What Barry says.
I had one of four new Yokohama tires on my 6 out of round. Chased that for way
too long.
Bud
Sent from my Commodore 64
> On Jun 9, 2017, at 12:03 PM, barry rosenberg via Fot <fot at autox.team.net>
> wrote:
>
> Have a really good tire shop true the tires and get them perfectly round.
> Balancing will not cure an out of round tire. Once they are round, balance
> them. New tires are not always round. This will help if it is a tire problem.
>
>
> On Friday, June 9, 2017 10:44 AM, Scott Janzen via Fot <fot at
> autox.team.net> wrote:
>
>
> 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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