Gearbox: Overdrive or Non-Overdrive

[kingrory01]

Hello,

Im currently in the process of rebuilding my Mk 2 GT6, and i'm wondering whether or not I should change the current non overdrive gearbox for overdirve, but what are the benefits?

Do I need to replace the gearbox for one compatible with the overdrive or will i go on to the current one?

I know that i would need a shorter Propshaft but are their any other mechanical differences between the two types?

Would i need to change the differential or could the same one be used, would it accept the power?

How much would it cost to replace it?

Any help on this would be much appreciated.

Regards

Rory

[Paudman]

Get a good S/H gearbox for under £200, shorten your prop or get an O/D one cheap, and all you need then is a mounting plate, a longer speedo cable and the switch. You cannot just bolt overdrive onto an existing gearbox. I kept my original non O/D diff for almost ten years, just swapped it last month. The engine is good for it as is the non O/D diff but obviously acceleration will suffer; I just liked the longer legs for long distance driving. The O/D gives an extra gear which can be flicked on and off by the switch - I used to cruise around the local town in 3rd just flicking O/D on or off as required, never touched the gearstick (column mounted switch). I'd recommend it if you're in a position to change.

[Velocita Rosso]

....and if you have`nt an O/D then the cost of that aswell £250.00plus or a second hand one that needs recon and thats £200

[don cook1]

Final rev/mph is pretty much the same for OD or non OD provided that the correct diffs are fitted. The benefit is that with OD and a lower diff (3:89) you will have better acceleration through the gears. If you change to OD and keep the non OD diff (3:27) you will, as Colin says, have a very long legged car...which may not be able to pull in OD 4th.

A good compromise is OD with a 3:63 diff, you will notice better accelaeration and a bit more relaxed high speed motoring.

[JohnD]

Thnaks to GT and his original book, here's a chart of final transmission ratios and what an O/d does to your speed.

[Richard B]

or my favourite  http://www.mintylamb.co.uk/gearspeed/  then you can work out permutations & combinations.

Thanks James!

[Paudman]

michael_charlton wrote:

....and if you have`nt an O/D then the cost of that aswell £250.00plus or a second hand one that needs recon and thats £200

That's what I meant when I said get a good secondhand  gearbox - the overdrive should be attached to it already.
Here's a current one for sale: Ebay item number 250584831320
Private prices are usually much lower than dealers.

[kingrory01]

Hello,

Thanks for all the advice, it's come in handy, but it's also giving me a few more questions.

Would the diff need to be replaced or can i modify the one i already have, to the correct ratio.

How difficult is shortening the propshaft is it a simple matter of cutting it with a saw.

With the gearbox, if i bought a secondhand one i'd like to rebuild it just in case, is this task difficult and is their any literature that explains it.

Thanks again

Rory

[Royboy66]

Hi Rory,

if you can get a go in a GT6 with o/drive I think you would surely want to have it for your car ;)

The propshaft would have to be shortened ,then balanced(quite important on our cars) ny a specialist. its not too expensive , Had mine done when I changed to o/drive 7yrs ago ,cost about £60 is then, guessing around £80-100 now.

Diff, depends on what you have already, our GT6's are 40yrs old now, so good chance the diff has been changed before,  for example  when I got my car it had no overdrive, but had a 3.89 diff,so was a tad low geared!

Find out what diff you have first, then take it from there.

Gearbox rebulid is quite skilled in my opinion,  having to source all the bits you need could sometimes be better to just buy a reconditioned one from a good supplier.

Just some of my thoughts, may contain Nuts! :)

Whereabouts are you?
are you going to Stoneleigh, you may get a ride in a Kind owners GT6 with O/drive  ;)

Roy 8)

[kingrory01]

Cheers Roy

Im certain that the overdrive is the route i want to go down, but my only worry is the price, replacing the gearbox, getting the overdrive and possibly getting a new diff,  will be expensive, and i'm only a student, hence the reason i'm thinking of rebuilding a secondhand one.

I live in South London and unfortunately i wont be going to Stoneleigh.

Thanks for the help.

Rory

[BrendanD]

Hi Rory,
I keep my O/D Mk3 GT6 in S London too - Bermondsey.
You can't avoid a bit of cost on an O/D conversion, I did my Spit 1500 last summer.

TSSC member sourced O/D, box, prop, mounts, solenoid and gearstick/switch from a rotten scrapped Spit - £300
Prop new UJ, replaced rubber joint with a sliding spline and rebalance -£120
New clutch kit £65
Swap recon gearbox £250
Speedo cable and angle drive (both broken) £70
- a weekends work fitting it all
Doubt you'll do much cheaper and still have a smooth ride....
Regards Brendan

[neilnaz]

I had an O/D conversion performed on my Spitfire 1500 by Max at Totally Triumph for just under 500 quid with O/D gearbox, propshaft, and all ancillaries provided by Max. I had looked at other options including secondhand gearboxes for sale on Ebay. The gearbox supplied by Max had been checked over and came with a 3 month warranty. I was happy with this rather than getting the gearbox and sundries that were in an unknown state.

The thing is that you don't always know exactly what you are getting with a secondhand gearbox. My non-O/D box was fine and I did not want to take on an unknown quantity and do all the work to find that the Gbox crunched and ground and the O/D did not function.

I have had no issues with the Gearbox since fitting some 3 years ago or more. In fact the gear change is sweeter than the previous Gbox.

You cannot beat the sheer driving experience of driving a car with overdrive. It is a sheer joy. Being able to change gear whilst accellerating hard being able to flick in and out of O/D in the twisty bits keeping the engine in the sweet spot - blinking marvellous.

Working out how to get an O/D conversion most cost-effectively is your problem. It might be worth waiting til you have saved up rather than cobbling together some parts of unknown quantity. You could probably get the bits together for 200 quid and perform the conversion yourself over a weekend and you might be fortunate to get a sweet Gbox and everything go swimmingly. There is a risk that it doesn't go so smoothly. You pays your money..........

[Deleted User]

For the money people are quoting, ford type 9 5 speed every time!

h

[neilnaz]

I do not agree with you Hrgserv at all.

Firstly the cost of an O/D conversion can be as little as 200 quid and as much as the cost of a recon conversion kit plus labour of fitting it. That probably means 1000 pounds plus 4 hours labour to fit (I am guessing).

I have outlined that my conversion cost me 500 quid fitted working and warranted.

A 5 speed conversion costs how much?

From what I understand the gearboxes are relatively bulletproof but you need to get the right one. You may end up with a compromised gear lever position. None of the kits, from my understanding, are straightforward to fit without a fair amount of work. You need to perform some metalwork removal and buy a specific bell-housing from Frontline or another provider. At the end of all that you have a 5 speed and you do not have Overdrive.

I have a modern(ish) car with a 5 speed gearbox and have driven cars with 6 speed geraboxes (etc) but nothing comes close so you cannot compare.

Neil

[Clive]

I reckon the price difference is marginal. And I know which one I prefer, even if it is a bit more grief. Saying that, many prefer the OD, indeed the tolly is OD, the spit was/will be 5speed. But long term......
Buy type 9's before the values go even higher though ;)

[DaveKent]

without doubt the ford box is a much nicer box to use, but it just ISN'T overdrive!!!

[Clive]

correct on both counts :P

[BrendanD]

An O/D is part of the Triumph 'thing' - If I wanted 5 speeds I'd drive an MGTF or a Mazda.........

[kingrory01]

Hello,

I will definetly get an overdrive gearbox, and will try to go to Totally Triumph as it sounds very reasonable, the only problem would be getting it there.

The 5 speed gearbox is not for me. I bought the GT6 because it a great classic car, despite some of it's problems.

Plus won't the Ford gearbox reduce the value of the car?

Cheers

Rory

[Deleted User]

clive
Agree with you,
What most people forget with a second hand  spitfire box/overdrive there is a very high chance they will both want overhaul, or soon will, if you factor this in the ford option is considrably cheaper as there is a much better chance of getting a decent gearbox, second hand
The ford box is also has less loss passing the power throught to the wheels, (instant tuning) decent parts to fix it are readily available,and will be for the forseeable future, it will also stand considerably more power than the triumph box so if your engine is tuned its a better option.
New parts for the small chassis gearboxes of whatever type are now getting thin on the ground, most  are now rebuilt with "good" second hand bits, and the life of the rebuilt unit can be quite short, particularly if yor engine is tuned.If you start specifying new gearbox parts in the rebuild of your triumph box the cost can exceed �1500
so long tern the ford box is the cheaper option
I know the problem of rebuilt triumph gearboxes as we have got through three in four years all rebuilt by reputable suppliers, in the case of the last one i had a look myself, all that was new was the syncros, chinese copies, the bearings again of chinese origin, everything else was "usable" second hand parts including the layshaft, which was pitted.
when you see this standard of rebuild which cost almost �300 and the poor life its expensive, and that doesnt include the overdrive which is a further �250-300 for a rebuild.

having fitted the ford unit its quiet, produces less heat, with a better gearchange and is very likely a fit and forget due to the greater strength in the first place

Case made

h

p.s when the o/d electrics play up for the umpteenth time, (as they all do) a large amount of cursing will issue forth!

[DaveKent]

have to say in 25 years of triumph ownership i've never had an overdrive fault, electrical or otherwise!

[Doug Paterson]

xyv wrote:

have to say in 25 years of triumph ownership i've never had an overdrive fault, electrical or otherwise!

I can't say the same ... 2008 was a bad year for overdrive for me ... but basically that was just worn out.  

The electrics are hardly rocket science in an OD so although it reasonably common for problems its nothing I'd say anyone needs to fear.  

Gotta say that whilst I was a ford man at heart for many years and agree the type 9 is the 'sensible' option my heart rules my head when it comes to OD in a Spitfire/GT6 ..... it is just soooo much fun both in terms of driving and the amazement that passengers seem to have with it.  

[Paudman]

hrgserv wrote:

Case made

Er..... no.
All you have stated is that Triumph gearboxes are unreliable and worn, and likely to give trouble, while Ford are wonderful and spare parts grow in plenty.
My s/h Triumph box is coming up on ten years fitted, no trouble at all, and no o/d electrical failure either. I don't think I'm unique.

Given that any second hand box is a risk, there's no guarantee that a Ford box from a scrapyard will give any less bother than a Triumph one.
So: you've put YOUR case, but it hasn't convinced.