85 Eldorado - Violent shake at certain level of acceleration
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Cadillac Seville / Cadillac Eldorado Forum Discussion, 85 Eldorado - Violent shake at certain level of acceleration in Past Cadillac Vehicle Discussion; So I picked up a 1985 Eldorado (non-Biarritz) a few years ago. A year in I replaced the rear calipers ...
  1. #1
    Kiriken is offline Cadillac Owners Member
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    85 Eldorado - Violent shake at certain level of acceleration

    So I picked up a 1985 Eldorado (non-Biarritz) a few years ago. A year in I replaced the rear calipers and around the same time I noticed (usually on the freeway) when I pressed down on the accelerator a certain "amount", I would feel a bit of a shake from the car, that seemed to be coming from the rear but wasn't sure. I thought it might have had something to do with the rear brakes but I checked everything and it was all sitting tight with the clips in place (didn't seem like anything could be rattling). Also, I tried applying the parking brake on the freeway while accelerating at that "critical point" that made the car shake and the shake did not change at all, but the car did slow due to the braking. So at that point I pretty much ruled out the brakes being the culprit.

    As time went by I noticed that at/near the same "critical point" of acceleration the car would shake more violently than before, so much so that the hood could be seen sort of bouncing around (looks like it's definitely coming from the front end now). This happens just about every time I drive on the freeway (any freeway) and the only way to make the shaking stop is to press harder on the accelerator. Once the car shifts, the shaking quickly disappears and driving is smooth again. I have to do this pretty often on long drives and it makes me feel horrible since the "critical point" it occurs at is pretty much the amount I'd press the pedal down to maintain about 18-22mpg on the instantaneous MPG display. Speed seems irrelevant, the shaking can happen at 40mph or 80mph. Also it could be my imagination, but it feels like this range that the shaking occurs in is getting larger as time goes on.

    My first thought was that this is probably a transmission problem since the cars seems to smooth out after shifting, but the strange thing is that, it seems as though I can punch the accelerator to cause the car to shift up a gear, and then release the accelerator a bit to the speed I was going at and the shake will not be there.

    Here's a list of things I've replaced/done since the problem began:
    • Fuel Filter
    • PCV Valve
    • Breather Filter
    • Air filter
    • All 4 Belts
    • Coolant Flush (added GM tabs)
    • Several Oil Changes
    • Sparkplugs (gapped to spec)
    • Sparkplug Wires
    • Distributor Cap + Rotor
    • Rear Shocks
    • Front Brake Rotors + Pads (ceramic)
    • Muffler (had rusted through)

    It might be worth mentioning that I have not replaced the front shocks but the car sits level and the only sign that it might be a good idea to replace them is the loud squeaking when going over speedbumps/dips; either way I feel bad shocks would not make the car shake violently on level road.

    If anyone has any idea what could cause this please let me know. I'm pretty good at basic repairs (the only time I took the car in anywhere was for the coolant flush and to have a new muffler welded on) but I'm afraid either something is bent up in the transmission (original to my knowledge) or there's some internal engine damage (HT4100, rebuilt about 60k miles ago).

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    carnut is offline Cadillac Owners Master
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    Re: 85 Eldorado Violent Shake at certain level of Acceleration

    Educated guess. A binding CV joint in one of the front drive axles. If it vibrates on acceleration maybe the angle of the joint causes it to bind.

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    Kiriken is offline Cadillac Owners Member
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    Re: 85 Eldorado Violent Shake at certain level of Acceleration

    Sorry to post in my very old thread but I'm still having the same issue and had some questions/updates.
    1. Replacing front shocks with KYB Gas-A-Just's made the vibration 'tighter' but no other effect.
    2. Replacing engine mounts had almost no effect.
    3. Took my car to an automotive place in town that's "been in business 47 years" and is staffed with only "BOSCH certified technicians". Told them several times I thought I had a "binding CV joint in one of the half shafts" because there was violent front-end vibration on light acceleration. The owner observed the vibration during a test drive. He told me it was probably the steering damper and wrote down "vibration at high speeds" for his mechanics to look into during diagnostics. I tried to correct him by saying "it ONLY happens when accelerating lightly" and he shrugged it off. The mechanic who inspected the car reported that I needed a new idler arm and the owner (I assume) tacked on steering damper. I asked about the CV/axle and he said no way was that related to my problem.

      He wanted $600 to do the idler arm and steering damper. That price was inflated and none of it made sense to me since the steering wheel has absolutely no play in it and is completely still while the hood and everything around it is bouncing violently on the highway. I wasn't going to pay that but decided to listen to "47 years of experience" and tackled the steering damper and idler arm myself last weekend. Unbolted the steering damper which felt exactly like the new Moog one so I put the old one right back on. Went through the pain of cracking the old idler arm off and replacing it. Didn't do a damn thing to fix my problem, in fact the old one felt just as tight as the new one.

    So I'm back to thinking it's the axle (one or both). The guy said it definitely wasn't the axles but that clown also said I should pay him $90 to steam clean my engine instead of getting new tires (the rears are completely bald and the fronts have wear indicators showing; note: I've swapped around the tires to make sure they are not the issue, I've been putting it off because I don't want to buy new tires for a car with this problem -it's almost undrivable).

    My problem now is that I don't know which axle is bad. Neither side has evident damage on either of the boots. For about a month I'd hear a *tch, tch, tchh* sound when making a right turn, so I bought a Cardone reman axle for the left/driver's side. After a simple car wash, I haven't heard it for a few days -who knows it could've been a leaf or something jammed in there that got sprayed out... (but the vibration problem persists).

    So what I want to know, is there any way to tell which axle is bad (without boot damage or any sound), either right now or once I remove it? I plan on trying to swap out the left one this weekend but I don't want to replace my original axle with a reman if there's nothing wrong with it.

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    carnut is offline Cadillac Owners Master
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    Re: 85 Eldorado Violent Shake at certain level of Acceleration

    Humor me and drive in 3rd instead of D on the freeway. That will rule out the lock up torque converter as the culprit. That should also rule out the drivetrain as well because the engine and trans are now at a different RPM at the same road speed. Also the front torsion bars can be adjusted to slightly raise or lower the front static height. There is a large bolt (2) at the center crossmember where the torsion bars sit in their seat. Turning that bolt in puts more wrap or tension on the torsion bar to raise the car. My thought is does raising the car height move the vibration to a different point? Measure from the frame to the ground to verify both sides are up the same amount. The height change would have the drive axles turning at a slightly different angle. Not a fix but a diagnostic aid to confirm an axle.

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    Kiriken is offline Cadillac Owners Member
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    Re: 85 Eldorado Violent Shake at certain level of Acceleration

    Thanks for replying so quickly (again).

    I drove home from work today in 3rd instead of D. 10 miles on the freeway and no shakes or vibrations. Tried driving at all different speeds and pressing down on the gas pedal at different levels, but no shake or vibration. I went back into D and within seconds had the car shaking again.

    I don't know what that means exactly?


    I'm also not sure if any of these additional details will help but:
    • The shaking is extremely easy to make happen. If I get up to speed on the freeway, let off the gas entirely, and then lightly press down on the pedal -that is the threshold for where the shaking will start. If I press down any more than that little bit you'd need to keep the car going a steady 55-60mph or so, the shaking immediately starts. The shaking will continue for as long as I hold the pedal down at that exact point but the shaking immediately stops when I either let off the pedal or press the pedal down harder (I hear the engine rev a little harder, the shake gets a bit worse, then I feel a gear shift and it's smooth again).
    • If I press the pedal down harder to get rid of the shaking, easing off of it until it's back to the previous level that caused the shaking does not cause any shaking this time.
    • The actual shifting knob in the car seems slightly offset (Leaving the shifter on neutral or drive seems to have the same effect. Borderline R to N puts it into neutral. Left edge of R puts it into Reverse. I didn't think shifting into 3 or 2 worked when I bought the car because the shifter doesn't seem to lock into either, but I could definitely feel the difference driving today.)

    I'll see if I can try adjusting the torsion bar tonight or tomorrow and check if that has any effect (I do understand this part).

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    Ranger is offline Cadillac Owners Member
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    Re: 85 Eldorado Violent Shake at certain level of Acceleration

    Quote Originally Posted by Kiriken View Post

    I drove home from work today in 3rd instead of D. 10 miles on the freeway and no shakes or vibrations. Tried driving at all different speeds and pressing down on the gas pedal at different levels, but no shake or vibration. I went back into D and within seconds had the car shaking again.

    I don't know what that means exactly?
    Carnut knows more out these than I remember, but boy that sure seems to point towards the trans to me.

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    carnut is offline Cadillac Owners Master
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    Re: 85 Eldorado Violent Shake at certain level of Acceleration

    I wouldn't bother with the torsion bars at this point. At the speed you mention and a light throttle, you are in lock up within the torque converter at about 51 to 53 MPH. Any change in throttle angle will disengage this clutch. I would remove the inspection cover on the bell housing and mark the flex plate to the converter. Then remove all the retainer bolts and rotate the converter relative to the flex plate and reinstall the bolts. Drive it in D at that road speed to see if it gets worse or better. That would confirm a faulty converter. The sloppiness in the shifter and misaligned indicator are worn and/or missing bushings at the linkage cross shaft or on the lever on the trans itself. In the past, I've used Hurst metal shifter bushings or HELP line brand GM door hinge replacement bushings with a circlip that places tension on the rod as it passes thru the trans lever. These spring circlips came in a package of Hurst shifter bushings years ago. Cotter pins still allow the rod to flop around. Once all play is removed, you can remove the wood plastic piece under the steering column and move the clip on the column either up or down that connects the wire to the indicator. I usually align it to neutral. Getting back to the vibration, the new DEXTRON/mercon synthetic tranny fluid was developed to lessen the shudder when the clutch engages and I use it on every Cadillac of that era that I've owned. I doubt the fluid alone will fix your severe vibration though. Another quick and dirty diagnosis is to drive the car in D and when the vibration starts, depress the brake pedal with your left foot gently. That disengages the clutch and then tell me if the vibration stops immediately.

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    Kiriken is offline Cadillac Owners Member
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    Re: 85 Eldorado Violent Shake at certain level of Acceleration

    Thanks for the shifter bushing & tranny fluid tips. I didn't bother with the torsion bars and won't have time to rotate the converter tonight but I'll post what I've got now.

    On the way to work I got into "shake mode" and lightly applied the brake. I needed to press it down about a centimeter before the shaking stopped, but when I did, the shaking stopped instantaneously (but the braking force was enough to also feel the car slow a bit). I tried this several times with the same effect each time.

    There might be some slack in the brake system because today I was in a parking lot and it seemed like I needed to press the pedal down that same amount before the car would slow any (just shifted from P -> D, rolled forward slowly and applied the brake to check this).

    I'm not sure it will help any but I made a sloppy amateur video of the shake in action on my way home.
    The video is at https://www.youtube.com/watch?v=dqu9gpUDBJI in case the video embedded in the post doesn't work for some reason.


    1. Video starts when gas pedal is applied just before that shaking point.
    2. I press down a bit harder and the shaking starts
    3. Car gets in front of me -> I ease off gas pedal -> Shaking stops
    4. Car in front of me speeds up -> I press back down on gas a bit -> Shaking resumes
    5. Shaking goes on for a while because I hold my foot pretty steady
    6. Car in front of me gets out of the way
    7. I accelerate and the shaking immediately the stops

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    carnut is offline Cadillac Owners Master
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    Re: 85 Eldorado Violent Shake at certain level of Acceleration

    2 more things you can do to verify a faulty TCC. Press off and warmer at the same time and hold them till the display changes, while driving below 45 MPH, on the climate control head. As you know that puts it in diagnostic mode. Just above the word AUTO as you approach 51 to 57 MPH you should see a yellow icon illuminate and I'll bet the second it lights up the shake starts! Let off the throttle and the light should go out at that moment telling you the clutch in the torque converter has released and the shake stops. Sneak back up to that speed and see if the shake starts again once the icon lights up. The diagnostics will quit once you shut off the car. Second, while you are under the car looking at the linkage, disconnect the wire harness just above the trans pan rail just behind the shift lever. That will prevent TCC ( torque converter clutch) engagement in D above 51 to 57 MPH. Low brake pedal? See if the car rolls forward in gear with your left foot firmly on the parking brake and your right foot on the brake pedal. Then slowly lift your right foot. The car should squat in the rear and not roll forward. If it does, the rear caliper pistons need to be adjusted on your new calipers. Lack of the use of the parking brake causes this.

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    carnut is offline Cadillac Owners Master
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    Re: 85 Eldorado Violent Shake at certain level of Acceleration

    Each and every time you depress the parking brake the piston rotates inside the caliper and ratchets out to take up the normal clearance caused by normal pad wear. Non use will cause excess clearance and a low and slow to react brake pedal. Quite a telling video! For sure not a faulty drive axle. Hard to explain here, but the caliper adjustment is explained in the factory service manual. And this test will only work if your parking brake automatic release works!

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    Kiriken is offline Cadillac Owners Member
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    Re: 85 Eldorado Violent Shake at certain level of Acceleration

    Amazing! I put the car in diagnostic mode this morning just before getting onto the freeway. A little LED light would come on and a second later the shaking would start. When it went off the shaking would stop (if I let off the gas pedal or pushed it harder). The shaking only occurred when that light was on!

    I guess the best course of action now would be to disconnect the harness as a temporary fix and to confirm if any shaking occurs with it disconnected. I'm assuming the only side effect would be slightly lower fuel efficiency?

    Is a standard remanufactured torque converter from a place like Rockauto an acceptable replacement (looks to be < $100 which is great)? Is replacing it something I can do at home in about a day (service manual made it look like you have to pull the transmission to replace it if I remember correctly)?

    As for the brakes, I actually ended up replacing the rear calipers after reading one of your posts on here explaining what the issue was! If I remember correctly, I didn't do any adjusting on the calipers themselves (just loosened a tensioner along the brake cable under the car to get the old calipers off and tightened it back with the new calipers). Since then it's become a subconscious habit to always use the parking brake. I remember checking the rear brakes with the method you suggested and was proud of myself when the car didn't move like it had with the old busted calipers. I haven't checked it in a while but I'll do that again today just to be sure.

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    carnut is offline Cadillac Owners Master
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    Re: 85 Eldorado Violent Shake at certain level of Acceleration

    Yes the trans must be at least moved far enough back to remove the converter. I would get an estimate locally to R&R the torque converter. That way you have a warranty on the part and labor. I do virtually all my repairs at my advanced age! but in certain cases on large repairs, I want some recourse with a shop. The car must be up high enough to swap the converter and that can be potentially unsafe at home. I would also recommend the TCC solenoid in the trans valve body be replaced at the same time. They do fail and now is the proper time so you dont do it 6 months from now possibly. And its great to hear we are making progress. Could it be thats why it was sold in the 1st place?

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    carnut is offline Cadillac Owners Master
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    Re: 85 Eldorado - Violent shake at certain level of acceleration

    I just re read my factory service manual and it says to rotate the t/converter 120 degrees relative to the flywheel to check for an improvement. If better, rotate it again 120 degrees. It also states to look for missing balance weights on the flywheel or the torque converter as well as loose bolts securing the torque converter to the flywheel. If weights are missing on either, it says replace that component.

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    eyewonder is offline Cadillac Owners Fanatic
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    Re: 85 Eldorado - Violent shake at certain level of acceleration

    Quote Originally Posted by carnut View Post
    I just re read my factory service manual and it says to rotate the t/converter 120 degrees relative to the flywheel to check for an improvement.
    I'm always looking to learn more, so help me to understand how rotating the torque converter, relative to the flywheel changes anything. There are only three bolts that hold the converter to the flex-plate, and no other synchronization between the two.

    Are we looking at something as simple as non-concentric axes of rotation between the crankshaft & the torque converter?

    Sure is puzzling to me.

    Cheers,
    Steve

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    carnut is offline Cadillac Owners Master
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    Re: 85 Eldorado - Violent shake at certain level of acceleration

    We are trying to narrow down a possible unbalanced rotational mass! Moving the torque converter to a different area on the flywheel will either rule out or in an imbalance between the 2. Much like rotating a tire on a rim to lessen the amount of wheel weights that are needed. It also provides a visual inspection of both for possible missing weights.

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