Bad shake on Highway. Out of ideas...
 

OK guys, need some help. I'm quickly running out of ideas.

I have a bad shake at highway speeds. I can't tell if it's coming from the front or rear.

So far, I have changed out both CV shafts, front wheel bearings/hubs, upper and lower ball joints, tie rod ends, pitman arm, idler arm, new tires all the way around, double checked tire balance, new alignment.

What else could it be? The only things left that I can think of would be possibly warped rotors or shocks.

This problem is while in 2WD at 60mph and above. Automatic transmission running in OD.

Mike
96 Blazer 4x4

If it is 4by your front end may not be disingaging. just my 2 cents.

not knocking your :icon_twocents:, but i highly doubt it. i've run in 4HI upto 130kph in all of my 4WD trucks, never had an issue.

you mention that it's a bad shake @ highway speeds, but not a death wobble, right?

with all of the work you've done to the front end, have you checked the U & L control arm bushings for any excessive wear?

you also mention that you don't know if it's coming from the front or rear, what have you checked out in the rear suspension?

i'd start checking the u-bolts first (i've actually seen a pair loosen over time), then start checking the spring bushings & bolts for any excessive wear or broken bolts.

what tires are you running? i know there are a few tires that greatly benifit from being done on a Road Force balancer.

Thanks for the feedback. Old skool, in answer to your questions, no I haven't checked the upper or lower bushings or U-bolts. I will check those. The tires I'm running are Firestone Destination A/T. The only real check I did on the rear was checking the seals, u-joints, and checking the axles for play in the bearings (which there wasn't). It was a "death wobble" until I changed the pitman arm and got it realigned. Now, it's calmed down some, but is definitely still there. It still shakes, but not as bad as it was.

I decided to take it back out on the highway and try to test a little more. I went about 10mi in 4WD to see if it made any difference (it didn't), then turned around and came back 10mi in 2WD. Both ways at 70+ mph. The shake definitely seems to be coming from the rear. There is no shake at all in the steering wheel, but I can feel it in the seat and back. Double checked my u-joints. Will change rotors/drums, brakes, and shocks this weekend and see if any of that helps.

don't waste any more money Mike-find the problem first!

while some of the front end parts you changed have helped, i can bet there was some parts replaced that were still good.

yu could throw a ton of money @ a vehicle trying to fix it, but then you'll never really know what was the cause & solution to your problem.

go through it one item @ a time, and test your results before moving on. as for the brakes, is your truck a 4 wheel disc set up? you mention rotors/drums, but not if that was for front & rear brakes. as for the shocks, don't just replace them, inspect them for leaks & strength before that.

this is the problem with an issue like this, without going for a ride in your truck, i can only go through a list of things to check-which can be time consuming. physically riding in a vehicle can do wonders for an accurate diagnosis, and has solved many weird "problems" with other vehicles i've tried to "help fix over the phone", if you get what i mean.

wait............i just noticed that you mentioned you checked & double checked your u-joints, were they replaced recently? have you ever had the drive shaft checked for balancing? i've only ever had one have an issue after i replaced the u-joints, but you never know. look into this before you replace any more parts first, 'cause i bet a coffee that is where it's coming from.

Thanks Old Skool, after talking to a number of people, I'm starting to really think it may be to u-joints too. They are tight, and they haven't been changed since I've owned the truck (about 5 years), but all the symptoms keep coming back to them. They are cheap enough and easy enough to change that it might be wise to do it in either case.

As for the wheels, I have have disk brakes up front and drum in the rear. The front rotors are pretty worn and grooved and have some wobble when braking, and on the rear drums, I noticed last night that one of the weights welded onto the right-rear drum is missing. Bad shake or not, they need to be replaced anyway.

I'm moving away from the shock theory. The more I check them, the more I don't think it's them.

I agree that I can't keep throwing money at it though. Can't afford that. I will pull the driveshaft and take it to a shop to have them check the balance. And spend the $30 on u-joints before putting it back in.

If it is the u-joints and/or shaft, I will be more than happy to buy you that cup of coffee! ;)

Thanks again for your help.

Mike

would an offset u-joint be more of a high end vibration at highway speed and a low vib. at take off from stop?

I'm going to replace the rear drums this weekend (one of the drums is missing a balance weight), and I found a driveline shop that will replace/balance my u-joints and balance my driveshaft, all for $68. So I'll take it in and get that done. I'll let you guys know how it goes.

that was gonna be my answer. you can have a bad ujoint that feels tight but if its offset might cause vibration. also a bent driveshaft or busted transmission mount. (also a bad center bearing in a 2 piece driveshaft but that doesnt apply here)