What happened?

[Wooshie]

so i was on the highway taking my time doing about 60 when this fox body mustang came up on me. needless to say we started having some fun we finally got even i punched it and stayed on it from 60 to almost 115 when along the way the whole car started shaking and the whole ass end seemed to "float" i immediately let off it and car returned to normal. i repeated this experiment on a backroad with several other people to help pinpoint the problem. it seems to happen at 85 and faster. i have heard everything from suspension to tires to unbalanced driveshaft. this sux i really want to run at the track this year ,but not untill i fix this problem. has this happened to anyone else? any ideas to help narrow this down? (btw) mustang was destroyed by about five cars.

[KissMyWhtSS]

so i was on the highway taking my time doing about 60 when this fox body mustang came up on me. needless to say we started having some fun we finally got even i punched it and stayed on it from 60 to almost 115 when along the way the whole car started shaking and the whole ass end seemed to "float" i immediately let off it and car returned to normal. i repeated this experiment on a backroad with several other people to help pinpoint the problem. it seems to happen at 85 and faster. i have heard everything from suspension to tires to unbalanced driveshaft. this sux i really want to run at the track this year ,but not untill i fix this problem. has this happened to anyone else? any ideas to help narrow this down? (btw) mustang was destroyed by about five cars.
Mine vibrates a bit at high speed, because my driveshafts is out of balance. It's hard to diagnose your car based on what you've said. Is the problem more from the rear/middle/or front of the car? Any play in your steering? How worn are your shocks? How was the surface you were driving on?

[SoulReaver]

I would put money on you not having z rated tires. Go buy yourself some new BF Goodrich KD's. You'll be a happy man.

[AChotrod]

Mine was terrible with the stock DS, switched to a LS1 alum and prob solved. Now running a strange CM DS

[KissMyWhtSS]

Mine was terrible with the stock DS, switched to a LS1 alum and prob solved. Now running a strange CM DSWheras mine is terrible with a LS1 DS. The problem was your old DS was inbalanced. You won't notice the LS1 DS being significantly smoother.

[Wooshie]

just to update from the responses.

1. steering seems fine ( i havent tried to jerk the wheel at high speeds though)
2. tires are z rated w/about 75% life left
3. suspension is basically stock
4. shmy is from the rear of the car(almost feels like a rudder)

my last f-body 01 ws6 could bury the speedo and i never had a shimy and the suspension was stock on that.

[IronOutlaw]

I hit 145 with h rated tires and they seemed fine, but maybe im insane.

[warnerTA]

I hit 145 with h rated tires and they seemed fine, but maybe im insane.

your insane guy :cool: but yet we are all that drive lt1s :shiner::cool:

[BLOWNDFIZ]

Check all of the suspension mounting points and bushings.
Make sure the tranny mount is in good shape.
Have all of your tires balanced.

At least you can eliminate some variables by doing this.

[AChotrod]

Wheras mine is terrible with a LS1 DS. The problem was your old DS was inbalanced. You won't notice the LS1 DS being significantly smoother.

90% of stock LT1 DS are out of balance bad, mine was a joke. It felt like the car was gonna break at 80+mph. There even was a service bulletin about it back in the day.
I switched to a LS1 alum because it only cost 75bucks and had other benfits besides being balanced. If its still the stock DS have it balanced of find a LS1 shaft.

[YZF]

Check the balance on the tires for sure. When does the shaking come into affect? Have you tried slowly increasing speeds until you find the point at which it starts shaking?

[Wooshie]

UPDATE.....
1. Have ls1 one driveshaft here in a week
2.tailshaft transmount was destroyed. polyurethane unit going in on sat.

If these two things don't solve problem i will repost and see what we can come up with.

[BLOWNDFIZ]

That will fix it. Actually the trans mount will probably do the trick, the driveshaft will just be a bonus I guess...

[AChotrod]

Im sure those will fix it.
The poly trans mount sucks IMO and the stock one is much smoother.

[KissMyWhtSS]

That will fix it. Actually the trans mount will probably do the trick, the driveshaft will just be a bonus I guess...
:stupid:

[YZF]

Those poly mounts are stiff! You'll feel everything. It might get annoying after awhile. Just my opinion.

[Wooshie]

i can deal with the stiffness. the poly mounts shouldn't break as easily though as the stock unit should it. my friend had a 95 formula with an autmatic and he broke stock mounts like every three months. i would prefer not to be doing this very often.

also a shout out to quick lube in channahon and the manager John for letting me have the use of their extra bay. it makes getting to it a lot easier.

[Wooshie]

new trans mount installed today. the deal on the ls1 ds fell through. i drop my ds off this week to be balanced.

i did notice my tailshaft seal was a little wet when i changed the mount. should i drop the trans and replace the seal? any long term effects that will stop my trans from making it through the year?

let me know.