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Discussion Starter #1
I’m at a complete loss.

since I’ve purchased the car 6 or so years ago, it will shake on the free above 50. It shakes really bad. The chassis, steering wheel, everything. The dash shakes up and down an inch.

I have replaced everything.

multiple sets of rims and tires
Everything suspension is new, springs, shocks, bushings, ball joints, etc etc.
All new steering arms.
All new body bushings and motor/trans bushings/mounts.
multiple alignments
Multiple driveshaft balances

It does it whether I’m in neutral or in gear.

I’m beginning to believe I have frame damage.
At one point, the front right body bushing punched a hole through the frame. I had to patch weld it shut.

Does anyone have any suggestions?

I can’t deal with it anymore. And I don’t want to put this new 383 I’m building in a car that can’t go 50.
 

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This might be where your problem is. The cause can be multiple things. There can be frame damage or possibly rear control arms damaged. The biggest problem I have seen is caused by a condition known a diamond frame where one side is set back from a collision causing the motor mounts to mis-aligned with one behind the other. On an ElCamino with the rear trailing arms there is also the possibility of the rear end being forward on one side. Also, extremely worn upper rear or lower rear control arm bushings can be a problem. I may not be right about your particular situation but it is a place to start since you have mentioned all the other common causes. Good luck!

Joie
 

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Discussion Starter #3
Joie,

Thanks for your reply.
I peeked underneath the car to check the pinion angle and it looks dead on like that last one in your picture, but flipped upside down.

The trans yoke is horizontal, and the pinion yoke has a pretty decent rake.

Looks like purchasing some adjustable uppers is on the horizon.
 

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Hope that gets you going in the right direction!
Sorry, I fat fingered my name and didn't see it! LOL!

Joe
 

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Dont know what year you have but many many moons ago I had a 74 big block vette that had a very bad vibration above 60. After chasing my tail turned out to be the clutch fan. It had locked up and caused a out of balance. Even my shifter was vibrating so hard you could hardly shift.
 

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On my last elcamino I placed the truck on a absolute level concrete pad, remove the carb and place a level on the carb mounting surface of the intake. Make sure it’s level . Next check your pinion angle. I set mine at -3* Good luck😎
 

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Joie,

Thanks for your reply.
I peeked underneath the car to check the pinion angle and it looks dead on like that last one in your picture, but flipped upside down.

The trans yoke is horizontal, and the pinion yoke has a pretty decent rake.

Looks like purchasing some adjustable uppers is on the horizon.
I had this exact issue and adjustable upper control arms and a good pinion angle adjustment from a reputable shop had me cruising down the highway comfortably. Also, not sure if you are running the factory trans or not but that can also affect pinion angle. I put a T56 in mine and with the way the trans was sitting, even though on paper the pinion angle measured out right, the trans tail shaft needed to be raised up a good bit to fix the highway vibration.
 

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Discussion Starter #10
I’m running a AGE M22z right now. Before it had the factory powerglide, and it still shook. The previous owner did have some HD rear springs on it, giving it a big rake.
Lowering the rear seemed to help a little, so did switching to solid engine mounts.
 

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Discussion Starter #11
Matteo, What about lowering the trans mount instead of messing with the control arms?
John, that's a great idea. Unfortunately I already purchased some adjustable uppers. I believe in my case I'd need to remove material from my trans bushing, making it thinner. My pinion has a positive rake, while my trans yoke is horizontal. Would need to come up a lot..

I'm going to look into your idea anyways, could save me a ton of money!
 

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The carburator is "close" to level. The engine is normally at 4 - 5 degrees lower in the rear. A quick easy ballpark check is to put an angle gauge on the alternator pulley + or - 90 degrees
 

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With the engine level and the pinion angle at -*3 there is no driveline vibration. I have set up 2 fifth gens in this manner and zero issues. One won a elky only dial in drag race the other was runner up 🍺🏁
Prize goes to who can guess the 2 cars belong to 🏁😎cheers...
 

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Discussion Starter #16
Bad news.
So I installed the adjustable control arms, set the pinion angle, and went for a test drive. Little to no help. Still drives terrible.

I used my digital level against the face of the trans tail shaft, set zero. Then set the pinion 3 degrees off of that.
i assume the 3 degrees is so that when you’re under load It runs parallel, correct?

So what can I look at next?
 

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Bad news.
So I installed the adjustable control arms, set the pinion angle, and went for a test drive. Little to no help. Still drives terrible.

I used my digital level against the face of the trans tail shaft, set zero. Then set the pinion 3 degrees off of that.
i assume the 3 degrees is so that when you’re under load It runs parallel, correct?

So what can I look at next?
Check the angle of the engine/trans..
 

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Have you had the driveshaft checked?
 

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Discussion Starter #19
Have you had the driveshaft checked?
Yeah, a few times over the past two years. Both yokes and u-joints aren’t more than a year or so old. Quality too. A shop assembled & balanced everything for me.

I redact my previous post...

...I took it on a better test drive this morning. The angle adjustment hushed my vibrations maybe 30-40%. But once I hit 60, I slightly feel it—then it gets worse as I go faster. At 90 it’s terrible. Not that I drive that fast but for testing purposes haha

I still feel it in the entire body of the car, and the steering wheel. The wheel shakes up and down, different than a misalignment.

The weird thing is is that is fluctuates. The vibrations travel from the front, to the rear of the car, to and fro.

Maybe whats left over is in the steel wheels I have? Maybe I messed up in setting the angle? Who knows, I’ll check this weekend and post some pictures. Till then suggestions are greatly appreciated!!!

Still glad I did the control arms, great suggestion!!!!!
 

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This is one other thing to eliminate, gotta think in 3D. Refer to the diagram from the second reply and look at it as if you were above your car and looking side to side. It is a possibility, unusual but possible. Many factors at work here. I once had a Trans-Am with a customer complaining of vibration. The fix was pulling the sub-frame forward on one side. The car had been in an accident and had the bumper replaced but they missed the set-back. The result was the third pic from the top. one motor mount was behind the other and the trans mount had enough flex to offset the drive shaft. Also, on one really outside chance maybe a motor mount or trans mount has been bolted in wrong? I've seen it happen, pretty rare but...... Good luck!

Joe
 
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