Gearbox Screaming Noise

This year for our lift we’re running a custom 2 speed 4 775 gearbox for our lifter, but when it’s running it makes an awful screeching noise. I love our robot to get other people attention but this wasn’t the kind of attention I was looking for. I think it maybe that the teeth just need to wear in, but if anyone else has had similar problems and fixed them let me know, thanks!

From what we have found, a four 775pro gearbox will always be loud. However, it can be much better if you dry run the gearbox at full speed for five minutes in each direction before basting it clean with compressed air and greasing it.

Usually gear pairs don’t perfectly fit when a gearbox is first assembled, so they need a few minutes running to chew each other up and give them the right amount of slop. Hook it up to a throttle for a few minutes and it should be a lot better.

If you’re using VEXpro 20DP gears, it’s recommended that you add .003 to the distances between your gears. Perhaps there’s a similar advantage to doing that with 32DP gears, but I don’t know what the adder would be.

Do you have any pictures of said gearbox? We’re doing 4-775 single speed for ours and it isn’t loud at all.

No sorry, the pictures I had were on my phone which suddenly died on me

I suggest you remove the motor so you can isolate the noise to the gearbox or the motor. We had a 775 start to screech and found the gear had been pushed on a bit too far.

I add 0.003" to 32DP gears as well and have good results.

My team (TJ²) is in it’s second year of running 4x 775Pro gearboxes on our drive train. I can tell you from personal experience, they are much louder than other gears. The steel 32DP gears used on the first reduction from the motor are the loud part for us. For example, I could hear our drive from the stands in some of our events, and I think our drive team could hear them through the walls in some cases.

Loud isn’t necessarily bad. Without hearing the sound for myself, I can 't tell if it’s something crying for help or all systems go. Could you post a video with the sound for us to listen to? I could send you what ours sound like for some context, if that helps.

The gearbox is in our bag at the moment, but if I had a video to compare to I may be able to figure out it sounds the same.

First check and see that everything is tight and not rubbing the wrong way, such as a gear from one axle touching a gear from another axle in a way it isn’t supposed to,make sure you are using the correct sized spacers and e clips if applicable, and if the screws for the 775 pro’s are tight, then after running at one speed for a short time and a different speed for a short time grease the transmission, I recommend using a white lithium grease, red lithium (red jelly) works too, you should run in the transmission for a bit before greasing, and make sure to lick your fingers clean after greasing(yum). If that doesn’t fix it then you probably have to do something a bit more dramatic.

Do you have pictures of your 4 775 gearboxes yet? I’d like to check them out. Thanks.