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mjr
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Post by mjr »

It was, but doesnt last! isostatic is just far too complicated and fragile, too many cheap components. when its worn, it is absolutely horrible and rubbery. I may be wrong, but the isostatic bits only really seem to shorten the gate, not the throw, at least that what I found with various 75's I drove. .,Surely its the long throw that makes for inacuracy, not the gate distance so much.?
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Post by Mats »

x-rad wrote:wasn't that the whole point of the system??
I think it was done to isolate the shifter from the transission vibrations and such.
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Post by x-rad »

Hmmmmm....never really thought about that, Mats

I figured that the name 'Isostatic" meant 'even' force for all gear selections.....
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Re: Short Shift

Post by MD »

So mjr. did you ever finish your shifter project ? What was the outcome?
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Re: Short Shift

Post by mjr »

HI MD, yes indeed. In the end I moved the ball up the shaft and cut nothing at all. I changed the bushings for phospher bronze ones though. I cut off the end of the selector fork at the shifter end, and introduced a kink so that the fork/rod would fit over the crossmember without any fouling. I left the gate crank length alone since I suspected it would make the gearchange too notchy and the gate distances too short, hence prone to selecting the wrong gears. I was right, because simply changing the front end made a huge difference, and the gate distances feel smaller than they did before, without even touching the gate crank. I originally bought the same set up from a local supplier over here, but it didn't lengthen the shifer rod enough for my liking, so I simply pressed the ball further up the shaft another few millimetres. The shift is still quite notchy and mechanical, but the throw is about 35% less and feels very similar to my BMW 1 series shift. I would say its much better than isostatic feel and stays very simple, i.e. nothing to wear out.

the only down side is that the shorter throw seems to increase the spring strength feel on the gear box side, and its a little too much for my liking, so I may at some point put in a slightly weaker spring? The heavier spring feel makes for a little more effort pushing the stick over to 1st and 2nd. I suspect it's because I personally bent the shifter over slightly further towards me, to compensate for the shorter shifter now in the car. I guess shortening the gate crank ever so slightly would probably address this too
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Re: Short Shift

Post by MD »

Well it would appear in the overview that you have made a success of it to your satisfaction which is always the aim. Congrats for having a go instead of just wondering...
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Re: Short Shift

Post by mjr »

cheers mate. Yea I had all the alloy rods etc ready to go and manufacture, but I decided to do just the pivot mod to start with and see how it felt as I went. To my surprise the pivot change alone improved the feel so much that I am well happy with it. As I say though, I may just shorten the crank a smidgen, perhaps a few mm, as 1st and second are still just slightly too far over to make it really slick. BTW I think Mats has it spot on with the ISO set up probably being designed to isolate the shifter from vibrations. Thats one thing this mod does not address. perhaps a small damper coupling somewhere in the longitunial rod would would have been a much better solution. ISO is too complicated, Its a ridiculous contraption. :lol:
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Re: Short Shift

Post by Duk »

MD, what did you make the distance of the gearbox crank/arm centre of the splines to centre of the welded on rod?
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Re: Short Shift

Post by kevin »

Mir , how much did you move the ball up the shaft ( sounds bad) and by how much roughly did you extend the linkage bar? Don't mind me asking. Need to do something about race car.
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Re: Short Shift

Post by MD »

Kevin,

I think for your puposes not having to be concerned about a console, you should do the modification suggested by Daniel which will give you a greater length extension without fouling the driveshaft.

Duk,

Not sure I completely understand the question. I am assuming you want to know the final length of the cut down crank. If that is the case, that would be about 45% of the original.

Here's some more photos of the mods start to finish. Hope they are self explanatory. Involves some trial and error for fit.
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Re: Short Shift

Post by MD »

..a few more to complete the sequence..

You can see that moving the base up on top of the tunnel say 20 -25mm means you dont have to do a fulcrum conversion and shaft thickness reduction to clear the cross member when extending the shaft under the main fulcrum ball.
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Re: Short Shift

Post by Duk »

Sorry mate, I shouldn't go foruming after nightshifts, I may as well be drunk sometimes :P .

The length of the splined arm in the last 2 photo's you just posted, preferably from the centre of the gearbox input shaft to the centre of the rod you welded on.

Good to hear that you 'nana benders and hopefully your Alfa Romeo's are okay :wink:
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Re: Short Shift

Post by MD »

Easy.
Look at photo.
Cut before the "00"
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Re: Short Shift

Post by MD »

Postscript

Something I discovered recently when I was building the Cab....

The shifters out of a 75 are modified already. The length below the ball is longer and the stick itself is made from much stronger tubing so it is less prone to flexing. If you do nothing else and just change the stick over to one from a 75, you will see an immediate improvment in a reduction of the throw length (fore & aft motion) and a more solid feel to the changes.

..not sure what effects this has on contact with the propshaft as I dont use it in that context. Worth a try.
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Re: Short Shift

Post by mjr »

kevin wrote:Mir , how much did you move the ball up the shaft ( sounds bad) and by how much roughly did you extend the linkage bar? Don't mind me asking. Need to do something about race car.


Kevin, pressed the ball up the shaft by 25mm IIRC. when you say linkage bar do you mean the longitudinal bar that runs from the shifter to transaxle?. if so then its a little trial and error. I heated it until it was hot as fk, and kinked it little by little on a roller, until it cleared the cross memer, then cut off the fork end and inserted what was required. this will be different for everyone as it depends how your kink works out, not an exact science I'm afraid. MD has the answer, go with Daniels mod seeing as you dont need to worry about the tunnel. i just decided i didnt fancy cutting the tunnel to relocate the selector etc.
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