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Spit Overdrive


TurboTux
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Hi guys,

I managed to grab a second gearbox for my Spit and was thinking about fitting an overdrive to it. My question is which type of Overdrive unit do I go for?

As I understand it either can be used and the things I'll need are:

  • Overdrive unit,
  • Overdrive to gearbox adapter,
  • Overdrive column switch, cover and wiring,
  • Shorter Propshaft?
  • New Mounts?

Is there anyhting I'm missing?

For reference I have a Mk1 '63 Spitfire 1147cc.

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I think pete's idea of a 3.63 diff would be too tall for the 1147cc engine. you would need a new mainshaft, adapter plate, overdrive, gearbox mount and plate, propshaft (same length as standard 1500 but different flanges), column switch relay and wiring. I have a mk4 4 synchro in my mk2 which is great and probably easier to source parts for. Talk to Mike Papworth he should be able to help. It really is a worthwhile upgrade though. 

it would almost certainly need to be a d type overdrive. The very late mk4 spits used the j type but the gearboxes and mainshafts will be very rare

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Thanks for the replies.

I think I would rather commit to the D-type overdrive than the Diff change for now. Perhaps it's an option for the future although would a 1147cc handle both a diff change and overdrive, I don't know.

I have a spare gearbox (3 rail - 3 synchro) to play with so rebuilding it with a new mainshaft is not a problem. Only the added cost of buying one 😅 which admittedly is now starting to add up. Anyone know where the best place to aquire these parts for reasonanable price? 

At the minute the prices I've got are:

  • Adapter Plate = £112 (Canley)
  • Reconditioned Overdrive unit ~ £500-£600
  • 3 Synchro Mainshaft = £170 (Canley)
  • Propshaft = £132 (Paddock)
  • Gearbox Mounting plate = £15 (Paddock)
  • Relay = £25 (Canley)
  • Overdrive Column Switch = £30 (eBay)
  • Column switch cover = £10 (Canley)
  • Relay = £25 (Canley)

So roughly £1100-£1200... 😬

 

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don't forget the surcharge for the od unit unless you have an old one as the recon price is exchange. If you have a good mk1 it's certainly worth that. Reconning. my mk4 box and od was about £1100. You will also need to factor in new bearings synchro rings etc as no point in pulling a box apart to not replace those if worn. I would start by talking to spitbitz, spitfire graveyard etc as they may have a complete kit from a scrap car more likely mk4. As I said Mike Papworth really is the gearbox expert though there are 2 very good overdrive places odspares.com and overdrive-repairs.co.uk

The 1147 works brilliantly with overdrive I can cruise at 70-80 mph all day ok my mk2 has a couple more hp but nothing significant. I wouldn't want a higher diff ratio certainly not in addition to od

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3 minutes ago, DanMi said:

don't forget the surcharge for the od unit unless you have an old one as the recon price is exchange. If you have a good mk1 it's certainly worth that. Reconning. my mk4 box and od was about £1100. You will also need to factor in new bearings synchro rings etc as no point in pulling a box apart to not replace those if worn. I would start by talking to spitbitz, spitfire graveyard etc as they may have a complete kit from a scrap car more likely mk4. As I said Mike Papworth really is the gearbox expert though there are 2 very good overdrive places odspares.com and overdrive-repairs.co.uk

The 1147 works brilliantly with overdrive I can cruise at 70-80 mph all day ok my mk2 has a couple more hp but nothing significant. I wouldn't want a higher diff ratio certainly not in addition to od

The recon price is taking into acount the surcharge as I don't have a unit to exchange. I forgot the rebuilt kit price which is £130 from Paddocks.

I'll do some more digging and I might find some better prices 👍 and cheers for the offer even if it's impossible right now!

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and don't forget that cheapest isn't always best I had my gearbox reconned cheaply in the 90s turned out they had badly repaired the main shaft by pinning in a replacement tip which was too short (can't complain to badly as it lasted 20 years and 30000 miles with a 1500 engine. Also my car used to eat speedos. Turns out the od had been badly reconned and was missing a part that stopped the speedo drive moving so oil leaked up the cable. so beware of cheap a it may cost in the long term.

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11 hours ago, johny said:

Used OD gearboxes do come up on ebay and as you want a 3 synchro it will be easier to win.... Also dont forget the OD gearbox set up uses a small angle drive to connect the speedo cable to it, available for 30 - 60 quid.

I'd second that; I bought mine second-hand off the small-ads in 2001 and it's been running perfectly ever since. Just use your head; a used gearbox at £50 might be good, might not, it's a gamble sometimes but a clean-looking version at £200 is a better bet. Last Spit box I bought was from Chic Doig, single-rail with J-type overdrive, so he may be worth a call; at least there you've got some form of comeback if it's not good.

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yes OD and 3.63 :1 would be too much

but we have a couple od 1147 Heralds down here running very happily on a 3.63:1 diff

 

on the parts list dont forget the pump cam and its woodruff key and circlip and the anti chatter spring ring on the mainshaft

spring ring  513223

cam  513216

key kw0316

circlip   ring  137308

these may vary if on 4 sync

Pete

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a 4.11 diff with OD is ideal. And according to John Kipping (who was obsessed by economy) the most economical. Longer gearing raised consumption when he did his testing. Plus the 4.11 keeps teh car nice and nippy. The factory gear ratios were very well chosen (poss except GT6 3.89? Discuss that! and controversially, I would say the the 3.27 was not a good choice in a GT6, they should have all been built with overdrive)

 

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I like the idea of running just the OD on my 4.11 diff as I believe that was factory standard.

Quick question, are all gearbox-overdrive adapter plates the same? I've found a plate on eBay which is listed as Mk4 1500 J-type but looks very similar to the ones I need from Canley?

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3 minutes ago, NonMember said:

No, the overdrive adapters are all different. Or, at least, there are more than two different ones - 3-rail vs. single rail affects the front and top, D-type vs. J-type affects the rear, and for extra fun there are different lengths, I believe.

Thanks, I thought that would be the case

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48 minutes ago, johny said:

One other thing, when buying an OD make sure it comes with the solenoid. They are quite expensive so often get removed and sold separately....

Well, the D Type quite a bit cheaper (last time I looked). Maybe don't dismiss, immediately one that doesn't have it, if everything else seems good. Maybe able to offer less £'s ?.    

Edited by daverclasper
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Don't forget you also need the different top remote with the cam for the inhibitor switch and the bracket for the switch.

Adaptor plates are scary prices now, try looking for the short one for a J-type on a 3rail small tip mainshaft.

A Spit 1500 / Dolly 1500 single rail one may be a alternative.

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