[DMCForum] Transmission Input Shaft Couplers
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[DMCForum] Transmission Input Shaft Couplers

Hi guys! - As you might recall, there was a lengthy flurry of
messages regarding failures of input and main transmission shafts.  I
took a good look at the reports, and have decided to do something
about what appears to be the primary failure mode in this area - the
splined coupler that connects the input shaft to the main shaft.  I
have focused in on two components; the coupler itself, and the roll
pin that is used to fix the coupler to the main shaft.  In a recent
local failure, the coupler stripped out, and the roll pin sheared. 
The sharp fragment of the pin caused irreparable damage to the
splines on the main shaft, resulting in the expensive replacement of
the main shaft.  The failed coupler is made from mild steel, possibly
4130 alloy, with a heat treat of about 115,000 PSI ultimate tensile
strength (very soft).  It is only partially splined internally
(perhaps 50%).  The theory has been proposed that this is supposed to
be a "fuse" of sorts to protect the main shaft from damage.  So far,
not so good.  The "protection" has become the primary failure of the
transmission, which is not acceptable.  I have commissioned custom
couplers made from 4340 alloy at a heat treat of about 150,000 PSI
ultimate tensile strength, and are fully splined for maximum
strength.  They are nearly done, fit the shaft splines better than
stock, and are beautiful!  I have also obtained a stronger variety of
roll pin that is much more resistant to coming out prematurely, and
also cracking.  For those of you who are contemplating  horsepower
increases, or want a better load path into your transmission to avoid
future expensive failures, I will have a limited number available by
mid next week.  Please contact me off-list for further information at
toby(at)delorean-parts.com.  We will have some available at PF,
unless they are sold out immediately.  See y'all there!

Toby Peterson  VIN 2248 "Winged1"
DeLorean Parts Northwest, LLC

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