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1500 Single rail gearbox troubles


Conor L
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The gearbox on my Spitfire has a badly chewed up reverse idler and gear along with oil leaks and a grumbling bearing. I thought id take it upon myself to have a go at rebuilding it. Following the workshop manual, ive removed the bell housing, removed the prop flange and im about to remove the rear extension. This is where ive got stuck, the manual says to select reverse, remove the role pin from the front of the select shaft and then the rear extension can be removed or something like that however by selecting reverse this pin has locked in so I cant remove the extension but the manual doesn't mention this. can someone give me some tips on what to do.

Heres a picture to show what im on about,

jOP1iXw.jpg 

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The roll pin mentioned is in the very front (in the clutch hsg)

Done a few single rails but cant remember removing the selector pin or the short one in front of it , having said that they have to come out to get the rod out the main case   dont recall a relief to allow these thro the case ,

I would remove the interlock plate and rotate the remote rod to clear the spool , im sure this pin is a loose fit in the rod 

The manuals are all pretty poor on this 

And the grey matter isnot helping 

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Take a note of how the spools and rod all fit or you can end up in a weeks time puzzling where heck which way round it all goes 

You  can see why the single rail was not the prefered one in later cars dont know if its conception was for costs or to improve the  remote and suchlike .

Pete

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Yeah I've taken pictures of parts before they were removed just to be on the safe side. Just another thing, what would you use to paint the case? I was thinking something like stone chip as engine paint might chip off easily. I always believed that the single rail box was stronger than the 3 rail box but I don't know that for sure.

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yes, although the tip was a weak point the layshaft and its bearings (another weak area) plus the maincase roller bearings are all the same in both types of gearboxes. I believe the single rail mainshaft is longer by an inch (at least in the non OD) but dont know what benefits, if any, this offers.....

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Its an odd design  evolution  some bits are the same as 3 rail but odd things are not, the reverse tooth count , and mainshaft hub splines 

And picked up a  3 rail fitted with 1 rail parts theres a lot of rattling good fit as someone paid a lot for a non working nightmare

I still reckon this was a cost reduced imposition to improve the remote selector of the 3 rail and used on Marina,  most Dollys stuck with the 3 rail the 1500 and 1 rail being common with the Midget   so Triumph kept 3 rail  BL used 1 rails

Well something like that, or not 

Pete

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21 minutes ago, Pete Lewis said:

  most Dollys stuck with the 3 rail the 1500 and 1 rail being common with the Midget   so Triumph kept 3 rail  BL used 1 rails

Not true. All Dolomites except Sprint (which uses the big saloon box) went single-rail in the mid-70s, roughly at the same time as the Spitfire. In fact, a sub-1850 "Dolomite" will always be single-rail; the 3-rail versions are the Toledo and the 1500TC.

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The introduction of the single rail box pre-dates the introduction of the Dolomite 1300 and 1500. The change over took place in 1974/5. Late Toledo's and RWD 1500 TC had the single rail.

Therefore all 1300 and 1500 Dolomite's were fitted with the single rail. Apart from the speedo drive this was the same as fitted to the Spitfire.

The early 1850 Dolomite used the three rail box i.e. GT6/Vitesse

The Sprint used the Vanguard ( Large Saloon) based box. Not the Standard Eight based box as above.

As interest the 1973 - 1974 RWD 1500 used the three rail box.

The single rail was a rework of the three rail and hence has components from the latter.

Dave

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9 minutes ago, johny said:

As Pete said, its strange that there seems to have been a fair amount of work to redesign, manufacture and implement the new gear change for very little gain.....

The first re-work was said to be required to adapt the box to fit the Marina. Odd as the Marina was a new model. It looks more like a cost cutting exercise to me. i.e. To reduce the cost of the box. 

The adoption on Triumph models I guess was to use common parts within BL.

I agree, Strange.

Dave

 

 

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On 08/12/2018 at 09:46, johny said:

still, if standard, wont have large mainshaft tip but will be an inch longer☹️

No. Early 3 rail Dolly box is the same length as the Vit/GT6 box even though J-type OD not D-type. Extra inch is in the adapter plate. No idea what they were thinking of. Very irritating though.

Quite right about mainshaft tip. OD stronger but not the gearbox itself......

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Nick, when you say the early 1850 box is the same length as the GT6, do you mean just the box, excluding the OD? The J-type OD is longer than a D-type and I don't think that's all in the adapter plate. The single rail box has a longer tail section when non-OD, doesn't it?

It all reminds me of a change made to one of the Range Rover models. The transmission engineers had identified a problem with the previous model stressing the tail casing between the gearbox and the 4WD transfer box. To avoid this, and improve NVH, they proposed to separate the two units and fit a flexible coupling between them. The bodywork was duly modified to accommodate this. Then somebody higher up decided the separate units cost too much and imposed a dictum that they be reverted to a single assembly. Except that by then, the mountings had all been set in stone, so the transfer box couldn't be moved back. The potentially problematic, stressed casing was now even longer and even more prone to flex problems.

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On 07/12/2018 at 23:48, 68vitesse said:

Early Dolomite 1850 used the Vitesse/GT6 three rail box with a J type overdrive, best box for a Vitesse or GT6 if you can find one.

Regards

Paul

That's the box I have in mine, for the benefit of the J-type overdrive, and it's still going great after twenty years in that car. It's a straight swap at the engine end, with the usual alterations at the overdrive end.

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On 12/12/2018 at 08:18, NonMember said:

Nick, when you say the early 1850 box is the same length as the GT6, do you mean just the box, excluding the OD? The J-type OD is longer than a D-type and I don't think that's all in the adapter plate. The single rail box has a longer tail section when non-OD, doesn't it?

The whole 3 rail J-type gearbox is a direct swap with the D-type version.  The 3 rail dolomite has a shorter adapter plate and mainshaft than the single rail one.  I have no idea why the single rail boxes are longer in both OD and non-OD forms.  Mid 70s BL "logic"?  Triumph vs BMC group infighting?  Big nuisance!

There is an aftermarket variant of the 3 rail Dolly mainshaft with the larger tip size, which allows the use of all the single rail gears in the 3 rail casing at GT6/Vitesse length.  As already mentioned further up, you can also do something like this but keeping the single rail mainshaft and adapter housing, which gets you a box that the bell housings bolts straight up to with no mods but that is 1" longer.  This is what I had before my 5 speed.  It worked fine but was a really tight fit at the back.  I actually had to chop a small chunk out of the chassis to clear the speedo drive, which was later put back when I fitted the 5 speed.

The only 3 rail Dolly boxes I ever found were knackered beyond all hope.

Nick

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  • 3 weeks later...

Ive got another issue with this bloody thing. After servicing the components, I reassembled everything as it came apart. However, when I was refitting the rear extension, ive got a gap between the rear extension and the casing. Ive had a look and I can't see what the problem could be, everything seems to be inline and correct. Had just about enough of it, can anyone give me some much needed advice?

Heres a picture to show what I'm on about,

yKivQSX.jpg

Many thanks,

Conor

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On ‎31‎/‎12‎/‎2018 at 11:00, Pete Lewis said:

is the anti rotation roll pin in the end of the layshaft spindle in the clear opening of the tail hsg. ?

Pete

Pete you dont realise how much of an idiot I feel right now. The roll pin wasn't lined up with the opening causing my terrible night. I suppose the simple things aren't obvious when youre annoyed. Thanks Pete you're a star!

Conor

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