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
<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
_______________________________________________
fot at autox.team.net
http://www.fot-racing.com
Archive: http://www.team.net/archive
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://autox.team.net/pipermail/fot/attachments/20170609/c9c9df30/attachment.html>
|