Hello all, I'm revisiting an old problem that recently came back. My Blazer is shaking at lot at highway speeds.

I made a thread some time ago trying to troubleshoot this after having bought new tires, shocks, and rebuilding the front-end suspension.
https://blazerforum.com/forum/2nd-ge...speeds-102080/

I thought it was a bad balance on the tires, so after many, many revisist to the shop I bought them from getting no better results, I just basically abandoned the problem.
The shaking felt like it was slowly going away, so I pretty much ignored it for the rest of the summer in 2020.

Fast forward a few months for October...

I noticed I had leaking gear oil on my rear, right axle. Obviously axle seal went bad so I replaced it. See photos below.
After having replaced the axle seal, I noticed an improvement in ride quality. It wasn't shaking from the seat as bad as it was before.
So at the time I assume the shaking problems was because of a bad axle seal. I should have replaced the other side while I was at it, but it wasn't leaking so I left it.

Fast forward to mid December...

Lately I've been towing light trailers to move furniture around. My office space was liquidating furniture, so I rented a small UHaul for that, and a buddy of mine lended me his 8x10 enclosed trailer to help a family member move across town.
Towing the UHaul, I noticed that the shaking I had mentioned before started to return, but it wasn't as bad. The more weight the trailer had, the worst the shaking was. I shrugged it off as the trailer axle possibly out of balance.

Fast forawrd to January 17, 2020...

I used my buddy's trailer for the first time to help a family member move, and the shaking came back ten fold while pulling this trailer. Something to me felt like it was very off balance, loaded or not.
I couldn't tell if it was just the trailer or something else, so I had to ignore it until the moving job is done.

Finally fast forward to today...

I'm back into my regular work commute this week, and the exact vibration/shaking I mentioned a while ago has come back. You feel it in the seat, wheel, door, center console...
It definately feels like something is off balance, but I can't figure out what it is. The thing is- it's an intermident shaking that goes away sometimes.

If I have a stretch of highway that's smooth enough for long enough, the shaking slowly calms down, but hit a bump like scraped pavement, a slight threshold to a bridge, raised arrows in the right lane, or if the pavement is wavy and the shaking comes back.
The shaking also gets very bad the faster you drive. If I try acccelerating from 55 to 70 very quick, the shaking gets very bad. There is still some shaking between 40 and 55, but it's not nearly as bad at 70, and the 40 - 55 range feels like something is grinding- even on a newly paved road. Sometimes it feels like something is grinding at 55 and other times it feels like I'm driving over rocks on what should be a brand new smooth black-top.

My father owns an S10 pickup RWD I've drivien a few times and it rides super smooth. So I know exactly how rough roads should feel like, and how smooth road should feel. My Blazer feels like it's driving over gravel all the time.

My Blazer has definately had good days where there's no shaking at all and it's handling just like a brand new truck. That's why I say the problem is intermident, and I have no idea what to inspect next.

One tech at one of the shops I visited said to let it coast from top speed in netrual and observe if it still shakes. I tried this and the answer is yes. I'm not sure what that does. The tech claimed it rules out transmission being the culprit if the shaking stops.
I guess there's a subtle change in shaking between netrual and drive at 70 MPH, but the difference is very neglegiable.

Is it possible that the transmission, or transfer case, or front CV axle can go out of balance?
I want to say it might be transmission related, because when ever my Blazer is not shaking, it's for the whole drive until I park and start to drive again later.


Leaking gear oil

New seal on the left vs old seal

My workspace

 

Of course you need to eliminate the tires and wheels as the cause. This can come and go as the wheels rotate to different relative positions. Tires can balanced but be out of round causing wheel hop. Wheels can be damaged and some tire brands are notorious for OOR either initially or as they wear. I like to look at the wheels slowly rotated on the balancer to see how out of round the assembly is. I also check this when the truck is on jack stands. Rotating can help to rule this out to see if the problem moves, front to back.

Did you check for rear bearing play on those rear axles? Those seals may have started failing with the bearings.

How is your front wheel bearing/hub play?

If you get pulsing in the brake pedal it can be the brake disks. A runout gauge can confirm.

Front end steering play can cause all of this and needs to be checked. Idler arms are like disposal air filters on older Chevy's. There is also tie rod ends, etc. Front tire wear is also a clue here. Suspension components also need to be checked like ball joints and shocks.

Are the brakes dragging? Out of gear at around 5mph and see if the truck coasts to a slow stop with no grab at the end. Does the steering pull when braking?

Does it remain if you take the truck out of gear at speed to isolate the drivetrain?

It's just methodical blocking and tackling, a process of elimination guided by the available clues.


George

 

I'd look at the axles and see if they are bent or maybe the housing. Have you hit anything or dropped into a big pot hole that could have caused a problem? Just a thought here, you said it comes and goes. Have you checked the U-joints?

 

Just to confirm, if a tire is OOR, it is possible that it can cause an intermident vibration? I thought if there was a tire balance issue, it tends to be persistent at all speeds and gets worst the faster it goes.
One guy at a family owned shop who took a look at this says that my tires are counter-balanced by as much as 7 oz. I also specifically requested a static balance because I didn't want weights showing on my OEM aluminum wheels.

I only checked the one axle I replaced the leaking seal on. I spun it around and it felt okay, so I don't think the rear bearings are an issue.

They've been replaced recently. There's no play in the hub itself, and I made sure the o-ring was properly sealed between it and the steering knuckle.
If the o-ring appears crushed, or worn in a particular way, would that indicate play?

Braking is smooth as silk. Replaced all 4 disks a while back.

I reviewed some of my older posts, and the idler arm is gonig to be the next thing on my list to replace. I'm still running the factory component. All the other suspension stuff has been replaced. Tie rod ends, ball joints, bushings, shocks.

I tried this and I do maintain speed and slowly cost to a stop. Calipers have never dragged on me, but I had the parking brake drag before. I've recently rebuilt the parking brake components to fix that problem.
The steering does pull to the left when I brake hard.

Yes. I've brought it up to 75 MPH, and let it cost in nuetral for a few seconds. I felt a negligiable difference.

When I had the one axle out, I didn't noticed any malforimty to it's shape. I don't think it's bent, nor the housing. I try to actively avoid pot holes.
I did check U-Joints, I have Moogs standing by ready to replace if I need to. But, they don't feel like they have play in them. At the rear, I feel rotaitonal play at the pinion gear, but not in the U-joint itself. They all feel solid playing them by hand.
I want to replace them eventually because the Moogs are serviceable and the factory ones are not. I'm just not motivated to at this time because I have to melt the plastic retaining clips to get the OEMs off.

 

Vibration can have an element of black magic to it, these problems can be elusive. Some vibration is cut and dried, it increases with speed and that's it but often its more complicated. I've had OOR tires that got smooth for a while and then got nasty as the humps got in just the right sequence to start rocking the truck and then smooth out again when they all behave better together as they change rotational position relative to each other. Some vibration goes away at speed, its worst at a lower speed. It depends on how good the shocks are damping the problem and if a loose front end gets excited and starts a sympathetic vibration. Sometimes you hit a bump and all hell brakes loose because a loose front end gets excited. If youve ever had a heavy trailer with the load too far back start rocking back and forth on the highway, same mechanism. Those kinds of problems are not linear with speed all of the time.

I used to have my tires "trued" on my high end sports cars back in the day, which shaved them round. No amount of balancing can eliminate an OOR wheel/tire. Also the tread can wobble laterally. I stopped all that when I manned up and went to high end Yokohama's and Michelin's, sometimes with no weights on a given tire. Smooth all the way down to the wear indicators. Dynamic balancing can be done with stick on weights inside the mag wheel. I have never had any luck with static balancing.

Rear axles: you need a bar under the tire to see if there is any lateral play.

Front end: You need bars, jacks and stands to check ball joints and pulling in and out and rocking 3/9 o'clock to check for loose steering and/or bearings/hubs.

George

 

You have rotational play at the pinion gear??? There should be no play. This tells me you have a bad bearing in there, Try removing the driveshaft after marking it and the yoke so it goes back together in the same position. There should be no side to side play or in and out play.

 

Id have to agree with eshaw. Im also willing to bet your axle bearing has some play in it as well.

 

I'm stumped 7oz of weight added to balance the wheel?

Thats about 2 times what I would consider allowable.

To diagnose vibrations on the drivetrain I would further suggest to figure out:

Is it rpm dependent? (i.e. does it change when you manually downshift or put it in neutral? - Careful don't do this if you are not savvy and know how to handle the car like this!)
Is it speed dependent? (i.e. it changes frequency and intensity with speed?)
Does it have a sweet spot where it disappears?
Have you done your front CV joints? What type of hose clamp has been added?
How about the wheel bearings?

Static balancing would not eliminate a wobble as it acts in one plane only. While the dynamic balancing of todays machines is able to address the imbalance in two planes.

Have "all" old weights been removed and the rim be checked inside and out before balancing? Does it have TPMS sensors?
I suppose the wheels are tubeless and no tube has been mounted?

 

Well it may actually be the transmission.
See, I often always apply the parking brake from neutral before shifting into park to ensure there is zero roll. When I check the u-joints and turn the drive shaft, there is play in it and I hear a clicking sound.
When I don't apply the parking brake and I allow it to roll slightly forward or back, then I check the u-joints, there is no play at all. It's solid.

 

Just to update everyone, I've replaced the idler arm, and it feels a lot better. The old one certainly had play in it when I pulled it off.
I still notice a bit of oscilation at highway speeds. I suspect this might be tires, or CV axels now.
So this doesn't seem to be one large problem, but a bunch of different small one compounding each other.