back to stock rubber and whine probably will be gone (setting aside noises related to also upgraded clutch, which sound usually different though). I prefer though sharper gearswitch feel, so chose to ignore NVH increase and left poly bushings.
As for break-in .. don't know, just drove normally mine since installing. Didn't observe much change over time in anything.
P.S. if draining excess oil, or some other fix will help (in long term), do report here results. It's always helpful for other owners to have more info on issues and possible reasons/fixes.

I actually like the gear whine. It is quite different from the sound, even with the stiff poly bushings in, than the original (new) transmission that came in the car. Just not used to hearing it. But it's fine. previous (cars original trans) unit was silent all the time even after the hard bushing install

As of right now, the car drives really nicely and the transmission operation is proper and quiet. But I as of now hesitate to say its "Fixed" as its only been 2 days and it went properly for that long after I put the trans back in. I'll have to update in a couple weeks to be sure that the changes and improvements that were done stick around

Did the vendor have any ideas?

Is this the first transmission you've rebuilt?

Update after a few weeks for cars trans

Currently, the car shifts very well. I normally get a couple 2nd gear lockouts and stiff shifts into 4th when cold but the trans warms up quickly with some hard pulls. Not 100% but it is a solid 90

What I did was adjust the reverse lockout plate to have about a 1/16" of play on the shifter when in 1st and 2nd to allow for room when the driveline torques around or just shifts. I also then replaced the gear oil with something my local import mechanic recommended for the BRZ. It is the 75W-90 Full Synth offered by Liqui Moly. it is lots lighter than the Lucas Oil that was in there and stinks a whole lot less too. I double checked all over the frame when leveling the car and left it sit and slowly drain out for over a half hour to be sure all the excess fluid is gone. Hopefully now it has been finally nailed down. The car is a pure joy to drive now and not the chore it was shortly after I bought it

Just wait until you stop using a full syn GL5 oil - then you’ll really start to enjoy it!