brake judder air?

John Plum · Post by **John Plum** » 22 Oct 2009, 23:16

When I brake, especially with force, I get a sharp judder a through the brake pedal and a pull to the left side. Is this due to air in the system, possibly on the left side brake?
When the brakes have been just used, they seem to perform a little better and the judder comes in more toward the end of the brake pedal travel.
I previously had a concurrent fault with n/s front Abs warning light on, which I cured by cleaning the sensor and cogged rotor. This fault in question continues.

Featch · Post by **Featch** » 22 Oct 2009, 23:29

I'd say the most likely culprits are air in system and/or degraded flexible hoses bulging under pressure.

citronut · Post by **citronut** » 22 Oct 2009, 23:31

its either air in the brake systom or warped discs, quite offten with air in the brake systom it will feel like you have no brakes on first pedel presure,

regards malcolm

vince · Post by **vince** » 22 Oct 2009, 23:38

I think your spot on Malcom with the warped disc diagnosis......

If its pulling to one side my money is that your caliper is binding on and has caused that much heat that its warped the disc....it happened to me exactly the same a few months ago.

Easy way to check? Is one wheel massively dirtier with dust on the inside than the other....if so then the brakes are binding on. (my outside pad was like new, but the inside one was down to the metal

I also had a guy in the shop a couple of weeks ago claiming his brembo discs suddenly warped after 6 months of being on his Xantia.....He was an elder gentleman so you can tell it wasnt down to silly driving. I asked him the same brake dust question...."funny you say that, one wheel is always dirtier than the other and ive never known why" He got the calipers checked and hey presto....i was right

John Plum · Post by **John Plum** » 22 Oct 2009, 23:41

I should have said: air in the d/s brakes, I think.
Could it be a sticky calliper piston on the d/s? The one I just put back after a cleanup and lubrication seemed hard to rewind, I noted, compared to the nearside piston.
I wonder if the judder is the abs kicking in as the opposite side is not locking the wheel as early, but I guess not as the symptom was there when the abs warning light used to be on, before cleaning up.
I'll keep an eye on the brake discs too.

John Plum · Post by **John Plum** » 23 Oct 2009, 00:00

In dismantling the discs and pads , I was unable to check for warp with a gauge. The pads were not unevenly worn, and i did not notice much more dust on any one side, there wasn't so much, mainly just rust and grease from a split gaiter. The pads were fairly new.
I'll do a careful bleed tomorrow, and more searching inspection of the pads/discs.

So, the pulling to one side would indicate warped disc and not sticky piston or air?

Xantidote · Post by **Xantidote** » 23 Oct 2009, 01:24

John said "mainly just rust and grease"

This wasn't on the disc was it? Presumably you mean rust dust from general brake application. I'd expect front discs to have nice shiny swept areas where the pads have contact.

My first thought on experiencing judder would be warped disc(s). Not sure how successful you'd be in checking warp run-out. Might just have to fit new discs as part of elemination process - they're a consumable item nowadays, and not that expensive. If you've got serious binding, then as Colin (Admira51) experienced sometime over the summer, the offending wheel/brake would be hot/very hot.

When you jack each side up, are both wheels relatively easy to turn or is one more difficult than the other, suggesting it's binding a bit. I had this, and I ended up removing the caliper and taking the piston out. Found nothing obviously wrong, re-assembled with plenty of lubricant around piston, and seems OK now. Presumably the handbrake cables are operating freely?

Wouldn't air in system affect both front calipers?

Your bleed and further inspection tomorrow (today?) may reveal more.

Martin

(Edit: unless the judder's related to the ABS, about which I've no experience)

John Plum · Post by **John Plum** » 23 Oct 2009, 07:37

@Xantidote: The rust (and grease) was on the hub carrier and calliper body. I removed the rust with a chipping hammer and wire brush. Not so much brake pad dust, which I have seen before in copious quantities on another car.

citronut · Post by **citronut** » 23 Oct 2009, 08:07

Vince wrote
"He got the calipers checked and hey presto....i was right "

whats it (no not PERCY) like beeing right all the time Vince,

i keep tryingit but i never get it quite right TEA HE,

John wrote
"So, the pulling to one side would indicate warped disc and not sticky piston or air?"

not nesa celery John,

its the judder that can indicate warped disc/s

if either of you front brakes are binding you should have one wheel centre hotter than the other after a good drive,

also the disc of the binding wheel/brake will be dis/coloured on its working surface

regards malcolm

Post by **RichardW** » 23 Oct 2009, 08:09

Damaged or clogged ABS rings can cause the ABS to operate sporadically at low speed. In this case you will get a definite 'clicking' noise and kick back through the pedal. In 'normal' brake judder you just get a vibration through the car and / or the steering wheel.

John Plum · Post by **John Plum** » 23 Oct 2009, 08:18

@Richard. Thanks.
I thought probably the ABS is working now, warning light off - after cleaning and de-rusting):
I'm going to check the calliper pistons again now, and for binding. However, I thought the symptoms you (and I) describe might be ABS, and what I am experiencing, but because of a sticky piston, or some air on the opposite side.
Could this be true, wonder, rather than a fault with the sensor/cog?

John Plum · Post by **John Plum** » 23 Oct 2009, 09:56

Thanks Guys, I'm getting more confident.

Examining the wheels for rotation and binding,
[NOTE: calipers have been dismantled, cleaned ,regreased and reassembled Last week: both were very dry were the pads move]:

Both front wheels spin OK, with no obvious difference of sound or tension throughout all points of turn.
* No obvious brake dust
* Noticeably less wear on n/s inner disc than outer disc (unlike d/s).
* Not particularly discoloured; though, since reassembling, I see some brighter steel than others in bands. - Only test driven 15 miles, since reassembly.
* Haven't tested disks for heat after long ride. Difficult to do at moment - no MOT and in London.

* I think i get judder and clicking of ABS.
* I don't get feint brakes on initial brake-pedalling.

I'm now going to bleed and see what that produces. But I think it's going to be a case of new discs and pads as a routine, and they should be better. About to order some. They seem to vary with Xantia year and even estate vs. saloon, according to seller details:

is this true for saloon/estate? I thought they would all be the same fitting.
By the way, is there an easy way for me to check part numbers online?

Thanks for answering and pondering with me. It sure helps a lot!
For now I am ruling out defective ABS.

John Plum · Post by **John Plum** » 23 Oct 2009, 10:05

The guy using a Brembo disk catalopgue tell me, for Years 1999 to 2002 there is no difference for saloon/estate, or abs/non-abs, but there is a difference for automatic and manual gearbox models, where the automatic's disks are 20 mm greater diameter (i.e. 286).

addo · Post by **addo** » 23 Oct 2009, 11:06

The lower suspension arm bushes should also be checked.

It's the nature of an inexperienced hand, to mis-ascribe effects and noises (best example being the "noisy tappet" which is frequently an exhaust leak).

John Plum · Post by **John Plum** » 23 Oct 2009, 12:08

No noticeable air bubbles coming out of the front calipers on a bleed just completed.
@addo You're right, That's coming after a test drive to come next. A lesser order probability on this one as the effect fades with repeated braking, and not noticeable except under braking, plus I did not notice anything undue when i had the hub carrier off last week, or with wheel test.