GT6 MK3 J type O/D gear box

[Alex Lowe]

Hi all I’m looking at purchasing a over drive gearbox for my late GT6 MK3. Iv found a unit which I believe is for a 1850 dolomite with J type overdrive fitted. My question is will this fit into my Gt6 by swapping the bell housing from my current Non O/D box? Or are there other things to consider. I’ll place a link to the add below. 
 

https://www.ebay.co.uk/itm/174346821436

[Colin Lindsay]

With the usual mods - chopped tunnel, different rear mount and shortened propshaft it's a straight fit; but the clutch plate will need to be Dolomite to fit the input shaft. Bellhousing requires no mods. I have one in my Mk1, almost twenty years now and no problems.

 

EDIT! This was a rough draft that somehow self-posted when I tried to cancel after realising it was a single rail... blame the software!! (Hides....)

[GT6M]

Err yes, but alot of work needed,

see other thread on single rail into a GT

 

Ye really need a 3 rail, as the adaptor bit is shorter too

the GL will be a better fit too.

M

[Nick Jones]

Ok...... so there are other things to consider.

That is the later 1850 gearbox.  The single rail - so named because it has a single selector rod  - it has the flat top.  The good news is that it is stronger than the earlier three rail (three selector rods, bubble top) typre used on earlier Dolomites and Vitesse/GT6.

The less good news is that unlike the earlier 3 rail Dolly box (also with J-type) which is a direct swap after a bellhousing change:
- It's 1" longer than the earlier box (adapter plate between gearbox and OD is longer as is the mainshaft) so you'll need a special propshaft 1" shorter than the GT6 OD one and the space is very tight at the back, especially around the speedo drive.  Some "relief" may be needed
-The single rail selector sticks through the front of the main casing without any oil seal.  The 1850 bell housing has extra material with a hole in it here to act as a closing plate for it.  The GT6/Vitesse one does not.  People have got around this in various ways - it's fixable.
- You'll need to modify the gearstick to resemble a GT6 one.
- Fine spline clutch plate needed (as observed above).  Late Dolly 1850, TR7 4 speed,  certain Sierras and Saabs all can be used.

It is possible to overcome the bell housing problem by building the internals into your original 3 rail casing but the length problem remains.  

That's a fair price at present.  Though there is no guarantee it's not knackered - they quite often are, but not as often as the early ones which almost always are!

 

Nick 

[Graham C]

Hello Alex

I wrote a detailed account on the forum covering this. It is located under the gearbox section. It is possible I enjoyed the challenge of doing this. The bell housing needs altering, prop shaft reducing, a small section of chassis cutting out for the angle driver, a speedo counter cable from a 2000, approx 5 feet long and a support plate for the OD making up

The gear box tunnel needs making longer .

I quite like the new position of the gear lever .

Yes it is a harder route but can be enjoyable than a standard switch.

Graham

Edited July 19, 2020 by Graham C
Correction

[Graham C]

Interesting price £400, 7 years ago I paid £250 for mine on eBay.

Graham

[Colin Lindsay]

Nya nya, £180 for mine back in 2001 and they threw an engine in too....  but it was seized solid. It was a 3-rail with J-type and I can very definitely recommend it.

[Graham C]

Colin, good deal. What happened to the engine?

Graham

[thescrapman]

I paid £250 for a reconditioned single rail one. That's was this year.

I also paid £100 for 2 3-rail 1850 boxes, but that was 30 years ago.

[Colin Lindsay]

On 20/07/2020 at 09:22, Graham C said:

Colin, good deal. What happened to the engine?

Graham

Seized solid - completely! I think the seller wanted rid of it. It was well beyond economic repair.

It still yielded a lot of good parts, though, being a MK2 GT6 engine, so repaid some of the outlay.