vibration revisited - how much is too much?

[toolboy62]

OK... for those of you that don't remember (most of you?) I posted before about a vibration issue I was having in my '88 NA...

original thread:

bad drivetrain vibration...

1st followup thread:

bad vibration update

2nd followup thread:

944 vibration update - what to do?

So here we are today. I just picked up the car from the 2nd shop that I took it to. This is one of those shops where they are real anal retentive about everything... they do the whole "free safety inspection" bit with every car that comes in before they even touch it, you know they are just looking for stuff to fix. Well anyway they said that my tires were worn funny, and that they didn't like the way my one new tire was balanced (the one that was replaced due to the incident.) The way the guy was describing it it sounded like the shop just left the old balancing weights on, mounted the new tire, and stuck even more weights on to get the tire to balance. They also said my front wheel bearings were slightly loose and they also saw a slight coolant leak, pressure tested the system, and ended up tightening one hose clamp. Also they recommended degreasing the engine to figure out where the oil leak is coming from (hey, I'm just reading off the paper) and that my rear brake pad wear sensors weren't functional (I knew that; the PO put in pads that didn't have a provision for them so they're dangling They also said my brake fluid was dark, which I believe - I've been flushing it regularly but I've never opened up the hydraulics other than to replace the front hoses, probably a lot of rust and crap in there. Someday I will replace the calipers... So anyway you know they went over the car pretty well. Makes me feel better that it sounds like all the bushings are tight and I don't have to worry about the dreaded ball joint failures... (why can't they just use $15 bolt-in ball joints like VW and everyone else on the planet?)

Basically the guy recommended that I replace the three old tires and have an alignment done as the car was slightly out of spec on all corners. So I said fine, go for it, just save the old tires for me (I will put them on the front of my '55 Stude coupe, it needs new skins anyway and I *really* don't think they were that bad; the guy just didn't want to work on the car with the old tires on there, and I was going to have to buy tires for something anyway.) After a fairly large bill, I will say this - the car drives better than it ever has since I've owned it. Steering wheel is dead straight and the car is a lot less "darty" but still feels nimble. That said... the vibration I was posting about before is SIGNIFICANTLY less, but still present. In fact, they did a good enough job balancing the tires that I can now detect it at a lower speed than I could previously, maybe 55-60 MPH now. It's similar to an engine vibration but at maybe 1/4 the frequency. It's "OK" now, as in my mirror doesn't vibrate, nor does my brain, but I can still feel that little rumbling in the seat of my pants. Let's put it this way - it's good enough that I would feel OK about letting someone test drive the car, but not good enough that I wouldn't worry if I knew I was going to have to drive the car across the country tomorrow.

Am I worrying too much? Is there some acceptable level of vibration that all 944s have (besides the usual 4-cylinder vibes?) OR should I take it back again and say "it's better, but it's still not right?" Is it possible that Yokohama ES100s are just not good tires? (were on the car when I bought it, and one was replaced without consulting me when it got hit) Part of the problem, I think, is that the shop guy didn't sound willing to test drive the car above the posted speed limit. (how the heck do they avoid getting rear-ended around here?) Can anyone recommend another shop, preferably one with some P-car expertise, to try near me? I live in Bowie, MD and if I have to travel somewhere to drop the car off it would be more convenient if the shop were towards DC/Virginia (I work in Sterling) rather than Annapolis/Baltimore.

nate

[AFJuvat]

Ok, you have a vibration at 75 - 80 MPH.

You keep having CV axle bolts work themselves loose. this does not make sense - they are only torqued to 30 ftlbs.

Therefore, either you, and every mechanic that has touched the car is incapable of tightening a bolt - which isn't very likely, OR, something is working these bolts loose.

We can't rule out the transmission - it floats in its position on a rubber buffered mount. When these mounts fail, it can cause a noise and vibration. Though usually it feels more like something is rubbing on something else. The easiest way to check this is by raising the car on a lift, and running the car - as the car is accelerated, you can see the vibration in the transmission.

You could also have a bent stub axle, a bent trailing arm (or both) and associated bearing damage. Symptoms like this would show up as odd tire wear on that side, also, it will be impossible to align that wheel - with every bit of rotation, the alighnment changes.

AFJ

[toolboy62]

I'm inclined to agree with your diagnosis, but I have neither the time nor the tools to R&R the bearing on that side... so again, does anyone have a recommend for a DC-area shop that is willing to work on problems like this?

nate

[gadgit]

You don't seem to have mentioned the normal cause of vibration on most cars, which is from the brakes (discs).
What are the discs like?
If they have been in a considerable time, they fall apart on the rear as the handbrake is vented as well. I've just taken mine of and replaced them, and they were in a state !!
Clean out the Callipers and check that all the brakes are releasing properly, nipping brakes will heat up and warp the disc sometimes.
Check the discs all run true.
You may well have allready checked this, but then you might not have, so good luck.

Let us know, so we can eliminte this area and work on the problem more.

[toolboy62]

The brake did not seem to be dragging; I just adjusted the parking brake recently and with the parking brake off the wheel felt like it was turning very freely. Now the brakes have had no maintenance since I got the car except to change the fluid, but they seem to be working fine...

nate

[toolboy62]

Based on driving the car, I have all but convinced myself that it is either a wheel bearing or something that would be revealed when replacing same. So I called the original shop and asked what it would cost to have both wheel bearings replaced. The guy called me back and gave me a quote of over $900?!?!?!?! Is this a polite way of saying that they'd be happier never to see my car again, or is this the going rate?

nate

(I don't *HAVE* $900 right now, so... if anyone wants a good deal on an almost-nice 944 let me know.)

[Zero10]

$900 is almost the going rate.... they really suck to do.
Honestly, no shop really wants to do rear wheel bearings on a 944.
Is that a quote for all 4 corners including parts?
The rears can take a couple hours per side if things get ugly.

I would be interested in getting your 944 for $900

[toolboy62]

No, that's just for the rears. I cleaned and repacked the fronts earlier this year with Redline CV-2, they looked magnificent.

nate

[AFJuvat]

$900 is a little high.

Figure about 5 hours to do them

AFJ

[gadgit]

your barking up the wrong tree here mate, you are not going to get vibes from a wheel bearing. You Will get rumbling or whiring sound.

I've done wheel bearings and when they go they do not vibrate like a worn shaft or bad disc's.

Jack it up and spin, you will hear it straight away !!!!!

I might be wrong ? but I'd put money on it not being a wheel bearing, don't waste your money on a wheel bearing yet!

[Razorback1980]

I would think a wheel bearing could cause a small grind if it had a rough spot and it would certainly make a noise but I'm not sure that would cause your bolts to come loose but I guess it could. I work on a lot of drag cars and we tend to put video cameras on the car to find vibrations. I would tend to look where the bolts are coming loose, somethings causing that and it is probably the vibration. Whether it's the transmission or the shaft or something else, it's hard to guess, so try using some science. Put a dial indicator with a magnetic base and slowly rotate the wheel to see if the shaft is bent. Test both sides to see if they are different by a large margin. You should also put this indicator on the sides (both inside and out) of the rims and make sure they are not bent causing the problem although you have probably already rotated the wheels enough to eliminate that. Also check the driveshaft to make sure it's not bent. I've seen similar things on other cars and on one of them it turned out to be a weight had fallen off the driveshaft causing it to be out of balance. One thing to also try is have a friend follow you down the road at the speeds you are having problems with and see if they can see anything that might be shaking but if it's reduced to a small vibration, then they probably won't be able to see it but it's easy to do, so it might be worth a try. I might do as the other guy suggested, put it up very securely and bring up the speed until you feel the vibration and place a video camera under there to see what you can see shaking. If that didn't work and it was mine, I would mount the video camera to the bottom of the car and film the parts going down the road until I found something that didn't look normal. It's probably going to be a shaft out of balance or bent.

Good luck

Razr

[Zero10]

If the rears have actually come apart and are broken (have seen this many times) they will make a lot more than noise. You will get a noticeable vibration. In the cars where I have seen this happen, the vibration was rather high frequency (5-10x wheel speed), and you could feel it through the floor and seats.
If they are making noise, change them anyways.

[gadgit]

Just as I said, A bearing in the wheel will be making a racket all the time, you would have noticed that, and not just at 80mph.

I'm in agreement with Razor, its something else !!