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Gearbox tunnel

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Flinty
Posts: 90
Joined: Mon Sep 24, 2018 7:34 pm
Location: Scarborough

Gearbox tunnel

Post by Flinty »

Can anyone give me some guidance on my gearbox tunnel.
I have just fitted an overdrive gearbox conversion { Overdrive Services, Sheffield are brilliant } to my Sp and I need to know where to enlarge the gearbox tunnel to accommodate the conversion.
Is there a simple way or do I have to keep guessing and cutting?
Any tips would be appreciated.

Steve.

User avatar
JohnM
Posts: 206
Joined: Thu Feb 11, 2016 1:31 pm
Location: N W London

Re: Gearbox tunnel

Post by JohnM »

Hi Steve,
I have some pictures of how and where I modified my tunnel -I'll pop them in Dropbox this evening and post a link.
Cheers,
John
John M in Middlesex, NW London
1962 SP250 "B" Spec
DLOC Herts Region Sec

Vortex O'Plinth
Extra-Wise Man
Extra-Wise Man
Posts: 1065
Joined: Fri Feb 12, 2016 8:15 pm
Location: Gloucestershire

Re: Gearbox tunnel

Post by Vortex O'Plinth »

Flinty wrote: Sat Jan 04, 2020 12:27 pm Can anyone give me some guidance on my gearbox tunnel.
I have just fitted an overdrive gearbox conversion { Overdrive Services, Sheffield are brilliant } to my Sp and I need to know where to enlarge the gearbox tunnel to accommodate the conversion.
Is there a simple way or do I have to keep guessing and cutting?
Any tips would be appreciated.

Steve.
Assuming we're talking about an SP250 and it's a 'J' type overdrive fitted and it's in the car.....
P1200118.JPG
....looking like this, first try a fit of the cover to see if fits. If it doesn't then by feel you should get a good idea of roughly where it's fouling.

I found the area of the cover that needed clearance was roughly as shown in this picture....
P1200791.JPG
It was about the same on both sides.

Having cut the clearance holes, I covered the overdrive in 10mm sticky back rubber foam and then covered the foam in clingfilm to act as a release agent. After refitting the cover I glassed over the clingfilm with a couple of layers of resin/glass and after it had cured, removed the cover. I then tidied up the new surface and blended it to the original where necessary. After final fitting the clearance was fine ....
P1200842.JPG
Bear in mind that the additional clearance will reduce finger access to the handbrake lever, so try to keep the cover growth to a minimum.
Nick

"Don't bother with the Air & Space Museum - there's nothing to see.......".

User avatar
JohnM
Posts: 206
Joined: Thu Feb 11, 2016 1:31 pm
Location: N W London

Re: Gearbox tunnel

Post by JohnM »

Hi Steve,
I see Nick's beat me to it with good advice as usual :D , but here's the link to how I did mine, which might give extra help in where to position your "bulges".

https://www.dropbox.com/sh/g5o23722ko4y ... mGsia?dl=0

You don't have to use my fabrication techniques ;) , but it was quite easy to do.
I finished mine with heat reflecting mat, which does help to keep cabin temps down.

As Nick says, the handbrake lever gets quite close to the expanded tunnel, so a few of us have opted to tilt the lever upwards to give clearance, using split spacers - I've added a pic which shows it.
I actually find this makes the handbrake more convenient to use anyway.
Good luck, it's no problem - just take your time!

cheers,
John
John M in Middlesex, NW London
1962 SP250 "B" Spec
DLOC Herts Region Sec

Flinty
Posts: 90
Joined: Mon Sep 24, 2018 7:34 pm
Location: Scarborough

Re: Gearbox tunnel

Post by Flinty »

Nick and John, Thank you so much, that information is just what I wanted, I can see a late night in the garage coming up.

Thanks again.

Steve.

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