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[Fot] vibration

Subject: [Fot] vibration
From: sjanzen at me.com (Scott Janzen)
Date: Fri, 09 Jun 2017 15:58:29 -0400
References: <15c8ca2e88b-7bfb-a6f@webprd-a04.mail.aol.com> <F4639BF1-F48F-41EF-9A7A-4637B459E14B@me.com> <61650029.6365036.1497031209925@mail.yahoo.com>
I do not think this is an engine vibration problem- that you would notice in 
lower gears.  It's either transmission back or suspension/tires, as these 
things never get to max speed except flat out in fourth gear.

Sent from my iPhone

> On Jun 9, 2017, at 2:00 PM, Brian Schirano <bschirano at yahoo.com> 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 TR6
> Brian 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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