[DaveN]

Is this not a common problem with any replacement knob due to the lack of mass as compared to the OEM knob?

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[flash]

i think it has more to do with the lack of the rubber expandable dampeners which are inside the OEM shift knob, and how they isolate the shift knob from the shifter and from the vibrating piece below - all of the aftermarket shift knobs have screws and such, which directly connect the shift knob to the shifter, thereby allowing direct transmission of the vibration

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[Cloud9...68]

I think the buzzing definitely comes from the linkage, and not from the knob itself vibrating against anything. In my case, I most recently wrapped the shifter shaft with teflon plumber's tape, which should thoroughly isolate the shifter from the shaft, but it didn't make a bit of difference. Mine buzzes like crazy, and any speed, all the time, including idle. Drives me up the freakin' wall, which is a big reason why I almost always drive with the sunroof off, even in the 100+ degree central Texas summer. Clark's garage says that a common cause of the rattle is some sort of missing shift lever bushing (item #2 in the blow-up diagram he shows on his site), but I can't tell from the diagram what this bushing exactly attaches to, and I don't know anybody else in town with a 968 to compare to. [img]style_emoticons/<#EMO_DIR#>/mad.gif[/img] [img]style_emoticons/<#EMO_DIR#>/mad.gif[/img]

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[blue968]

I added that spring shim to make it as tight as possible and that didn't work.
I had also drilled 3 holes in the shifter and and installed rubber it to help reduce the vibration, helped a little but still there.
I am going to try to find a small rubber hose to fit around the shift shaft and get it to slide in the bar to help isolate the 2 metals, probably will not last long but just want to see if it will work.

Thoughts

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[blue968]

Hey Cloud,

Mine only vibrates at 2K and is fine every other RPM, but I COMPLETELY agree with you regarding the buzzing driving you up the wall. I just did mine today and I'm not sure if I can deal with it, If I cant fix it I will probably put the stock shifter back on.

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[flash]

you need to use a pliable component, like the "accordion" formed rubber to isolate the vibration - no closed cell solid membrane, nor high durometer rubber (like a hose or something) will do the job - wrapping it with tape, or anything that, which merely fills the gap, will not work - all those things do is make a more solid connection between the vibrating component and the shift knob

fluid might work, if you could figure out how to get that in there

injecting something that dries pliable might too (like a very soft silicone - softer than RTV) - to do this though, you will need to completely remove the shifter assembly, invert it, inject it, let it dry, and then reinstall

you will also not be able to use the set screws in the shift knob, so keeping it on the shifter will be totally dependent upon the tension limits of the injected compound

good luck

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[DaveN]

I would be more inclined to fill the shift knob base with lead to add mass and lower the resonant freq of the knob and thereby suppressing the connnected linkages ability to vibrate. I know Flash doesn't really agree but If it were me I would test this theory out; maybe a combination of extra mass and the rubber damper is the answer.
I'm all for a solution as I would like the same shift knob but I couldn't live with the rattle either.

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[Cloud9...68]

I don't see how there's enough room between the shaft and the shift knob to fit a material with the properties Flash is describing, though I agree that doing so would probably be pretty effective. I wonder if different people actually have different problems, though. Mine sounds like a vacuum leak on steroids, and, as I said, it's ALWAYS there, whereas Blue968's only buzzes at 2K rpm. Of course, his has a different shift knob than mine, so we're dealing with multiple factors. Mine definitely seems to be emanating from the linkage below the shaft, but of course it can be very tricky to diagnose where exatly it's coming from. I have the original knob - I think I'll try putting it back on just to see if this actually cures the problem. If it gets rid of the infernal racket, I may find myself in not too big a hurry to put the GT3 knob back, pretty as it may be...

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[flash]

dave - a few have done that - talk to ds968 about it for example - no good - it's not appearing to really be a mass issue - it isn't the knob that's buzzing - it's the connection below it - the knob just amplifies it because there is no dampening

you might cure it by adding mass to the shift linkage though - not sure what that would do to the shifting feel and effort

agreed that there is likely not enough room as the shifter exists now - you would have to open it up like the OEM shifter is and create room for a material that can dampen the vibrations

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[Cloud9...68]

"agreed that there is likely not enough room as the shifter exists now - you would have to open it up like the OEM shifter is and create room for a material that can dampen the vibrations"

Flash,

Sounds like a plan. Now stop working on that silly supercharger and get to work on something that's REALY important [img]style_emoticons/<#EMO_DIR#>/wink.gif[/img] [img]style_emoticons/<#EMO_DIR#>/laugh.gif[/img]

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[flash]

lol - true enough

seriously though - until we started talking about it, i never thought about adding mass to the linkage rod, but the more i think about it, the more i think that might just work - i think that a shaft collar clamped to it just might do the job

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[Cloud9...68]

"seriously though - until we started talking about it, i never thought about adding mass to the linkage rod, but the more i think about it, the more i think that might just work - i think that a shaft collar clamped to it just might do the job "

I try to support your products as much as I can (the lower suspension brace, clutch high poressure line, and heat shield are on my car, and the chassis brace and supercharger will be as soon as I can come up with the cash), and a fix to the shifter buzzing would be something I would order the instant it became available. I sense a groundswell of support for something like this...

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[Fox944]

Design 1 products rock. I never thought about it untill i read your post, but i have several D1 products in my car.

-Lower Brace
-Strut Brace
-Firewall Brace
-Short Shift Kit
-Heat Shield

very happy with all of them.

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[DaveN]

I definitly think it's a mass issue and maybe the linkage is where it's at. Seems to only happen when people change from stock knobs(?)
We all remember our old friend F=MA. Increase the mass and lower the acceleration vector which is inversly related to Freq. So if you add mass the resonant freq that's is bothering Blue968 should be displaced to a lower (or dissappear) harmonic.
I would like a new knob (yea yea I know [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img] so I will be very interested in the outcome of Clouds knob reversal. (yea yea I know [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]

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[flash]

could very well be the solution to add mass somewhere along the line - i do get the physics, but i also am aware of the OEM design and how it works - i figured that out during the shift kit design process

i think i have the right size shaft collar here, and the next time somebody comes over with a buzzing knob, i can clamp it on and see what happens

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[Cloud9...68]

Has anybody tried simply removing the knob altogether? I wonder if the removal of the weight and rubber dampening provided by the stock knob would make the linkage buzz as bad, or even worse, than replacing the stock knob with a lighter one. I'll try puttting my old knob back, as well as leaving the knob off altogether, as soon as I finish my taxes, which I will tackle as soon as I log off.

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[blue968]

Hey guys,

I'm glad this is getting discussed and hopefully resolved. I really love the knob and confident it can be resolved.
I did remove the whole shifter and just had the shift linkage by it self and it had the same vibration at the same RPM.
Then installed just the lever and same vibration at same RPM.

I went on Clark's Garage and read that there is a plastic bushing located in the tranny and tends to get worn. I am going to put the car on the lift and see if I can locate it. My opinion is you eliminate the source it will rectify the problem.

Thoughts

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[ds968]

I believe there is one under the car at the rear, but I heard it's a PITA to get to it, to replace it

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[blue968]

Is there a DIY write up somewhere??

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[flash]

i have yet to see this plastic bushing - there are bushings at the rear, but i cannot see the coupling of the linkage to the rod

   
   

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