84 caprice wagon violent shake on the highway

hello to all I've been hanging around for a while so I figured it's about time I sign up
this forum is great tons of great useable info

so here's my problem I have a 84 caprice wagon that has a VERY VERY violent shake that occurs after driving several miles on the highway above 45 mph faster or slower makes no difference once the shake starts it doesent stop until I stop and let the car sit for 20-30 minutes. the car starts out driving perfectly smooth after about a mile or two the whole car go's in to a violent shake the hood shakes the seats shake and just about anything else you can think of.
driving around town the car is perfectly fine smooth as silk

the things that I've done so far to try to eliminate the problem are

tire balance also tryed a another complete set of tires and wheels
new u-joints
alignment
new motor mounts
new trans mount
tryed unplugging the torque converter clutch [no difference]
complete tune up
plugs wires cap/rotor all filters pcv valve check timing
checked the parking brake and made sure its not dragging
new shocks all 4

so far everything I've done has had no effect on my problem



some info on the car
1984 chevy caprice wagon
motor is a 78 vintage lm1 350 [small rv cam] from an old 78 impala wagon
the electric carb has been replaced with a conventional q-jet from the donor motor
also the est distributer has also been replaced with a conventional distributer fron the donor car
trans is a 700r4 with 4th gear lock up conversion [the trans came from a 92 chevy van]
rear is from a 93 caprice with 3.23 gears and posi

I love my wagon I've had it for 12 years but now I'm afraid to drive it because I don't want to hurt it
any input would be greatly appreciated

Have some one pace you on a multiple lane highway. looking at both sides. Hopefully they can see when it starts to shake and where it shakes. If the other person says the shaking is  worse at the front vs rear,  right vs left, it gives you a starting point.

My gut feeling is parts related to steering, pittman arms, bushings etc. But it's only a poor guess. I noticed that steering related parts where not on the list.



Dave

One way to isolate the vibration between the powertrain and chassis would be to drop from OD to Drive during the shaking while maintaining the same vehicle speed. If the shake doesn't change even when the engine is now revving higher then most likely the vibration is in the chassis or driveshaft. You could even try the opposite by putting the transmission in neutral allowing the engine to drop to idle while the car is at speed.

The fact that the shake takes several miles to start and goes away for a time after a cool down seems to indicate that the engine/transmission are involved.

I rebuilt the front end 3 years ago approx 40k all control arm bushings balljoints centerlink idler arm tie rod ends swaybar links and bushings new springs [front and rear] all moog parts and a rebuilt steering box I also replaced the intermiedate shaft from the column to the box$$$ [dealer item]
I just checked it over and all is tight and the car tracks straight as an arrow

lakeffect wrote:

Have some one pace you on a multiple lane highway. looking at both sides. Hopefully they can see when it starts to shake and where it shakes. If the other person says the shaking is  worse at the front vs rear,  right vs left, it gives you a starting point.

This.

I'm going to ask one of my friends to pace me on the highway to have a look and we'll see what we find

thanks,
Danny

84 box wagon wrote:

so here's my problem I have a 84 caprice wagon that has a VERY VERY violent shake that occurs after driving several miles on the highway above 45 mph faster or slower makes no difference once the shake starts it doesent stop until I stop and let the car sit for 20-30 minutes. the car starts out driving perfectly smooth after about a mile or two the whole car go's in to a violent shake the hood shakes the seats shake and just about anything else you can think of. driving around town the car is perfectly fine smooth as silk

When you say "faster or slower makes no difference", do you mean that the vibration doesn't quit, or doesn't change quality? If this is in some way engine related (eg: coil, cracked flexplate, etc.) then I would expect the vibration to intensify under load -- that is, it would be worse going up a hill or accelerating. It would go away completely if you put it in neutral and shut off the engine to coast.

Does the frequency of the shaking vary with vehicle speed? Something like an out-of-balance driveshaft or brake drum will vibrate faster at higher speeds.

Since it takes several minutes at highway speed to trigger, and since it will go away temporarily when the vehicle sits for a while, I suspect it is caused by something that is heating up -- like a dragging brake pad or a bad bearing. Do you have access to a handheld laser thermometer? (they are pretty cheap these days). You could use it to hunt for hot spots. Even without one, you might be able to use the back of your hand on things like wheels.

In general terms, things that cause vibration associated with the front wheels tend to be felt most strongly in the steering wheel. Things associated with the rear wheels tend to be felt more in your butt. Sometimes popping the car up on jack stands or a hoist can help identify the location of the problem -- but requires an assistant to "drive", and extreme caution in case the vibration shakes the car off the supports.

Sir, that was a good set of questions and supporting thoughts!

Ok today I had my buddy pace me on the highway he couldnt see anything so we switched cars and and I paced him the most that I could see was the hood shaking from the outside.
I also tryed shifting from 4th to 3rd no difference
I also tryed a non contact thermal thermometer on all 4 wheels nothing to be alarmed about the rears were a couple of degrees cooler than the fronts
as far as faster or slower with the shaking it does'nt change quality or frequency
I tryed shifting in to neutral at 65 to see if the shaking would change and it did'nt
I put the car in neutral and shut the engine off and the shake was still there

I haven't a chance to get the rear up on jack stands to run it to check for a bent drive shaft
but I'm beginning to think that it might be in the trans or the driveshaft

It's definatly not coming from the front end the steering wheel does'nt shake or vibrate like the rest of the car of course you can feel it because it go's through the whole car but it tracks straight

 the best way to describe the ride is a coin operated bed in a sleezy motel

This problem is really really bugging the bejusus out of me because I work as a gm mechanic in a shop that is mostly gm and I fix theese type of problems for customers on regular basis and the worst thing is that I can't figure out a problem in my own car that I've owned for 12 years

thanks again to everybody for all the input I really appreciate it
            Danny

So it sounds like you've replaced the entire front suspension, all the shocks, and tried two sets of tires.   It also sounds like you've isolated the shake OUT of the drivetrain and it's something in the rear suspension.

FWIW, I've had replacement suspension bushings fail at 30k / 8 years after they were installed.  
Here's what I'd do next:
1. Swap the tires/wheels front to rear, then go for a drive.
2. What tire pressure are you running the tires at?  32psi or so?  Try cutting it down to 20psi and see if that changes the shake.  Likewise, try running the tires at max pressure (40psi?).  If it is the tires, doing this will change the stiffness and therefore the natural frequency of the tires and you should be able to detect a difference.  
3. Do you have access to a set of low-profile 17" rims and tires, something completely different than what you're running right now?
4. Check the shocks again.  I don't care how old they are - go pace the car and have your buddy drive over bumps and see how well the body and wheels are controlled.  

I think at this point you shouldn't trust any of the new parts you installed unless you can actually test them.

There's a couple of weird things about your symptoms.

First is the delay before the shaking starts. You can take it out on the highway and be fine for the first several miles. And if I understand correctly, the shaking will continue -- even at low speeds, even if stopped for a moment -- until the vehicle has sat for 20-30 minutes.

Second, nothing seems to change the frequency of the shake once it starts. If it was engine related, one would expect the frequency to vary with RPM. If it was speed related, one would expect the frequency to vary with vehicle speed. Really, any vibration caused by rotational action should vary with the speed of rotation of the guilty part.

Is there any unusual tire wear that might suggest whether the issue is unsprung vs sprung components?

Shutting off the engine and coasting rules out everything in the driveline forward of the torque converter. Next in line is the transmission itself -- or at least, the parts that are still spinning with the engine off. But to shake the whole car takes a lot of mass or deflection. What in the transmission could possibly be heavy enough and/or with enough clearance to vibrate the whole car without also causing shifting problems?

An imbalanced, bent, twisted or improperly phased driveshaft can certainly shake the entire car. But again, that's rotational vibration. In fact, the driveshaft spins considerably faster than the wheels. I can't think why vibration from the driveshaft would "reset" after sitting for 20 minutes, unless there is another factor involved (more on that in a moment).

The differential and rear axles have a number of associated bearings, and also a lubricant that will thin out as it heats up. If it's a limited-slip differential, there's even more things that can go wrong in there. When you do get the car up on jack stands, it wouldn't hurt to evaluate the axle bearings and take the cover off the diff to examine the inside for wear or broken/cracked parts, but I would think any vibration from their would vary with the speed of the car. Same with the brake drums.

Speaking of which, sherlock9c1 raises a good point about new parts. I had a vibration that shook the whole car in my 92. Tires were balanced, but the brake drums had lost some fins due to corrosion. I replaced them, but the vibration was just as bad. I spent a lot of time chasing other possibilities before I clued in and put the drums on a balancer -- both brand new drums where out of balance by several ounces each, despite the presence of factory-welded balance weights. I rebalanced the drums (welding on my own balance weights made from scrap steel as required) and the vibration was cured. (However, unlike your case, my vibration definitely varied in intensity and frequency with the speed of the car, so I don't think this is your problem. Still, it's a cheap and easy thing to check.)

So if the source is not rotational, perhaps it's associated with physical size or length, like a tuning fork? Every object has a fundamental natural frequency. When some sort of shock or vibration is applied, energy is transferred most efficiently at the natural frequency, somewhat efficiently below the natural frequency, and with decreasing efficiency above the natural frequency. Strike a tuning fork once, and it will vibrate at it's natural frequency. Strike it repeatedly and it will continue to vibrate at it's natural frequency, regardless of how often you hit it.

Fellow motorcyclists may have experienced a "tank slapper" at one time or another. The bike is rolling along happily until a certain speed is reached and suddenly the handlebars start to shake violently. Slowing down doesn't help and often makes it worse. Touching the brakes makes it crash. The answer is to accelerate, keep your arms flexible, get it under control again, then slow down cautiously. In other words, get out of the harmonic that started the vibration and damp the vibration to change the natural frequency.

The obvious damper element on your car's rear end is the shock absorbers. They contain a fluid, which can heat up and change viscosity, reducing the damping effect. I don't think the shocks could cause the vibration in and of themselves, but maybe that's the explanation for why the vibration requires a minimum time to start and a cooling off period? In other words, perhaps the driveshaft/bearing/brake drum/whatever induced vibration is damped by the shocks until the shocks can't handle it anymore? In which case, you may have two problems: the vibration-causing part(s) and prematurely worn-out shocks.

I would put it up in the air and "Drive" it. On the lift, or on good jackstands. You'll know pretty quick if it's suspension or not.

When I first bought Ms. Roadie she had a terrible shake that started at highway speeds. I could tell it was coming from the rear. Turned out to be a bad rear drum. a "Just replaced POS from China" that warped in less than 1000 miles. Just my $0.02.

Just a thought could the problem be related to the EGR?

When he said the hood was shaking, I was thinking motor mounts at first. But the part that it doesn't change with engine or road speed, and that it doesn't show up immediately wouldn't correlate to  the engine mounts.


Is it above a certain speed only, or when in overdrive?

Make me wonder if on an '84 that a  rusted suspension point is flopping around.

Did you check the drive shape U-joints to make sure that they are at 90* to each other? They should not be aligned in the same plane.

I had a bad vibration on a dodge van after it was on a lift. You could see the mark from where the lift dinged the shaft.. nice yellow line, same color as the lift.

Nasty vibration but it was absolutely  vehicle speed related, not engine speed. When the clutch went it, the vibe (Like groovy baby!) was still there.


Dave

Two other thoughts:

1. Once the tires heat up good and warm and you get the vibration, can you immediately take them and have them checked on a Hunter RoadForce balancer? That unit actually puts pressure on the tires and will find sidewall stiffness variations that can contribute to vibration, whereas standard spin balancers do not check this.

2. This car is 29 years old. Have you replaced any of the rear control arm bushings?

X2 on the rear drum. I bought a 96 B4U caprice a few years ago, pulled it out of dealership to drive it home. Got on the highway and everything was smooth. Accelerated a little together up to 65 mph and all of a sudden I hear a thump and then the car starts shaking like I'm rolling over broom sticks. I did what you did looked at everything. Ended up being a huge chunk of the rear drum rotted and fell off. Was smooth riding up to about 40ish mph. Over that and the car was almost unbearable to be in.

I would also check the frame for any rot where the rear control arms mount

Have you taken the rear drums off to check the springs? Maybe a rusted component causing the shoes to bind up against the drum? I've had those little pins that hold the shoes in place snap and it caused the shoes to move all over the place.

When you come to a stop on the side of the road your saying that even if you instantly start driving the car from a stand still say 0-20 mph the vibration is still there once it's happened at 45+Mph?

Hello again everyone,
the brake drums are 2 years old[ac delco] and I did pull them and spin them on the wheel balancer they were fine they were at zero and no visable wobbles,I also checked all the brake hardware springs,hold downs etc all looked good.I even went so far as to loosen the adjustment on the rear shoes to see if it would help but it did'nt

when I had my buddy drive my car we also drove it around town to see if one wheel was bouncing or pitching more than any other they all seemed fine it does have ac delco air shocks in the rear and I run them at 30psi when unloaded

I also tryed adjusting tire pressure to see if it would make a difference there was no change I normally run them at 32psi
tire wear is even I rotate them every 2,000 miles

I checked all of the body mounts because I had to replace them 7 years ago the rubber had dry rotted and some of them had split and at the time that caused a problem with a shake and vibration but they are fine

I checked all of the attaching points on the frame and its soild no rust or stress cracks anywhere

I double checked all the suspension bushings and attachment points front rear upper and lower everything looks good and solid no rust

I tryed to run it on the lift last night the u joints did'nt like it to much of an angle I have to get the rear on jack stands to run it.

yes it does have a posi rear but the car had this problem before I swaped the rear and I'm not saying that there couldn't be a problem with the rear after all it was a used unit and all that I did to the rear was to change the gear lube several times and i did add the gm posi additive each time

So I'm starting to think it's in the transmission because I don't believe a bent drive shaft would be affected buy heat but as soon as I get up the nerve to go work out in the cold wet weather to check the drivshaft I will, that will be next thing that I check,the boss does'nt want me to do it in the shop he's afraid that it may fall off the jack stands

thanks again to everyone I really do appreciate the input

thanks again,
Danny

We wish we could help nail it for you.

Dave

I once had a 4L60E I bought off Craigslist that was out of a wrecked car but only had 10k on the rebuild before the wreck. I put it in my car and had a nasty speed-related vibration. I put the whole car up on jackstands (jack the rear axle so it's not just hanging there with a nasty angle on the u-joints) and I put it in gear and let it idle. Sure enough, looking at the output shaft, it was oscillating back and forth. I tore the trans apart; it was definitely low mileage on the rebuild, but the entire geartrain was shot. At least 0.080" runout in the driveshaft. Sounded like a schoolbus with straight-cut gears when you backed it up in reverse.

So just throw the car up on jackstands and check. No need to go fast, just let it idle.

Here is my 2 cents,sounds like the T/C is going in and out of lock-up causing a drivetrain shudder that feels like its coming completely apart.

Yes but he put it neutral at speed which kills the TCC and there was no difference. He even killed the engine altogether without change.

yup I got this trans off of craigslist they told me that it had never been rebuilt and I believe that,they told me it came from a wrecked 92 chevy van and had around 70k on it and it was only a hundred bucks so I gambled and went with it that was three years ago and it's also K case

as soon as I get a chance I'll have it up on jack stands and I'll have a look but it'll have to wait snow's comming and I'm on call for plow duty

thanks again everyone
Danny

sorry for the delay I was out pushing snow for 12 hours then I crashed for a day

ok back to the subject at hand I had a chance to put the rear up on jack stands and run it
the driveshaft spins true and no wobble at the trans output shaft or the diff input.
I guess my problem is in inside my trans, I'm leaning towards a good reduild this time versus a used unit.

I can't thank everyone enough for all the help I really appreciated it
Thanks,
Danny

here are some pics of my cars

quick update,  
Hey guys I talked to the transmission guy that we use for all of the rebuilds for our shop and he swears that it can be the torque converter causing my problem, I'm not totally convinced but it's worth a shot.

He suggests that I try a new torque converter [dacco rebuilt],I personally don't think this will help my situation but he said he would give me the converter and if it works to pay him for it if it does'nt then he said not to worry about the money [but I'll pay him anyway].I guess I'll give it a try I've got nothing to loose but some time and $75.00.
time should'nt be a problem I can have a 700r4 out in about 1/2 an hour depending the on the amount of rust and I have changed a a lot of
700r4's/4l60e's.[4x4's are the worst always rusty]

It's especially easy when the car in question is rust free underneth and all the bolts come out easy,
well I guess I'll be staying late at the shop one nite to swap it
I'll let everyone know the outcome when I'm finished with the swap wish me luck,
If I remember I'll take some pics of the under side

I whish that I could have used the 4l60e from my 95 9c1, that was a gm rebuilt and that unit worked better than any rebuilt that I've ever installed

happy new year to everyone
thanks again,
 Danny

Well, I do wish you luck on the converter swap especially since you said that killing the engine while the car was vibrating made no difference.

yup killing the engine also stopped the converter, which makes me skeptical to his suggestion about a converter fixing the problem but I'll give it a try.
thanks,
 Danny

Undo the rear yoke at the pinion yoke and rotate it 180*.

Hi, I have also suffered with shaking in my 1988 Oldsmobile Custom Cruiser. It was fine when I first bought her but she had a 10 year old set of Goodyear Regatta tires which I replaced with a set of Hankook tires. A bad mistake. I found vibrations coming up the steering column at around 60 to 75 m.p.h. making any driving uncomfortable.

As soon as I drove it out of the shop I knew there was a problem and had them re balanced the again the following day. The dealer said it was the rims and I put up with it for two years.

I swapped tires round, looked at rims and suspension and tried coasting to see if I could identify the issue without success.

It was only after I replaced the Hankooks with Maxxis tires that I have got rid of the vibration problem. Now a smooth drive. Still underpowered but that's a 307 for you.

If I were you I'd suggest you try putting another set of wheels/tires on and going for a drive at various speeds. I hope that helps. Cheers.

hello everyone I'm sorry for the really long delay on the update on the wagon this was a really brutal winter with lots plowing and salting and the wagon sat all winter with all the snow and the long hours pushing snow anyway I finally got around to doing the touque converter swap this past weekend and I must say that I was surprised and discouraged at what I found when I did the swap,

first thing changing the torque converter did make a huge change for the better as far as the violent shake it's gone and it feels like a different car alltogether

the bad news is that before I removed the old torque converter I undolted from the flywheel and turned it slowly buy hand and you could hear broken parts moving around and when I had it out of the car I turned upside down to drain it and broken pieces started to fall out [NOT GOOD]
 
so I installed the rebuilt converter and reinstalled the trans then I took the pan down expecting to find bits of metal and such on the magnet and in the filter I cut it open and it was clean no chunks or metal filings the fluid was nice and pink

I was very skeptical that the torque converter would help with my problem but it did [guess my trans guy nows his stuff] so for now its seems great I'll keep my fingers crossed

I've got a 300 mile trip planned this upcomming weekend to visit my older brother and his family so it will be a good test mostly highway driving

Glad you got to the bottom of the problem.

Tom

how interesting,...if a torque converter breaks inside,. then how does it still turn the trans and the pump,..

I'm surprised it still vibrated coasting with the engine off in neutral. What the heck was still spinning the torque converter during that test?

phantom 309 wrote:

how interesting,...if a torque converter breaks inside,.  then how does it still turn the trans and the pump,..

It's possible to break things like the sprag in the stator, the stator blades, bearings or lock-up piston all of which would still allow the pump to function and the turbine to drive the input shaft albeit not for very long as all the trash will quickly foul everything up.

Olds Weighty Eight wrote:

phantom 309 wrote:

how interesting,...if a torque converter breaks inside,.  then how does it still turn the trans and the pump,..

It's possible to break things like the sprag in the stator, the stator blades, bearings or lock-up piston all of which would still allow the pump to function and the turbine to drive the input shaft albeit not for very long as all the trash will quickly foul everything up.

anything is 'possible'  

exactly my point, from detonation to no forward motion would be a very short time,..

and as was mentioned, a key off test was done at speed.

Yes I'm glad that the torque converter fixed my problem but I'm just wondering how much life the bad torque converter took off the trans.
After this upcoming trip I'll drop the pan and see what's inside.

Again thanks to everyone who gave their the time and input to to help me out I really do appreciate it and hopefully I can return the favor in the future.

Thanks,Danny