Spitfire & GT6 Forum

3 rail vs single rail o/d

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Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, Nevada, USA   USA
In reply to # 1501151 by balloonfoot What is interchangeable between the 3 rail and the single rail Spitfire O/D transmissions?

Sounds like one or the other is about to be available.

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Melbourne, Victoria, Australia   AUS
I've just completed a single rail g/box internals into a 3 rail box with a J type O/D. The 3 rail casing had to be the Mk4 or Vitesse/GT6 306468 box remember the single rail mainshaft with J type O/D is 1in longer and will need a 1in spacer annulus between the gearbox to O/D adapter and the J O/D. Also you need a spacer washer on the reverse selector to avoid selecting rev & 1st simultaneously. Another thing from left field for me was I had to bend the reverse selector lever forward about 1/8in. Besides which you'll have to check replace several the mainshaft spacer/adjustment washer's.
The reason I went down the 3 rail path was the cost of the alloy bellhousing for the single rail with protruding selector shaft, I had 2No. 3 rail alloy bellhousings one early Herald thinwall and one thicker same as cast iron unit.
I can supply more info if wanted,

Peter T

3 Rail J Type OD with 1500 internals.jpg    37.9 KB
3 Rail J Type OD with 1500 internals.jpg

grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
Peter - I'm interested in your comments about engaging 1st & reverse simultaneously. Some of the later single rail boxes (maybe those with the larger teeth on the reverse gears) do partially engage the reverse idler gear with the reverse teeth on the synchro hub in 1st gear, which can lead to some strange noises in 1st. It's a known issue, probably just a consequence of squeezing larger components into a fairly small casing without spending the cash on a gearbox redesign. Also, the bending of the reverse gear lever - I've heard of this being done, presumably to give better engagement of the idler gear when reverse is selected? Or maybe to move the idler away from first gear?

When I built my close ratio box, I used components from a late Dolomite 1850 OD box, which had the later reverse gears with fewer (& larger teeth), and the later first gear on the mainshaft. (Early single rail boxes used the 'thinner' 1st gear, and the later ones got the TKC3001 'thicker' gear. Introduced across the range around 1977 to help prevent the 4 speed TR7s from stripping teeth in 1st gear.... eye rolling smiley ) I think I may have used the thicker single rail spacer, 22G1435, on the reverse idler shaft, but I think that was about it.

It's the first time I've seen the 1" thick spacer ring fitted to enable the single rail OD mainshaft to be used with the three rail adaptor plate. I had considered using the single rail mainshaft with the single rail OD adaptor plate, but decided against it, on the basis that I didn't really want to change the propshaft - and I already had a three rail TKC899 mainshaft with J type OD. I machined a steel sleeve for the mainshaft tip, to increase the diameter to 15mm, and bought a hardened needle roller inner sleeve to increase the outer diameter to 18mm. All were a press fit, with a drop or two of loctite for good measure.



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Melbourne, Victoria, Australia   AUS
I too had a TKC899 J type O/D shaft with the thin/small input tip, purchased from Mike Papworth a few years ago, and bushing it up to fit the later 1500 input shaft was too daunting for me so I went down the path of a 1500 gearset with its O/D mainshaft RKC767. The main reason was I'd purchased a Midget 1500 engine and non O/D gearbox locally. I already had a J Type O/D which I'd rebuilt with a full new pump, filters and reco cone clutch, & I'd also purchased the adapter plate 313085.
Some where I'd read about the two gear selection issue and the reqd reverse selector shaft spacer washer 158585, I had researched what was reqd over a couple of years & had to thank the TSSC Forum, Mike P and a blast from the past John Kipping (NZ) who was very forth coming. I had purchased the later 3 rail g/box casing 306468 ex US/NY and single rail 1500 O/D mainshaft RKC767 ex US/Texas. Also most of the spacer washers were also ex US, with some from Rimmers.
The reverse selector spacer washer was very rare it's only a washer but I didn't know its thickness, asking around on the various forums didn't come with the answer then whooa on ebay from the US again.
Ref the 1 inch spacer it was an Eureka moment after trying to slide the O/D down the mainshaft and being sure the splines aligned it just wouldn't slot home. Fortunately a neighbour has a large gear manufacture business and made the 1in adapter annulus for me, and finally success!! but I had to make longer studs.
Ref the reverse selector lever I hit it hard with a 3lb lump hammer but was too scared to take it all the way 1/8in, so I drilled a hole above the pivot pin halfway thro the lever, hacksawedthro the lever to it , then knocked the lever over the 1/8in and got a very good welder to weld the slot up, so good was the job no filing was necessary.
I also have a Dolly 1850 single rail gearbox with J type O/D which I want to adapt for my 68 Mk2 Vitesse (owned it since 70), so as I have to use the GT6/Vitesse alloy bell housing I will have to either adapt the bellhousing for the single rail selector shaft protruding out the front OR go down the route of putting all the single rail gearset into the 3 rail casing 306468 AGAIN, whether I'd use the TKC899 mainshaft and bush it up, or the RKC767 single rail 1500 mainshaft currently in the dolly O/D box and fit another annulus adapter I'll have to sleep on that one.
Hope that explains why and where, I'd like to have used a Spit 4, 3 rail J type O/D set up easy peasy, but in Aus there very very rare, ie not obtainable like Spit Mk3 1300 engines.
Peter T

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