Retro fit overdrive

[Jezza]

I've got a GT6 Mk2 ('69) non-overdrive, and wanted to find out if I could either (i) change the gearbox to a 5-speed or (ii) retro fit an overdrive to the car. Is it really as easy as that? 

 

I've heard that retro fitting isn't that easy to do, requires modifications to the loom, shorter prop-shaft and a different rear diff.. 

 

Is a wholesale change to a 5 speed box an easier option? Presumably fewer other modifications needed?? Or is there a way to convert the existing box to a 5-speed?

 

Or are there other options?

 

Any help / advice appreciated!

[Clive]

Much easier to convert to overdrive as it is a simple nuts and bolts operation. You can keep your diff, just gain the extra long od top gear (if you swap diff to the 3.89 it means od top would be exactly the same as your existing top gearing)

 

The realistic choice is either a type 9 conversion (T9 gearbox with longer input shaft, ideally shortened remote, adapter plate to bellhousing, new prop, clutch plate swap to dolly 1850/tr7 type, special speedo cable, speccial mounting, then cut gearbox tunnel about and remake gearbox carpet, gearstick several inches further back)  or od  (complete overdrive gearbox with od attached, different but std overdrive mounting plate and mount, speedo cable with angle drive, GT6 od prop, and yes, a few bits of wire and a relay)

 

OD conversion probably cheaper and more widely acceptable and no changes to interior trim. T9 ultimately stronger but lots more grief. And if a seller tells you no changes to interior they are lying. If they tell you tell you short input shaft is OK they are lying and don't understand the conversion. Walk away.

[68vitesse]

If going for an overdrive conversion go for a J type rather than the D which would have been a factory fitment.

Kits are available from the usual suppliers.

 

Have one in my Mk1 2L Vitesse, 3.89 diff and just under 3500 rpm at 70 mph.

 

Regards

 

Paul

[Clive]

J type is stronger and no need for a relay.

Having said that, I have had to replace a j type od (the cone clutch started slipping) but never a d type.

D type isn't too weak at all, it is absolutely fine on even a 2.5 as many will testify. But j type is ultimately better...

What am I trying to say? if you stumble across a d type conversion (rather more likely) don't dismiss it.

 

And with the conversions, the devil is in the detail. Things like the extra OD inhibitor switch and actuator arm on the gearbox remote can be hard top find and expensive. Also a decent OE angle drive (I would use a sh one rather than a repro, unless there has been a huge improvement in the new ones available)

[68vitesse]

Early Dolomite 1850 used a three rail gearbox with a j type overdrive, would think quite scarce now. If your gearbox is good you could get it rebuilt to accept an overdrive by someone like Mike Papworth but as Clive say's it's the odd bits, switches and brackets etc you need to make sure you get.

 

Regards

 

Paul

[Steve C]

Hi Jezza

 

If determined to do it, my preference would be for either a D or later J type overdrive conversion, as opposed to the (by no means simple) Ford T9 conversion, for which Clive has given a fair summation of the amount of work involved, and for which a look out there on t'interweb will give you some pictorial evidence. The Ford is undoubtedly a good box, but they are expensive, considering they made so many of them, and the engineering involved is (IMHO) a bit of a hotch-potch. It would probably be simpler to fit the Pinto or Zetec as well, but then is it still a Triumph?

 

Since no-one seems to be offering conversion kits any more, you will probably be looking at an overdrive box and a prop shaft out of wreck, or that has been sitting in someone's shed. If it can't be tested running, assume the worst and budget for a rebuild - most gearboxes out of cars came out for a reason. You might get lucky, but it is more typical to acquire a box that will have had a hard life being thrashed in a sports car, that was a bit marginal when new!

 

Neither route is cheap, and if your existing non-OD set up is working well, and you are only doing a limited annual mileage, you may wish to ponder the option of leaving well alone. With all such exercises, the law of diminishing returns comes in to play, and it does pay to remember that non-OD cars were produced in large numbers and did work perfectly well in period!

 

Good luck with your choice

 

Steve C

[Pete Lewis]

if your existing gearbox is sound , you need tck923 mainshaft to convert it and then the adaptor hsg, plus all the hardware,  the cam for the inhibitor operation may be hard to locate, even canley dont list a full kit anymore

and propshaft get that shortend by any local drive shaft/prop shaft reconditioner ..like  in yellow pages 

mounting plates for  j and D to the chassis and rear mounts are all available  

 

Pete

[AidanT]

As a MK 1 GT6 originally non-overdrive owner here are my thoughts for what they were worth  - It depends on what you want,what you care about, and how big your wallet is!

 

For me it was - Cost / Reliability and Originality (to some respect). My original gearbox was quite tired and pretty sloppy,I was not happy about the cruising speed on longer runs, but I didn't want to fit something that just doesn't belong!

 

So, purchased a Mk 3 box with J Type o/d and all the ancillaries, This was re-built, and also fitted by Mike Papworth. I kept the same rear diff as mine is lovely and quiet. There was a tiny bit of tunnel removed (A few inches) to make the fit easier. mike got me a new prop shaft to fit, there's no point in my mind to getting them re-built as they are not expensive new, in fact its the same price to refurbish so why bother?

 

My engine is not the original either so another reason I was not worried about the Mk 3 box, plus I was advised that this was the best of the Triumph boxes

 

This was the least expensive option I could find for the quality so how big is your Wallet ??  Leave it to you

 

Aidan

[Jezza]

Thanks for all the comments, suggestions and input; it's certainly food for thought!

 

For context, the current non-OD gear box is the original one I believe, and I've had a new (well, reconditioned) diff fitted. The engine block and all the major ancillary components have been replaced so, to Aidan's point, changing the bit in the middle of the engine and diff isn't itself an issue. I'd prefer a retro-fit if I can just for originality's sake but I'm not averse to considering a 5-speed replacement. After all, as time goes on bits will need to be replaced / upgraded and it will essentially become like Trigger's broom!

 

My main concern is the ability to source all the parts needed and having (or not, as the case more likely is) the knowledge to do this without balls-ing it up versus a straight replacement which is likely easier to both source and fit!

 

I see Mike Papworth's name has come up a couple of times to it might be worth me getting on the phone to him and discussing things.

 

~ changes to the interior aren't really a problem as I still have to replace the original interior on mine. 40+ year old carpets aren't something I want to keep hold of!!!

[mishmosh]

if the carpets are original , bear in mind new ones wont fit as well. Also keep the gearlever cover with the chrome top. You wont see another....

[Jezza]

if the carpets are original , bear in mind new ones wont fit as well. Also keep the gearlever cover with the chrome top. You wont see another....

 

Am aware of the fitting issue(s), but thanks for the tip about the chrome top to the gearlever cover

[mishmosh]

even if you salvage the small moulded partof the carpet with the gaiter attached it helps. I have one on my herald its a lovely detail.

[Jezza]

I won't be salvaging the carpet part! It's completely threadbare especially on the RHS of the 'box tunnel where the drivers leg rests. I might try and salvage the gaiter part and use that with the new carpet... somehow. I'll have a look and see how it could be done. 

[mishmosh]

I simply cut around the gaiter leaving a three inch margin of carpet. Fit this onto gearbox tunnel and slipcarpet over. 

[Alan C]

Another option to consider is a gearbox from one of the big saloons. I fitted a J-Type equipped unit from a 2500S. This box is much stronger than the standard GT6 box. It will fit between the chassis rails with only a very slight trim on the passenger side chassis rail upper flange. The gearstick location is near identical to the standard set-up. The standard slave cylinder is on the passenger side and needs to be mounted above the thrust bearing release shaft to clear the chassis.

I fitted this unit 25 years ago when the perceived wisdom was that it wouldn't fit. Well it does almost fit with a little thought and there are still plenty about the last time I checked.

 

Cheers

 

Alan

[Clive]

I fitted one to my Vitesse, along with te 2.5 engine.

Downside is a very low first gear, though using a Sprint first gear would help a lot. Still not a close ratio box though.

And yes, teh saloon gearbox is much much stronger and very difficult to break (you have to really try!)

I used a dolly sprint slave cylinder mount and modified cross shaft. Clutch bearing a bit of an issue, I never got a good pedal, always heavy. Though it is fixable. And getting a crank spigot bearing needs some thought, the saloon normally uses one fitted in the flywheel