Blueprinting Shift Lever

[randywebb]

I'm confused about something on this and maybe those who've done it before can help me out.

I have a late model shift tower (1986 - the one with the front adjustment screw) and am planning to fit it with the SC-RS (M241?) short shifter parts. {The plan is for this to gt mounted in my 1973 911 which already has a 1971 type 911 transmission in it - the one with 1st gear doglegged off to the left, like it should be}


The Seine Systems info on Blueprinting the Shifter say:
To reduce the interference fit, reduce the OD of the shift lever directly above and below the pivot pin hole in the lever as indicated. Existing rub marks on the lever indicate the areas to remove. Remove an equal amount from each side of the lever. The objective is to reduce friction without introducing excessive play.

Shift Housings w/1-piece fork:
The factory-supplied interference fit is approx. 0.020 - 0.025" (0.50 - 0.64 mm).

Decrease the interference fit to around 0.010" (0.25 mm) between Lever OD (Fig. 2) and Fork dimension B (Fig. 3).

... and it talks about grinding the shift lever with a belt sander on both sides.

BUT, in my factory short-shift kit, thelever already has 1 mm + clearance between the lever (which appears to be tapered a bit) and the one piece fork (the bracket shaped thing)



(parts featured on a Natuzzi couch)


So it sounds like I should be looking for shims, not thinking about grinding anything. Right?

If so, where would I go to find 0.25 mm shims with a hole in them?? I assume that if I cut them out of sheet Al they'll just wear really fast, and that I need to use steel.

Maybe I can try to find steel washers?

My assumption is that I need to put 2 shims in - one on each side of the lever (?)

And BTW, the fork weighs 69 grams, while the pivot pin only weighs 30 g. ...

[Gearbox]

I recently just performed the blueprinting outlined in Sherwood's site, along with his Gate Shifter and the factory short shift kit on a 915 housing, so I know what you are talking about. Generally, the fork (bracket thing) is tighter than the diameter of the shifter, but I noticed that if you tweek the fork's sides (bow them out or in) you could get the shifter so it fits perfectly. I still sanded and polished the sides of the shifter, and got the fork set up with zero slop. I guess yours is bowed out a bit, so just tap it on both sides to get the proper fit. Don't get too carried away with this, it's not like you have to get perfect tollerances or it'll blow up at speed, it'll just make the shifting a bit smoother for a while.....until it gets sloppy again, and you know it will Good luck

[randywebb]

Thanks - I looked at your old thread -- fabulous polishing job you did.

I noticed Sherwood's site shows the fork bowed in, so I checked mine. It is flat as can be.

I _could_ bow it in but I'm not sure that is the way to go... if bowed in, it could indeed bow out again from the side to side pressure of shifting over time, just as you allude to. But if I shim it, then wouldn't it be less likely to bow out again? Or not.....

[Gearbox]

I like the way you think Randy, like me, I love overthinking everything I do on the car before doing it lol. But honestly, polish the shifter to a mirror shine so it glides efforstlessly, tap in the sides lightly so you get zero slop, and grease liberally, and you're good to go. Now if you still want to "overthink" this I'm game. By bowing the sides in, you in fact will be strengthening the fork. How you say? Well if you look at how it assembles into the housing, you have a pin that goes through the shifter and fork where the sides will be bowed in, we'll call that the Y axis, then you have the adjustable set screw that holds the X axis that is adjusted just until you have lateral movement (there is also a spring washer in there) so inturn, in theory, you will have pressure maintaining the length of the fork preventing the sides from bowing out again. Now do you have little voices in your head talking to you all the time like me? Mine are saying do the SSI heat exchangers, do the timing chain up grade, it never stops. Is it just me? LOL Good luck Allan

[randywebb]

I see what you mean - makes sense.

Actually, the little voices in _my_ head are saying "don't waste time on this hobby... research the science on the next endangered species to file listing petitions on and get going on some more endangered species lawsuits, before more species go extinct..." -- I never let them force me past 60 hrs/week on that.

[Gearbox]

Man, that's not the little voices, that's my wife lol. But being pragmatic, without extinct species, there would be no fossil fuels, without fossil fuels, we would not have the technology and lifestyle we have today, and yes battling the greedy land developers of the world may be a nobel cause, but hey, when the big asteriod hits it won't really matter, and we get to start all over again in a millenium or two. In the meanwhile, I'm buying and driving as many cars I can get my hands on. Life's short, enjoy the ride.

[Walt Fricke]

Myself, I think Sherwood got a bit carried away with this fine fitting stuff for his fine product.

The most straight forward way to go is the cut and try method. Put the shifter in the holder (but not in the big shift tower) and install the cross pin and its clips. See how much sideways slop there is in the pin. Play around if you want with bowing the holder in. Install washers between the shims and the holder until slop goes away, or mostly so. And be done with that part. If things start feeling too tight, use a thinner washer, or one less washer. Hint: put all the washers/shims on the right hand side - the new cross pin has no extra length there, so you don't want it retracted at all (unless it is now longer than it was a couple of years ago). Plus this way you can preassemble all the washers, and only have to wrestle with intalling the left side keeper when putting the whole shebang together.

What to use for washers? Well, just dig into your washer box and find ones that fit. If too thick, make one thinner (rub over sandpaper or use a file). Of course you could just take a piece of sheet metal from your junk box that was a suitable thickness and drill and deburr a hole in it - doesn't have to be round on the OD.

Washers should be easy to find. I forget what the diameter of the cross pin is, but it is a common size. Bill Walker just found a long bolt that fit when making his home brew version of this. Ground grooves for the keepers (drill press is the closest to a machine tool he has), had the bolt stick way out to the right, and hooked a tension spring on its rar right end pulling down to someplace on the floor pan he made a hook for that end of the spring.

This use of washers ought to also serve to bow the holder in, should that be needed. If close but a bit tight, I suppose you could narrow the shift lever.

If very little slop, and it moves reasonably easily, you should be good with a little grease. No way you will significantly increase shifting force here - if way off you won't be able to get the spring clips into place!

Be sure to use the hose clamps only as a way to locate the hook on the shift lever before welding. If you have a welder of your own, I think it is simpler just to weld the new plate onto the old one while everything is apart. I cut off the ends of the new plate so I didn't have to worry about nut engagement, and welded it on.

Walt Fricke

[rusnak]

I think overly anal Porsche nuts are an endangered species.

Just my own question: shouldn't it be possible to either make or buy a thin washer that could provide the necessary amount of tension/ fit/ clearance?

[911pcars]

Walt may have described my behavior accurately.

The objective is to reduce fore-aft friction without causing the lever to rattle from excessive clearance. Randy, you've accurately assessed your setup as too loose. Most housings are set up relatively tight from the factory. I feel sanding the OD from the shift lever a more precise method to fit the lever to the fork.

However, if the lever-to-fork clearance requires more serious persuasion in either direction, here are my suggestions:

1. To bend the fork outward (more internal space): Use internal expanding pliers to spread the sides of the fork.

2. To bend the fork inwards (less internal space): Measure the beginning space, then sandwich the fork between two large sockets (tape all three together). Apply the appropriate pressure with a bench vise, then remeasure. It doesn't take much. If it's too much, return to step 1.

Earlier shift housings may instead have a two-piece fork. With this type, the lever-to-fork clearance can only be determined after installing the fork in the housing. In this case, sanding the shift lever is the only practical recourse for a tight fit and the addition of shims for a loose fit. However, FWIW, I haven't yet experienced a loose fit with a 2-piece fork.

Hope this helps,
Sherwood

[randywebb]

Thanks Sherwood. Bending it is.

Your site also note the 2 piece fork... maybe the 1 piece is not an improvement in performance but was just cheaper to make?

The one piece fork does have a seam where it is joined at the end - looks like they just wrapped a piece of sheet metal around and welded it.