High speed problem

[10 sec TTa]

Around town and at normal highway speeds under 80MPH I have absolutly no problem. I am not sure it is a tranny problem at all. I thought maybe there was a problem with the driveshaft or the rearend, but after being told by multiple shops there is no problem with either I am thinking maybe it's the converter or the transmission. Like I said the thing runs perfect around town and at speeds under 80 on the highway, however at speeds above 80-85 I get a vibration that gets worse the faster I go. It feels like the driveshaft is not balanced or something is out of round. I am running an art carr 9 inch non locking converter and I am aware that it is not recommended to drive at excessive speeds for extended periods of time, however every now and then we all have to see what it can do. It is on these blasts that the car feels like it is shaking apart, like I have reentered the atmosphere at the wrong angle and the whole car will surely vibrate to pieces. As soon as the speedo drops back under 85 everything is fine again. Any ideas or thoughts are greatly appreciated.

 

[turbotwister]

hi,
i would highly recommend having the tires checked for balancing first.this solution may sound too good to be true but i have seen this be the problem all to many times in this situation.you may be doubtfull but don't rule it out.if it was the converter it would happen more in relation to engine rpm's ,not vehicle speed.

nick,

 

[2quiktocare]

Tire balance will give you troubles between 65 to 70 mph(actual speed) and then again at around 125mph. If you are having trouble at 80 plus, I would look for something that has a direct connection to the output side of the drive line. I would have the drive line checked for possible bad pinion angle and also re check the balance. Make sure the u joints are centered. Let us know what you find if you can.... thanks, Mark

 

[turbotwister]

actually if the balancing is out bad enough it will do it from about 80 on.i have seen this problem many times and have experienced it myself.i have been an automotive tech for 15 years and have experienced many different situations.i guess the key word here is "experience".unless you have come across this problem you wouldnt think it would happen in this manner.also,it usually happens worse with the wide in back/thinner in front scenario.

and on a side note.dont you think checking all possible angles is the right way to handle this?


nick,

 

[2quiktocare]

You are right Turbo, do check every avenue first. From my 33 years around the tire business I have seen many things caused by tire balance and dynamics. If a tire is that badly out of balance, it will shake bad at lower speeds as well. It may well be a tire coming apart. The speeds I spoke of are where tires will act more severe than any others. I didn't notice if he said that it was more intense then, or if it was constanly bad. It will be very interesting to hear the outcome on this problem for sure. Mark

 

[chris718]

vibration at hi speed.lets get a look at this in a simpler picture as to weed out what it isnt.what happens if you shift to neutral and lift the throttle momentarily on a descend during the shakedown?does it get worse or better.at this state of operation the rear wheels are driving the vehicle ,not the transmission or torque convertor .what happens if you shift to third and still maintain 80 plus mphour?does it get worse or better?do these tests and post results. this is after thoroughly checking all 4 tires by a visual inspection for embedded debris ,out of round or balding and running your hand across them where they meet the road.visually inspect the driveshaft for dents or bald spots where a weight may have fell off and checking play of the front and rear universal joints.check for exhaust system grounding out on the chassis or undercarriage / tires .broken engine or trans mounts.

 

[10 sec TTa]

Not the tires.

It's not the tires. This is the third set of rears and second set of fronts with the same issue. I haven't tried downshifting because I am running close to 3,000 RPM when it gets bad at close to 90MPH. I normally don't drive on the highway, but when I go on trips I find myself opting to drive the Honda Civic because I don't want to deal with the issue. I was thinking maybe it is a converter problem since I was warned not to run the non locking converter at high speeds for extended periods. I have tried running the car in 3rd at the same 3,000 RPM and don't get the vibration. It feels as if the pump is cavitating when it happens. I have had the Ujoints and driveshaft looked at on more than one occasion at different tire shops. The first time I found the transmission mount was busted, I had the tire place replace the transmission mount. Almost a year later I thought it busted the mount again, but the bolts in the mount had just fallen out. I figured that the idiots just didn't torque them properly, but now wonder if this vibration may have loosened them. Figured either way they shouldn't have come out. I thought that maybe some damage was done to the Ujoints when the bolts were out and the tranny was floating around so I asked them to check it out at Tire Kingdom. They brought me out in the bay and showed me that the Ujoint had no play in it at the transmission or at the rearend. I took it to Don Olson Tire about a month later with the same results. I was hoping someone here can point me in the right direction. I figure I will take it to a rearend specialist or 4WD shop next. Thanks for any help you can give me.

 

[Slow91z]

Hello...F-bodies have always had driveshaft problems...I'd take the DS out and check that it's str8 and runs true...and I'd get it rebalanced...I'm sure the longer this goes on the easier it will be to figure out...My Auto-tech instructor always told us if you can't figure it out just keep driving it, and eventually it will get bad enough that it'll be easy to figure out...I know that sometimes this isn't the best or safest diagonstic technic, but I guarantee that when all else fails that one will eventually work.