72 Blazer got the shakes bad - HELP

[Scrat]

Hi All.
So I have a '72 Blazer that has an annoying shake/shimmy at 65mph. (It feels like a tire is out of balance) It starts to shake around 55-60 and is worst at 65 and then is better at about 70. I know, no biggie, drive 75 but my problem is the road I travel on mostly has a 65mph speed limit. I've been dealing with this for years now and dont drive the blazer as much as I'd like because of it. I cannot replicate the problem in the shop, only on the road.

What have I tried so far...
Balancing the tires, new tires, checking the axles/wheels for runout.
New shocks all the way around including steering stabilizer
rebuilt rear end - new bearings and axles
repack/check hubs etc on front end and new ball joints
new u joints/ balance drive shafts
New/rebuilt drive train including engine/tranny/transfer case
installed power steering

All this and I still have the shakes. Anybody else have anything like this happen? What did you do? Is there anything I have left out/overlooked?

I'm thinking my next step is to do body bushings and suspension (lift 3"). Perhaps the springs are shot ? I dunno.

Thanks for any help or guidance.

(pics to follow )

[cleszkie]

Is the shake/shimmy in the steering wheel, or in the seat of your pants? If in the seat of your pants, you may be dealing with a driveline balance/worn u-joint issue). If its in the steeing wheel, its probably an alignment issue. Are you running a lift and oversized tires? The reason I ask is that when you install a lift kit, the camber and caster settings on the front axle can get out of whack when the axle tube is rotated to mount the the new spring packs. It only takes a few degrees of change to affect things. Running oversized tires further aggravates the situation by amplifying the resonant wobble. I suggest you get the front end professionally aligned. However, a lot of shops will only be able to adjust the camber, which will not fully elimnate your problem. You may have to source out some shims to put your caster back to spec before you have the camber set. Good luck.

[Scrat]

Thanks for the reply. I should have mentioned: Its a stock blazer at stock height (no lift yet) running 10 -15 LTs (stock tires). The suspension is original (and may just be tired).

The shake is in the "seat of my pants" (no comment =-P ) .

Already tried new u joints and balancing drive shafts and tires.

[Steve-W]

Hmmm this is a difficult one.. my first thought was; did you balance the wheels while still on the car? some shops have a small car-like thingy they ride up against your wheel and then balance it while mounted. sometime balancing components seperatly isn't enough.

If you're suspension is so bad it starts dancing around by itself you must notice it when driving over speedbumps, or offroad-ish conditions. a shot damper will be noticed, clonky sound while going over bumps, body roll etc.

wheel alignment could possible be a factor, but then your car would most likely be pulling into one direction when you let go of the steering wheel. Let alone the tire wear and the 'off' reaction to direction changes. if you do realing, try to go to a place where they do the 4-wheel allignments.

I'll toss this one into my think tank and see if they can come up with a solution.

[bweezy]

Maybe loose/worn body mounts?
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[pound41]

My friend had a 90 ram 250 4x4 that was 8-9yrs old he told me he was driving on the highyway 55-65 mph and the front end on his truck started shaking/bouncing and he said it got worse and was like going over 1 million moguls or a low rider bouncing a hundred bounces a minute. He was scared. Said it was scary as hell he couldn't turn the wheel just hang on. I laughed at him and one day we were on the highway Washington DC semi rush hour it started doing it and I was shocked. people could see it in other cars and they started slowing down to get away. it finally stopped and we went home. I told my Dad who had owned a gas station for 40 years at the time and he knew exactly what I was talking about. Told my friend to take it to a Spring front end shop and they fixed it. My dad told him what to tell them. My Dad has since passed away or I would ask him but I am thinking it had to do with the springs

[richard2717]

took one of my heavy trucks to the spring shop and they said it had way to much camber (6.5 degrees) backed it off to 3.2 and it has not done it since, but mine was shaking in the steering

[old man jimmy]

not knowing who or how they ballanced your drive shaft. I would be looking into making sure it's not tweaked. Put it in a couple v blocks, and put a dial indicator on it while you turn it. should give you a rough idea. especially if it's a 4 speed. They have a nasty habit of blowing u-joints, and hitting the ground hard enough to bend.

[71RestoRod]

65 MPH is right in the "first harmonic" zone so I would bet dollars for donuts you're looking at a wheel/tire problem. Is it possible that you have a bent rim?

[Scrat]

Thanks for all the replies and suggestions/information guys...

I checked the runout on the wheels/rims with them on the blazer with a dial indicator - they seem good, all less than 1/16" out of round.

The shake/bounce is definately not in the steering wheel.

The shop that balanced the driveshaft is a reputable shop and it doesnt seem out of round nor does it throw u joints. (I'll check it for runout with the dial indicator though)

This blazers been in my family since it was born and I know it was never riden hard and put away wet so to speak.

Speedbumps/offroad, no problems/clucks or funny noises.

I'm thinking about having my wife video tape me driving down the freeway (focusing on the drivetrain/tires) from her car so that I might be able to see a tire bouncing or something... I dunno still.

Worn spring bushings?

[Steve-W]

OFFTOPIC:

Originally Posted by Scrat

I'm thinking about having my wife video tape me driving down the freeway (focusing on the drivetrain/tires) from her car

I can just see this ending up on youtube, but not the way you intended it
sound a bit hazerdous to me! (My wife would end up with a great video totalling her car hahahaha)


back on topic

[cleszkie]

This may sound stupid, but have you checked for out of round tires (manufacturers defect or flat spot from braking). An out of round tire will balance just fine, but will roll like crap. I have heard of people encountering this issue with certain tire manufacturers. Just a though. Good Luck.

[jaros44sr]

Or a broken cord or belt in the tar

[Steve-W]

Originally Posted by cleszkie

This may sound stupid, but have you checked for out of round tires (manufacturers defect or flat spot from braking). An out of round tire will balance just fine, but will roll like crap. I have heard of people encountering this issue with certain tire manufacturers. Just a though. Good Luck.

you don't sound stupid because cars standing on the same spot for a long time (at least several months) can get "flat spots" on the tires.
but: this creates a tremble also in the stearing wheel (front tires..duhh) and is very noisy, it sound like your wheel bearing has gone.

[coyote72]

You said you had checked the wheels and axles for runout.... was that up and down or side to side. Maybe its a bent axle flange? I had a similar problem with mine and it turned out to be sand in the tires from airing down and playing in the dunes. Good luck with the problem, it sounds like you have covered all the bases.

[Scrat]

Originally Posted by Steve-W

OFFTOPIC:


I can just see this ending up on youtube, but not the way you intended it
sound a bit hazerdous to me! (My wife would end up with a great video totalling her car hahahaha)


back on topic

LOL... what I meant was - Wife driving car, son in back seat video taping

I have checked the tires for out of round and flat spots, they appear good.

I havent noticed any signs of a broken tire belt on the exterior of the tire (inside may be different).

[Firebirdjones]

Originally Posted by Scrat

Worn spring bushings?

If they are original, I'd replace them anyway. 40 year old rubber bushings do strange things even if they appear in okay shape.

Since these trucks rely so much on the bushings (front springs especially) to run true, any play in those front bushings can cause a pull, vibration, sloppy feeling, etc....

That's the first thing I did is replace all the spring bushings with Poly. New rubber would be better than nothing, but I use poly to eliminate as much movement as possible. Any movement is transferred through the truck and the steering wheel, and how the truck reacts to steering movements.

[cleszkie]

Regarding balancing of tires,thought I'd also like to the list of things that could be done wrong by the tire balacing place based on my experiences:

1) Some rims are lug-centric, and some are hub centric. I believe the stock steel rims on out trucks are lug-centric (centered about the lugs not the hub). However, most tire balancing places have machines that balance tires by securing the rim by the hub openning, thus balancing a lug-centric rim by assuming that the hub center is the same as the lug center, which it isn't in most cases. This results in a poor balancing job when the rim is put back on the lug-centric mounts of the truck. This is a little know fact (maybe not on this board), and others will chime in if I'm making any sense here. Find a shop with a lug-centric balancer, and you will get much better results.

2) Some of the tire balancing monkeys try to load all of the weights on the inside or outside of the rim. Yes, it looks better if there are no weights on the outside, but you will be sacrificing the effectiveness of the balancing job. If you want a good balance, you may need weights on the inside, outside, and even some stuck on the backside inner dish of the rim between the inner and outter lips.

[Firebirdjones]

I do Static balance wheels (weight inside only) if the rim doesn't have a beauty ring to hide the weights, or if the wheel is aluminum.

Simply because it's clean looking, plus a painted steel wheel, come balance time again, those outside weights will be moved, which leaves chunks of paint missing. Can't have that on a show piece.
Technically wheels should be balanced much more frequently than people do. I balance every second rotation. Those painted wheels would start to look pretty ugly on the outside pulling those weights off all the time Not to mention I hate to mar up an expensive aluminum wheel.

As long as the wheel is straight, and it's a well made tire, along with a good balance machine, you shouldn't have any trouble static balancing. I've done it for years without an issue.

[allchevy58]

Just a thought, we had a 1978 Blazer that started shaking at highway speeds all of a sudden. Knew it wasn't tires/wheel problem, checked drivelines, okay. Opened hood and noticed one of the fan blades broke off. Didn't hear anything, didn't damage radiator or shroud. No signs of exit of blade. Replaced fan, problem solved.

[old man jimmy]

have you tried getting up to the speed it starts bouncing, and kick it into N and just let it coast? does it stop, or still keep bouncing?

[AJs72K5]

Threw a weight off the drum??
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[jaros44sr]

Originally Posted by AJs72K5

Threw a weight off the drum??
Posted via Mobile Device

good one aj, wouldve never thought of that

[mcampbell]

Big O Tires has dinged me a couple of times so I will cheerfully use their name here. First time I learned to never go back. The second time I bought a 99 Suburban with Big O tires already installed. I took it in for balance every month or two because it had vibrations in the front tires. Every time they rebalanced the speeds changed but they could never remove it completely. Sometimes the vibration was from 65 to 72 mph and after a balance it would be from 58-67 mph etc. Stock Suburban I had changed the cv shafts, rebalanced the drivelines etc.
After 6 months of this I asked,"At what point do you decide these tires are junk and give me a warranty?" I got the ol dance about how they had changed computers and it did not show me in the database and they would not help because this was my first complaint. I have since had Michelins, BF Goodrich, and Toyo's on the truck. (213,000 mi)with absolutly no vibration at different freeway speeds.
I would borrow tires and rims from one of your buddies and give them a test drive. You might also rotate tires and see if it changes. I would personally recommend as I already do to my friends to not patronize the Big Zero( but just not going there will likely not fix your vibration issue.) Good Luck.

[Firebirdjones]

There is alot of truth to that.
I have my own mount and balance machines here so I do my own tire mounting.
I've had alot of different brand tires on that spin balance machine and I can attest that some of those cheaper tires are much harder to balance and take more weight to do so.
I've always been a believer in a good quality tire, and just bite the bullet on cost. In the end it pays off.