Z51 Shifting Issues: 1-2 Grind
Intermediate
Joined: Aug 2019
Posts: 48
Likes: 8
I understand, yes quite possible but this was not the case in any sense. This transmission did not want to shift into 2nd gear more then half the time. It was defective. When I sold the car I told the new owner of my issue with the trans. A year later he contacted me to say GM had “rebuilt” the trans, but with no improvement. So there you have it. A skunk in the woodpile .
Melting Slicks
Joined: Feb 2018
Posts: 2,193
Likes: 1,055
From: North Texas
Both sides of the synchro need to work properly for a 'good' shift. (smooth, no block out or crunch.)
The engagement side, the side with all the 'points' and the clutch side , the side that grabs the shaft speeding the shafts up or down to get them both to the same rpm.
If one side is not working properly, you will have shifting issues.
The engagement side, the side with all the 'points' and the clutch side , the side that grabs the shaft speeding the shafts up or down to get them both to the same rpm.
If one side is not working properly, you will have shifting issues.
5th Gear
Joined: Nov 2022
Posts: 5
Likes: 1
So this is damage accumulated on your tranny, and it doesn't happen during upshifts, but rather during downshifts. If you're feeling vibrations during the shift, especially when cold, it's fine, synchromesh gears are doing their job. If you feel outright grind, however, it means that you synchromesh gears are no longer effective in syncing gear speeds. These are very high torque cars with relatively high weight, and the transmissions come with big gears to withstand it. As such, they can't be rushed during shifting, or the gears and synchros start taking a beating.
Another important point to mention is rev match feature. If the car did the rev match before transmission gears are ever engaged during the downshifts, you'd likely never have this issue. However, the rev match in Corvettes only engage when the synchromesh gears are already engaged (you can feel the vibration of the engagement before the rev match), and as such, the transmission is not protected (only engine / remaining driveline is). If you, however, blipped the throttle yourself at neutral before your downshifts to the neighborhood of the expected RPMs, you could've greatly increased the life of the synchros, and keep your buttery-smooth transmission. Since this has to be done in neutral, it's also called double-clutching, which is used to increase the speed of the main shaft (Neutral is still connected to transmission shaft).
Anyway, long story short:
Another important point to mention is rev match feature. If the car did the rev match before transmission gears are ever engaged during the downshifts, you'd likely never have this issue. However, the rev match in Corvettes only engage when the synchromesh gears are already engaged (you can feel the vibration of the engagement before the rev match), and as such, the transmission is not protected (only engine / remaining driveline is). If you, however, blipped the throttle yourself at neutral before your downshifts to the neighborhood of the expected RPMs, you could've greatly increased the life of the synchros, and keep your buttery-smooth transmission. Since this has to be done in neutral, it's also called double-clutching, which is used to increase the speed of the main shaft (Neutral is still connected to transmission shaft).
Anyway, long story short:
- Shifts (especially downshifts) in any manual car with high torque engine cannot be rushed. Don't let the rev match fool you.
- It is the downshifts that cause most of the damage, so focus there if you want to keep your tranny buttery-smooth.
- Car's rev-match feature helps, but only to a small extend.
- You can do most of the work done by synchromesh gears by merely double-clutching and getting the engine to the target RPM range. You get used to it, but if it's too complicated, just shift to neutral, blip, and then engage clutch, shifting down to the gear.
