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Brad,
I think "danger" is too strong a term. I doubt there is any danger of using either a universal coupler, or any style of precision bush in the shift coupler.
I too doubt that smooth shifting will accelerate wear. By far the greatest hazard to the transmission is the driver - driving style and lack of mechanical sympathy more that anything else. Any device that encourages or assists the driver in making better shifts is going to help a transmission like the 915.
It is more a matter of compromise.
The round hole bushes do not allow sufficient pre-load-free misalignment. This will add radial loads to the bearings in the shift mechanism and the bearing bore for the main shift rod where it protrudes from the transmission. This might require more frequent servicing of the shift mechanism bushes, or perhaps some long term remedial work on other parts.
The universal joints offer an unequalled balance of precision and misalignment freedom. The compromise is that these are the most expensive solution.
As with the round hole bushes, a second consideration is the potential of noise being transferred from the transmsission through the shift mechanism.
The stock components have the lost motion fore and aft, making neutral about 1" long as opposed to about 1/4" long when you install any product that eliminates the slop. The compromise in this case is the extra free play and the longer shift lever throw.
An interesting comparison between all the products mentioned here would be the longevity. New factory bushes feel good for how long? and new aftermarket bushes feel good for how long? XX brand Universal joint feels good for how long. This BB is probably one of the best resources to set up such long term tests.
With the newest, new delivered 915 coupler now 17 years old, I think it is safe to say most cars would benefit from some attention to the coupler, even if only to restore the shift mechanism to the factory intent.
Regards
Hayden
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