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Brooklands

Gt6 Gearbox Strengthening

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Hi,

 

I'm well on with a Spitfire 6 / GT6 2.5 convertible build and would like some advice about strengthening the GT6 gearbox. I suspect many will ask why I'm not fitting a saloon box or a five speed, so let's deal with that first.

 

I don't want to cut the chassis, or mod the gearbox tunnel, and although many say these conversions are easy, just as many say they are not. Recent reading on the net also suggest the 5 speed ratios are not good for the GT6.

 

That's one of the problems I have with making my choice. I'm finding lots of conflicting opinion (some of it strong) about the subject. It can't all be correct, as the opinions are often in direct oposition to each other.

 

So, I'm sticking with the GT6 box and my question is this; -

 

What's the strongest build spec for an OD GT6 gearbox, and who can do this work to a high standard? I'm UK based.

 

Thanks.

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Here I have to say I'm completely biased.

 

If you read the Kevin Ginger thread between the lines, you will find the gearbox was ALWAYS BRAND NEW.

This is the only full proof way to give it a chance of survival, and it was always true for circuit cars.

After a season, the thing was always pensioned off and another new one fitted.

 

Even then, the failure rate on brand new syncro rings wasn't clever.

The gearbox had to stripped and rebuilt usually 2 or 3 times before finally getting a set of syncros that was 100% perfect.

 

There is NO GT6 gearbox that was designed for the torque and weight of that crankshaft, all you can do is fit brand new, forged selectors, reinforced mainshaft, brand new J type overdrive, anyone that says you can do otherwise isn't straight up.

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Ok. I'll attempt a summary.

 

First off, I agree with Gareth with the proviso that he's talking about RACE use or at least 10/10ths road use. How you actually plan to use the car, the state of tune of your 2.5 and your driving style will ultimately determine the life of any GT6 based box.

 

There are people out there using various versions of the GT6/Vitesse box with powerful 2L and tuned 2.5 engines and getting acceptable life from them. There are also people who have suffered major failures.

 

Fact is, the standard box was under-rated for the standard engine and is definitely marginal for 2.5 (see above about usage!)

 

There are some things that can be done to help the "standard" box. The internals from the later single rail variant as used in the dolomite 1850, TR7 4 speed (and Marina 1800?) do fit into the 3 rail casing. If you want overdrive (which no doubt you do) this complicates the issue a bit as the factory overdrive mainshaft, as only used in the later Dolomite 1850 is 1" longer and is used with a different OD adaptor plate so the gearbox ends up 1" longer meaning shorter non-standard propshaft and a very tight fit in the chassis at the rear.

 

Note: Both earlier 3 rail and later single-rail Dolomite 1850 boxes are fitted with J-type overdrive. The earlier, 3 rail ones are the same length as the standard GT6 box (and may even have been fitted in the last of the export GT6s too - separate debate). These earlier ones are NOT any stronger that the standard GT6 one although the J-type OD could be considered an advantage.

 

It is possible to have a three rail box built using a special, shorter hybrid mainshaft, which uses the beefier single rail parts, the OD adaptor plate from the earlier Dolly box and J-type OD. This is probably the ultimate "spec" BUT, the actual strength of it will depend on the condition of the parts used (bearing mind that new parts are pretty much gone now) and the skill of the builder.

 

Mike Papworth seems to be highly regarded. There are a couple of others too (John D uses someone else I think, but can't remember who?). Also Gareth himself if he's prepared to do any more......

 

I think it's fair to say though that if you have a tuned 2.5 and use the car hard over decent mileages, then gearbox life will be fairly limited.

 

Regarding gearbox swaps.

 

First problem is that there really is nothing out there that directly matches the close ratios of the standard offering. Closest approach is probably the Toyota W58. Next comes the 2.8 V6 variant of the Ford Type 9. The type 9 does have other possibilities from the aftermarket though - if your pockets are deep enough.

 

Triumphs own TR/saloon/Sprint box can be made to fit, even with the J-type OD. (Forget the A-type OD though - no way is that going in!). I don't think the chassis needs cutting. Not sure about the tunnel cover as I've not done this myself but the gear lever does at least come out in the same place.

The show stoppers for me with this option are the very "saloon" ratios and agricultural change. The ratios can be improved using parts from the Dolomite Sprint box.

 

Ford box option is pretty well covered elsewhere. Possibly worth mentioning that the T9 itself will be somewhat marginal with a powerful 2.5 unless it's the beefed up version used on the later 2.8 V6 cars (or after market mods). Gear lever comes out quite a bit further back even when the box is modified.

 

Toyota W58 is strong, has pretty decent decent ratios (including a nice tall 0.79 5th) and a nice change. It's not a cheap option, as kits are very pricey and as the 'boxes are now quite hard to find and commanding strong money even diy won't be cheap. Should be fit and forget though. I like mine.

 

I didn't cut my chassis but I did have to bend the inner flanges down out of the way. The tunnel cover did need a mod but only because I was too mean to buy the proper Toyota remote to move the gear lever forward. I made my own and the change is in the same place as standard but it is less compact than the Toyota part.

 

There is also the Toyota T50, but in UK these are really rather rare. I think kits exist from Conversion components (NZ) and Dellow (Oz) but they'll not be cheap.

 

Cheers

 

Nick

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Greetings,

 

I've been a little obsessive collecting all the parts I need for my conversion (4 gearboxes, 2 engines, a spare head and 3 diffs). Anyway those gearboxes are all T50s. If someone is desperate enough for one to pay the shipping I have one going cheap(ish).

 

Cheers

J2

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There are some things that can be done to help the "standard" box.

The internals from the later single rail variant as used in the dolomite 1850, TR7 4 speed (and Marina 1800?) do fit into the 3 rail casing.

 

It is possible to have a three rail box built using a special, shorter hybrid mainshaft, which uses the beefier single rail parts, the OD adaptor plate from the earlier Dolly box and J-type OD.

 

This is probably the ultimate "spec" BUT, the actual strength of it will depend on the condition of the parts used (bearing mind that new parts are pretty much gone now) and the skill of the builder.

 

Here's som info.

"a special, shorter hybrid mainshaft".

Which is all I ever turned out from about 1983 onwards, even made them for D type.

 

I used up all the old stocks of adaptor plates and recycled masses of overdrive units mostly from saloons....made literally 'undreds of them.

I finished off all the old stocks of the non OD mainshafts too, so they would have had to be remade after that, which was why I said it was time to pack it in.

(probably Walsh Coventry remade them).

 

FYI the 3rd gear is identical in size whatever you do.

This and the 1st motion shaft are always the ones the gear teeth sheer off.

I bought quite a few of those BRAND NEW, and I never had a new one break.

 

I have some of the last original syncro rings (which were made by a co called Sagar Richards).

The part was for a marina, so they must have made 100s of thousands, and the tooling wore out.

 

The later 2nd gear is wider and the old early weak thrust face was instead pinned on the shaft with a tiny ball bearing with a reinforced thrust face on later ones and a "top hat" inside 2nd gear.

This stops it breaking and getting excess play.

 

I bought ALL the new VERY late second gears there were left in the world, this was the very small late gearset which has a different gear cut and runs quieter.

 

I also bought all the normal late 2nd gears there were left in the world.

 

I bought ALL the new gear clusters there were left in the world.

On later gearsets the 1st gear is actually slightly wider, but it's identical to the one from a 1500 Spitfire anyway.

 

I bought the last few new gearbox casings there were left.

 

Some other people may also have some new stock, but all the rest will be recycled gears from Dolomite, which I used for making Spitfire close ratio from time to time.

 

The selectors from Marina were the ones that provided the "forged type" selector hub centres.

Goodness knows why they did that, but it was the only way to get a FAST gearchange without it either wearing out or feeling nasty and sticky, like on the original Triumph boxes.

 

There is ONE major weakness on the GT6 gearbox. The circlip groove just in front of 3rd gear.

If the tool is too sharp that makes this groove, it weakens the shaft and they will fracture at this point.

It's impossible to tell if that shaft is OK or not.

 

If you always fit a decent manufacture circlip at that point I have NEVER seen the circlip jump off.

If you ever re-use that circlip it will ALWAYS jump out of the groove.

Edited by Nick Jones
No private disputes on here please!

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If you always fit a decent manufacture circlip at that point I have NEVER seen the circlip jump off.

If you ever re-use that circlip it will ALWAYS jump out of the groove.

 

There's a Fact worth writing down!

 

I've done away with that piece and use Two Spirolock snap rings in there., completely eliminates the failures. McMaster Carr #91665A440

 

I don't trust the Chineese copies of the original clip we get here in the US of A.

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I've done away with that piece and use Two Spirolock snap rings in there., completely eliminates the failures.

I don't trust the Chineese copies of the original clip we get here in the US of A.

 

Pointless.

In all my years of doing them, I have NEVER EVER had a circlip there fail.

As for chinese ones,- never seen, never heard of.

Perhaps you like buying sub-standard kit.

 

If you were a trader, you would get the same offers as we did....buying boxes of 10 000 laygear needles at a time, and plastic bags of 1000 circlips at a time, as well as the proper gearbox bearings for £2 a shot....

 

There are several other points.....

This is the STOLEN gearbox which people KEEP trying to edit out (!) notice the number of the missing item HC 18497.

 

GT6_box.jpg

 

The overdrive unit was built by a noted specialist, who like to experiment, and drill out the oil ways.

He managed to squeeze up the oil pressure to 680psi on this one.

 

If you look closer notice how the gearcut of the 2nd gear is cut, it's unique to this gearbox.

I only built 4 of these as UKC7874 the 2nd gear part was never correctly listed.

 

If you check,

You will see neither UKC7874 nor UKC3364 are available (which is normal as I bought them all).

UKC 8963 is listed as available but it's pointless because I bought the last 4, 2nd gears.

Without the 2nd gear you can throw it in the bin.

 

Here is the STANDARD looking GT6 gearset. Notice how the lubrication hole is just a ROUND HOLE in the drive dog of 3rd gear and the 2nd and 1st gear are narrower. The reverse gear has the old fashioned 21 tooth,whereas the later 1 has 17.

 

gt_box.jpg

 

Now can you understand why I get REALLY angry when someone "knocks off" one of my best gearboxes,- in fact it was the one out of my race Vitesse, as well as the famous 2.3L, 80.5mm bore block....(or are you gonna edit this too???)

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Thank you for the advice and comments.

 

Nick, good point about state of tune, driving style and what I intend doing with the car. I know that the GT6 box is marginal, but I believe it will be fit for the way I use the car. It also suits the idea behind the build. Although it's a hybrid, I would like to keep it all Triumph and contemporary with what could have been done at the time (1972). I really admire those who significantly re-engineer their cars for racing (or for personal satisfaction), but I just don't have the skills required.

 

The engine build is to sensible "fast road" spec. running on HS6 carbs. I'm not looking for ultimate performance as it's a road car not a race car. My driving style is smooth these days, but I would like to be able to do the odd track day, and I do want it to pull away from the lights well. I will not be reving it till the valves dance on the bonnet before dropping the clutch.

 

Interesting point about the ratios in the saloon box. Heard of others doing this swap, but the ratios don't appear to be considered, only the strength.

 

I've read about mods to the mainshaft tip and two different hardening processes? Any more detail on this? Gareth, you say this is what you did for years, and you quote a list of new parts you bought the last of.

 

Do you still do this work, and do you still have new parts for sale that I will need to have a strong gearbox built?

 

On the subject of who could do this work to a high standard, Mike Papworths name comes up in gearbox threads pretty regularly, but opinions are mixed. Some think he's a gearbox wizard, while others have commented that the only thing he does to recon a gearbox is to wipe the crud off the outside. Gareth, I appreciate your professional opinion on the gearbox build spec. and I have already read your comments on Mr Papworth in other threads.

 

Anyone got personal experience of running a modified gearbox built by Mr P, either good or bad?

 

Who else do the tuners and racers use to build Triumph gearboxes? What are your experiences?

 

Thanks again for all the help. :thumbsup:

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There is a close ratio gearset available for around $600 that converts the gears ogf the Saloon box. It's really what you need to use the Saloon box in the GT6. It's a relatively easy swap and would be pretty robust for your use. It's Moss TT2210A on this side of the pond. Couple that with the Quantum Mechanics top hat bushings and it's a pretty stout box.

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Brooklands,

 

Smooth driving counts for alot where transmission life is concerned. A knock-on effect of gear ratios is that the standard box has really pretty high first and second gears - which reduces the maximum torque that the diff and driveshafts see. Take a saloon gearbox with it's low first gear and the torque passed to the rear end is much increased - and the diff doesn't have huge reserves of strength either.

 

Gareth,

 

I'll definitely edit names and I'll keep doing it too! Your personal disputes have no place on here please.

For the rest of the info I thank you. Very interesting. What is the benefit of this special 2nd gear? From the pic it looks like it has a steeper helix angle compared to 1st gear - almost the same as third gear - which I guess will make it quieter (as you said) but also increase thrust loads and losses?

 

Steve,

 

I completely agree about the Spiralocs (and thanks again for your help with these, the PI box is working fine!). While it may well be true that the proper OE standard circlips are fine, like so many other things sold today, I don't think the ones currently available from the usual suspects are the proper OE standard ones. I know the ones I tried were being permanently deformed by the minimum stretch needed to fit them - and I had several goes and tried several suppliers. (this on saloon box not the GT6 one). It's odd, spiralocs seem to be accepted and established tech in the USA but a still new and scary here (it seems) and consequently very hard to buy.

 

Nick

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Nick, the numbers I gave you are different than the ones quoted above for the Herald based box. McMaster Carr is an incredible resource with any bit imaginable available. http://www.mcmaster.com/ . I'm sure shipping would be minimal for small items like these.

 

McMaster is about 80 acres of warehouse with their own UPS facility on premises. Anything I order from them I have the next day. They are pricier than a lot of places but the convenience more than offsets the extra cost. To my mind at least...

Edited by GT6Steve

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There is a close ratio gearset available for around $600 that converts the gears ogf the Saloon box. It's really what you need to use the Saloon box in the GT6.

It's Moss TT2210A on this side of the pond.

I'm afraid it's a pile of old rubbish.

If you check it's got ZILCH to do with moss....it's even got STR part numbers which means...

IT'S FROM A RACE DOLOMITE SPRINT.

 

One of the main reasons I developed a better gearset than this, (in Germany in collaboration with some "homers" at ZF) is because it's a nightmare to use.

 

1st gear is unuseably high, which meant in the old Sprint racing days, it was a toss up between wrecking the clutch or bogging the car down on the line as there was practically no useable power with that cam below 6000rpm.

 

200rpm either way and you would be sitting there like a lemon, watching the rest of the field disappear around the first corner, while you struggled with 2, 48DCOE webers and fouled plugs....

 

Use a low axle ratio to get away off the line, and the engine would shed its rods and blow up down the back straight........too high, and you had to literally wreck the AP racing clutch off the line...

(THAT IS WHY THEY MADE THE GREY SPRING COVER, with all that extra clamp load!!)

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Mike Papworths name comes up in gearbox threads pretty regularly, but opinions are mixed. Some think he's a gearbox wizard, while others have commented that the only thing he does to recon a gearbox is to wipe the crud off the outside.

 

TBH I think it would be entirely inappropriate for me to post an opinion here, despite the fact he has, and continues to post fairly ludicrous things about me, especially to please his kind of customers in TR register.

It's a form of marketing which works for some.

 

In this game there's no real wizards.

It all depends what you are prepared to pay for "GOOD STUFF", what you are happy to fit, and what you are happy to throw in the bin.

It's called "quality control", and its also called being "sensible" or plain "mean", and knowing where to sell for the best margins.

I sold probably the LAST spitfire Mk3 BRAND NEW axle this march for about £280., and had NO END of time wasters on about it!

 

In this game, there is no free lunch.

The more you do, the higher absolute numbers of warranty returns you are going to get.

SIMPLE MATHS.

 

I can't go into the ins and outs of how to run that kind of business, there would be pages and pages of boring detail, suffice to say, the world is a pretty small place, and we all know each other....even Esposito & Kai's "super micro polished" gearsets...or Bast...(ouch did I mention him!)......sand or beadblasted gears that howl....(ahum!)

 

At the factory they had pretty large numbers of things go wrong, and there again they also subcontracted a lot of the work out in the end, to BEANS industries of Tipton, who believe it or not, used to spend a deal of their time and money picking out odd crown and pinions and relapping them together to make pairs again.

(ahum.. I can spot one a mile away & most of this stuff was re-sold as NOS!)

 

I remember JK giving me a stillage full of old NOS Toledo axles to recon.......took me a month to do....and had to scrap almost all the tapers in them.

They were all done up WAAAAYY to tight, and I think out of 90, 3 crown and pinions were SOFT!!

There you go 4% return rate....not bad considering Triumph usually reckoned 10%.

 

FYI:-

Luckily they were all brand new 3.89s and the housing were by chance ALL GT6 ones (without the bolts and cross pieces) so at 40£ a shot they were (I think) a bargain even then.....

 

Did you know that all the TR6 brand new NOS cranks got sold for 50p a shot??

There were 1000s of the darn things...never mind Hillditch's scrap yard Coventry and the mountain of Salisbury LSDs they dumped in there!

 

I gotta stop...spilling too many old stories!

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Two Sprint competition gear sets it seems

 

http://www.sprintparts.triumphowners.com/uploaded/89/480148_58dolomitesprintspecforgp.pdf (page 2)

 

lots of other interesting (and irrelevant) stuff there too.

 

The ST0053 does have a pretty tall first. Using that with a 3.89 diff is similar to the standard GT6 box with the 3.27 diff (8.45:1 overall vs. 8.665:1)

 

Nick

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I think you will agree, the ST 53 gearset is far too narrow for any form of road use.

 

There is already a big issue fitting even the close ratio gearbox in road car on a Spitfire. (GT6 ratios)

A 1500 really struggles with that high 1st gear in town.

The 1300 finds it not so easy even with the 4.11 axle.

 

I first discovered this gearbox back in the 80s fitted in a TR3 "race" car in France with the original 3.7.

The car was literally undrivable, especially as they had fitted a ceram paddle clutch in it as well.

 

The car was agony to move around the paddock, and murder to get away from the line in 1st.

 

With the extra torque of the 2.5L six cylinder and injection, you could get away with it, but anything on weber carbs....and I mean the dolomite 4V which becomes excruciating using the original Leyland 324 degree race cam, 48DCOE carbs with 42mm chokes (!)and that horrible exhaust they fitted, because there was no room

(I know about how poor the modified heads were too.....)

 

Some people like to be plain masochist.

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Agree that the ST053 is no good for the road unless possibly used with a 4.11 diff or lower but then why would you use such a low diff on the road - especially with a 2.5. Best compromise possibly a normal sprint/ stag ratio ie high 1st gear and ( decent) overdrive on second ?

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OK Folks, first post on here. Although I recognise a couple of posters and been running modded Spitfires for almost 30 years.

 

I have a 2.5 L roto Spitfire (Mk2) which I fitted with and O/D TR box and ST053 gearset after going through various GT6 O/Ds. Gearbox is a bit notchy but I like it and will pull away in 1st no problem with a 3.63 diff. My 2.5 runs twin HS6 carbs and a TR5 cam with a 6-3-1 manifold but is pretty mild mannered. Gearing is high and probably a too bit close for the 2.5 but it will pull 40 mph in first. then again with the engine hot it will start and pull away in 4th off the starter motor! Now 25 years old since I first rebuilt it and has done almost 200k miles in that time. Last 60k or so has been on the TR box which now needs a rebuild as the synchros are getting weak, but I have used it for sprinting and hillclimbs. Fits in OK if a little tight, I needed to modify the chassis rails around the mounting. basically extended the two existing cut out areas.

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Sorry for digging up this old thread, but I believe I have also built a gearbox for my GT6 Mk1 using a 3-rail Vitesse casing, Dolomite 1850 internals, with a GT6 Mk3 1st gear, and J-Type OD. I think I used the standard 1850 shaft, but have an adapter plate which is a little deeper than usual (and looks a little awkward, but it seems to fit - not sure where it's from).

You guys obviously know what you're talking about, so I thought you might have a quick look and let me know your thoughts. (I've never rebuilt a gearbox before)

22728740_10214558825946507_7236512394947691730_n.jpg

22728700_10214558825826504_9033886446392364536_n.jpg

22788646_10214558825786503_288686825978163904_n.jpg

22814275_10214558825746502_5856485266716003838_n.jpg

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Hello Guy, and welcome.

That is the recipe for pretty much the strongest combination of standard parts.  Not sure about the GT6 mk3 1st gear and whether that's any different from the 1850 3 rail one.  As it's presumably meant to be meshing with an 1850 laygear cluster - hopefully not!

For the standard Dolly 1850 single-rail mainshaft to fit you must be using the single rail adaptor housing and that is what you have as I can see the extra bit on the top for the selector rod.  This produces a gearbox which is 1" longer than a standard d-type OD GT6 gearbox (or the earlier 3 rail Dolly 1850 gearbox with J-type) so you'll probably need a shorter propshaft and find that space is very tight at the back, especially around the speedo drive.

Another possibility, using an aftermarket hybrid mainshaft with the larger 5/8" spigot and J-type spline, but the same length as the standard GT6/3 rail Dolly mainshaft is to use the shorter adaptor plate from the early 3 rail Dolly 1850.  However, functionally the only advantage is the 1" length saving and there is nothing wrong with what you have.  I had one just like it in my Vitesse before I fitted the Toyota 5 speed and I never actually managed to break it.

What about the rest of the car?  Start a thread in the Members cars and projects section and show us some pics!

Cheers

Nick

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