[Fot] vibration

Brian Schirano bschirano at yahoo.com
Fri Jun 9 16:00:34 MDT 2017


20,000 comedians out of work.... and you're makin jokes

Cheers Mates 26A GT6+, 28 TR6Brian Schirano
585-305-0349 Cell 
BSchirano at yahoo.com

      From: Duncan Charlton <duncan.charlton54 at gmail.com>
 To: Brian Schirano <bschirano at yahoo.com> 
Cc: Scott Janzen <sjanzen at me.com>; "kkjjk at aol.com" <kkjjk at aol.com>; 'Friends of Triumph' Triumph <fot at autox.team.net>
 Sent: Friday, June 9, 2017 5:59 PM
 Subject: Re: [Fot] vibration
   
Mmmm — sounds like an excuse to swap the two engines to see which car ends up with the vibration!
Duncan Charlton
1121 Lower Elgin RdElgin, Texas 78621USA




On Jun 9, 2017, at 1:00 PM, Brian Schirano via Fot <fot at autox.team.net> wrote:
echoed problem here w/my GT... still

motor was completely balanced, alum flywheel balanced and the pressure plate balanced indexed to the flywheel, decent damper. Driveshaft re balanced and phase corrected like Scott. I run different axle so only have inboard u joints, no phasing there. rebuilt the diff last year, bearings good, still have rubber mounts, but newer, and the pressed rubber mounts in the diff new neo. I will have to study driveline angles, I've read about this but have not addressed as such. I remember it's counter intuitive, they should not be completely straight. 
This year when I finally get to my only event, VRG at the Glen, I will be running last years tires on TR7 steels vs my old alloy BWAs and see if that makes a difference. My buddy that mounts and balances took extra care and saw no runout or flat spots. 

Interesting, we also run a TR6 w/completely stock motor, and do not have any vibration there. Given the care of the GT motor build and none in the TR and it's longer stroke, make me wonder. (although the GT does run sometimes up to 1000 more RPM on periodic long passing straight occasion 

welcome more commentary here

Thx 
Brian 26A GT6+, 28 TR6Brian Schirano
585-305-0349 Cell 
BSchirano at yahoo.com

      From: Scott Janzen via Fot <fot at autox.team.net>
 To: kkjjk at aol.com 
Cc: 'Friends of Triumph' Triumph <fot at autox.team.net>
 Sent: Friday, June 9, 2017 10:58 AM
 Subject: Re: [Fot] vibration
  
I used to have the exact same problem with my GT6, also noted in the same spot at Summit Point.  I’m still not convinced it is not related to RPM - in lower gears, you run through this range much more quickly, and I think it’s the RPM combined with the speed and the longer time you spend in this RPM range.
Anyway, I found that both my driveshaft u-joints were slightly out of phase, as were the u-joints on the rear axle half-shafts.  I don’t know what your half-shafts are made with - cv joints, u-joints?  Mine are Spicer splined sliding half-shafts with inner and outer u-joints.  A good driveshaft shop corrected both of these issues, balanced everything, made sure all the u-joints fit tightly in the yokes, etc.
The other thing I spent some time with was the alignment and mounting of the differential.  The GT6 has far from optimum alignment of the differential relative to the transmission - poke around on this subject but here’s one article http://www.markwilliams.com/driveshafttech.aspx  
Anyway, the best I could achieve was to get the nose of the differential as high as possible and the rear as low as possible, if I remember correctly.  Also, look at the mounts themselves - are they in good shape, tight?  My diff is mounted with all aluminum spacers front and rear, no rubber, and i had the rear ones made eccentrically so that I could adjust the rear up and down a bit.  
It seemed that a combination of these things worked. No one item was the silver bullet.  Not sure if this is a new problem for the car - if it is, I’d  suspect the diff mounts or poor balancing of one of the rotating components.
Of course, we are assuming this is not suspension or engine vibration related - good to eliminate all of those as well, but also relatively easy to check at speed and you can usually feel it if it’s out at a wheel.
Scott
On Jun 9, 2017, at 7:35 AM, kkjjk--- via Fot <fot at autox.team.net> wrote:
 I have a significant vibration with my GT6 which occurs only at speed, in 4th gear starting about 300-400 before redline (approx 6600 RPM).  In any other gear to redline there is no problem, so it is related only to speed.  I had the driveshaft universal joints replaced and balanced with no change in the vibration.  The tires are brand new and balanced as well, although I did have a bit of shaking of the car, so I will have them re balanced again.  But I need to know what I should look at next to find the solution to the problem.  The diff?  Rear axles? And what items specifically?  I have to back off a bit near the end of the straight at Summit Point due to this problem, which sucks.  A longer straight at another track would be even worse! Any help would be appreciated!  Thanks- Jay De Pol
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