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<944> Clanking from Front Left on Braking?

Gruppe:

I received an 87 944 from my brother. I've fixed over 20 items on the car (hatch, door locks, key cylinders, coil, crank sensor, stereo, general maintenance, etc., etc.) and it runs OK-ish, but I have one major concern.

When I hit the brakes I get a clanking from the front left. Cannot find any loose parts in the brake caliper or ball joints, but the clanking is pretty loud even when I hit the brakes at slow speeds. My brother says it has been like this 2+ yrs and nothing has fallen off, but I'm VERY concerned and can't drive it like this.

Any suggestions on where to look or how to check? Thanks!

Neil Deshpande
Old 10-10-2003, 10:48 PM
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Did you check the pads themselves? Or even make sure the wheel is completely torqued down?
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Old 10-10-2003, 11:05 PM
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Take it in for a free brake inspection.
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Old 10-10-2003, 11:22 PM
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To the former suggestions, add checking control arm & sway bar bushings on both sides.


drew1
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Old 10-11-2003, 04:34 PM
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Gruppe:

Many thanks for the suggestions! I'll have some time on either Monday or Wednesday evening to check into them. I'll post my finds to the Board. If I can get this safety concern addressed, the car will make a nice daily driver for me, I think. I've already driven it about 8k miles with the clank, but my foolhardiness is at an end!

Neil Deshpande
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Old 10-11-2003, 05:07 PM
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strange. usually the clank is from loose brake pads. but that usually happens in reverse. it clanks when the car is moving and stops when the brakes are applied
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Old 10-11-2003, 07:15 PM
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Yes, its worth checking out. I'd just do what the guys above are suggesting. Can't think of anything else but I know its not supposed to clank. Something is wrong and you should find out. Each clank could be the sound of an expensive cash register ringing. Let us know what you find!
Old 10-11-2003, 07:25 PM
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Newoldguy:

I took the wheel off ... again ... and checked out all the joints. Found that the nut on the control arm rear bolt was slightly backed off. Not loose by any stretch, just not snug with the bushing. The arm could move back and forth. My brother (the PO of the car) reports that the noise started after he had the dampers replaced so I'm guessing the tech never put it back properly. I snugged it up. Once I put the car back on the road (fuel line work on Nov 9) I'll report on the noise.

Thanks!

Neil Deshpande
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Old 11-08-2003, 09:22 PM
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Gruppe:

I put the car back on the road since having torqued down the rear control arm bolt and there is much less clunking. Not zero, but nearly zero. Now that I have nicely balanced wheels, I can feel a distinct looseness from that side though. Nothing clunky, just looseness.

However, I checked out the PET (Parts Catalog) and found that that bolt is an alignment eccentric and fairly important. I'm going to take the car for an alignment shortly, but I want to replace that corroded (OH, MA winters) hardware there before I do that and, perhaps, even the bushings. Basically, try and tighten up the car as much as I can.

Any suggestions on what all to replace are very welcome. The arms are about 35k miles old so I think the ball joints are fine. In any event, the looseness is too large to be ball joints. If it was, the wheels would be off by now!

Thanks!

Neil Deshpande
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Old 12-07-2003, 04:48 PM
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What are the "dampers" he had replaced?
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Old 12-07-2003, 07:16 PM
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Hugh:

Dampers=shock absorbers. I'm a vibrations engineer so I'm a little pedantic about calling them by their proper name even if product packaging calls them shock absorbers.

If you meant, what brand, they are Bilsteins.

Thanks!

Neil Deshpande
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Old 12-07-2003, 08:01 PM
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Oh.
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Old 12-07-2003, 08:46 PM
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Quote:
Originally posted by neildeshpande
I'm a vibrations engineer
hmm what does a day in the life of a vibrations engineer entail? vibration seems like it would be difficult to calculate
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Old 12-08-2003, 12:50 AM
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Hasn't check the wheel bearing play yet.

I would disagree that shock absorbers are dampers as the term is used in harmonic (vibration) control. Now the balance shafts are dampers as these are calculated to control a known and predictable ocilation/vibration.
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Old 12-08-2003, 08:41 AM
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hmmm, interesting thought. this begs the question of what the official definition of damper really is

Hugh, as for the wheel bearing play. would there be any grinding noise associated with thst once the bearing is on its way out?
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Old 12-08-2003, 12:48 PM
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Bad bearings have a rumble to them before they pit and pean. Then they have the rumble and a clunk, clunk, clunk.

If the front bearings are loose then the rotor is going to drag against the calliper housing.

I also wonder if the spacer is gone off of the wheel and the lug nuts can't tighten against the wheel. Then a loose wheel whould play hell with the road feel.
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Old 12-08-2003, 03:05 PM
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(Semi-) Official Definition of a Damper!

Ronin:

Loved "Ronin", by the way. Thought of it as a huge ad for the 92 M5 that is my daily driver.

I have never found this in the literature, but I was told by one of the pioneers of vibrations analysis at a conference that damping, as using in vibrations, comes from de-amplifying, which was shortened first to de-amping and then to damping. Frankly, I have never made an effort to look it up and now that I'm not attached to a university, it would be hard to look.

I'm pretty sure it is not the bearing. I changed pads and had to hammer that area quite a bit (don't ask!) and there was zero bearing play. Also, there is no grinding, or steering-dependent noise, or any roughness when you turn the rotor. OTOH, the rear bolts on the C/A is definitely not kosher.

At any rate, I'm going to order up all the bushings, front and rear, and replace them. I have to do this anyway before I get an alighment and it should be fun in a cathartic way, I suppose.

Neil Deshpande

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Quote:
Originally posted by ronin
hmmm, interesting thought. this begs the question of what the official definition of damper really is

Hugh, as for the wheel bearing play. would there be any grinding noise associated with thst once the bearing is on its way out?
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Old 12-08-2003, 08:37 PM
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Quote:
Originally posted by ronin
hmmm, interesting thought. this begs the question of what the official definition of damper really is
a damper is any external body that reduces the motion of an oscillator... just got out of my physics final. so shock absorbers are technically dampers. hence the bounce test to see if they are working properly
but how do balance shafts work?
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Old 12-08-2003, 08:39 PM
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Vibrations Engineering.

Mr Pants:

There is quite a bit of math and signal processing, but also some nice hands-on work to reduce actual problems to the math before you compute them. I enjoy the diversity of problems and the hands-on part. The head and the hands know different things, as they say.

Difficult? Just a matter of training and education, I think. I've been working on some body work on the 944 and that seems tough to get right, but it is likely that some 16-yr old in the local body shop is doing better with his eyes closed.

Neil Deshpande

Quote:
Originally posted by MrPants
hmm what does a day in the life of a vibrations engineer entail? vibration seems like it would be difficult to calculate
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Old 12-08-2003, 08:40 PM
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Damper, Balance Shaft Function, Bounce Test, etc.

MrPants:

A damper is anything that dissipates the energy in an oscillating system and reduces the amplitude of oscillation. In the automotive suspension, this is the shock absorber. In a radio oscillator it is circuit resistance that dissipates energy that is being exchanged between inductor and capacitors in the circuit.

944 balance shafts work by producing a force equal and opposite to the second-order vibration (vibration at twice crank frequency) of the engine's piston and crank assy. This cancels the second-order component of engine vibration, which is the bulk. This is probably not the right place to go into the source of the vibration, but an internet search on reciprocation engine vibration will yield all kinds of animated gifs and such that explain it well.

The balance shaft is not a damper as it reduces vibration by applying an equal and opposite force, not by dissipating the 'problem' force's energy.

The 944 design (Mitsubishi) is particularly elegant as it is staggered so it takes care of one other force apart from second-order vibration. Sort of like killing two birds with one stone.

The bounce test is a great test of critical damping, i.e., damping where a deflection to one side of the mean (at rest) position is restored to the mean position w/o crossing past. So, if a car bounces more than just back to rest the dampers are shot. HOWEVER, modern cars are highly overdamped (that is, damping is far greater than critical) to the greater chassis stiffnesses available today that permit this. Any newish car would have shot shocks way before it fails the bounce test. Just pop in a showroom and try and bounce test.

Neil Deshpande


Quote:
Originally posted by MrPants
a damper is any external body that reduces the motion of an oscillator... just got out of my physics final. so shock absorbers are technically dampers. hence the bounce test to see if they are working properly but how do balance shafts work?
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