TRExp

Spitfire & GT6 Forum

3 rail vs single rail o/d

Moss Motors
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor

balloonfoot Avatar
balloonfoot Gold Member Lloyd Faust
Southlake, TEXAS, USA   USA
What is interchangeable between the 3 rail and the single rail Spitfire O/D transmissions?

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
spitlist Avatar
spitlist Joe Curry
Sahuarita, Sahuarita, AZ, USA   USA
Not much I'm afraid. Perhaps the laygear cluster and that is about it.

Yellowhawk Valley Avatar
walla walla, washington, USA   USA
1969 Triumph Spitfire "Walla Walla"
1969 Triumph Spitfire "Portland"
1972 Triumph Spitfire MkIV "Spokane"
1975 Triumph Spitfire 1500 "Dayton"    & more
Maybe the shifter knob too.
Dan

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
spitfire50 Avatar
spitfire50 Paul Mugford
Rochester, N.H., USA   USA
Lloyd,
It is probably best to get the parts diagrams for both on-line from someplace like Rimmer Brothers that uses Triumph part numbers and go through them to check the overlap. But as Joe put it not much in common as far as gears and shafts go.
All the best,
Paul

balloonfoot Avatar
balloonfoot Gold Member Lloyd Faust
Southlake, TEXAS, USA   USA
In reply to # 1501203 by spitfire50 Lloyd,
It is probably best to get the parts diagrams for both on-line from someplace like Rimmer Brothers that uses Triumph part numbers and go through them to check the overlap. But as Joe put it not much in common as far as gears and shafts go.
All the best,
Paul

Right, I can do that but I just thought someone would know off hand and save a bit of time.....since we both know the shift knobs have different gear patterns.

balloonfoot Avatar
balloonfoot Gold Member Lloyd Faust
Southlake, TEXAS, USA   USA
Alright I just looked at a couple of items. The synchro hubs and rings are the same and the cluster is the same. I didn't look any further. What I am asking is this: is there anyone on this site who has actually swapped parts around between the 3 rail 4 synchro box and the single rail box? No guessing please.

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, British Columbia, Canada   CAN
Yes, I have mixed bits between 3 rail, single rail, GT6 and Dolomite boxes but, to be honest, for me it was a matter of checking part #s' of what I had, or just 'seeing if it fits'

Too many parts to have a encyclopedic knowledge of what fits where.

What do you have? What do you wish to accomplish?

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
balloonfoot Avatar
balloonfoot Gold Member Lloyd Faust
Southlake, TEXAS, USA   USA
In reply to # 1501234 by Tonyfixit Yes, I have mixed bits between 3 rail, single rail, GT6 and Dolomite boxes but, to be honest, for me it was a matter of checking part #s' of what I had, or just 'seeing if it fits'

Thanks for the response.

grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
About 4 years ago I built a close ratio box into a 3 rail case, using the gearset from a single rail box from a late Dolomite 1850 sedan/saloon. It needed a remachined input shaft, and a 3-rail mainshaft with a modified front tip to suit the single rail input gear. There's a longish thread here:- http://www.triumphexp.com/phorum/read.php?8,927491

It all depends on what you need, and how determined you are to source the parts!



Edited 1 time(s). Last edit at 2017-12-05 03:03 PM by grumpicus.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
balloonfoot Avatar
balloonfoot Gold Member Lloyd Faust
Southlake, TEXAS, USA   USA
I have a single rail Spitfire O/D box. I want to install the close ratio GT6/TR7 gearset and use the single rail shifter and GT6 bellhousing (for install into a GT6). Thanks for the link.



Edited 1 time(s). Last edit at 2017-12-05 06:58 PM by balloonfoot.

grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
In reply to # 1501475 by balloonfoot I have a single rail Spitfire O/D box. I want to install the close ratio GT6/TR7 gearset and use the single rail shifter and GT6 bellhousing (for install into a GT6). Thanks for the link.

OK, it shouldn't be that difficult.....

If you use a TR7 gearset, the only major problem will be the input shaft, as the TR7 bellhousing is much deeper than the GT6, and the input shaft is longer. It may be possible to use the shaft, but it would need machining to length, and new splines for the clutch cut into the shaft. It would also need re-hardening, as the new splines would be cut into softer material. It may be that the shaft is too thin to accept new splines, so check that first!

If you use a GT6 gearset, the input shaft is again the major problem, as its bore (for the needle roller which runs on the three rail mainshaft) is only 3/4". To use the single rail overdrive mainshaft with its larger 18mm tip & needle roller bearing, the bore in the input gear would need to be opened out to suit - and re-hardening of the surface may be required (I've never done this, so please check that out).

Don't try to mix gears from the two types - the helix angles on some of the TR7 gears are different from the GT6 (especially second gear). There are also detailed differences between the thrust washers on the mainshaft, plus the TR7 has a proper oilseal on the input shaft, compared with the scroll seal on the GT6.

balloonfoot Avatar
balloonfoot Gold Member Lloyd Faust
Southlake, TEXAS, USA   USA
Steve, the only difference I've found in the helix angles is with the early GT6 gearset (they were the same as the 1600 Vitesse). They won't mesh with the other helix angle (ask me how I now that). Perhaps I didn't encounter the different TR7 helix. Every set I used was the same as GT6.

The GT6 input shaft uses a proper oil seal....only the early Spitfire had the scroll seal. I have bored the input shaft on other occasions to take a stand alone needle roller bearing (has its own case). The needles ride in the case and not on the surface of the bore in the input shaft......hence no need to harden the hole. Perhaps this would work here as well.

I have yet to disassemble the boxes, so I'll know more later.

Thanks for the input.

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, British Columbia, Canada   CAN
For what it is worth. The input shaft case bearing can be purchased as a shielded or sealed bearing. If the shielding is removed from the inside face when fitted, it makes for a very effective oil seal if used with a scroll type shaft.

grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
In reply to # 1501547 by balloonfoot
The GT6 input shaft uses a proper oil seal....only the early Spitfire had the scroll seal. I have bored the input shaft on other occasions to take a stand alone needle roller bearing (has its own case). The needles ride in the case and not on the surface of the bore in the input shaft......hence no need to harden the hole. Perhaps this would work here as well.

I have yet to disassemble the boxes, so I'll know more later.

Thanks for the input.

Apologies - I've spent too long playing with Spitfire gearboxes, you're absolutely correct about the six-cylinder three rail gearboxes having a proper seal!

The earlier Spitfires used a drawn cup needle bearing (up to & including the Mk3), and it was the Mk4 which got the floating needle cage. It should be possible to get a similar bearing with a drawn cup outer case for the single rail setup - the difference being that it's metric, running on an 18mm mainshaft tip. If I remember correctly, the bore in the single rail input gear is 25mm, but please check.

balloonfoot Avatar
balloonfoot Gold Member Lloyd Faust
Southlake, TEXAS, USA   USA
Will check, Steve. Thanks.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

To add your reply, or post your own questions

Members Sign In   or   Create an Account

Registration is FREE and takes less than a minute!


Having trouble posting or changing forum settings?
Read the Forum Help (FAQ) or contact the webmaster