Snaps

So I recently picked up a '09 and I'm having a shifting issue I would like some input on. When going from 2nd to 3rd at say 3k RPMs or more I'm kinda locked our or get a grind. At lower RPM's it goes right in no problems. Also it doesn't matter if i "double clutch" attempting to go into third like I would on an old truck with bad or no syncros. Car has 10k miles in it and was just serviced by previous owner with a resurfaced flywheel, new clutch and new slave. Ive only had this problem in 3rd right now but dont think its happening when downshift from 4-3 or 5-3 at high RPMs. I will be flushing the clutch fluid today.

INTRCUL

Super common problem on all C6's because of the crappy clutch master cylinder. At least a new slave was put in recently. Use fresh DOT4 brake fluid when you flush (Castrol SRF is popular) and flush both the master and the slave if you can. Most likely, the problem will still be there and will require replacing the master cylinder which is a heck of a lot easier than the slave. Either get the newer style C6 master with the black fluid reservoir or a Tick master for an extra $100-200 or so. Both can be replaced in 1-2 hours by any shade tree mechanic.

If you're feeling extra DIY, you may be able to mod the OEM master, but only attempt this if the pedal isn't sticking to the floor. If it sticks the piston is probably bad or cracked. If it just "hangs" on some 3rd gear shifts you can do the mod. Do some searches and there's an old magazine article (maybe in some generic Chevy mag) that a shop owner went the extra mile to find the cause of why so many C6's and F-bodies shift like crap. he pulled a master and slave and got it all working on a test bench so he could trace what happens at each step. He isolated the issue to a reduction in diameter of the fluid line between the master and the slave, which slows down the flow of fluid to the slave and slows clutch engagement. When shifting fast it, the clutch isn't fully disengaged fast enough before a quick handed driver attempts to catch the next gear and it feels like a lock out. 3rd is the worse, and the heat from repeated shifting or burnouts makes the problem worse. When this is happening the slave also isn't fully engaging, possibly leading to accelerated clutch wear due to slip. By slowing down the release of clutch fluid GM hoped to reduce shock on the transmission and reduce failures, but created a whole slew of shifting problems by doing so.

When disassembled, you can bore out this restriction with a basic drill bit and hand drill. I can't remember the diameter so you'll have to find the article where he pin mics the diameter of the line and the restriction and then bores out to the same diameter of the line. Or you can just buy an adjustable Tick and be done with it, because there's a chance the newer style GM master still has a restriction in the line.

Gary '09 C6

...and while you're at it, check the shift-linkage adjustment.

wera78

what did you use SRF in ? curious? I'm a former superbike motorcycle road racer and used SRF for my brakes hands down the best brake fluid bar none!!!!!!!!!!!!!
question

wera78

I'm also having a grinding feel in my 2011 17k zr1

INTRCUL

GM uses a lot of hydraulic clutches and brake fluid is used in both the slave and master cylinders. DOT3 originally, then eventually DOT4 in the last few years of the C6. Motul 600 is another popular one I forgot to mention but a lot also uses off the shelf Prestone DOT4.

Snaps

Update, Ive flushed the MC a bunch of times including driving on it for awhile and letting it flow. Still no change, now Ive tried to adjust the shifter and to my surprise there was a MGW short throw. I knew something felt off while driving it was incredible notchy. Rowing through the gears seems easy but 3rd still has a grind. But like i said its not all the time, just when I bury it in 2nd and try to upshift. I think now it might have something to do with the shifter itself not centering properly. Because i can hammer down and if i slowly guide it is slips in just fine.

Snaps

So I have found the time to swap shifters with a friends stock shifter, still getting the grind into third. Was doing some driveway shifts standing still in all gears clutch in and out and even got a grind going into third when not even moving! Took some video of me driving down the road with the console off, is it just me or is that a lot of drivetrain noise? Sounds almost like rubbing of metal on metal in all gears. I'm I just being paranoid and this is normal? Should I start a re-attack on the dealership who did the Slave, Flywheel, Clutch work?

INTRCUL

Sounds normal to me and is actually quieter than I would have thought given that you have a completely exposed tunnel there. I can hear more lifter tick (normal) that transmission gear whine.

Master cylinders usually cause a fast shift to feel like it's locked out, but there shouldn't be and grinding. I kinda glazed over the grinding part in your original post. Unfortunately that problem is either linkage alignment or synchro related. Carefully go through the instructions on how to check the linkage alignment, especially since the shifter has been swapped multiple times now. I think you can download the instructions from the MGW website.

If it's not an alignment issue, it's probably something in the tranny. Praying that it's not synchros which would require a rebuild, you can try to swap fluid. I lost track of the differences between the years of when paper blocker rings were used and when carbon fiber were used. I would hope carbon rings were used in all ZR1's but I'm not sure. If they're paper you need to stick with organic fluid, like OEM and maybe Red Line if they still make an organic (ATF?). Most of the good ones are synthetic and a lot of ZR1 guys use Royal Purple, but there a lot of good ones to choose from. I think Red Line MTL might be synthetic and I think GM SynchroMesh is organic but am not sure if that was the factory fill or not.

Just to make sure....are you letting it warm up fully before doing any crazy shifting? Even the OEM fill needs a good amount of warm up time and can easily grind when cold or be hard to engage gears even when taking it easy. It's part of the design. Because this was GM's 1st 200+mph capable car, the fluid must hold up to all the extra heat generated when under load for that duration on a top speed run or during road racing. Getting lubrication to remain stable at high temps usually means sacrificing cold temp performance. My daily driver shifts great at freezing temps, but would overheat quickly at track temps. The ZR1 is the exact opposite. Usually by the time the engine oil is above 170 degrees the transmission should be good to go. If you have a DashLogic or any other scanner you can tap into the transmission temp gauge if you're curious.

timmyZ06

The only way to fix it, is a Tick master cylinder!! I tried evrything else, ,mantic clutch new slave didn't work! The OEM master is a heap of ****, dont even bother!

I also had the MGW shifter and lower box as well!