I wanted to create a thread that described the known issues with this transmission and their resolution. This contains the collective knowledge and experience of the CruzeTalk forum for the past couple of years, knowledge acquired from our brothers and sisters over on the Sonic Owners' Forum, and knowledge taken from overseas where the M32 is used in many Vauxhall and Holden vehicles.
This will develop as early as 5k miles and will worsen as it goes by. If you are reading this thinking to yourself "but my transmission is fine," then you don't know what this transmission should feel like. I thought mine was fine until the problem was explained to me. If you have to force your shifter into gear as you accelerate with even a moderate amount of power, you have a problem. I'm talking up-shifting, not down-shifting. I can shift my Cruze up with a pinky. The cause of this is degraded transmission fluid.
1-2 Shift Grind
This is the result of the design of the synchros, a high 1-2 gear ratio change, and the stupid thin OE fluid shearing down too easily. The gear is fine, and the issue is mostly harmless, but it is rather annoying. Since it is synchro related, you will notice it more on the Cruze Eco than on other models, as the Eco has a higher 1-2 shift ratio change. There is no known mechanical fix. However, keep reading.
We have learned from our cousins with Holdens and Vauxhalls overseas that this transmission reaches dangerous operating temperatures with only 20 minutes of in-town driving. It is a very compact transmission and the heat has nowhere to go. A high engine operating temperature contributes to this problem.
5-6 Shaft Lubrication
Filled to the GM recommended level, the transmission starves the 5-6 gear shaft of proper lubrication. This was discovered on the Vauxhall forums when they were losing shaft bearings left and right. The solution was to overfill the transmission by half a quart, for a total of 2.5 quarts.
Fluid, the solution...sort of.
From the factory, the transmission uses a rather thin fluid, chosen for fuel economy purposes. However, it does not lubricate well (see 1-2 shift grind & notchy shifting), and it does not hold well up to heat. The solution to the notchy shifting is new fluid. Our members have used Royal Purple and Redline's offerings, and none of them perform as well as Amsoil Synchromesh. In fact, Royal Purple was the worst fluid we have tried, and the fluid ended up coming out dark and burnt.
This will sound like a sales pitch, but know that this has been tried, tested, and verified by the Gearheads on CruzeTalk. Amsoil Synchromesh completely eliminates the notchy shifting. It has a very high quality formulation of fully synthetic base stocks, and a very good friction modified package that greatly improves the function of our synchros. While it may not completely eliminate the 1-2 shift grind, it does help, A LOT. The 75W-90 GL-4 fluid has been reported to completely cure the 1-2 shift grind for many people. On my Cruze ECO, I have not yet been able to make it grind. Those who can note that even under hard driving, it happens rather rarely, in the range of 2 times a month as opposed to several times a week. Filling to 2.5 quarts total also helps with the heat issue, and provides better lubrication of the 5-6 gear shaft. EDIT: GM has officially updated the transmission fill specification to 2.32 quarts as of at least 05/2016!
Here is the fluid recommended as an OE replacement: AMSOIL Manual Synchromesh Transmission Fluid 5W-30
For tuned vehicles and vehicles driven more spiritedly, I recommend the 75W-90 transmission fluid and transaxle gear lube: AMSOIL Manual Transmission & Transaxle Gear Lube 75W-90
Disclaimer: These products aren't officially recommended by AMSOIL's technical team due to variations in specification (and the constantly changing OE specification). Use at your own discretion, as I cannot be held liable for any side effects or problems. This product is offered as an option based on the success others have had with it.
More information on Gen1 Cruze Clutch and Shifting upgrades: https://www.cruzetalk.com/forum/10-g...-upgrades.html