I need to ask a few questions about the "poppet spring" in the 5 speed manual gearboxes;

1 - Can i remove/replace this spring/bolt without the gearbox falling apart?
2 - Does this spring act on the select arm shafts like i believe it does?

This is part of my amputee/manual project. I believe (hope) that there is a difference in the spring rate of this spring between the 3.5 and 3.8 (380) gearboxes. I'm keen to try a poppet spring out of a 3.5 in my 380's five speed to see if it makes the shift lighter.

The difference is shift feel between my sons 3.5 and my 380 is night and day - the 380 shift is HEAVY. Well, heavy when you're an LAE amputee.

Question one is most important. If I can take this spring out easily enough I'll just measure it up and have a few custom springs made. Or, initially, source one from an old Magna gearbox.

I gather from studying the images in the manual that this spring is used to locate the shaft/s carrying the selector forks of the gearbox. or, it the very least locates the shaft connected to the shift cable. This is the "notch" you feel with you shift back and forth with the gear lever.

Here's an image for reference;
http://i.imgur.com/5HOOIdl.jpg

As always, all help appreciated and rewarded with good karma and warm hugs.

UPDATE:

Some research reveals there are three of these things and they do actually work directly on the selector fork shafts.

Images;
http://i.imgur.com/V42X2O6.jpg
http://i.imgur.com/cXyRtmj.jpg

Can't comment from experience but i'd be surprised if the box fell apart. Numbers are from an export model F5M51 3rd gen


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You may be disappointed though, I just looked at a 380 cat and it has MD771660 also so you may have to check with the dealer to double check

Gearbox will not fall apart, its one of the first things to be taken off and last things to be put back in. Its to hold the gear forks in place

Pretty sure the spring is inside the bolt assembly and not something you can remove without destroying it all.
Put a washer under it and put it back in, it'll reduce the pressure it holds the detent against the notch in the shaft.
You should be able to back it off out of its threads and keep trying the feel until its good, then measure the space for the appropriate thickness shim or washer?
But i suspect it'll make the box more prone to jumping out of gear.
I would think that you may get better advantage with increasing the leverage on the throw of the shifter, but that obvioulsy has the downside of increasing the distance you pysically have to move the shifter, this might not be suitable for you?

But i suspect it'll make the box more prone to jumping out of gear.

On the old Sigma rear wheel drive gearbox, the shifter detents were simply a short bolt + washer, a spring and a weight.
Each shifter fork has 3 positions, neutral and one of the selected gears, ie 1/2, 3/4, R/5.
Interlock mechanism ensures two of them are in the neutral position, while the third is in neutral or one of the two gears.

Problem I see is that if you weaken any of the springs, it is possible for one of the shift forks to move from its neutral position accidentally, so it tries to mesh a gear unintentionally. So it is not just a matter of selecting neutral on whichever shift fork you are using, accidentally.

ie you are in 5th, but the 1/2 shift fork moves about and tries to select 1st or 2nd. Guess what happens next?

(Just a hypothetical, I'm sure the relevant spring can be weakened a bit without danger. Shims under the bolt head, as suggested above?)