A Frustrating Shake

[dytch2220]

When I bought my car recently, the previous owner disclosed a few issues it had up front and I felt like they were ones I could solve on my own or with help diagnosing from a shop and then doing the work on my own. The main two were: 1) the car has a vibration that becomes pronounced between 55-65mph which seems to come from the front right wheel and 2) at hard acceleration the car hesitates until you feather off the gas then it begins to accelerate. I'm fairly certain the acceleration will be fixed by getting a new carb and it gives me a good excuse to move up to a 4 bbl rig. I've had the car to two shops, both of which gave up on figuring out the problem. One was the best alignment shop in my area, the other was a tires & service joint. Here is what they've tried or checked so far:

• Loose bearing, front right. Tightened, no change.
• Rotated front right and left rear tires. No change.
• Checked brake rotors, no runout.
• Checked wheels, no runout.
• Replaced all 4 tires. No change. And thankfully they put my old tires back on after the test drive.
• Drive shaft, good to go.
• Suspension components, good to go.

I suspect either a worn out harmonic balancer or bad shock absorbers. I am leaning towards the shock absorbers because the tires seems to bounce/shake excessively when traversing relatively small changes in the road like a manhole cover for example at slow speeds - so I'm going to start there. Since the header panel and grille were replaced with that of a 5th ave, I am entertaining the possibility that there was an accident so I'll have the car checked out for frame issues at a body shop also.

I just wanted to share what's going on with my car in the hopes that you all may have some other ideas of what to try next. Right now just waiting for my bigger payday in about a week so I can purchase a set of shocks all around.

 

[Oldiron440]

I'll give you A for effort and I think your on the right track. One thing I would look at is all the plastic shields and make sure all fasteners are in place, some of thoes parts can make a hard flapping that you could feel.

 

[AJ/FormS]

I see alignment shop, but I don't see alignment check
If the caster/camber has gone sour, that wheel can act like a shopping cart wheel, and the faster you go the worse it gets. And if one or more bushings is soft, or a steering component is loose, or a spindle is bent,......well that just allows it to begin earlier.
Check the SAI and the Thrust Angle. If you've already had it done, post up the results

 

[XfbodyX]

I've had the car to two shops, both of which gave up on figuring out the problem. One was the best alignment shop in my area, the other was a tires & service joint. Here is what they've tried or checked so far:

bad shock absorbers


Im confused by your statement, wouldnt the best shop easily determine if a shock was bad?

Did they actually go drive the car and try to duplicate it?

If its a 318 and youd like to try a balancer and dont have one om me, ive several good ones laying around that have been begging me to toss them in the trash metal bin.

I think I have some new front shocks I will never use if you want just oem or a hair better, but I dont have the rubber mounting hardware, I used them to use a insulators for side pipes.

 

[dytch2220]

I see alignment shop, but I don't see alignment check
If the caster/camber has gone sour, that wheel can act like a shopping cart wheel, and the faster you go the worse it gets. And if one or more bushings is soft, or a steering component is loose, or a spindle is bent,......well that just allows it to begin earlier.
Check the SAI and the Thrust Angle. If you've already had it done, post up the results

I didn't request an alignment, only described the problem and asked them to see if they could diagnose and repair it. They were able to repeat the problem on a test drive. I feel confident they wouldn't have given up on solving the issue if it was alignment related. If for no other reason than I believe they would have been glad to charge me for an alignment if that would have solved the problem. They have a good reputation and they spent about 3 hours working on the car but only charged me $30 for tightening the bearing and diagnosis which means I didn't make them any money. Tire wear is normal and even, vehicle does not pull to any direction which have usually been indicators of a problem here in my past experience.

Since I don't know if it was specifically checked, I won't rule out alignment or steering components as a source of the problem at this point. I will ask for the SAI and Thrust Angle and share once I have the opportunity to get back to an alignment shop. Thanks for the suggestion.

 

[dytch2220]

I've had the car to two shops, both of which gave up on figuring out the problem. One was the best alignment shop in my area, the other was a tires & service joint. Here is what they've tried or checked so far:

bad shock absorbers


Im confused by your statement, wouldnt the best shop easily determine if a shock was bad?

Did they actually go drive the car and try to duplicate it?

If its a 318 and youd like to try a balancer and dont have one om me, ive several good ones laying around that have been begging me to toss them in the trash metal bin.

I think I have some new front shocks I will never use if you want just oem or a hair better, but I dont have the rubber mounting hardware, I used them to use a insulators for side pipes.

To be more specific, they are the shop with the best reputation locally and have been recommended to me by several people. I agree that they should have been able to determine that the shocks were a problem. This simply makes the most sense to me based on what I'm experiencing over bumps at slow speed. Additionally, I am planning to do a complete upgrade to this suspension package, so purchasing new shocks will not be out of my way and will eliminate this possibility.

It is a 318 and I will gladly take you up on the extra balancer. Once I've completed the shock replacement, if that does not address the issue, I'll send you a message. Thank you.

 

[Oldiron440]

Please note if the shaking continues while coasting in neutral.

 

[AJ/FormS]

I used to run front shocks with the oil purposely let out of them. They did not create any vibration. Good shocks will damp a vertical wheel hop, caused by an out of round tire or a slipped belt/cord.The tire/wheel can still be in perfect balance, yet it will create a vibration.But you eliminated this possibility already
Shocks are vertical motion dampers. They cannot damp a sideways motion
You can have up to .5 degree camber in either direction, and it won't cause a wear pattern.
You can have a negative castor and a loose steering, and there it could be.
You could have a negative offset wheel on that corner negatively affecting the scrub radius.
or a bent spindle, or SAI crossed up from a displaced frame rail.
Or messed up ride heights from a bad rear spring
Or even an apron rusted off at the firewall.
I think I've seen them all.
In any case.... Good luck.
.EDIT
or a bad strutrod bushing/ bent rod

 

[XfbodyX]

Good God! I hope its a easy fix. Its hard for me to even find a shop that knows older cars so I ended up doing my own and it seems I got lucky so far.

I used to run front shocks with the oil purposely let out of them. They did not create any vibration. Good shocks will damp a vertical wheel hop, caused by an out of round tire or a slipped belt/cord.The tire/wheel can still be in perfect balance, yet it will create a vibration.But you eliminated this possibility already
Shocks are vertical motion dampers. They cannot damp a sideways motion
You can have up to .5 degree camber in either direction, and it won't cause a wear pattern.
You can have a negative castor and a loose steering, and there it could be.
You could have a negative offset wheel on that corner negatively affecting the scrub radius.
or a bent spindle, or SAI crossed up from a displaced frame rail.
Or messed up ride heights from a bad rear spring
Or even an apron rusted off at the firewall.
I think I've seen them all.
In any case.... Good luck.

 

[89.Fifth]

I'm dealing with the same problem right now and trying to track it down. Replacing the wheels and tires completely has helped but not eliminated the problem.

I'm doing complete new rear suspension in a couple weeks so I'll post if that helps.

 

[dytch2220]

Please note if the shaking continues while coasting in neutral.

I will test this out and let you know.

 

[dytch2220]

I'm dealing with the same problem right now and trying to track it down. Replacing the wheels and tires completely has helped but not eliminated the problem.

I'm doing complete new rear suspension in a couple weeks so I'll post if that helps.

Yes, I'm interested to see what solves your problem. May give me a clue on what I should do next.

For now going to the body shop on Friday to see if the frame is not square. Since they should be able to fix any problem, hoping if it's not a frame use a they can track it down.

 

[Justwondering]

AJ --
I bow to your experience.
But I don't have a clue. can we start with one of the things you said?.

You could have a negative offset wheel on that corner negatively affecting the scrub radius.

This sounds really complex. Could you dumb it down for me?
Thanks in advance,
justwondering

 

[AJ/FormS]

If you draw an imaginary line thru the upper and lower balljoints,down to the road, then the center of your tire-tread should be near that point, but not on it. The scrub radius is the measurement from the enter of the tire to that point, and it has to be the same on each side of the car, to avoid this kind of problem.
The factory wheels place this point in an advantageous spot with the factory ride height. The scrub radius changes a little with the suspension traveling up and down, as the control arms are of different lengths. This is by design to keep the center of the tire from wandering too far from the centerline of the car,(with changes in suspension height), because that would cause abnormal tire scrub and toe-changes, which would cause steering issues.
But if you have a scrub radius of .5 inch on one side and of 1.5 on the other, that is sure to cause steering issues, as the suspension cycles, and a mild pull in a straight line. The pull can lead to a shimmy with worn parts, because it is causing a different toe change/toe pull, on one side of the car than on the other.
Shimmies, when they start, usually don't go away until you slow down to well below when they started. But they give plenty of warning before they go crazy.
A shimmy is started by a tire that is being steered in a direction other than straight ahead, by the camber, the caster/camber, or the scrub-radius, or some combination of those.
The scrub-radius is built in. But a tire diameter different than factory, or a rim with a different than factory offset, will change it. If you don't stray too far from factory, it's no big deal. But if the spindle goes up an inch and the offset goes out an inch, and the camber is set to 3/4* negative, well then hold on tight.

 

[JLN5thAve]

I know I had two issues that caused a really bad shake - although I do not know if it will help in this..

I had a U-Joint drop out on the side of the road once.. Replaced it in a parking lot, however within a few days the bearings went bad and it was shaking like crazy.. Had the wrong type from AutoZone.. Replaced with correct one from NAPA and it worked fine..

The second issue I had that caused a bad shake was an upper ball bearing on the passenger side..

You said the driveshaft is good to go - so was mine, I had to drop it again and check the joints.. Dont know if you have gone that far yet. You said the front left bearing was loose, I assume you are talking about the wheel bearing?

I am by FAR not an expert, however I have dealt with a 88 Fifth quite a bit.

 

[89.Fifth]

Mine happens between 55 and 65mph, decreases outside of that range, doesn't seem to be a wheel balance issue, and only seems to affect the front wheels. I can feel and see the shake in the steering wheel. It was worse before (could have been multiple issues) but got better when I replaced my stock steel wheels with Snowflakes and changed to 215/70 R15 tires. Rotation did nothing regardless of what wheels were on. You can also see the hood and fenders shake.

My vehicle does pull to the left slightly and always has. I have to try and track down a decent alignment shop to see what they say.

Things I have fixed or changed:
New Wheels and Tires: all 4
New Brakes (complete): all 4
New Shocks: all 4

Things to be done soon:
Complete rear suspension: New leaf springs, poly isolators, new shackles and bushings, new front spring hangers.

Things I suspect:
Front alignment
Driveshaft balance
Pinion angle

Things I might try:
Borrowing a GoPro and filming in various key places in the car to see if I can watch what's vibrating.

 

[80mirada]

A Brake caliper not retracting fully can cause a similar issue. Also chec you rotors, i have seen after market rotors with balance issues.

 

[gomopar89]

You guys are not the only ones. My '89 with 42K on her does the same thing. She shakes like a cheap motel bed from 55 to 65 mph. I have had new tires, new rotors, new pads and a new steering gear box replaced. The shake has lessened a lot but is still there! I don't really feel it in the steering, mine is more in the body. The hood shakes and the passenger front seat vibrates real bad. I am still on my quest to eliminate this entirely.

The funny thing is my '82 NY'er with 86K on her is smooth as silk at all speeds!

 

[Oldiron440]

The reason I wanted to know if the vibration was there in neutral coasting at speed was it would rule out drive train. Otherwise you need to look at converter clutch lockup, motor mounts, harmonic balancer or combinations of all the above. I had an Olds powered Pontiac the had a mis at a certain rpm because of a valve guide.
So get it up to speed and shaking then kick it into neutral and coast and see what shakes.

 

[80mirada]

A bad K member bushing can cause a shake.