Was the Sprint ever fitted with a single rail gearbox?

[cleverusername]

Basically bought a nos clutch kit on eBay that was suppose to be Sprint compatible, but it has a 20 spline single rail clutch plate.

Before giving the seller hell, was the Sprint ever fitted with a single rail or fine spline box?

[xvivalve]

No

[cleverusername]

No

So the only way a 20 spline plate would fit is with use of a very big hammer, thought as much, thanks.

[Jon Tilson]

Question answered already but its worth repeating that the single and 3 rail small boxes are only good for 110 bhp tops....

Hence the large car box in the Sprint.

Jonners

[cleverusername]

Question answered already but its worth repeating that the single and 3 rail small boxes are only good for 110 bhp tops....

Hence the large car box in the Sprint.

Jonners

Just out of interest, what actually goes bang when you exceed the power rating?

[xvivalve]

One of my Sprints does use the 20 spline clutch plate, but it is fitted with the non standard LT77 gearbox from an SD1 Rover/TR7/Sherpa van.

[GTS290N]

The gearbox goes bang.
Trust me, it doesn't need the full 110 bhp to break it either, look around the forum and see the wants for gearboxes - they are invariably for 1850 or 1500 cars.
I still cannot understand how it could have been cost effective to design and produce a new gearbox for an 1850 when there was a known good alternative already being fitted to other cars.....

[Magenta Auto Sprint]

Just out of interest, what actually goes bang when you exceed the power rating?

I would think that bearings may suffer first which would lead to excess play in the shafts cause impact with other gears etc, otherwise I think a loss of teeth on the gears in mesh, these parts then become entangled with other gears causing more damage.

I had something similar on my 1942 Jeep, some large needle roller bearings became stuck in the main drive gear in the transfer box, the net result was that the gears tried to mesh and due to insufficient clearance, the gears in mesh spread apart causing the casting to break.

Malcolm

[Jon Tilson]

There is nothing much wrong with the single rail box and it wasn't just designed for the 1850. The original 1850 used the same box with suitable bearings
and ratios as the Vitesse and GT6 mk2. This explains why the dolomite will rev out to over 40 in 1st and 60 in second due to the 6000 rpm rev range that the 5 bearing
ohc slant gives over the 4 bearing ohv six, which only revs to 5k.

The single rail box was probably first used in the Marina, but is an adpatation of the earlier 3 rail box with loads of common parts in gears, bearings and layshaft etc..

But its a small box and this limits the power it can safely handle. It was used in Spits Midgets Dolomites Marinas and Itals and 4 speed TR7's too. I'd say it was pretty successful
and if not abused capable of high mileages.

I'm not sure what the "known good" alternative was. To have used the large car gearbox was not practical. The tunnel is only just big enough on a dolomite. It also has an intergral bell housing and is all alloy, so I suspect too expensive. The Rover P6 box may have been a possible, but is similar and barely capable of the 150bhp from the 3500S. Its also alloy cased and expensive to make with oil pumps and other typical Rover "we do things our way" enginering. The MGB box was/is nice, but its huge. If you put one in a Spitfire the gearchange would be where the back axle is...

So the single rail has it for smaller BL applications. I'm not moaning too much. It generally does the job.

Jonners

[GTS290N]

In 1979 I bought a 1975 Dolly 1850 with 3 rail od box, 25,000 miles on it. Soon after it needed a new box, luckily my brother worked in a Leyland garage and found out this car had received a replacement box...so I got a foc warranty replacement. In 1983 with 75,000 miles on the clock this Dolly was scrapped, mainly due to needing yet another box.
In 2009 I bought another 1850, no od, reportedly (who knows the truth) with genuine 24,000 on the clock and a perfectly functional single rail box. I've converted to od and both od boxes I've fitted have 'issues'.
So my personal (limited) experience of 1850 boxes shows they're made of chocolate. 6 boxes, 5 of them soft-centred..... And revving to 40 in first and 60 in second will kill the boxes sharpish....
Just my experience. They should have fitted the big Triumph box as per the Sprint.

[sprint95m]

The original 1850 used the same box with suitable bearings
and ratios as the Vitesse and GT6 mk2. This explains why the dolomite will rev out to over 40 in 1st and 60 in second due to the 6000 rpm rev range that the 5 bearing
ohc slant gives over the 4 bearing ohv six, which only revs to 5k.

They later sixes came in 2 litre versions with that gearbox and will very happily rev beyond 6000 rpm,
but they gearboxes didn't last a bang,
hence why so many GT6s and Vitesses now have five speed 'boxes, most commonly from Ford but also some Japanese like Toyota.

Being wider, the TR6/T2000 type gearboxes won't fit a GT6/Vitesse without body modifications and
furthermore the gear ratios are not well spaced having a big jump from second to third and a T9 box is lighter than
either a T2000 'box or a GT6 o/d.

If you have the money, it is possible to uprate a GT6 'box…..



Ian.

[cleverusername]

I am using the ebay return policy to send back clutch, others of which are still being advertised for Sprints, so beware.

As for the small Triumph gearboxes, couldn't some of the failures be down to c**p rebuild parts that are available today? My guess is many will have had a rebuild by now and all it takes is one substandard bearing.

[tony g]

I was an apprentice in a bl garage from 80 to 84. We were fixing marina/ital gearboxes on a regular basis, so I've never rated them. Same goes for the rear diff. I had a 1.3 ital that broke a diff, ooh the power it had lol.

Tony