: 96 RWD vibrates at 60-75mph



mharker
08-16-07, 05:25 PM
Hi folks.

My 96 vibrates in the back, to the point that beyond 60mph it's very annoying. Tires are new and wheels are balanced. I'm taking it back to the shop but don't want to leave after yet another wheel balance, just to find it does it again.

Friend said maybe drive shaft is out of balance. Possible? Car has about 70,000 miles and is in very good shape.

(OK I admit it's not my Caddy it's my Roadmaster, but admin please don't bump me I need advice from the FWB owners who read this group)

96Fleetwood
08-16-07, 11:45 PM
Do you have factory wheels? If not, are they hubcentric?

Could be your driveshaft. I haven't heard of one failing with low mileage like that.. so I am stumped.

FASSTWOOD
08-17-07, 01:16 AM
Maybe you could get some jacks stands on the axle tubes. Put the car in gear and see if you see anything not running true. That might be your best bet.

The Ape Man
08-17-07, 08:33 AM
Maybe the shocks aren't damping. Worn out u-joints can do that too.

z06bigbird
08-17-07, 12:12 PM
U Joint, as other post says!!

jayoldschool
08-17-07, 12:29 PM
Get your wheels balanced at a different shop. The balancer that I had been using was wrong, and my Roadmaster had a pretty good vibration at highway speed. Had my buddy redo the wheels at his shop, and the balance was way out. The car is butter smooth now.

If that doesn't work, U joints. Check the trans mount, and the bushings on the trailing arms, too.:thumbsup:

mharker
08-17-07, 03:17 PM
Thanks for all the suggestions guys. Talked to my tech and I'm going back Tuesday. He seems to think U-joint would give me vibration at lower speeds also.

Anyway we'll see what he says after looking and I'll post an update.

Unrelated: I get a scraping sound from LF wheel when slowing down and turning right into driveways. This has stumped my shop as well. Buddy suggested maybe my original soft FE1 shocks/springs are dipping too low and making the tire scrape. Maybe time for police car suspension upgrade soon.

jayoldschool
08-17-07, 05:15 PM
The scraping noise when you have the wheel cranked all the way over is the spindle rubbing on the steering stop. Just grease it with a thin film of grease. There is actually a TSB for this.

One more thing: have your tech check your upper A arm mounts to make sure the alignment shims haven't fallen out. Happens all the time, and people don't realize it.

N0DIH
08-17-07, 07:28 PM
Does it occur in drive AND neutral? Under load AND not under load?

If you get up to 80 mph, and get off gas, does it do it in the 60-75 mph range still?

Please be safe if there is something wrong.

What gearing? If non stock, the stock driveshafts aren't very well balanced for cars with shorter than 3.23 gears....

rlyons
08-17-07, 11:08 PM
I am working on the same thing on my FWD and it is the driveshaft. It is not properly balanced from the factory. I have it close and by tomorrow I should have it right. Just place it on jack stands and put it in low gear with the engine running. Place a piece of chaulk close to the drive shaft and slowly move it closer to the shaft. The chaulk will mark the heavy side of the shaft. Then place two radiator hose clamps around the shaft with the screw parts on the light side. Then rotate the clamp screws a little bit apart and try running it up to the speed where it vibrated. If the vibration is still there then place the screws closer together and try it again. Rotate them a little bit at a time until you get the balance right. The screw parts of the clamps will work as a weight to counter balance the heavy side of the shaft. Crude way to balance but it works.

rlyons
08-22-07, 08:55 PM
Any luck yet with your vibration? I am still chasing mine. I am at the point now that I am looking for a place to get my driveshaft balanced to see if it cures it.

N0DIH
08-22-07, 09:54 PM
Another thing to note on driveshaft balancing, note that the vibration is 3.08xvehicle speed in harmonics. Or 3.42xvehicle speed, etc. Gear ratio is the multiplier.

Also, I fought with a nasty vibration in my 80 Turbo T/A some years ago. I knew it was engine related, but more so under load. Drove me batty. I did find swapping harmonic balancers helped, but wasn't the answer.

Ultimately I found the engine to trans bolts had got loose (lower ones) and the engine was trying to separate from the trans under power. Snugged up and all was gone.....

mharker
08-28-07, 10:45 PM
NO. NO luck. Took it to my regular shop and they did the stoopid re-balance the wheels and it still does the same thing. Then tried an alternate shop and they said my tires are no good. But my Goodyear Regatta 2s are like 6 mos old and it was doing it before my new tires anyway.

Let me know if you find a solution. This makes me so mad I am thinking of trading in for a FWD Park Avenue. (OK maybe not that drastic but you get the idea).

N0DIH
08-29-07, 12:14 AM
So you have confirmed, it is NOT engine speed dependent? i.e. does the vib at the exact same speeds, no matter what transmission gear? 2nd, 3rd and 4th? TCC locked/unlocked (lightly touch brake pedal to disable TCC).

Is the rear axle straight in the car? Has a lower control or upper control arm been bent? Is there a tweak in the frame?

Is the car riding high or low? A driveshaft that gets lined up too straight with the pinion will vibrate wildly. Change the ride height. Make it ride high, get the rear fender skirt to near the top of the rim. This will eliminate that driveline phasing issue if it exists.

Is an axle shaft bent? Is the driveshaft bent?

Obviously a wheel is NOT bent if they balanced the wheels ok. They should have screamed if one was.

Is it an ignition miss that is causing it? Are you 100% it is the axle? Could it be the engine? Could it be the TCC?

Sorry, gotta rethink the whole thing from start to finish.

rlyons
08-31-07, 05:33 PM
Mine does vibrate the same at the same speed no matter what gear or coasting. It is way too fast for a wheel, not engine related at all. Not the torque convertor as I can shut it off and coast and still get the vibration. I went through all the procedures in the factory manual, to include balancing the shaft with hose clamps, removing wheels and checking for vibration on stands and it still vibrates at the same speed. It vibrates at 60 to 70 and above, a fast vibration vibrating the rear view mirror and a drumming type noise. Nothing has ever been bent on mine and everything looks good and straight. I am going to raise the rear and drive and see what happens.

N0DIH
08-31-07, 05:54 PM
Honestly it does strike me as driveline phasing. Somehow change the rideheight of the car. Either pump up air shocks (I would shoot for this, you can disconnect link in back on switch, and make compressor run and pump up, then pull fuse on compressor to keep it from bleeding back down), or air bags in the coils (cost, so not best choice), or this ring type coil spacer (http://www.jcwhitney.com/Coil-Springs/600003419.jcw) in the coils installed with springs full extended, and jammed as far down as you can get it, to do it right you might need 2 in each coil. Again, expense. Just pumping up air shocks is best and cheapest. You might be able to load up the trunk heavy with a bunch of people, let it pump up, and then pull fuse when it is up and then think about letting them out. Or disable and load up trunk and drive it. Bags of sand at HomeDepot and the link are "dirt" cheap and load it up good and heavy.

Driveline phasing issue is hard to detect without cameras underneath while you are driving and still can be tough to figure out. And jacking up car will eliminate the problem as the suspension will hang and you "fix" it.

Basically the issue ends up being the 2 u-joints get in line with each other and the shaft itself goes bezerk because it isn't supported under the proper load. Driveshafts must be off to the side slightly and up or down slightly. Typically down, so the car doesn't get into the out of phase issue over a bump.

I would go this route, you have got most other issues ruled out. If you are near Chicagoland or north between Madison and Milwaukee, maybe you can stop by too and we can look at it together. I am sorta in between this "triangle" area.

deVille33
09-01-07, 11:11 AM
Why do you post on this board? This board is supposed to be up to 1985.

N0DIH
09-01-07, 10:36 PM
This is the up to RWD forum, not FWD.

RWD 19xx-1985 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum