Message: 5
Date: Tue, 20 Dec 2005 08:52:06 -0700
From: Kirk <hillman88@*****.net>
Subject: Re: [lro] series transfer ratios
To: the Land Rover Owner Mailing List <lro@****-*****.****.net>
Message-ID: <001e01c6057d$54514160$6601a8c0@kirk>
Content-Type: text/plain; charset=iso-8859-1

Chaz,
    If I understand you correctly, this is what you have done:

1) Take a 31T output gear and machine out the middle
2) Take a 27T input gear and machine off the outside
3) Weld the 31T ring onto the now toothless 27T hub.

    You've likely already figured out where the intermediate shaft must go
for this to fit.  It won't go in the stock location because of the
interferance between the larger input gear.  The intermediate shaft needs to
stay the same distance away from the output shaft to keep those gears in
proper contact, while getting farther away from the input, thus rotated up
or down concentric on the relevant radius.  I'm curious, did you calculate
where the intermediate shaft needed to go or what?
    My appologies on leading you astray with incorrect info previously.  It
is NOT possible to acheive 3.313/1 gear ratios by machining only one gear.
In the past few years I've -contemplated- so many iterations to fit inside
the Series t-case I sometimes forget what goes where.  To get this setup you
need to make two gears and modify a third.  First, the large end of the
intermediate gear ('B' suffix) needs to go from 44T to 48T.  Then the low
gear wheel needs to be 41T instead of 39T.  The high range output needs to
be a 27T modified input gear.  Finally, the intermediate shaft needs to be
offset from the current location to 0.9008" up/down from center.  That would
give you the following:

Input gear-
27

Intermediate gear-
22/48

Output gears-
41/27                    <-- note from WRM : This should be 31/27 I think

    While my design is certainly more work, it does something many people
don't directly consider.  It changes the 'spread' between high and low.
What I mean is that high and low range get farther apart so that there is
less and less cross-over between them when you factor in the transmission
gearing.  The larger the spread, the faster you can go in high range while
at the same time going slower in low range.
    By performing this 2.516/1 mod you haven't changed the spread (think of
it as another ratio 2.516/1 = 2.516) over a standard 'B' suffix box
(2.889/1.148 = 2.516).  What you have done is shifted the RPM band down by
about 15% for any given speed.  If, however, you are comparing with a 'C'
suffix case it's a dramatic improvement since you get both a higher and a
lower gear.  If your motor can pull it, you could even put a 4.11 R&P in
there to drop your RPM even further for cruising.  That's a huge change from
a final drive of 5.40 stock to 4.11!  Roughly knocking 1000 RPM off your
cruising speed.  What's better is that your low range will be almost
unaffected.  (If you have a motor that will pull 4.11 final gearing I
wouldn't be too worried about going from 39.8:1 to 37.2:1 low range).
    My own vehicle is going one step further though (actually two).  Instead
of the 4.11 R&P it's got the 3.54's.  In addition it's got a 6.68:1 1st
gear.  That translates into ~1350 RPM drop at cruising speed and almost a
100% gain in crawl ratio.  The only 'unfortunate' part of the deal is that I
don't have the machinery to make the gears so I cannot just pop out tonight
and do the machining on the t-case parts like you!  So I will have to make
do with standard 'B' gearing until such time as I either can find someone to
do it, or Timm comes up with his set in production.

Kirk