Measurement of tip of input shaft to the gearbox case

[Peter Truman]

I have a spare Dolomite 1850 Single rail gearbox with J type overdrive, which I believe has the same gear ratio's as the standard Vitesse 4 syncro 3 rail box.

I'd like to know if the input shaft protrudes the same distance forwards from the gearbox/bellhousing interface as the standard GT6/Vitesse 3 rail gearbox, I don't want to have to remove my Vitesse 3 rail gearbox to check. 

I've measured the Dolly single rail gearbox input shaft protrusion from the gearbox/Bellhousing interface to tip at 158mm, the tip of the input shaft also protrudes approx 3mm beyond the GT6/Vitesse standard alloy Bellhousing front face. 

Hoping someone has a spare 3 rail Vitesse/GT6 3 rail box they can measure.

 

[68vitesse]

I have a gearbox wrapped in heavy duty shrink wrap bought from Fitchets years ago, as near as I can measure it from the face of the gearbox case to tip of input shaft is 7 inches, 178mm.

It is a three rail J type overdrive box.

Regards

Paul.

[Peter Truman]

Thanks must check what the Spitfire single to 3 rail conversion measurement is just checked 155mm

More investigation needed!

[johny]

Peter dont think exact measurement is too critical and certainly Dolomite 1850 single rail input shafts have definitely been used with 3 rail bell housings in past gearbox upgrades on here... 

[Peter Truman]

Thanks for that Johny I’m starting to look at options but I still prefer to transfer internals into a 3 rail 4 synchro case but the’re very rare here, also I’m not a lover of the single rail set up.

[68vitesse]

The gearbox in my Vitesse is a three rail J type with big tip main shaft and a fine spline input shaft. My other two gearboxes are three rail J type with small tip main shaft and the coarse input shaft. If I change the gearbox the only other changes is the clutch disc, the early Dolomite 1850 used the Vitesse/GT6 box with a different bell housing.

Regards

Paul.

[johny]

54 minutes ago, Peter Truman said:

Thanks for that Johny I’m starting to look at options but I still prefer to transfer internals into a 3 rail 4 synchro case but the’re very rare here, also I’m not a lover of the single rail set up.

As you probably know the mainshafts are longer for single than 3 rail boxes on both OD (+1") and non OD versions (+3"). What was usually done was to have a special 3 rail length main shaft adapted with a big tip to suit the single rail input... 

[Peter Truman]

I’ve used a 1 inch aluminium annulus in addition to the Spit IV gearbox to overdrive adapter so the overall 3 rail box and J type is the same length as a single rail box

I also have a new TKC 899 J type main shaft ex Papworth that I could convert my existing non overdrive and Original Mk2 Vitesse 3 rail gearbox using another Spit IV gearbox to overdrive adapter.

so I can go either way but I wanted to use the stronger single rail internals. 

[johny]

The trouble with the first option is fitting in that extra inch which I believe makes it very tight! If you had TKC899 main shaft modified to a large tip it could then be used with the single rail internals and still give a standard length gearbox....

[Colin Lindsay]

21 hours ago, johny said:

Peter dont think exact measurement is too critical and certainly Dolomite 1850 single rail input shafts have definitely been used with 3 rail bell housings in past gearbox upgrades on here... 

How not to do things: back in my unenlightened botch days I famously seized a big-six saloon engine, fitting the Dolomite box to an MB engine. The mate helping me tightened the bellhousing bolts from the engine bay end while I held a socket to the nuts in the footwell, so couldn't see what was going on. 

The engine seized solid within 30 seconds. He had found that the engine and bellhousing wouldn't come together closer than about half an inch apart so forced them together by sheer bolt power. This pushed the crank forwards against the thrust washers and ate them. I freed up the engine by hammering the front pulley backwards, replaced the thrust washers, and refitted the gearbox after grinding half an inch off the input shaft and rounding it off with a grinder. 

Anyway the moral of the story is that in some cases, measurement is indeed critical.

[johny]

yes the 2000 and 2500 saloons definitely never used either single or 3 rail gearboxes so some delicate modifications are needed to retro fit them🤣

[Peter Truman]

Johny when you say having the TKC899 adapted with a larger tip ie single rail size do you mean shrinking a enlarged bush on it or more extensive mods

[johny]

Thats it. I believe thats the usual modification done by turning the tip down slightly so a commercially available precision ground hardened sleeve can be fitted. These will be as good as or even better than the original tip as the hardening can be more precisely controlled...