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Old 10-22-2018, 03:16 PM   #565
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Join Date: Jul 2010
Location: Belgium
Default Need to know more

So i got myself this M90 gearbox to install in my Amazon Combi B230 Turbo.
I am now running a M46, it is still holding up with the 227HP/373nm but i don't want to wait for d-day and prepair a stronger unit. Ofcorse more tunnel work and other mods will have to be done.

My guess was it was a M90L2.
Turing the input and count the revs in versus out, first and second gear confirmed it is indeed a L Type (L1 or L2).
Then doing the same on fifth gear to know if it is the L1 or the L2.
BUT... to my surprise it matches neither one of those

The L1 type has a 5 ratio of 0.81 to 1 and the L2 type 0.7 to one.

Mine has a 0.7525 to one ratio!

I googled about an hour to find other gearing types for the box but ALL showed the same, know as 0.81 and 0.7 5th gear.
I learned the internals *might* be interchangable between FWD M56/M66 and M90 boxes, so i looked that too (maybe someone switched the gearing on 5), but also for these boxes no 0.7525 or anything near that seem to exist.

I'm sure i did the correct measuring:
I first turned the input shaft until the out made a full turn. The in made about just 3/4 of a turn, just a tad more.
To find out how much exactly, i then turned until the out made 4 turns. The in made then 3 turns and a bigger tad.
So then i turned until the out made 16 turns, the in made 12 and about 14 extra.
Then i made 12 times 12 turns (on input) and found that the mark i made on input then almost made 1/2 turn extra to align the out on it's mark.
So i turned input again 12 times 12 turns (now total 24 x 12) and fount i needed to turn it once more 12 turns to get the input mark straight up (360 degrees) again.
Margin of error reading marks is very small now the input shaft turned 301 times, so the fault is devided by that! 2x(12x12), +12 (+1 the mark turned 360 extra)
while the out made 25 x 16 = 400 turns. 301/400 = 0.7525 gear ratio.

Now i suspect ALL documentation is WRONG about the L2 being 0.7 in 5
Did anyone alread did the math turning and counting, or did anyone already OPEN THE BOX AND COUNT THE TEETH ON FIFTH GEAR GEARS?

or do i just have an exotic and spooky M90

Last edited by RolinOldies; 10-23-2018 at 01:45 AM..
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