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6 Cylinder Gearbox


Darren Groves
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Longer first gear. Friend has one, in a spit. Can be a struggle to pull away on a hill.... 

I use a t9 box, and have the longer first gear. Not a lot of point really unless you need to do 30 or so in first. Guess for acceleration it means you will still be in the powerband when you change to second. But standing starts are incredibly hard on the synchros, and the car in general.

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You need to change the input shafts  ,, 

Of you have crash on first then a 4 sync unit would loose the first gear whine

And the internals of 4sync 4 pot is pretty much the same as a 4 sync 6 pot 

Apart from the stem/input shafts  its easy to mix and match infernals  

2 nd 3rd ratios can vary  ive just rebuilt a spitty 4 sync witha vitesse layshaft cluster and corresponding mainshaft gears to match

It drives fine  not looked at the figures but its closer ratios 2 / 3 with original 1st

Pete 

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The six cylinder gearbox, GT6/Vitesse, is close ratio when compared with the four cylinder, Standard 8/10, Herald, Spitfire gearbox. A version of the close ration gearbox was used by the ST competition department in the Spitfire around 1964.

I agree with Clive re the first gear and pulling away.  

Dave

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Pete - The 3 rail Dolomite 1850 (1972-3) gearbox was the same as the GT6/Vitesse.

The Toledo/1500TC/Spitfire, up to 1974, used the 3 rail  4 sync version of the Herald box. i.e. small input shaft and wide ratio. The Sprint used the TR gearbox.

1974/5 onward the single rail gear box came in. The Toledo/1500TC/Dolomite 1300/1500/Spitfire all used the small input shaft wide ratio type.  The Dolomite 1850/TR7 used the larger input shaft, close ratio type. Both types had a greater number of splines that the 3 rail. 

Dave

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Pete, I don't think it is possible to swap over the two input shafts i.e. swap a small wide ratio with a large close ratio. And the other way around. on any versions of the gearboxes. Having said that I don't know what the Morris Marina  arrangements was! 

As for the ST competition department, well they had special stuff built for them. Lucky people. 

Dave

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I believe there were some conversion input shafts produced. The only person i can think of who may have one is Mike Papworth.

My friend did it the way that "doesn't work". He cut both input shafts, drilled one, and cut a spigot on the other and pressed them together, welded. Then a fly press to get to 2 thou runout (a fraction of factory spec) He also machined the end of the mainshaft, and replaced the bearings with a bronze bush. Nearly 100k later all is well...... But of course it couldn't possible work.

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From what ive converted the input (stem wheel) and primery gear on the cluster are all the same across the range( well they match up ok )

The ratio change is in 2nd and 3rd  my initial convert from 3 syn to 4 sync used spitty IV internals and vit stem gear

When the mainshaft spigot gave up I had a M Pap 18mm spigot and machined stem gear , 

Just my findings trying to keep the boxes running 

Pete

 

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