ned
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| posted on 5/2/06 at 07:18 PM |
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Brake problem - everyday car.
Maybe something obvious but seems odd to me...
Did a front brake pad change today on my tdi vw bora. Wheels off (jacked up) calipers unbolted pads changed (piston pushed back in by hand) refitted,
no problems.
Did both sides as you do, but since the brake pedal is acting strangley.
Pushing the pedal does slow the car down, but not anywhere as sharp as it was/sholuld be. This is not just the new pads. You can be stationary, put
your foot on the brakes and the pedal will very slowly go to the floor.
I can't believe it should need bleeding as I've not been anywhere near the brake lines for any air to get in! The calipers were correctly
supported, not hanging on the lines or anything when the pads were changed. Also if it was a bit of air they'd be spongey surely. You can be
stationary and the pedal will slowly go to the floor.
I can't see any leaking fluid anywhere and the fluid level on the resovoir doesn't seem to be falling.
Pumping the brakes helps you stop a bit quicker but the pedal still eventually goes to the floor.
I've done 25-30 miles since changing the pads earlier today and its no different, apart from I'm having to leave plenty more room for
braking than normal.
Any ideas?
I've got an easy bleed kit which I'll try in the week and someone else I know wondered if it might be to do with the front/rear automatic
biasing or something ?!
The abs still cuts in if you really stand on them but doesn't work as well as it should.
Anyone got any suggestions? It just seems bizarre to me as I know what I'm doing and have done brakes numerous times before and have never had
this sort of problem. It is the first time I've done it on this car, but did check the haynes beforehand and did as directed.
cheers,
Ned.
beware, I've got yellow skin
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stevec
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| posted on 5/2/06 at 07:21 PM |
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Very strange, Have you tried posting a question on a VW forum.
Steve
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rusty nuts
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| posted on 5/2/06 at 07:32 PM |
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When you put the pads in and pumped the brake pedal did you use longstrokes and push the pedal to the floor? If you did it's possible the master
cylinder is damaged. Common on later vauxhalls. When fitting pads I ALWAYS just pump the pedal gently and only push it down about 2 " until
pedal is hard. Doubt if bleeding will help but I hope I'm wrong.
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ned
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| posted on 5/2/06 at 07:32 PM |
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posted on http://www.uk-mkivs.net at the same time as here..
Ned.
beware, I've got yellow skin
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diyer
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| posted on 5/2/06 at 07:34 PM |
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I had a similar issue with my Audi 1.9TDI, when i changed the front discs and pads, but i got full braking back after maybe 50miles due to bedding in.
I have heard that the master cylinders on some VW/audi's can suffer seal damage when the brake pedal is depressed down to the floor - as in
first press after caliper/ pad service.
Simon
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the_fbi
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| posted on 5/2/06 at 07:35 PM |
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If they are ATE calipers, did you put the spring back on correctly?
You may think you did, but I've been there with my Calibra and took months to figure it out.
If the spring isn't positioned correctly, with the square end pushing against the part of the caliper its not connected to, then as you press
the pedal, the 2 parts of the caliper gradually "bend" away from each other.
Stick a photo of the caliper/spring up.
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the_fbi
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| posted on 5/2/06 at 07:40 PM |
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Note the spring behind the tab, not in front of it.
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britishtrident
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| posted on 5/2/06 at 07:47 PM |
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Seal reversal --- these days when changing the pads it pays to clamp the hose and force the fluid out via the nipple. Also bleeding should be done
with a posative pressure bleeder.
As already said Astras are famous for this problem but some makes of continental european systems have been prone to it since the days of the VW
beetle and Simca 1000.
Never got problems like this with Lockheed or Girling system ---
Next you will have me moaning about the p*** poor quality of French and Italian car electrics.
[Edited on 5/2/06 by britishtrident]
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madman280
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| posted on 5/2/06 at 08:34 PM |
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You mentioned you changed just the pads and didn't mention the rotors. A common problem..or perhaps obstacle is a better term. I work as a
mechanic at a Ford dealer, so I don't have much experience with VW brakes but I have seen this. All brakes work the same.
As pads wears they don't wear flat..they develop a wavy surface..same with the rotor..now if you change just the pads..the rotor is still
wavy...it doesn't stop quite right because not all of the pad surface is touching the rotors, just the high spots. The solution. If its really
bad either re-surface or replace the rotors (if its too thin replace them) ..or.. if its not too bad just bed the pads in to the rotors with some
progressivly harder stops from about 80kph with a couple mins between each stop to let things cool (so you don't not induce a brake pulsation
from over heating the rotor). Hope that helps..if it doesn't I'd have the wheel off and have a peek again..never hurts to look.
As for the seal reversal thing..thats a new one... I really don't think there's enough clearance for this to happen. I've done
thousands of brake jobs...they either stick or leak from what I've seen. But I don't doubt anything is possible.
[Edited on 5/2/06 by madman280]
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ned
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| posted on 5/2/06 at 10:30 PM |
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So is it likely that sufficient bleeding or even use may correct the seals? Or is it new/recon master cylinder time?
thanks,
Ned.
beware, I've got yellow skin
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locogeoff
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| posted on 5/2/06 at 10:38 PM |
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Ned
This link may be of assistance
Geoff
[Edited on 5/2/06 by locogeoff]
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MkIndy7
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| posted on 5/2/06 at 10:48 PM |
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Bit of a long shot and somebody here might know better but it could be something to do with the Vaccume Servo.
It might tell you in the Heynes but after doing a similar thing with My Fiesta it sempt as if it was practically back to having manual brakes, the bit
well when stomped on but were useless when applying light pressure.
I think you had to pump the pedal 4 tims with the engine turned off to re-instate the vaccume or something equally as strange!
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madman280
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| posted on 5/2/06 at 11:30 PM |
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Appoligies. I didn't read your post fully. Stupid me. Disregard all what I posted before. If it goes to the floor you have other bigger
problems. I agrre its most likely the master cylinder. Like has been mentioned fully stroking the pedal causes the problem. Normally nothing wipes the
bore there so crap and corrosion collects. When you push the pedal to refil the caliper it ends up there. The seal usually gets nicked or full of
crap. Then when its time for the seals to do their thing the fluid just bypasses them.
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Chippy
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| posted on 6/2/06 at 12:13 AM |
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All been said really, it's definately a master cylinder fault. Seal damage! I hope that you can get an overhaul kit, and not have to buy a new
unit.
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the_fbi
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| posted on 6/2/06 at 12:20 AM |
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quote:
Originally posted by Chippy
All been said really, it's definately a master cylinder fault.
Not definately.
EXACTLY the same symptoms are had if you've got ATE calipers and install the springs wrongly, or not at all.
Plugging the outlet from the MC or the ABS to the front calipers and checking the pedal feel then, would help diagnose more.
Although you'll need to do a bleed afterwards 
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rusty nuts
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| posted on 6/2/06 at 06:42 PM |
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Ned , try clamping the front brake hoses to stop fluid getting to caliper . If you then get a good pedal then master cylinder is OK and problem is at
caliper end. I would have thought that 25miles was enough to bed pads in .
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