tract0rman49
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| posted on 10/10/14 at 08:43 PM |
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Mitchell Cots MT75 - with BDA to Rocket Bellhousing
Hi all
I recently bought an unused Mitchell Cotts Gearbox with ratios 3.6; 2.08; 1.36; 1:1 and 0.76 that I intend to fit into a 1971 Lotus Elan Sprint to
replace the original 4 speed 3 rail box.
I have managed to find a really nice Magnesium BDA to Rocket Bellhousing that gives me the correct engine block mounting holes and includes the lug to
take the standard Ford/Lotus clutch slave cylinder. I have an RS2000 215mm diameter clutch palte with the matching 23 splines.
The problem I have is the 1st motion shaft length is some 23mm INSIDE THE BELLHOUSING TO CYLINDER BLOCK FACE!!!! My thoughts are that this box was
intended for a Caterham or Westfield to mate to some other power unit and the bellhousing dimension from the gearbox front face is approx 124mm
compared to the Ford/BDA 178mm.
Can anyone help me identify the correct replacement 1st motion shaft that will match my engine/bellhousing??
Thanks 
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MikeR
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| posted on 10/10/14 at 10:00 PM |
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sounds like you want a 1 inch spacer. on type 9 gearboxes there are two sizes of bellhousings. the difference .... 1 inch. people with the wrong size
housing just fitted a space & longer bolts. this may be the same problem.
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Paul Turner
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| posted on 11/10/14 at 01:01 PM |
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I would suggest that you sell the Michell Cotts Gearbox. A first gear with a ratio of 3.6:1 has no place in a performance car. 1st in your 3 rail box
is 2.98:1 and is much more suited to an Elan. If you go to the trouble and expense of fitting the box you are going to be very disappointed, I can
guarantee it.
I would suggest you speak to Steve Perks at SPC (01527 894232) about one of his close ratio type 9 boxes. Physically the type 9 is quite a bit smaller
than the MT75 and even with Steve's most economic conversion you still get a set of ratio's almost identical to what you have with a 5th
for cruising and the correct length input shaft.
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tract0rman49
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| posted on 13/10/14 at 09:19 AM |
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Mitchell Cots Box - For Elan
Hi, I appreciate your comments re Type 9 box and shorter 1st gear ratio. The biggest challenge fitting a type 9 to the Elan is the gear linkage being
around 10" to 12" too far back which is unacceptable. The MT75 Mitchell Cots conversion has the advantage of a separate bell housing and a
gear linkage only slightly further back (around 2" I believe) than standard. My Elan is running a 3.55 diff so while I accept the 3.6 longer
first gear is not ideal I cannot see it being massive. Early Elans ran a 3.9 and 3.7 diffs so negating some of the benefit of the 2.9 first gear which
would end up overall being 10% shorter than the 3.9 axles. My aim is to have a taller cruising top gear with speed in 5th around 23 mph / 1000 rpm
compared to 17.5 dropping revs at 70 by around 1000. Have seen some attempts to create a forward gear selector position on Type 9's but
it's a serious amount of engineering which I am not prepared to do.
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