Mystery Noise and Vibration, Contemplating Suicide

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Guru Meditation
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Mystery Noise and Vibration, Contemplating Suicide

Post by Guru Meditation »

You may have read my previous posts about having a spot of trouble with the brakes on my Citroen ZX 1.9td Aura. The problem was a bad vibration through the pedal and poor stopping power. I have since replaced both front pads and discs with Brembo discs and Halfords pads, had the rear wheel cylinders and shoes replaced at Mr Clutch and I fitted two new drums and wheel bearings at the rear. And guess what? Yep-there is still vibration under braking. The strange thing is that it is not always bad vibration. Sometimes the brakes feel smooth (since the aforementioned work the brakes feel as powerful as they should be) and basically as they should be, but then the next time I apply the pedal there is the vibration that goes right through the car. Sometimes there is also a mega weird noise that I am really, absolutely stumped about and don’t know if it’s related or not. This noise only ever occurs under braking, not every time and although it doesn’t occur at all under light braking it sometimes occurs under normal-medium braking other times it won’t occur even if you stop really hard. The noise almost always occurs if you pull the handbrake on while moving (although the brakes feel a lot smoother through the handbrake now, unlike before, although there is still a small amount of vibration felt). The noise is very hard to describe but I’ll try [:-)]: It is very loud and fills the whole car but I cannot tell if it is coming from the front or rear of the car, it sounds like a kind of rubbing/friction type noise rather than a knocking sound and like I say not always under heavy braking. It has occurred since I owned the car. At first I thought it was because of the dodgy exhaust (replaced exhaust with a full new one, no effect on noise), then maybe front or rear brakes (replaced both but no effect on noise) so now I’m stumped. I have never, ever heard it while not braking-never under cornering, never under hard acceleration, never going down a bumpy road or through a pot hole etc. There are no signs of any wheel fouling the arches on any of the arches. There are no unusual suspension movements apparent under cornering etc.
I thought maybe it could be an engine or gear box mount but causing the noise and vibration but there are no other symptoms e.g. noises under hard acceleration etc even then noises caused by a loose engine or subframe mount would be a knocking type noise rather than a frictional rubbing noise.
So what could be causing my vibration and this mystery rubbing noise and are they related? Excessive run out of front discs caused by the discs or hubs? Discount this on grounds of vibration not being felt through steering and have known good brake discs although will check run out if I get desperate (more desperate!). Maybe warped stub axles on the rear? Why is there not constant vibration in this case? I have not tried different wheels yet but could they be the cause of all this grief? The tyres don’t have nay obvious signs of damage or defects. I don’t understand why I can’t sort this problem out-a car is a piece of machinery. The vibration problem MUST be being caused by some component/components that come into play under braking being faulty/broken/out of balance. Why me?! Have you ever heard of a car with such a problem that wasn’t cured by good old set of new discs and drums! Maybe I’m just being stupid and missing the obvious if I am please feel free to tell me how daft I am. Any advice appreciated.
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tomsheppard
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Post by tomsheppard »

Well, Guru - free advice is worth what you pay for it and I am not sure that I want your death on my conscience but I'll see what could be tried. If it was a bent rear stub axle then this part isn't rotating. It ain't that. Try swapping the rear tyres to the front. When you do so, take a good look at the sidewalls for any contact marks. If the noise is the same, then the tyres are probably not to blame. You will of course be rotating them when you lift the car to check them for buckle. Grasp the wheels top and bottom and check the wheel bearings for looseness and then , finally, check that the rear shoes are bedded into the drums properly and not scraping as they go round. if it isn't any of these, then you may have a worn inner driveshaft joint, or a diff bearing that is a bit slack and allowing the crownwheel to chatter as the load on it is reversed. It is always difficult to diagnose remotely; some idea of the magnitude of the vibration needs to be conveyed. The second time I drove a car with a broken crankshaft, I knew exactly what the fault was even though it was years between incidents and two very different engines. Just a thought. I once had a Mini where the exhaust hung badly. The noise and vibration under braking was terrifying because the pipe was making contact with the body.
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Post by Guru Meditation »

Thanks for the advice, I think I'll put off the suicide attempt for now!
I'm gonna bung some wheels from my 1.6 205 gti on this evening see if that makes any difference. Fwiw I have never noticed any wheel out of balance type effects at any speed and I've had the car up to an indicated 110 and I have driven several cars with out of balance wheels before so I don't what could be wrong with them but I will try. I'm going to nip to the place who did the exhaust tell 'em I think it may be rubbing and ask them to try move it further from the body. I have looked at front suspension components ie given drop links and tie rod ends a good tug seem fine.
The extent of the vibration is this: The vibration is felt through the whole car, it lightly rattles the interior trim. Can't really be felt through the steering but can be felt slightly through the brake pedal. It is hard to explain.
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tomsheppard
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Post by tomsheppard »

Hmm.. I am inclined to think that this is an inner driveshaft joint because it is difficult to replicate the fault at will. I've seen it before on Saabs where the driving side of the shaft has taken an indentation which puts a little slack into the joint but only at certain driveshaft angles. Once the mass of the driveshaft is clamped at the outer end by the brake, the inside is sometimes free to rattle about and sometimes it is not, depending on an intricate equation of speed, steering angle and driveshaft droop as the brakes are applied. To find out for sure, it may be necessary to get underneath and try to find any looseness in a driveshaft while the steering is turned and with the car jacked to different heights. Worse, you won't be looking for a lot of play so If you find it you won't be sure if it is the problem... Cars - who'd have 'em.
Jon

Post by Jon »

Hm, Citroen ZX "Everything about it says quality" it said on the cover of the brochure that came with my car.
On top of what Tom has mentioned, I'd have a careful look at the front arm P bushes, get a prybar between the arm and subframe and check for any play. Also check that your dodgy exhaust is not hitting the rear bumper, or that the downpipe is not touching somewhere.
Of course, if you are really lucky, it may be the tyres.
Let us know. If it all goes quiet I will assume that you have driven said ZX into a river.
Jon Wood
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Post by Guru Meditation »

Can anyone tell me if this is normal: When I put my new drums on I noticed that the drum would rotate half a revolution freely then slightly bind for about half a revolution (not binding greatly, just a little bit). Does this show that the drums are out of round? I thought that if the drum was rotating in a perfect 'circle' the inner diameter would never change through a revolution and therefore the drum would be in contact with the same amount of shoe constantly so the pressure required to rotate would never change throughout a revolution if you see what I'm saying?
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tomsheppard
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Post by tomsheppard »

Drums are only SO round. This binding you speak of may be an ovality of 2 thou in 7 inches. You could always reverse the drum on the hub and check it with a dial gauge or try cleaning up the mating face to which the drum fits. If there is another position that the drum could be fitted to then try that. Check with the Manual the ovality tolerance. Find out if it is in spec...
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Post by Guru Meditation »

Update:
On my way home from work I took a detour and did a little bit of road testing. Maybe my 'mystery vibration' is not such a mystery anymore... After much braking, pulling the handbrake etc I think I may have identified more about this noise. It sounds more like a muffled rhythmic knocking like two surfaces being banged together but never actually coming fully apart (maybe why I initially thought it was a 'rubbing' noise) and I THINK it is coming from the front left of the car. Kind of like a rhythmic juddering (rub,thump,thump,thump,thump) like ¼ second intervals or less. I noticed if I brake and it’s stopping smoothly I then lift off brake and quickly reapply it may prompt the noise and shuddering to occur. When braking and this noise doesn't occur braking seems smooth with very little vibration and the pedal feels fine-vibration certainly gets a lot worse when this noise is occurring.
Now I'm thinking I have some bush or mount gone in the engine bay area. Could explain a few things ie even when I get some vibration but not the noise it could be that whatever is causing the noise is also causing the vibration but it doesn't always make the noise, it just depends what position it happens to be in at the time. I have discounted exhaust just about I think as the dodgy exhaust I was referring to was the one that fell off (rusted through at the back box union and fell to the road). I have just had a new one put on and I saw the underside of the car while on a lift and the new exhaust doesn't look like it could rattle it seems to be fairly solid in position. Also made this noise with the old exhaust. I must admit once when my nearside wheel went over some bumpy ground and although the ride was fine I heard what sounded like some thumping but just assumed that was the suspension-don’t know if that indicates anything.
So after all that pain it sounds like I may be suffering simply from a worn out bush or mount somewhere, but which one? Bearing in mind the car feels stable at all speeds, the steering feels absolutely fine, the handling feels absolutely fine both left and right handers, I have never ever heard the noise occur other than under braking, on occasions when I have pulled away with max acceleration or spun the wheels (even spun up in second on boost in the wet the other day) there has been no jumping or banging noise associated with broken gearbox or engine mounts. Funnily enough pulling the handbrake on while driving along (not enough to lock the wheels or even decelerate particularly rapidly) usually causes the noise to appear with a vengeance. Maybe this is because: Applying the handbrake retards rear wheels only, causing some weight to transfer to the rear, this has the effect of ‘lifting’ the front of the vehicle slightly causing whatever bush or mount that is worn/broken to sag as the weight of the front suspension/engine sub assembly causes it to ‘drop’ down to stay in contact with the road. As the road is full of constant undulations the front subassembly is constantly being ‘bumped’ by the road then dropping back down (maybe the gap is just a millimetre or something) this has the effect of ‘banging’ whatever it is that is worn out together. May be why applying the handbrake makes the noise appear more reliably than just normal braking?
Jon says “Citroen ZX "Everything about it says quality"” Aye
Apologies for the unfeasibly long post, may this thread live on to help some other tortured soul.
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sooty
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Post by sooty »

As Tom has already mentioned,
have you tried changing your tyres around, because if you think about it, when you are driving along as normal your rear tyres are just free wheeling with no loads applied, but when you apply your brakes you apply torsional stress to the tyre wall(your inner part of the tyre on the rim, trying to stop rotation and the outer on the road surface wants to keep rotating). So you may have a fault in one of your tyres and the vibration maybe amplified if your rear shock absorbers are worn, not dampening/controlling the vibration.
Good luck Sooty
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Post by jeremy »

I take it you have looked at the similar thread 'ZX Volcane - vibration under braking?'
You are not alone!
Jeremy
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Post by Doc »

Have you checked to see if the front sliding caliper bolts are not excessively worn and/or seized allowing the caliper to twist in relation to the disk?
Have you checked to see if the disc retaining screws are secure?
Were the discs checked with a dial gauge after they were fitted as even new discs can run out? (though Brembo components should be top quality)
Have you tried removing discs and replacing them 180 degrees from original position?
Any vibration when braking but not apparent when driving means that there is a rotating mass somewhere that is revolving out of balance when an external force is applied, i.e. when braking.
Has car suffered any driveshaft/CVJ's problems in the past or problems with the shaft intermediate bearing?
I know I may be clutching at straws but I also know how frustrating unusual noises can be. I have had problems in the past with Halfords pads. My dad has a Rover 216 tourer that suffered a loud intermittent brake noise and excess pedal and it turned out to be Halfords pads which were slightly smaller than the Rover originals allowing excess movement. Even though Halfords claim that their braking components are the same quality as competitors, the slight difference in size and accuracy of fit make me think otherwise.
Good luck with tracking down the problem.
Doc
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Post by Guru Meditation »

Thanks for the reply Doc. Here's an update. I'm pretty sure my problem is caused by some play/wear/shot bush in the front suspension (I suspect nearside) as the vibration and noise is intermittent and when it doesn't appear the car brakes smoothly (no pedal flutter or noise etc). I didn't check the discs for runout when I installed them but it did exhibit the same behaviour with a different set of discs and pads. When I changed the pads both the calipers were rusty but both seemed to move freely enough, the old pads had worn evenly and even with the vibration and noise the car pulls up in a straight line so I don't think it is the brake caliper (will still keep it in mind tho).
I had the car on my tiny axle stands on saturday but I had little luck checking for play in the bushes etc. Putting a crow bar to the lower suspension control arm rear bush-the 'p bush' I think- (this is with the wheels still on and suspension hanging, car supported under front sub frame) I was able to get it to move by a few millimetres but I don't know if this is normal or not. I couldn't get to the anti roll bar mounts in the middle of the car to check them. I'm gonna give the car to Formula 1 tomorrow and ask them to check front and rear bushes for being f**ked. Ye Gods this car only cost me £995 now I know why, ba*tard machine.
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David W
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Post by David W »

GM,
You can waste a huge amount of time looking for things that are never going to be the fault.
If you are certain that this exact noise is produced every time you apply the handbrake it must be connected with the rear brakes or rear tyres/ suspension...or the exhaust at a longshot. If it produces a pulsing vibration through the car it won't be the exhaust and is less likely to be the suspension but still could be the tyres.
Do bear in mind this trailing arm suspension causes the rear to squat on braking and could allow something to rub that doesn't normally.
Keep looking at the rear end I'd say!
David
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