<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>What Barry says.</div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature">I had one of four new Yokohama tires on my 6 out of round. Chased that for way too long.</div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature">Bud<br><br>Sent from my Commodore 64 </div><div><br>On Jun 9, 2017, at 12:03 PM, barry rosenberg via Fot <<a href="mailto:fot@autox.team.net">fot@autox.team.net</a>> wrote:<br><br></div><blockquote type="cite"><div><div style="color:#000; background-color:#fff; font-family:Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:13px"><div><span>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.</span></div> <div class="qtdSeparateBR"><br><br></div><div class="yahoo_quoted" style="display: block;"> <div style="font-family: Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 13px;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div dir="ltr"><font size="2" face="Arial"> On Friday, June 9, 2017 10:44 AM, Scott Janzen via Fot <<a href="mailto:fot@autox.team.net">fot@autox.team.net</a>> wrote:<br></font></div> <br><br> <div class="y_msg_container"><div id="yiv8573525053"><div>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.<div class="yiv8573525053"><br clear="none" class="yiv8573525053"><div class="yiv8573525053">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.</div><div class="yiv8573525053"><br clear="none" class="yiv8573525053"></div><div class="yiv8573525053">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 <a rel="nofollow" shape="rect" class="yiv8573525053" target="_blank" href="http://www.markwilliams.com/driveshafttech.aspx">http://www.markwilliams.com/driveshafttech.aspx</a></div><div class="yiv8573525053"> <br clear="none" class="yiv8573525053"><div><div class="yiv8573525053">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. </div><div class="yiv8573525053"><br clear="none" class="yiv8573525053"></div><div class="yiv8573525053">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.</div><div class="yiv8573525053"><br clear="none" class="yiv8573525053"></div><div class="yiv8573525053">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.</div><div class="yiv8573525053"><br clear="none" class="yiv8573525053"></div><div class="yiv8573525053">Scott</div><div class="yiv8573525053"><br clear="none" class="yiv8573525053"></div><div class="yiv8573525053yqt9161393965" id="yiv8573525053yqtfd17341"><div class="yiv8573525053">On Jun 9, 2017, at 7:35 AM, kkjjk--- via Fot <<a rel="nofollow" shape="rect" class="yiv8573525053" ymailto="mailto:fot@autox.team.net" target="_blank" href="mailto:fot@autox.team.net">fot@autox.team.net</a>> wrote:</div><br clear="none" class="yiv8573525053Apple-interchange-newline"></div><div class="yiv8573525053"><div class="yiv8573525053yqt9161393965" id="yiv8573525053yqtfd86669"><font class="yiv8573525053" size="2" face="arial"><font class="yiv8573525053" size="2"> 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<br clear="none" class="yiv8573525053">
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