I could use some advice on this one please.

When highway driving, my car drives ok up to about ~ 65-75MPH.
Sometimes at these speeds the car will shake/vibrate bad enough to skip the cd in the player.

stepping on the gas smoothes it out, I let off then I hear a rumbling sound. It is not too loud of a sound, but very noticeable.

I don't think this it is suspension or alignment because it smoothes out by driving faster, and there is no problems until about 65MPH.

Any suggestions on the bad shaking between 65-75, or the rumbling sound when I let off the gas?? (the rumbling sound occurs most times I let off the throttle, not just when trying to get rid of the shaking.)

 

Sounds like something in your drive train is loose...

Check your U-joints, and make sure the pinion nut is tight.

 

Make sure your tyres are round, with no slipped belts, cupped wear, or high/low spots.

Balance the tyre/wheel assemblies.

Check the rear axles for true-running by jacking and supporting the rear end and running the car in gear at idle. Bent axles, flanges, worn bearings, and bent wheels can be identified in this manner.

Inspect the driveshaft to see if any of the spot-welded balance weights have been thrown off, although driveshaft imbalance is normally apparent at 45MPH or less.

Check for brake interference and rotor/drum warpage and/or hard spots.

Inspect the driveline as RB suggests.

 

If none of that reveals any problems, you may also have a torque converter balance or lockup problem.

 

Thanks for the hints guys. I should have described my car a little better to start.

The tires are new- this year. So they are not worn or anything. As for balancing them, I don't know how to do that.

-maybe the tire shop can rebalance them for me.

Rotors and brake pads are In Transit from Summit. Maybe that will cure it, if it is rotor warpage.

I am seriously thinking this could be driveline related as you both suggested, given that I have been hearing what I thought was a u-joint going.(sort of whistling/loose metal type sound coming from underneath my seat.)I need help describing noises, I know.

-Thing is, I had a mechanic check the noise- he said the driveline was fine, and he made sure it was lined up right, but you never know.

Vader- the car is a 5sp. as I should have mentioned before, so, a tclu is probably not my problem here.

?Could you help me with identifying "true-running" of the axle, and also the safest place to put jackstands in the rear- since I have never started the car while it was jacked?
-I have been supporting it just inside the lca's

?also how many spot weld weights should be on the driveshaft?
?finally, are wheel bearings a likely cause of this problem?

Thanks again for leading me in the right directions

 

Sometimes shops will offer free future rotations with new tires.
Maybe go to get them rotated, and in the process they will generally rebalance them.

Things like bent axles, and de-balanced driveshafts will do what you're describing, but unbalanced tires are probably the most common cause of high speed vibration.

Another possible cause is a broken radial belt. I had a set of new ('bout 6 months old) Goodyears on my daily driver Escort, and managed to get the little beasty up to 110 on the highway. Well, sortly after that, my car developed a bad shimmy at speed. A tire also developed a slow leak. When refilling the tire, the sidewall buldged out probably (no kidding) 3" straight out. This was with about 30 PSI. Turns out the belt broke during my 110 mph run. Anyways, make a long story short, have you recently exceeded the speed rating for your tires? Any air loss? Buldges?

 

I haven't exceeded the speed rating. Doubt my car could even go 145. Anyway, the rear right tire does leak. I have to fill it about once a week. I can fill it up with no bulges. I took it back to the shop once, they said it was a bead leak, and that it was fixed. But that was probably , because it still leaks.

Maybe that should be my first step before I get out there and start searching.?

Thanks for the help.

Oh yeah, could the radial belt be my problem? It doesn't sound like it is lapping.

 

I would definitely focus on the tires.

Go to a reputable tire shop, and have them inspect the tires. Most tire shops I've been to have been very good at troubleshooting vibrations.

Hmm, you mention no sounds coming from the suspect tire. I don't know what kinds of experiences you've have with broken belts, but the 2 I've had broken (one on the Firebird, the other on the Escort) made no noise. I wouldn't use the lack of noise to rule out a tire problem.

Bead leaks are usually easily fixed by reseating the tire. To have 2 attempts at sealing a bead fail, makes me think that the tire is faulty.

Again, see a tire shop, talk to them about it, see what they say.

 

You would put the car on jack stands, with the stands under the axle tubes, and the tires a couple of inches off the ground.

From your description I doubt it's wheel (or rather, axle) bearings. They don't usually change between drive, float, and coast conditions. Tire balance and wheel out-of-round doesn't either. Your symptoms to me seem to point clearly to a drive line issue.

 

What about struts? Could bad struts, and/or mounts cause this speed-induced vibration.

If not, I guess I need u-joints.

tx guys

 

Whoa, old thread!

I'm guessing the tires have checked out fine if you're still hunting for the source of the problem, eh?

 

could also be your flywheel.

 

How about the torque arm mount? I'm not sure of this, but I would think that if it was worn, it would throw the pinion angle off and possibly cause a vibration.

I'm having a similar problem, but mine is over 70 MPH (I know, that's faster than the speed limit, but it's all good until you get caught! ) My car vibrates, and you can hear it also.
Thing's I'm checking : Torque arm and trans mount (Both are fairly recent Energy Suspension units), Pinion angle, Bent axle (Doubt it, would show up at the speeds brett is having troubles with). The only other thing I'm questioning is the ouput shaft bushing on the trans. Mine has a littl bit of play in it, just enough to make a small permamnent leak, even with a new seal).

I'm gonna keep following this thread, maybe I'll think of something more to help, or something that someone suggests will help me, too!

 

Sorry if someone else said this:
Low air pressure in tire or bent rim.

 

Tires, wheels, etc. cannot cause this. Shocks, struts and springs cannot either. Out-of-balance flywheels cannot do it either. Even bad mounts won't make it act like this. The ONLY thing that will cause it, is loosenss in the drive line.

Check your U-joints, and make sure the pinion nut is not loose.

 

My car is up on axle stands in at the moment as I'm doing some rust proofing, underseal on the floorpan, grease on brake pipes etc.
I get a vibration as described in this thread so I took a look at the driveshaft. If I grab the driveshaft I notice it moves slightly due to play where it pushes into the gearbox and due to play in the UJ bearings. How much play is acceptable? Also where is the pinion nut?

Thanks

Simon

 

You should be entirely unable to detect play in the universal joints, moving them by hand. If you can feel play, then they're just about ready to fall out from under the car.

When you take the drive shaft out, look at the place it came from.... you'll see a big nut right behind the rear U-joint. That's the one in question.

There should be very little side play where the drive shaft plugs into the transmission. A very very small amount is acceptable, enough to see would probably be too much.

 

Thanks for your words of advice. i removed the driveshaft and clamped it in the vice and there was no play in the UJ. The movement I saw when it was on the car must have been all due to where it pushes into the tranny.
Also, as my car was on stands the rear axle was at its lowest point and in this position the DS is pulled quite a way out the tranny hence more play. I jacked up the back axle and it was OK.
While the DS was out I tried moving the output shaft from the tranny and it moved a hell of a lot. Looking at a diagram of the tranny there is no bearing near the back of it. So the driveshaft must run in a bushing.
Pinion nut was tight.

thanks

Simon

 

Yes, there is a bushing in the tailshaft housing of the transmission.

 

I must say my car did the exact thing!!!!!!!!!!! I took me a long time to figure out that I had a Bent Axle. Thats why I looked this up, to see if anyone else had this problem so I could help.

 

Thanks for the input! That's what the boards are all about!