The Costello 5-speed gearbox was slick, quiet and strong. It also required no modifications to the car when fitted; could be removed without disturbing the engine - and even had synchromesh on reverse! Unfortunately, it is long out of production. The original MGB/C gearbox is not really up to the job in the long run, especially if you are running a tuned engine, and of course, it lacks a fifth gear.
There are several other alternatives, but the leading contender is the Borg Warner T5. This was made in a number of configurations, but the one to find is as fitted to TVRs and the 2WD Ford Cosworth Sierra.
New, nicely made bell housings to suit, complete with concentric clutch release slave cylinder and bearing (much better than the standard set-up) are available from J E Developments.
New, stronger gear sets in a choice of ratios and stronger selector forks are available from Competition Transmission Services, who can also supply Quaife products - including limited slip differentials. The foregoing two suppliers have been used by Costello owner Roger Cook and are recommended. You will also need a new clutch and flywheel. Sourcing the TVR version of the T5 could also provide the former, plus the bell housing - though it's not as good as the John Eales product.
Slight modifications are necessary to the top of the transmission tunnel, as is a new rear gearbox mount/cross member - and you will need to have your existing speedometer recalibrated. For that task, we suggest you try: SpeedyCables.
Then there's the Rover SD1 (LT77) gearbox, which although a five-speeder and more robust than the original MGB, does not enjoy a very good reputation. Presumably that's why it was redesigned and re-launched as the R380. It's your choice and they're not particularly hard to find, but budget permitting, you would probably do better looking elsewhere.
Other alternatives might be the modified Ford MT 75 gearbox offered by MTC ReMan; though as yet there doesn't appear to be any suitable bell housing available - which seems odd since the same group now manufactures the Rover V8 - or theToyota Supra gearbox. The latter is available in several configurations and a company called Dellow Automotive in Sydney, Australia offers suitable bell housings and other conversion components. Once again, transmission tunnel/bulkhead modifications may be necessary, as will be revised gearbox mountings and a new prop. shaft. A 3.07:1 crown wheel & pinion (MGC) is the best choice of final drive ratios.
More Information from the Forum:
Ben Tovey posted such an informative piece on gearbox alternatives in the Forum that it has earned its place in the Technical Details section. So here's his list of gearbox options in slightly edited form.
Have the original gearbox rebuilt. (This is not entirely satisfactory, particularly with higher-powered V8s, and is therefore not Ken's preference. The overdrive in third gear is especially fragile, which is why Ken used to disable it - and is one reason why he designed his own gearbox. (That said, my MGB 4-speed - reconditioned in 1998 - is still going strong, has overdrive working on 3rd and has survived several hard-driven track days - LW).
Modify the transmission tunnel and fit a five speed LT77 gearbox as found in SD1s, TR7s etc. However, apart from the relatively ready availability of these gearboxes and suitable bell housings, this option is not all that straightforward. Besides enlarging the transmission tunnel, you may need to locate a manual flywheel, change the clutch, adapt the prop shaft, modify the gearbox cross-member and fabricate new gearbox mountings. Note that the LT77 comes in a multitude of different versions, so you need to make sure that you look for the correct ratios and the serial number suffix 'D'. Even then, this box has a poor reputation.
As above, but use the later Rover R380 gearbox as fitted to the MGRV8. In simple terms, the R380 is a much improved version of the LT77, though sharing same physical dimensions. A better option, but it's still not the best.
The 'Ford option', which uses the Borg Warner T5 gearbox. This sturdy gearbox has found its way into all sorts of vehicles from Ford Cosworths to Volvos and TVRs. The ones we are interested in are original equipment on the V8 TVRs and 2WD Cosworths. These are to be preferred because they have the gear lever in the right place and can provide the ancillary bits we need: i.e. bell housing, clutch, flywheel etc. In common with all the options listed here, transmission tunnel and gearbox cross-member modifications will be required, as will new gearbox mounts. This link provides more details of the T5 option.
Toyota gearbox from behind the Supra 7M-G engine (non-turbo 1986-1992) which has the W58 gearbox*.
This is also a strong box with the right ratios and physical dimensions to fit. As with the others, you will need all the associated parts, but there is a company in Australia which does a complete conversion kit, including gearbox if you need it. Follow the link to Dellow Auto, but be warned, it isn't cheap
* The W55 version of the same gearbox has also been successfully used. Please also note that we can take no responsibility for the information which is gleaned via the links that Ben has included - LW
So there are the five main contenders. Your decision on which one you choose needs to be based on what you want the car to do and how much you intend to modify it. If you intend to keep the engine output as original, then I would probably get a quote for re-building your existing four-speeder. After all, it has lasted over 30 years. If you intend to upgrade the engine for a little more power, then the R380 becomes a possibility, with the advantage that pretty much all the parts can be bought off the shelf.
You can learn more from the MG V8 Homestead website.
If you are planning a serious engine upgrade though, then you need to look at the T5 and Toyota options, as both are capable of handling around 350BHP (or so I am led to believe) Neither of these are particularly cheap alternatives as they require lots of extra parts and time. And just in case the information above has not left you totally bored (but hungry for more) here are some additional links for help with parts and information:
- Aluminium V8 Conversion.
- V8 Tuner
For details on T5 ratios and dimensions:
- All Ford Mustangs
- Ford Muscle
For further information on some T5 options:
- Ford Muscle T5 Options
Yet more T5 facts and dimensional data:
- DD Performance
Ben Tovey isn't the only owner who's not backward in coming forward with technical information - which in this case also happens to be gearbox-related. Racer John Kemp sent us a useful spreadsheet all the way from Adelaide, Australia. It calculates your gearing for you and displays (by selecting the appropriate tab at the bottom) road speed in relation to rpm. John says it's "quite useful for working out up change points and whether or not your differential ratio is appropriate, amongst other things".