modern manual gearbox upgrade for Stags

[garyf]

Is there a modern manual gearbox that will fit a Stag?
I did see a 6 speed ZF manual gearbox on eBay
just wondering
Gaz

[mjheathcote]

I was in discussion with these guys about a kit, and they where looking into doing a kit for Triumphs using the Mazda MX5 gearbox.

https://www.vitesse-ltd.com/pages/triumph-gearbox-upgrades

It looks like they have progressed, but no Stag listed.
Might be worth a call for an update.
They where certainly buying the Stag engine/original manual gearbox adaptor plate to investigate the possibility.
What Triumph did to fit the original manual OD gearbox was use an adapter plate spacer to get the gear lever in the correct place, and then extended the input shaft accordingly, and beef it up slightly for the increased torque. The main bellhousing casting the same as the TR's the box was borrowed from.

[mole42]

If the ZF manual is anywhere near as good as their automatic it will be a super upgrade.

[garyf]

found some chat on the net about using a

Toyota W58 5 speed from a Supra in the stag
but not enough to get excited about

[Phil S]

they do the supra box conversion for the rover v8 by cutting and shutting the bellhousing, needs someone with a spare block and even more enthusiasm to have a go

[Manuel]

Mog frame.jpg
The Tremec T5 is often used in a Morgan +8

http://www.tremec.com/menu/t-5/

I put a Tremec TKO with a adapter plate in my Morgan

[Phil S]

the T5 is originally from the mustang so will take the power but because it was then used in the 2wd Cosworth the prices can be stupid, I have seen clapped out ones sell for over £500 and that's before very costly rebuild

[marshman]

I was in discussion with these guys about a kit, and they where looking into doing a kit for Triumphs using the Mazda MX5 gearbox.

https://www.vitesse-ltd.com/pages/triumph-gearbox-upgrades

It looks like they have progressed, but no Stag listed.
Might be worth a call for an update.
They where certainly buying the Stag engine/original manual gearbox adaptor plate to investigate the possibility.
What Triumph did to fit the original manual OD gearbox was use an adapter plate spacer to get the gear lever in the correct place, and then extended the input shaft accordingly, and beef it up slightly for the increased torque. The main bellhousing casting the same as the TR's the box was borrowed from.

My wife has an MX5 (NB MK2.5) and I am not overly impressed with the gearbox. Once warmed up the change is OK but it is stiff when cold (and always has been - seems no different to other MX5's I have driven), it also whines a lot in first - not a nice sound in a "refined" car like a Stag (in my opinion). We have had the car since 10,000 miles and the box has always been the same. To be honest the 5 speed LT77 in my Landy has a better feel to it than the MX5 box (could be due to the longer gear lever!). Just my opinion - (bear in mind my Stag still has the BW35 auto and I am quite happy with it)

I would also be a little worried about the ability of the box to handle the torque from the TV8 - don't know the actual figures but would imagine the TV8 pushes out more at lower revs than the MX5 does.

Roger

[bullstarz]

Mog frame.jpg
The Tremec T5 is often used in a Morgan +8

http://www.tremec.com/menu/t-5/

I put a Tremec TKO with a adapter plate in my Morgan

That looks more like the T56 magnum box . I know as one of those is on my Stag and its a six speed double overdrive box.

The supra w58 box is a decent box it was also fitted to the Lotus Excel. A far better box is the R154 toyota box. It will handle 500 bhp with easy. The 161 toyota box is a similar strenght box but a 6 speed but hard to find and costly.

The magnum box is a good value box , at £3000, will handle 700 bhp and 880 Nm 650 lb-ft without breaking a sweat. Its slightly longer than most boxes so there has to be a few mods to the transmission tunnel and the centre console.

Any gearbox can be made to fit the Stag engine you just have to get an adaptor plate to mate the two together and a flywheel that keeps the the clutch in the correct place to engage all of the input shaft splines.

A bit of CAD work and they can be easily made/designed.

I had a T5 WC borge warner box when I has the rover engine. nice box but could only handle 400 ish bhp. They were fitted to many cars like the TVR's. These can be very expensive now as they are becoming hard to find. Mine which was the World Class, WC, sold for £1000 7 years ago.

[mjheathcote]

My wife has an MX5 (NB MK2.5) and I am not overly impressed with the gearbox. Once warmed up the change is OK but it is stiff when cold (and always has been - seems no different to other MX5's I have driven), it also whines a lot in first - not a nice sound in a "refined" car like a Stag (in my opinion). We have had the car since 10,000 miles and the box has always been the same. To be honest the 5 speed LT77 in my Landy has a better feel to it than the MX5 box (could be due to the longer gear lever!). Just my opinion - (bear in mind my Stag still has the BW35 auto and I am quite happy with it)

I would also be a little worried about the ability of the box to handle the torque from the TV8 - don't know the actual figures but would imagine the TV8 pushes out more at lower revs than the MX5 does.

Roger

Can't comment on the shift quality/whining, but with regard to be able to handle the torque they have been offering the same gearbox as part of their MGB Rover V8 conversion for a while.

[Manuel]

The T5 is still new aviable

https://www.summitracing.com/int/parts/awr-trfo-30001/overview/

[bullstarz]

If you want a new gearbox then here's the UK Importers for Tremec

https://roadcraftuk.co.uk

[Carboy0]

I have done various gearbox conversions on other classics, designing gearbox to bellhousing and bellhousing to engine block adaptors, so am interested in the conversation. The points about power and torque handling capacity of various gearboxes is important, but in my mind in an upside-down way. If you are running a standard or close to standard engine, then having a gearbox capable of handling 500 bhp & 500 lb/ft is unnecessary (and expensive).

Most LT77s and non World-Class BW/Tremec T5 gearboxes are rated up to around 200 bhp & 200 lb/ft., as has been mentioned the World Class version of the T5 will handle 400/500 bhp. There are various ZF (ex-BMW) gearboxes with similar or greater power/torque handling abilities. The Aisin gearboxes found in various Mazda & Toyotas are another good source.

So, when considering a gearbox, I would suggest that you look at your expected Stag engine power output (including any future plans) and then look at other vehicles that already have similar power/torque characteristics. In general, most manufacturers factor in around 30% excess power/torque capacity as a means of building in long service lives. As mentioned when Triumph fitted the OD gearbox, you have to consider the relationships between length of input (first motion) shafts and relevant bell-housing depths. I.e. if the Stag bellhousing is 10” (guess) and is retained and the input shaft is 11”, then an adapter plate of say 3/4” thickness, will require a new gearbox with an input shaft of 11.75” will be required. Conversely, if the new gearbox has an input shaft of 12” then you need an adapter plate of 1” thickness.

Looking at Far Eastern car sources

1. The old normally aspirated Nissan 300ZX used the non World Class Borg Warner T5 gearbox.
2. There are a family of Aisin inline gearboxes that include Lexus 200/250/300, Mazda RX8 (5 & 6 speed version), Nissan 350ZX & 370ZX. Most of these have an integral bellhousing, where the bellhousing forms the front plate of the gearbox and carries bearings and oil seals. This means that the only adaptor option is between the bellhousing and the engine block.
3. The old Toyota Supra has what’s generally agreed to be bullet proof up to 500 bhp.
4. There are also very strong gearboxes in the Mazda RX7 Turbo, but the non-turbo version are very similar to Mk1/Mk2 MX5s.
5. The Mazda MX5 gearboxes are split between Mk1/Mk2 and later versions which are in the same family as the Aisin gearboxes mentioned earlier. They all have integral bellhousings. The earlier gearboxes will handle up 180 bhp / 180lb/ft, but no more for any length of time.

America

1. The Borg Warner (now Tremec) T5 gearbox came in various version in a whole range of cars (Ford, Chevrolet etc,), with various input shaft lengths and also usefully 3 different positions for the gear selector on the tailshaft. As I mention above they come in 2 power handling types non World Class (lower power) and World Class.
2. The BW 6 speed T56 gearbox is similar, although the gearbox bolt pattern is different from the T5.

Europe

Looking at the range of rear wheel drive cars available means either BMW or Mercedes, both of which use ZF gearboxes. Again, they use integral bellhousings, some of which can be weird shapes to accommodate engines like the slant 4 & 6 engines used on many BMWs - a better option is to look at the V8 & V6 versions available as making up a suitable adaptor plate will be more straight forward. The diesel BMWs have enormous torque, so their ZF gearboxes are really tough.

Rover Group LT77 - well known to Rover V8 users, used in Rover SD1, 5 speed TR7s, Sherpa & LDV Commercials and various sports cars, including TVRs and Morgans. The gearbox’s ability to handle power/torque varies dependant on its source. There is a table on the internet that lists the gearbox codes to look out for. There are also various linkage lengths for the remote gearstick.

Ford MT75 - designed as the replacement for the Type 9 gearbox, some early ones had a bolt on bellhousing, but most had an integral bellhousing. In 4x4 form it had a very high power/torque rating, so it’s possible to swap the important bits into a standard rear wheel drive casing, or using a standard tailshaft onto a 4x4 gearbox. They can be found in Late Sierras, Granada Scorpios, some Transits. The rallying fraternity know lots about these gearbox and so there is a W health of knowledge about adapting them.

Ford Type 9 - these all have a bolt on bellhousing, input shafts come in two lengths with versions from V6s and diesels being 25mm longer. The highest power/torque capability is with the V6 versions. As per the MT75 gearbox, it’s possible to swap 4x4 parts into 2wd casings. As per previous comments check the source of the gearbox to check its power handling capacity, compared to the spec of you Stag engine, it may be marginal.

There are also Volvo 240/740/940 and Vauxhall Omega gearboxes, both of which have good reputations, but I don’t know much about them.

Using gearboxes with integral bellhousings, normally commits you to using their clutch control mechanism, unless you engineer an hydraulic concentric clutch arrangement. Usefully most of the Far Eastern gearboxes use hydraulic control so it should be possible to use the Stag clutch master cylinder.

Lastly whichever gearbox you opt for, you are going to need a bespoke prop-shaft to join the gearbox output shaft to the back axle and a bespoke gearbox cross-member.

[mjheathcote]

Excellent write up, just need someone to offer a kit.

[jakesmig]

I use a T5 gearbox in mine, which has an RV8 fitted which is a lovely box and cost about £1500.00 fitted once serviced, including concentric hydraulic clutch, clutch plate (which required modification to reduce the diameter), propshaft and shortening the lever shaft.
According to the gearbox number it came out of a 5.0 Litre Camaro and has a 0.63 final drive which gives 33mph / 1K rpm so cruising is quiet and economical.
It was expensive but the old LT77 was beginning to show signs of wear so I bit the bullet during a restoration. It is a slightly wider box and the tunnel had to be eased using a jack at one place. The difference was very small and isn't noticeable in the car. If the sound deadening hadn't been installed no easing would have been needed.
Buying a bare box was 'cheap' at £350 from Ebay, the difficulty was finding a bellhousing, then a clutch plate to fit the huge input shaft spline.
As Carboy0 indicated, the input shaft lengths need consideration. Mine was too short so I made an adaptor to fit into the crankshaft which thankfully has worked without fault (so far, touch wood, keep fingers crossed) for several thousand miles since installation.

PS, I admit that replacing the LT77 with a similar rebuilt LT77 would have been smarter and cheaper, but the T5 has proved to be a lovely smooth box, ant there was entertainment value in making it fit, which to me is what it's all about.