98 ZR2 Blazer Shake @ 70 MPH

I have new tires so the balance should not be a concern, however the ride is smooth until I hit 70mph and than the whole truck starts to shake violently than about 75mph and above it smooths
back out. I replaced the steering stabilizer that was bad but did not help any.
Sometimes it will ride fine for a couple of miles @ 70mph but not often.
The switch to enable the 4 wheel drive is bad so it is disconnected and the vacuum port pluged under the battery.
Something funny going on here, any ideas?
TIA
LockJaw
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LockJaw wrote:

Does the steering wheel shake when it does this and is it stock or lifted with oversized tires.
----------------- www.thesnoman.com
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LockJaw wrote:

are your tires wearing normally and evenly? if not, you may have a ball joint problem
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LockJaw wrote:

    U-joints in the back driveshaft. Charles
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My Truck did the same thing around 70mph. It ended up being a warped brake disc. I had the discs resurfaced and then it drove smooth.

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: :: :::> : :: :::> I have new tires so the balance should not be a concern, however : :: :::> the ride is smooth until I hit 70mph and than the whole truck : :: :::> starts to shake violently than about 75mph and above it smooths : :: :::> back out. : :: :::> I replaced the steering stabilizer that was bad but did not help any. : :: :::> : :: :::> Sometimes it will ride fine for a couple of miles @ 70mph but not often. : :: :::> : :: :::> The switch to enable the 4 wheel drive is bad so it is disconnected : :: :::> and the vacuum port pluged under the battery. : :: :::> : :: :::> Something funny going on here, any ideas? : :: :::> : :: :::> TIA : :: :::> : :: :::> LockJaw
The steering wheel is solid. The tires are new and look good, no strange wear. Drive shaft joints are tight. Brakes are new ( rotors and pads ). Ball joints are tight. Every thing is stock, no big tires ( ZR2 - stock size ).
All very good suggestions, but this is where I'm at the end trying to figure this thing out.
I may have the balance rechecked on the tires
LJ
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wrote:

I had a similar problem, turned out to be the u-joints. They checked out as tight, but they were actually binding. Took a tech a little time to actually find the problem. I let it continue and get worse over the course of several months. Eventually I was getting a squeak/creak on acceleration. The u-joints were dry and bound up.
My vibrations were at 30 MPH and at highway speeds, but there were certain conditions needed in order to produce the problem, that's why I didn't suspect the tires as the culprit. This was also on a ZR2, but a pickup.
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: :: :::> I had a similar problem, turned out to be the u-joints. They checked : :: :::> out as tight, but they were actually binding. Took a tech a little : :: :::> time to actually find the problem. I let it continue and get worse : :: :::> over the course of several months. Eventually I was getting a : :: :::> squeak/creak on acceleration. The u-joints were dry and bound up. : :: :::> : :: :::> My vibrations were at 30 MPH and at highway speeds, but there were : :: :::> certain conditions needed in order to produce the problem, that's why : :: :::> I didn't suspect the tires as the culprit. This was also on a ZR2, : :: :::> but a pickup.
I'll give the U-joints another look. Thanks,
LJ
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: :: :::> : :: :::> I had a similar problem, turned out to be the u-joints. They checked : :: :::> out as tight, but they were actually binding. Took a tech a little : :: :::> time to actually find the problem. I let it continue and get worse : :: :::> over the course of several months. Eventually I was getting a : :: :::> squeak/creak on acceleration. The u-joints were dry and bound up. : :: :::> : :: :::> My vibrations were at 30 MPH and at highway speeds, but there were : :: :::> certain conditions needed in order to produce the problem, that's why : :: :::> I didn't suspect the tires as the culprit. This was also on a ZR2, : :: :::> but a pickup.
That was it. Rear drive shaft bearing had a dry one that was also rough. The shake isn't as bad now. Gonna tackle the other joint tomorrow.
LJ
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wrote:

Glad I could help. I let mine go for a while before trying to find the cause, it was pretty obvious once the diagnosis started...
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wrote:

switch was bad too. Can't remember what she found out about it. Will ask her tomorrow and get back to ya
--
Regards
Gordie
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LJ,
I seem to remember hearing this problem being caused by an out of balance rear driveshaft. If your u-joints check out, I would check that next.
-John
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On Sun, 25 Sep 2005 19:46:07 -0400, The Nolalu Barn Owl <&#103&#111&#114&#100&#105&#101&#64&#110&#111&#108&#97&#108&#117&#46&#111&#110&#46&#99&#97> wrote:

The rear drums were really rusty and some rust chunkies fell off putting the rear wheels out of balance. The critical speed in her case was 70 Km. in her case, so I doubt if the same problem exists in your case. Sorry I couldn't be of any real help.
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Gordie
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On Mon, 26 Sep 2005 21:03:17 -0400, The Nolalu Barn Owl posted that:
: :: :::> OK, here is what she found out. : :: :::> The rear drums were really rusty and some rust chunkies fell off : :: :::> putting the rear wheels out of balance. : :: :::> The critical speed in her case was 70 Km. in her case, so I doubt if : :: :::> the same problem exists in your case. : :: :::> Sorry I couldn't be of any real help.
Ok, my breaks are all new - disks all around. Thanks for trying
LJ
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