[Fot] Driveline angles

[Scott Janzen]

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, damys at charter.net wrote:

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

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?



_______________________________________________
fot at autox.team.net

http://www.fot-racing.com

Donate: http://www.team.net/donate.html
Archive: http://www.team.net/archive
Forums: http://www.team.net/forums
Unsubscribe/Manage: http://autox.team.net/mailman/options/fot/sjanzen@me.com



-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://autox.team.net/pipermail/fot/attachments/20160304/4efa926c/attachment-0001.htm>