Lotus Elan

Info wanted on output flanges for MT75 gearboxes

PostPost by: worzel » Wed Apr 18, 2012 6:49 pm

Hi

Can any owner out there (or non-owner if they know the answer) of a Spyder modded car fitted with a MT75 box clue me in on what's available in terms of gearbox output flanges. As far as I know there are 2 types only- a 3 lug type that takes a doughnut and a 6 bolt round one. I'm asking because I'm hoping that a small flange is also available- I'm looking for one of a size that will fit within the centre spine of the chassis. I know the 6 bolt one can be machined down to a 4 bolt one but ideally I'm looking for one small enough to spin within the opening of the centre spine (because the bellhousing in question that I'm considering using will place the flange at that point).

This issue has arisen because the measurements I've worked to pertain to the depth of a std Rocket to BDA bellhousing. A std one is 173-173.5 mm deep. Guess what- mine is clearly non std and is 184mm deep. The result is that the splines on the input shaft are 9mm too far away from the clutch disc. Result is the friction plate splines overhang the splines of the box. Swapping to a std depth bellhousing would obviously solve this problem but would result in the output flange of the box lining up quite nicely with the narrowest part of the chassis centre spine. A small output flange would solve the problem quite nicely leaving about 12-14mm space each side- hence my question.

Regards and thanks

John
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PostPost by: c42 » Wed Apr 18, 2012 8:49 pm

Hi John

There is a 4 bolt flange that was fitted I believe to a Transit box but I am currently experimenting with a blank uj flange to see if it can be drilled to fit the 3 eared ouput shaft which I believe is almost the same drilling as the driveshaft spider.

Regards
John
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PostPost by: worzel » Thu Apr 19, 2012 8:31 am

Hi John

That's interesting- you don't by any chance know the dimensions of the one fitted to transits do you? Regular visitors to the forum might well recall my earlier postings on fitting a MCT75 box to a std chassis as opposed to a MT75 unit. The annoying part of the whole operation has been this part ie the clutch arrangement. I reasoned out a MCT box which is pre-drilled and tapped to the same pattern as a Type 9 would bolt straight to the bellhousing I already had (a Rocket to BDA item). In turn this bellhousing would bolt straight to the elan block. This method would retain the std flywheel/clutch cover, external clutch hydraulics/flywheel/ring gear and starter. All of this works as I planned. What I didn't realise that the bellhousing I have is deeper than the std Rocket to BDA one by 10mm. So unfortunately this in turn means the input shaft splines are 10mm too far away from the engine ie they don't engage enough with the clutch disc.

The option of using a shallower bellhousing isn't an option (even though they're available new) because a shorter bellhousing would in turn move the box forward by 10mm in turn this would put the box output flange right by the opening of the centre box section. Therefore I need a smaller output shaft that would be able to turn at this point without hitting the chassis. My associate who was working with me has sort of thrown in the towel hence my recent ad offering to sell the whole package as I didn't fancy doing the donkey work of proceeding alone (my friend isn't very technically minded). However I've since cooled down and rationalised things and am digging in my heels as I don't like being beaten so I'm scouting around for a solution. Modifying an output shaft might (just) be a solution but opinion is that this might not work as per earlier comments on altering an input shaft.

Any bright ideas anyone?

John
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PostPost by: worzel » Thu Apr 19, 2012 6:54 pm

Hi- again

I should have added the following info. If I eventually manage to locate/fit a smaller output flange this would enable the use of a shallower bellhousing since moving the box forward wouldn't cause any inteference issues with the chassis. I reckon it would be feasible to modify an output flange by using a blank, thick disc and machining this to fit to the original flange. The disc could then be welded to the output flange and the excess material of the original flange machined off and the whole trued up. The new flange would then need to be drilled and tapped to match the corresponding prop flange. I don't see how this might cause problems with the integrity of the modded flange since the diameter of the welded part isn't much different to a small diameter propshaft.

Any thoughts on this idea?

John
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PostPost by: c42 » Thu Apr 19, 2012 8:56 pm

Hi John

For information I have a picture of the blank flange for you, the diameter is 110mm. Unfortunately you need about 115mm to safely bolt this onto the spider and a plate needs to be welded to the flange and then turned in a lathe to true up face; this can then be drilled to suit the output spider.

Does your output spider sit in the tunnel or in the small bulkhead?

Regards

John
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PostPost by: worzel » Fri Apr 20, 2012 1:02 pm

Hi- again again!

Thanks for that info John about the blank flange. Just paid a visit to the firm that have made props for me in the past. Ran my idea past him- he couldn't see any reason why my idea wouldn/t work - provided the welder was very competent. Borrowed a suitably sized flange from him to get the dimensions. Quite confident this will sort out the last but one problem which is the bellhousing depth.

As I see it I've 4 options-

Shorten the existing Rocket one I already have- not very keen on that idea since this would involve removing 10mm of material

Get a correctly dimensioned new one cast

Experiment with altering a std cast iron 4 speed item.

Buy a new Rocket one and reduce its depth by 5mm (the new ones are 178mm deep compared to mine which is 183mm and compared to a std 4 speed cast iron one which is 173mm)

3rd option would involve welding cast iron and having the centre round aperture machined out to suit the other box but might be worth investigating since these bellhousings are pretty cheap.

I'll have to investigate further.

John
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PostPost by: worzel » Tue Jun 04, 2013 8:05 am

Hi John

a bit of a "blast from the past"- we conversed some time ago about modifying an output flange for a MT75/MCT75 box.

You mentioned you were using a blank prop flange. Are these readily available or do I need some sort of secret password?

Also- could I trouble you further- (apologies if I've previously asked this) but do you know of what material the six bolt output flange on a MT75 is composed- and is it weldable?

Regards and many thanks

John
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PostPost by: c42 » Tue Jun 04, 2013 1:28 pm

Hi John

The blank prop u/j flanges are available from http://www.davemacprops.com/DMPHOME.html
I am pretty certain they are available in a couple of different diameters, I am also pretty certain that I had to use a 125mm or 130mm diameter flange and turned it down to suit the flange on the MT75 box.

The output flange on the gearbox seemed to me to be steel when I cleaned it up and therefore I would say that it will be weldable but not having tried to weld anything onto the flange I cannot be wholly certain but John at Dave Mac will probably know.

Sorry for being a bit vague.

Regards
John
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PostPost by: worzel » Tue Jun 04, 2013 6:19 pm

Hi John

Many thanks for the info- I've sent an enquiry to Dave Mac's place.

I'll keep you posted just out of interest.

Regards and thanks

John
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