Hard to get 1st gear on side shift conversion chassis, shift rod hitting on the original bushing support in tunnel Options

[PlaysWithCars]

Wondering if anyone else has had this issue. This has been a multi-year saga and now I've kind of been all the way around the barn and only made small improvements but I think I've narrowed it down to the final culprit.

Backstory:
1970 914-6 chassis that has a side shift transmission in it that has always been tough to get into first gear. It feels like it just barely gets into gear but once there its never popped out.

When the car was new to me, I didn't have history on the transmission and assumed it was just worn or the shift bushings were worn so I put it on the to-do list to rebuild it someday. In the meantime I invested in a Rennshift shifter and installed it with new bushings at the shift console on the transmission (all other bushings seemed fairly tight). Improved shifting overall, but no real change to the issue with 1st gear.

Fast forward and I bought another transmission to rebuild with the help of the Doc's DVD. Tore down the transmission, rebuilt with a mix of new and used parts expecting the problem would be solved. To my disappointment, no real change in the behavior when I put the rebuilt transmission in. Mind you though, I'm thrilled with other aspects of the rebuild: new gearing (A, F, Ka, S, ZA is a nice combo for autocross / street use), Guard limited slip helped keep the car connected at corner exit. Now this is where I began scratching my head. This is a completely different transmission with no shared parts from the old unit. How can I have the same problem? Clearly its something on the chassis not in the transmission.

So, I started looking real close at all of the bushings in the linkage. As I said each was pretty tight but each had some small amount of play so I started replacing each one with small, incremental improvements made each time. And each time I went through the process of adjusting the shift linkage but still wasn't getting first to work much better. All the other gears? No problem. But first was not cooperative.

Getting ready for the autocross season this year, I decided to try and tackle it again. I'm tired of pulling up to the start line and fighting to get into first. And last season my 16 yr old son started racing it with me. It was heartbreaking to see how it added so much anxiety in him trying to get into first gear so as not to delay the start of his run. So, I went through it all again. Checked bushings, adjusted the shifter and still could not get it better until I decided to adjust the shifter focusing only on the R-1 shifter plane. When I did that? First was like butter, but I couldn't get into the 4-5 shift plane at all. After some more head scratching and investigation I snaked a bore scope down into the tunnel and found what I think has been my problem all along. When moving the shifter left / right into the R-1 and 4-5 shift planes the shift rod is hard up against the support that would have held the bushing for the original side shift linkage (item #14 below). I haven't read of anyone having this issue when a car's been converted to a side shift. Is this a know issue? Is there a common cause / solution to gain clearance in this area?



For now, I readjusted the linkage so that I minimize the interference in the R-1 and 4-5 planes but it is negatively impacting shifting in all but 2-3 gears until I can figure out a solution.

[PlaysWithCars]

Hi guys, thank you for the input. I've been following Raynecat's thread over here where he is solving the same problem: http://www.914world.com/bbs2/index.php?showtopic=351402

But, to answer some of your questions:
- not a -6 conversion, original -6
- using the late style shifter from Rennshift w/ a late style front shift rod
- using a brand new firewall conversion bushing

I think as Raynecat found, there are tolerance stack up, variances in build, maybe slight changes in the center shift rod bend, etc that leads to rubs. I wonder if there could even be variance in the shift fork adjustment in the transmission that require more/less movement to get R-1 and 4-5 shift planes. It wouldn't take much of a change in the adjustment to require just enough extra movement in the shift rod to cause this problem.

@Dr Evil - hey Doc, do you have any thoughts if this situation could be influenced by the adjustment of the shift forks? Is it possible for there to be wear in the shift forks or for them to be adjusted such that the shift "comb" has to move further to engage R-1 and 4-5 shift planes? Could that require more side to side movement of the shifter and contribute to interference between the shift rod and the support bracket in the tunnel?