Root Cause Found?... short shifter RATTLE
 

That gear stick rattle has bugged me for years.
I've fitted 4 different short shifts, the latest being the IRPv3.
The only one that didn't have some degree of rattle was the TRD version.
I loved the KartBoy, but it was bad...and I really love the IRPv3...but it is bad.

So I've recently decided to spend (many) hours and hours under the car, under friends cars, looking, playing, padding, insulating, greasing, installing, uninstalling, changing bushes, tightening, loosening, pushing, pulling, prodding....you name it.

I think rattle has nothing to do with the shifters themselves (although they transfer the effects differently). It also has nothing to do with the shifter being body mounted or on its original gearbox mount (ie. KartBoy and IRP both rattle)

I believe the rattle comes from the gear selector shaft after it passes through the oil seal into the rear gearbox extension. There is up to a millimetre (and maybe more) of "play" or "wobble" in the shaft, which then vibrates passing along the selector shaft then up to the shifter lever.

This "play" has been evident in pretty much every 86/BRZ that I've now crawled under. There is no bearing holding the shaft in place, it simply sits in a flexible oil seal that allows easy movement, and transfer of internal vibration from inside the box.

To test my theory I took a (large) zip tie, looped it up over the selector shaft near its entry point at the oil seal, and zipped it up as tightly as I could around the bottom of the rear gearbox extension.... securely holding the shaft down. Not practical, and not a real solution.

BUT it worked...no rattle at all in 3rd ( but because it is such an agricultural solution, then 4th worked less well until I changed the position of the zip tie along the shaft.... and of course 3rd started getting noisy again...and vica versa)

Could the oil seal be replaced by a bearing? If not, is there a way of holding the selector shaft firmly, centred in its action, in place (without forcing it downwards)?

Sadly, if I'm right, this is not good news as far as I'm concerned, as it indicates a fundamental design flaw.

Can you pay pictures of what you're talking about? I design mechanical stuff daily and might be able to come up with a solution for you

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Thanks mate, its very late here, but these are the best I can find at the moment.

The gear selector shaft that attaches to the bottom of the gear stick, attaches to the shaft in question at the entry point into the rear gearbox extension, just outside the oil seal.

My gearshift doesn't rattle and never has.

But then, I don't have a short shifter. My is OEM.

Works fine, lasts a long time.

I have had the similar thought but I think it comes from the other end of the floor shift control shaft and where it passes through the base of the shifter. On most shifters this is a plastic bushing, on the IRP it is metal. I also think some of the rattle is the retainer clip and washer. I am going to measure it next time I have it apart and try to find a plastic bushing and washers.

I agree with NOMSG. The shaft passing through the seal should not really be able to "rattle" due to the seal itself. Also, that seal can't be replaced with a bushing or it will leak. I think your next test should be to dampen the joints of the floor shift shaft. Obtain or make a soft or flexible washer that can be compressed to add to the pins connecting the shaft. Perhaps some foam or neoprene can be cut into a washer.

If it is the stub shaft then we could look at making a secondary "seal" that would hold the end of the shaft

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I did check since I have my spare transmission in the warehouse and take this quick video. There is a pivot on the shift rod that has a bit of rattle to it. I don't think it is what is making the noise, since the noise is usually more metallic sounding, but it could be contributing resonance.

https://www.youtube.com/watch?v=5ZN0nQEFmlc

How were you wiggling the shaft? In/out? That appears to be a spherical joint of some variety. You could try packing it with grease for testing

Edit: this is the stub at the transmission tail, correct?

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I am wiggling the shift shaft extension side to side with a little up and down tension. Yes, this is a pivot that goes on the shift rod tail. I didn't notice that pivot before, it moves a bit stiff but there is some play in it.

So do you believe the clicking is at the spherical joint or inside the tail of the transmission?

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I don't think so but I am not sure. I just think it could be contributing to the rattle at the shift shaft extension where it goes into the shifter. On my car with an IRP it is pretty high frequency. I will have to mess around with it when I work on my car this weekend since I need to get under it anyway. It's all just speculation that I have had about the cause.

Sure. It's just when you said the joint was stiff, that would indicate that it can't vibrate. But the shaft inside the transmission could possibly wiggle

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I put a plastic washer on the shifter which I believe got rid of my rattle but it would be nice to have someone else try this and report back:

https://i.imgur.com/Wo3hHok.jpg

The pivot is tight to move but the rattle in the video is from that pivot which I found odd.

Exactly what I was thinking along with replacing the sintered bushing in the IRP with plastic bushing.