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Mnaual Gearbox Conversion
2

Mnaual Gearbox Conversion

Mnaual Gearbox Conversion

(OP)
Hi,

I would like to be able to modify a 5 speed manual gear box so only 2nd and 3rd are to be used for forward movement as well as keeping reverse. The desired movement for the change would be as simple as it normally would be for changing from 3rd to 4th, the clutch would also need to remain.

Any information greatly appreciated

Thanks
Grant

RE: Mnaual Gearbox Conversion

Ummm

Only ever move gear lever to 2nd or 3rd or neutral or reverse positions.

To go one step further place an obstacle in the way of the lever so that it can only move to those positions.

Regards
Pat
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RE: Mnaual Gearbox Conversion

(OP)
hahaha thanks, I'm trying to achieve a basic 2 speed shift in retrospect. The problem I face is that the gearbox is a standard H pattern with 2nd to 3rd being on a diagonal shift, I was hoping to find some way to keep the ratios of those two gears but have them in line with each other, make sense?

Regards
Grant

RE: Mnaual Gearbox Conversion

Not really. The shifter will operate selector forks. Each fork has 3 indented positions which are:-

Engage the gear forward of the selector.
Engage none.
Engage the gear behind the selector.

The H pattern chooses which selector you are moving, so lever far left hooks the 1/2 selector, lever middle hooks 3/4 selector, lever right hooks a two position selector that can engage 5th or none. past the reverse lock out then further over hooks the reverse selector which may actually slide a gear on a splined shaft rather than engaging syncro cones and dogs on the sides of the gears on the mainshaft.

Try to get an old non repairable gear box from the scrappers and pull it to pieces and see how the selectors main shaft, lay shaft and cluster gears work together.

Regards
Pat
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RE: Mnaual Gearbox Conversion

Does the tranny have a cluster gear or is it individual gears. The reason I ask is you may be able to re-stack the 2nd and 3rd  gears on the same selector with blank spacers for the other gears.
At any rate as others have said you need to address the each gear selector for your 'H' pattern.

 

I don't know anything but the people that do.

RE: Mnaual Gearbox Conversion

(OP)
yes that was what I was thinking of doing; rearranging the clusters so that they basically 'swap' 1st for 2nd and 2nd for 3rd..??
I'm in the middle of a house renovation at the mo so this been put on hold for a month but in the mean time, Ill just keep gathering info and annoying you guys!

RE: Mnaual Gearbox Conversion

It is really only gear boxes designed for racing only that have a splined lay shaft where you can change the ratios on the stack. virtually all production boxes have a cluster gear on the lay shaft. Some have a set up where they have a half lay shaft, half main shaft arrangement like VW Beetles.  

Regards
Pat
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RE: Mnaual Gearbox Conversion

You could do it by grinding off the synchro teeth on 1st gear and 4th gear, locking the 1-2 and 3-4 shift rails together, defeating the blocking mechanism that prevents simultaneous movement of the 1-2 and 3-4 rails (but retain the blocking betwen 3-4 and R rails).  See what I mean?  As you moved to 2nd, it would also be moving the synchro hub to engage 4th, but nothing would happen with 4th gear because you have prevented the hub from engaging the teeth on 4th gear.  Same scenario for 1st gear when 3rd is engaged.

RE: Mnaual Gearbox Conversion

You guys have my head spinning...

Rod

RE: Mnaual Gearbox Conversion

Further to Ross's idea, you could actually remove the unwanted gears from the main shaft and replace them with spacers, and lock the linkages together so you select 1 and 3 together and 2 and 4 together.

Regards
Pat
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RE: Mnaual Gearbox Conversion

The thing I would worry about is the synchro hub.  I think it might bind up if not supported at both ends of travel.  Ideally you would gring the mainshaft or countershaft gear teeth off on 1st and 4th but leave their synchro teeth there, to prevent the hub from cocking when slid that way.

RE: Mnaual Gearbox Conversion

(OP)
A few good ideas but Ive been talking to some mechanic friends and one of suggested a 2 speed power glide. Thoughts?
I think it would be a lot simpler, no need for modification...  

RE: Mnaual Gearbox Conversion

IIRC, 1st gear in a PG is around 1.8:1, 2nd being direct.  

Can your application tolerate that much gear ratio spacing (or a loose enough torque converter to crutch it)?  

Was your original plan of using 2nd and 3rd in a conventional 5-speed manual intended as a way of getting around the rather large "gap" between 1st and 2nd that's common to most such gearboxes?


Norm

RE: Mnaual Gearbox Conversion

Powerflides are a very robust trans, but getting pricey, they haven't been made for nearly 40 yrs.  Aftermarket versions for drag racing handle huge HP, check Summit and TCI.    

RE: Mnaual Gearbox Conversion

Lenco also make a 2 speed planetary type gear box. They are also pricey.

Powerglides also have an optional taller first gear. 1.7 something:1 Still a short gear when the only other in the box is 1:1

Regards
Pat
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