Subject: [Fot] Driveline angles

From: [email-masked]
Date: Fri, 04 Mar 2016 05:07:22 -0700

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=0A=0A=09The front of the motor is slightly lower than stock. I believe=
 the=0Arear of the trans is approximately stock. =0A=0A=09Can anyone giv=
e me an idea what the front diff angle should be.=0AIdeally inclined upw=
ard at 6 1/2 degrees for the current downward=0Aangle of the rear of the=
 trans.=0A=0A=09Although the frame looks straight, and we have had it ch=
ecked by a=0Aframe alignment company, if the rear has been rolled up in=
 an accident=0Athis would create the condition we are experiencing. Just=
 thinking out=0Aloud?=0A=0A

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<html><body><p>The front of the motor is slightly lower than stock.&nbsp=
; I believe the rear of the trans is approximately stock.&nbsp; </p><p>C=
an anyone give me an idea what the front diff angle should be.&nbsp;&nbs=
p; Ideally inclined upward at 6 1/2 degrees for the current downward ang=
le of the rear of the trans.</p><p>Although the frame looks straight, an=
d we have had it checked by a frame alignment company, if the rear has b=
een rolled up in an accident this would create the condition we are expe=
riencing. Just thinking out loud?</p><p><br></p></body></html>

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From: Scott Janzen <[email-masked]>
Date: Fri, 04 Mar 2016 10:26:56 -0500

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So, I spent quite a bit of time on this several years ago, when I had =
some high speed vibration in my GT6, mostly at 5,500 rpm and above in =
4th gear.  The reality is Triumph did what they could with this car but =
the driveline angles are not what engineering theory recommends, which =
is what Chris reported - parallel flanges, and offset centerlines for =
the diff and tranny.  It is impossible to achieve in this car.  I did =
several things to minimize vibration, and if it's still there, I guess I =
don't notice it much anymore!  In a race car with everything hard =
mounted at high road speed and 6-7,000 rpm, and the exhaust no doubt =
contacting the frame somewhere, the whole thing is buzzing!

Here's what I did and it eliminated most vibration:
find a good driveshaft shop, one that does race work and recognizes the =
RPMs you are operating at.
Have them ensure the u-joints on the drive shaft and half-shafts =
(assuming that's the construction you have- I have halfshafts with inner =
and outer u-joints) are absolutely aligned/in phase.  My halfshafts were =
off 5-10 degrees.
Have all those rotating assemblies balanced.   Get that checked every =
time you change u-joints, as it seems to change a bit.
Use high quality u-joints - I think I have spicer everywhere - and =
replace these at the slightest sign of wear.
Differential - Jason suggests poly for the front mountings - I have =
aluminum spacers.  Either will work. Get those sized so the front of the =
diff is as high as possible - essentially the outriggers on the diff are =
virtually touching the frame mounts.  Where the long bolt at the rear =
goes through the ears on the diff, I have replaced those bushings with =
aluminum ones, drilled offset and rotated so that the diff sits as high =
as possible (bolt hole toward the bottom).  This has two benefits - it =
improves the driveshaft alignment and it lowers the car slightly.
The goal with the diff angle adjustments is to make the angle of the =
diff flange relative to the driveshaft line as close to the angle of the =
transmission flange relative to the driveshaft.  I can't remember where =
I read that, but that was indicated as preferable if the "parallel =
flange, offset alignment" objective is unobtainable.  Again, it's the =
flange angle relative to the driveshaft, not relative to vertical.
Bottom line, most of the vibration is gone.  Now the vibration I deal =
with is typically old race tire stuff.
Hope this helps.  Bottom line, you would have to reconstruct this car to =
get the engineering ideal here, and it's virtually impossible without =
major surgery.  Didn't seem to be necessary once everything else was =
tweaked!  Sorry for the windy message.

scott

On Mar 4, 2016, at 7:07 AM, [email-masked] wrote:

The front of the motor is slightly lower than stock.  I believe the rear =
of the trans is approximately stock.=20

Can anyone give me an idea what the front diff angle should be.   =
Ideally inclined upward at 6 1/2 degrees for the current downward angle =
of the rear of the trans.

Although the frame looks straight, and we have had it checked by a frame =
alignment company, if the rear has been rolled up in an accident this =
would create the condition we are experiencing. Just thinking out loud?

Archive: http://www.team.net/archive
http://autox.team.net/mailman/options/fot/[email-masked]

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<html><head></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">So, I =
spent quite a bit of time on this several years ago, when I had some =
high speed vibration in my GT6, mostly at 5,500 rpm and above in 4th =
gear. &nbsp;The reality is Triumph did what they could with this car but =
the driveline angles are not what engineering theory recommends, which =
is what Chris reported - parallel flanges, and offset centerlines for =
the diff and tranny. &nbsp;It is impossible to achieve in this car. =
&nbsp;I did several things to minimize vibration, and if it's still =
there, I guess I don't notice it much anymore! &nbsp;In a race car with =
everything hard mounted at high road speed and 6-7,000 rpm, and the =
exhaust no doubt contacting the frame somewhere, the whole thing is =
buzzing!<div><br></div><div>Here's what I did and it eliminated most =
vibration:</div><div><ul class=3D"MailOutline"><li>find a good =
driveshaft shop, one that does race work and recognizes the RPMs you are =
operating at.</li><li>Have them ensure the u-joints on the drive shaft =
and half-shafts (assuming that's the construction you have- I have =
halfshafts with inner and outer u-joints) are absolutely aligned/in =
phase. &nbsp;My halfshafts were off 5-10 degrees.</li><li>Have all those =
rotating assemblies balanced. &nbsp; Get that checked every time you =
change u-joints, as it seems to change a bit.</li><li>Use high quality =
u-joints - I think I have spicer everywhere - and replace these at the =
slightest sign of wear.</li><li>Differential - Jason suggests poly for =
the front mountings - I have aluminum spacers. &nbsp;Either will work. =
Get those sized so the front of the diff is as high as possible - =
essentially the outriggers on the diff are virtually touching the frame =
mounts. &nbsp;Where the long bolt at the rear goes through the ears on =
the diff, I have replaced those bushings with aluminum ones, drilled =
offset and rotated so that the diff sits as high as possible (bolt hole =
toward the bottom). &nbsp;This has two benefits - it improves the =
driveshaft alignment and it lowers the car slightly.</li><li>The goal =
with the diff angle adjustments is to make the angle of the diff flange =
<u>relative to the driveshaft line</u> as close to the angle of the =
transmission flange relative to the driveshaft. &nbsp;I can't remember =
where I read that, but that was indicated as preferable if the "parallel =
flange, offset alignment" objective is unobtainable. &nbsp;Again, it's =
the flange angle relative to the driveshaft, not relative to =
vertical.</li><li>Bottom line, most of the vibration is gone. &nbsp;Now =
the vibration I deal with is typically old race tire =
stuff.</li></ul><div>Hope this helps. &nbsp;Bottom line, you would have =
to reconstruct this car to get the engineering ideal here, and it's =
virtually impossible without major surgery. &nbsp;Didn't seem to be =
necessary once everything else was tweaked! &nbsp;Sorry for the windy =
message.</div><div><br></div><div>scott</div><div><br></div><div><br></div=
><div><br></div><div><div>On Mar 4, 2016, at 7:07 AM, <a =
href=3D"mailto:[email-masked]">[email-masked]</a> wrote:</div><br =
class=3D"Apple-interchange-newline"><div><p>The front of the motor is =
slightly lower than stock.&nbsp; I believe the rear of the trans is =
approximately stock.&nbsp; </p><p>Can anyone give me an idea what the =
front diff angle should be.&nbsp;&nbsp; Ideally inclined upward at 6 1/2 =
degrees for the current downward angle of the rear of the =
trans.</p><p>Although the frame looks straight, and we have had it =
checked by a frame alignment company, if the rear has been rolled up in =
an accident this would create the condition we are experiencing. Just =
thinking out loud?</p><p><br></p></div>
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w.fot-racing.com<br><br>Donate: =
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http://autox.team.net/mailman/options/fot/[email-masked]<br><br><br></div>=
<br></div></body></html>=

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