warped disc? no but it feels like it..any ideas?

Post by **c.morewood** » 05 Nov 2004, 14:39

Hi, I've got a '99 Xantia 90Hdi estate. After the original discs were replaced about 130K I started getting a pulsing of the brake pedal, only under braking and in time with the wheel rotaton. Over time, 6 months or so, it got so bad I replaced the front discs and pads with new ones. The garage couldn't figure out what was wrong as the discs were true and not warped, they think it might be an ABS problem.
the problem immediately stopped as soon as I had got the new discs and pads on, but now is gradually coming back. Just to try to find out what is going on I replaced one of the pads with an older, half worn set. Immediately the pulsing restarted. this would seem to suggest that its something to do with the hydraulics or pistons? Any ideas/soloutions would be appreciated.
Chris

jeremy · Post by **jeremy** » 05 Nov 2004, 15:10

The manufacturers of the discs will claim that most roblems arecaused by careless fitting or excessively hard braking before the discs have been run in.
When fitting it is very important to make sure the hub face is very clean and free from rust etc. braking is supposed to be gentle for the first 250 miles.
Due to your Xantia having a fully pumped braking system I wouldn't have thought you would get much feedback through the pedal.
I would have also thought interferance from the ABS was very likely - and can be checked by persuading the ABS system that it has a fault whereupon it will probably shut down and show a light. You could break a sensor connection or remove a fuse.
An older pad fitted to a new (or different) disc will not perform well until it has bedded in and worn to the correct pattern. In fact it will probably overheat in sections and may cause the disc to warp. This is one of the reasons that the disc manufacturers insist on new pads being fitted. I can also vouch for this problem as an experienced Citroen machanic couldn't get a bleed nipple undone on one of my front calipers and fitted a second hand caliper with my existing pads. I was getting moans and squeels for about 50 miles before everything settled down.
What are the track control arm bushes and ball joints like? If slack they will allow the tracking to change under braking and if extreme could cause a vibration.
Otherwise you'll have to check the discs for runout using a dial gauge. Its not unknown for them to distort quite quickly and I seem to remember this happened to Dave Burns who, I'm sure fitted them properly.
http://www.andyspares.com/discussionfor ... IC_ID=3988
jeremy

NiSk · Post by **NiSk** » 05 Nov 2004, 15:15

I think its been mentioned a number of times that a badly charged accumulator sphere, or air in the hydraulic system seems to cause this pusating effect on Xantias. Then again, if you/the garage bought cheap discs, they could well have warped - I've just diagnosed the same problem with my newly purchased XM 2.5 TD - new discs fitted by previous owner for MOT - 3 months later one of the discs has an 0.5 mm warp - I've had it turned up on a lathe and all shaking has now disappeared.
//NiSk

Post by **c.morewood** » 05 Nov 2004, 15:28

Wow what quick replies .. thanks. both the sets of discs had/have been checked for warping with a dial guage.. the spheres, as far as I know haven't been changed in 145K miles the track rods are both new.. ball joints are an area I could have looked at... as for my braking.. I use engine braking most of the time (ex motorcyclist 330k miles) and do mostly motorway driving. I just tried the older pad just to see if i could determine which side, if it was ust one side, the vibration was coming from. I'm puzzled about the spheres theore.. from other posts I've read there seems to be a constant pulsing when the pedal is depressed .. moving or not.. maybe I misunderstood this..associated with suspension problms .. my Xantia has no suspension probs and the pedal only pulsates when braking.
Thanks again for the sugestions.

NiSk · Post by **NiSk** » 05 Nov 2004, 15:36

I couldn't get a sensible reading using a dial clock with the discs on the car, however, once fitted to the lathe, the real truth appeared.
//NiSk

fordsone27n · Post by **fordsone27n** » 05 Nov 2004, 19:20

About 6 months ago I replaced the discs and pads on my Xantia. I used GSF supplied brembo discs and I think bendix pads. Within a couple of months it felt like it was juddering under braking. I needed a new set of front tyres, so had a pair fitted. I immediately noticed the juddering was gone. 3K on and there is no sign of juddering and the brakes are excellent.
I know it doent make sense since the wheels and tyres were balanced off the car and you can normally feel out of balance wheels when cruising, not necessarily in the braking zone. It might however be worth checking
Adrian

ghostrider · Post by **ghostrider** » 06 Nov 2004, 04:25

The other thing to check is the tyre carcass, sometimes they break internally, get someone to stand in front of the car while you drive it forwads, get them to look for the tread moving from side to side
pete

Post by **c.morewood** » 06 Nov 2004, 11:44

Thanks for all the suggestions.. it isn't the ABS i've pulled the fuse and the juddering is still there.. I put the original pads (fully bedded in) back in yesterday.. the part worn ones hadn't even fully bedded in..now I have the slight i.e. not too severe juddering...very perplexing. I think its something to do with how far the piston/s are protruding and how much fluid is in the system so to that end I'm gong to work on the other wheel this afternoon and put the older pads in that side this should, if I'm correct result immediately in the severe juddering coming back. I can't see how the tyre change would be the cause as the juddering changes in intensity when i change the thickness of pads .. but will give it a try thanks.

alan s · Post by **alan s** » 06 Nov 2004, 13:48

I have seen people fitting new pads or rotors manage to daub greasey hands all over the rotors with the result that the rotors can get hot spots on them.
If the new pads were contaminated with oil or LHM then there's every possibility the pads are grabbing & releasing.
Blown accumulator sphere is usually indicated by the pedal kicking back when initially applied followed by a short sharp hissing sound.
There was a recent case out here that was caused (on a Peugeot) by the new rotors being fitted whilst the rust and crud between the hub and the rotor wasn't properly cleaned off and created a warped disc sensation.
Another had "green stuff" pads fitted and immediately noticed a wobble when braking that was supposedly singled down (somehow or other) to a worn lower ball joint.
Alan S

G4EIY · Post by **G4EIY** » 06 Nov 2004, 13:55

Hi,
If all fails, then check out the condition of the sliders on the calipers. If there is movement up and down, then this could agrevate the situation, if in good condition, remove the sleeves, clean and lubricate with correct grease, check the rubber boots for damage or spits, and make a note of the orientation before removing as one end from the boot groove projects more on one side that the other.
Best of luck, and if you do find the cause, then let us know.

Post by **c.morewood** » 07 Nov 2004, 14:39

The latest news... I swapped the spare tyre with the one from which I think the vibration is coming (Thanks Fordsone27n and Ghostrider) but unortunately no change.

Then I put an old, part worn set of pads in the opposite side, the result, an immediate reduction in the vibration.
This has really got me stumped....Why should an old set of pads+new disc on the n/side together with new pads & disc on the o/s produce bad vibration .. but not when the configuration is opposite?
Actually reading through the posts again the pulsing pedal is not as noticible(when its bad) as the vibration on the steering and the cyclical retardation of the car under braking.. so maybe the original post of just a pulsing pedal might have given the wrong idea to some of you.
Thanks for all of the greatly appreciated suggestions.
Chris

Post by **c.morewood** » 15 Nov 2004, 05:33

Just as an add on question. I was sitting in a queue of traffic yesterday on a downhill slope holding the car on the footbrake. I just happened to have my hand on the handbrake but it was not on. I could feel a slow faint pulsing through the handbrake lever whilst stationary and whilst the handbrake was not on.. I then realised that I could feel a slight pulsing through the footpedal as i was holding it down.. so faint that I had not noticed it until I had felt it thorough the handbrake.
Is this normal? Any idea what might be causing it? I can't say I've felt that before in 150K miles or so.

beezer · Post by **beezer** » 15 Nov 2004, 05:42

Just for the sake of elimination, check your engine mountings.

Richard Gallagher · Post by **Richard Gallagher** » 15 Nov 2004, 12:00

Have/do your suspension spheres need/been replaced? A pulse felt through the brake pedal when stationary is indicative of air being trapped in the brake pipes as a result of a leaking sphere.
Try bleeding the brakes to get rid of the air in the system in addition to doing 'Citrobics'.

broomie · Post by **broomie** » 15 Nov 2004, 18:58

/*the spheres, as far as I know haven't been changed in 145K miles*/
MMmmm I'd say that's a fair clue!