Gearbox Options for a +2

[kwhittle]

As I am having to undertake a chassis change, I suppose I have the opportunity to fit a 5 speed gearbox in place of the current Ford 4 speed.
The car is fitted with a 1700cc BDA with the dyno sheet showing 166 at 7000rpm.

So, what do Members think ?
Stick with the existing 4 speed.
Fit a Lotus 5 speed with propshaft and gbox mount.

Fit a modern Ford 5 speed
Or even the MX5 6 speed

What do members think is best option. Cost Vs ease of fitting Vs longevity Vs originality.

My past experience with the Lotus 5 speed was entirely positive
Kevin

[RichardHawkins]

Kevin,

I am currently struggling to fit a Ford MT75 to my Elan. Superficially this is a simple swop as the gearbox bolts to the engine, but there are numerous details to sort out which have taken much more work than I anticipated. Spyder fit this gearbox to the Plus Two, but the position of gearlever and exhaust are less than ideal. The MT75 that fits our chassis is from a Ford Scorpio, it has the starter on the right hand side of the car, and comes with a few variations in the ratios available. I imagine finding a Scorpio would be difficult now as they were never popular and are old.

Should you choose this option I may be able to help you avoid the mistakes I have made.

Richard Hawkins

[mbell]

On the Lotus 5 speed:

Pros:
- It fits easily
- Good gear ratios
- Nice gear change (when sorted)

Cons:
- Hard to find and expensive
- Not the most robust box, ~160BHP is probably pushing it's limits
- Limited parts supplies
- Likely need mods (e.g. uprated input shaft bearing) for this use case

I think the other boxes will generally be more robust but require a lot more effort to fit and find a solution with good ratios.

[prezoom]

A friend and neighbor (Evora, Esprit, S7) recently told me that BGH is in the process of making a new tail shaft housing for the T9. Other than the original shift lever location, that gearbox seems to be one of the easier ones to fit. It also allows for a decent number of gear ratios both in helical and straight cut. Having another choice for a new rear housing would be welcome.

[stugilmour]

Kevin, I would suggest the MT75. Well trod path with good support from Spyder. The frame change is the ideal time to take this on. A few details....

I sourced the rebuilt transmission with the required linkage modifications directly from Spyder. Note they have since modified the linkage to reduce sizzle. My shift lever sits slightly aft of stock, but I find it better positioned than stock.They can probably supply the correct clutch for your BDA. The MT75 uses an axial style internal slave cylinder, and Spyder will supply a flexible hydraulic line to connect directly to your existing master cylinder. They also have the corrct length prop shaft to match to your Plus 2 diff, starter motor, conversion fitting for the Plus 2 speedometer cable, and a transmission mount that matches the MT75 casing. For some reason my package did not include the sheet metal sandwich plate pieces to cover the bottom of the bell housing, but Spyder may have something available there and just forgot to supply. If all of the details are too much to take on, I am sure Spyder would attach your engine to the new gearbox ready for installation.

Note the MT75 is best fitted to a replacement Spyder space frame. As you are doing the frame anyway this is the right time. Make sure Spyder fully understand you are fitting the MT75, as they modify one of the members next to the starter to ease fitment issues. You will also want to confirm clearance for the harmonic balancer at the frame vacuum tank/crossmember. I am not familiar with the BDA details, but Spyder have different crossmembers for the TC and their Zetec builds. The best is to fit everything into the new built up subframe prior to re-installing the body.

As mentioned, the preferred MT75?s are from the Scorpio. The Scorpio enthusiast?s site has the complete service manual posted. The parts drawings are posted, but unfortunately not the corresponding Ford part numbers. This becomes confusing as there were several distinct versions of the MT75 and a few running changes. My local shop had to make up a few relatively simple special tools to rebuild the box. Even though my tech is very experienced, he found the box service quirky; not a immediate issue if you purchase a rebuilt box from Spyder.

Two important details from my build. Shorten the Spyder shift lever and have a threaded connection made. This allows removal of the lever so the engine and transmission can be removed as a unit with the body in place. Note the threaded bellhousing holes are all metric threads; although your SAE bolts from the four speed will fit they will destroy the metric threads; you don?t have to ask how I know.

There are some drawbacks to the MT75. The gearbox was not used in North America so we have parts sourcing issues over here, not an issue in the UK though. The first gear is somewhat lower than ideal; the rest of the gearset is pretty well spaced and the 0.82 overdrive is great. Routing the exhaust around the bellhousing is a bit difficult and compromised; I have taken a second try at mine with a new big bore exhaust and have my fingers crossed regarding ground clearance.

HTH

Stu

[mikealdren]

The Sierra MT75 box has a higher 1st gear than the Scorpio (which needed the lower gear for the heavier car) but has the starter on the wrong side and a cable clutch.
Has anyone had the higher 1st gear fitted to the Scorpio box? I currently have both boxes and am contemplating the options.

[RichardHawkins]

Mike,

As both boxes are MT75 I assume that the internals are interchangeable, but it would be a bit of a gamble. The 75 in the name, is the distance in mm between the main shaft and lay shaft. I have been surprised at the variety there is within different MT75 applications, so I wouldn't be surprised if the gears from one casing will not fit in the other.

My option was to use a 3.54 differential ratio to raise the first gear ratio as much as I could.

Richard Hawkins

[mikealdren]

Thanks Richard,
My car will be Zetec so I am using a later diff and will be gearing as high as possible to take advantage of the extra torque. It's the gap between 1st and 2nd that is the main issue for me.

[Spyder fan]

I second Stu?s reply as the way to go. I believe that the donor box is an MT75 from a 2.4 RWD Scorpio or Ford Taunus. This has a hydraulic clutch with the starter on the Rh side. The starter on the RH side is important as it allows reasonable routing for the exhaust manifold/headers.

1st is lower than a 4 speed Lotus and well matched to modern traffic jams and useful to get peaky low torque engines going along the road (at low revs).

If I had bought your car an MT75 would be on my list along with fuel injection, a Scorpio LSD and a Grumpy Bodger exhaust manifold.

[stugilmour]

Mike, quite possible the first gear wheels can be fitted. One possible issue is fitting the synchro?s. There was a running change on the Scorpio MT75?s, the early first gear synchro is a two piece deal and the later assembly is a three piece. I had a heck of a time getting my three piece type replaced from Canada, but a forum member here helped me out big time by checking with his local Ford dealer to get the correct parts once I found the Ford part numbers. This issue will be easier to assess once you have both boxes apart, and might be resolved with custom machining/shimming or whatever.

Agree with comments above about the merits of going with the 3.54 or 3.55 diff ratio to mitigate the low first gear. As posted to the Original Poster before on a different thread, this combo in my car delivers approx. 80 mph at 3,500 rpm in fifth, which would be heaven with the BDA.

I believe first goes to only about 30 mph at redline. Agree with Spyder fan that one doesn?t actually drive this way on the road; tend to shift into second much lower, say 4,500 rpm. Even the TC has plenty of torque to hook up in second at 3,000, although the gap from first to second is definely a bit larger than ideal. Really first is not a total Granny Gear, but is handier to ease start/stop issues in heavy traffic than for ripping off drag strip starts. Even on our relatively low speed technical track second gear is as low as I ever go, so it is not a real world issue.

I am not knocking the T9, but there have been discussion threads here for over seven years on the imminent release of a full featured & complete T9 kit for our cars. In that time I have put over 50,000 miles on my MT75, which I was able to sole source from Spyder. Although the MT75 parts availability in NA sucks, props to Sean and Andy for their support of their overseas clients with supplying everything required to install the thing.

HTH

Stu