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Vibration at high speeds (1988 5L T-5 )

I'm having a problem with a bad vibration when I get up to about 120 kph. It gets worse the faster I go.

I have tried to narrow it down, it's not rpm related so I think the drive shafts fine. It happens in both 4th and 5th gear so that also indicates to me that it's not rpm related. Its speed related I think. Now I have changed over to 3.73 gears and haven't changes the speedo gear yet, is this a problem? I wouldn't think so but it might take a reading and send funky stuff to the computer, I don't know. My motor mounts aren't in the best of shape but I think that would be rpm related, I have new ones on the way anyway. Now as soon as I let off the gas the vibration lessens then stops, once say to 110 kph. Now I can feel it though the entire car and the shifter vibrates like hell when it does it, but it seem to be centered on the transmission.

Now the car was an automatic before I got it and the other owner changed it over to the T-5 . So I don't know if that helps, maybe something got out of alignment? I just had the rear end done with the

3.73's and new posi clutch pack so it should be fine. The backlash is set a little off but I don't think that's the problem since it seems to be coming from the front to the back of the car.

Any suggestions?

Reply to
SonicMonkey
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Rotate your tires. I've had vibrations before... took the tires off & put 'em back on & the problem went away. It's a free fix if you do it yourself & it's not going to cost you anything if it doesn't work.

-Mike

Reply to
<memset

When you did the gears, did you take it easy for the first 500 miles? Also, at the very beginning did you make 5 or 6 trips of 20miles or less just to get the lube warmed up then allow it to cool. When you first pop them in the metal is still very soft. By running them till they are warm then allowing them to cool for no less then 3 hours allows the metal to harden. If you did any smoke shows or drag racing style launches before you went the

500 miles, it could be those gears giving you the problems. They should really be pampered the first 500 miles. After the 500 miles the lube should be changed and the pinion/ring should be inspected for metal shavings. Might want to go ahead and set that backlash to spec. I am not saying that this is the problem, but it can be related.. I also think if it was the gears it would happen in all gears not just 4th and 5th. just some thoughts. Might want to take a look at the pinion/ring to check it's wear patterns.

Brandon

Reply to
indi

Most likely thing would be a tire balance issue.... separated tires usually "announce" themselves at parking lot speeds. The driveshaft has little to do with engine rpm and everything to do with how fast the car is going..... it could also be the culprit.

Best suggestion, get all four wheels balanced and retest...... you can spend a lot of time and energy farting around trying to avoid the inevitable (not to mention, the car will not be pleasant to drive until you address the problem)..... we wont mention the 120 and up kph...

Reply to
Jim Warman

Reply to
SonicMonkey

Don't worry it was at night on a secluded road that i did my "dignostic test" and it was at the track when I first noticed it.

Thanks guys, off to the tire balancer 4 me :)

Reply to
SonicMonkey

I spent tons of time chasing a problem similar to this on my car a few years ago. The tires on the front (even after two alignments) would "cup" on the inside and would produce a wicked vibration at 70+mph. You could also have an out of round tire that is causing the problem, or a bad u joint in the driveshaft. You really can't tell until you have somebody take a look at it or start screwing around with it yourself. The problem with U-joints is that you can't always tell by sight that they are bad, even if they dont feel loose they could be just loose enough to make a vibration at high speeds. Usually an out of round tire will be noticable at well below highway speeds, but "cupped" or out of balance tires dont always make themselves noticable until you get up to speed. Mike MuscularMustangs.com

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Reply to
Mike

Reply to
Michael Johnson, PE

What is funny is that this post is almost exactly the same as two others here very recently. One of the posts was mine.

Check your front U-joint.

Don Manning

Reply to
2.3Sleeper

Welcome to ramfm. Sometimes it gets really monotonous here. ;)

2.3Sleeper wrote:

Reply to
Michael Johnson, PE

I have a speed sensative vibration, its my driveshaft rubbing on the e-brake cables, I guess the FMS aluminum driveshaft is thicker than the std unit. I'm not sure how to fix it yet, but I'm about to redo my entire suspension, so that might change it. I thought my driveshaft was fine too, but I noticed some rings around it, from ebrake rubbing. Just double check yours for marks.

J

Reply to
jbeez

has anyone mentioned HARMONIC BALANCER? when this is out of balance, ie, the weight starts to walk on the spindle, it will cause all kinds of wacky stuff, from wasting the seal in the timing cover, to motor mounts, tranny mounts, driveshaft, driveshaft yolk, u-joints, and pinoin seal.

I had this problem years ago on my 90gt, went through all the stuff, never got rid of the vibration, well, eventually I did when the crank snapped. From what I could tell, the harmonic balancer weight had walked, there were two distinct cracks in the crank where it snapped, one part of the snap was dark and the other light, hence old stress and new, which when it snapped, tore the whole front of the block out, funny part was the #1 main cap and it's mated part of the block were still attached to the broken part of the crank....

I say replace your harm>

Reply to
killfilewhat?

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