Brake woes, front disc failure at low miles and other problems
- Thread starter Little Dog
- Start date
Little Dog
A2OC Donor
Feel warped; I don't know if they are, I think probably not. The cyclical increasing and decreasing of brake effectiveness that you get with warped discs is only there at low speed. There is no rapid cycling at high speed. The problem was intermittent too.
A bit of a mystery as to the cause.
Little Dog
A2OC Donor
Agreed, this is a Pagid disc that has done 80K miles and used two sets of Pagid pads. It is just the A2 that plays me up.
Howey
Member
And still looks servicable!!
Never come accross soft and hard disc/pad set up other than all pads since absestos was abolished seem to wear the discs
Yours look more like they have been dorment for a year or so and suffered in the weather, one of my rear galaxy ones did the same during lockdown as off road but looks ok now
Never come accross soft and hard disc/pad set up other than all pads since absestos was abolished seem to wear the discs
Yours look more like they have been dorment for a year or so and suffered in the weather, one of my rear galaxy ones did the same during lockdown as off road but looks ok now
Rusty911
A2OC Donor
You're an engineer Phil: got a DTI with a mag stand? Be interesting to see the run-out. Only thing you do have to be careful of is to use some pipe / sleeves to allow the disc to be held by all five wheel bolts during measuring.
Rusty911
A2OC Donor
That's the other way and looks very healthy for 80K doesn't it?
The odd thing is within the last 12 months I've had five different A2's (no, I've no idea how that happened either) and all have had very good discs and pads, little wear, no overheating and no warps. Ages go from 2001 to 2005, and all variants except 90TDi. So far, I've not really seen anything that makes me worried the A2 has any particular disc-eating characteristics.
Little Dog
A2OC Donor
I know, both cars are in daily use, just look at the difference. The A2 discs look like they have been parked in a swamp for several months
Little Dog
A2OC Donor
I don't have a DTI; I was playing with the idea that this A2 problem justifies one. If I had one I would have the runout figures by now. Also needed for adjusting wheel bearings on Mercs.
Going to see if I can clamp my verniers and to a big lump of cast iron and get a reading.
Edit: the drive flanges are clean and rust free so there is no misalignment introduced there. They are genuine Audi parts. I would be looking for bearing wear, they have done about 60k miles and feel good.
Rusty911
A2OC Donor
Looking again: do you live in an aggressive environment? I don't mean 'whattta you looking at, do you wanna take it outside mate?' so much as being near the coast / waterfalls / muddy lanes etc?
It's just that the inside of the 'hub' looks remarkably rusty to me for a young disc, plus those screws usually come out O.K.. The other thing is looking at the slider rubbers, the piston and the rust on the sliding portion of the pad edges, it's hard to think that the pads were being fully released as per my above post.
I forgot to add another element to my caliper notes above, so will do that now ...
Little Dog
A2OC Donor
When you have a full set of caliper notes, they are good, why not copy them to the How-To section.
A a problem you raised that doesn't cause me problems is seized bleed nipples. I fit them into clean dry threads with a smear of dynax UC on the nipple thread. It can't contaminate the fluid in the calipers and they crack open every time.
Rusty911
A2OC Donor
Interesting, not heard of that before.
Anyway, they are ever so cheap to buy.
I should point out BTW, I am fully aware of your engineering prowess and attention to detail so I hope you don't mind me posting the above. I always think that if a thread's running, all info can be gathered together for future reference, even if the OP has the matter well in hand.
Likewise on shearing nipples: I've had one since 1988, but some people naturally seem to shear things off ?. I ran a main dealer workshop for a while (Citroen) and we had one tech that time after time would shear off bolts, round off heads, break plastic moldings. He was a grumpy disaster!
Thanks for the tip on Dynax UC, that's new to me.
Little Dog
A2OC Donor
@Rusty911 I don't mind at all, E Class front wheel bearings have a run out specification. I did them by feel.
If I had to put a few quid on the root cause of my problem I would gamble on it being these pistons sticking. One is really bad around around the main seal and was weeping fluid. That one was really stuck and took some pressure of compressed air to blow it out. Both of them have uneven rust build up on the piston to pad back plate surface. I don’t suppose this would be a problem until the pad anti squeal coating wore through. May explain why I don't have problems for 6 months? Once the pistons are contacting the metal of the pad back plate applying the brakes will attempt to twist the pistons in the bores causing metal to metal friction. Only slight but that may be just enough to leave just too little drag.
The new pistons now blow out very easily, had to blow them a little further out to fit the dust shields correctly.
If I had to put a few quid on the root cause of my problem I would gamble on it being these pistons sticking. One is really bad around around the main seal and was weeping fluid. That one was really stuck and took some pressure of compressed air to blow it out. Both of them have uneven rust build up on the piston to pad back plate surface. I don’t suppose this would be a problem until the pad anti squeal coating wore through. May explain why I don't have problems for 6 months? Once the pistons are contacting the metal of the pad back plate applying the brakes will attempt to twist the pistons in the bores causing metal to metal friction. Only slight but that may be just enough to leave just too little drag.
The new pistons now blow out very easily, had to blow them a little further out to fit the dust shields correctly.
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Rusty911
A2OC Donor
Ah, well I think the latent engineering gene in us would say you couldn't draw any conclusions about the quality of the pads / discs until the rest of the system was perfectly healthy. I'd tentatively suggest case closed?
As a wider comment, anyone doubting their brakes are releasing properly, do the following quick test:
Securely jack the front (or indeed rear if FSi / 90) on both sides. Get an assistant to start the engine and push hard on the brake. As soon as they release the brake pedal try to turn the wheels in question: it should be completely free. Anything less than this means there is drag somewhere. This will get worse as the temperatures come up and this will absolutely happen if you have a slight brake drag. Therefore, you set off, the brake drag gets worse, creates more heat, more drag, more heat etc etc.
It should be noted that the bar for an MOT pass is very low, they'll let a surprising amount of drag go through before failing a car.
This check is well worth doing as part of your servicing routine: the critical part is engine running and instant release. Just spinning the wheel on a jacked up car isn't enough ?
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Little Dog
A2OC Donor
To be honest I have never had brake problems before in 40 years of motoring, 12 cars, all up 1 million miles (two of us contributed), all cars DIY maintained. I started the thread to learn about brake problems because I really don't know. What do you think the cause is?
I had 'warped disc' syndrome on my S8 which the previous owner had also encountered and tried to address with new discs/pads. When it became more than annoying, I also bought a new set of discs and pads and gradually worked through with progressive replacement of components and with little or no success until i stripped all the pistons from the Brembo calipers and rebuilt them- problem has not returned in 18 months!
Little Dog
A2OC Donor
Thanks @vagdream I’m going to assume the problem was calliper pistons Interestingly my wife drove the car and commented on how smooth it is running Drove it this morning and yes it is smooth, very smooth for a little diesel, and the only thing that has changed are the brakes. So I conclude, at least for now, job done.
Also, I think it was @Rusty911 made this point, we shouldn’t assume the problem is the disks / pads until everything else checks out as good. I would be happy to fit Pagid again in the future, I’m getting good disc life on other cars fitted with Pagid.
Also, I think it was @Rusty911 made this point, we shouldn’t assume the problem is the disks / pads until everything else checks out as good. I would be happy to fit Pagid again in the future, I’m getting good disc life on other cars fitted with Pagid.
whatevershebringswesing
Member
My hands-on experience is small by comparison with many talented folk who make generous contributions on here. However, I have recently fully rebuilt ATE calipers and fitted new Pagid pads (replacing Pagid) on my year 2000 Saab 9-5 Aero Estate. The issue started with a front brake fully locking on after an emergency stop. The calipers needed a rebuild anyway but the fault recurred after the work (inspected and approved by a master technician for Saabs). Despite passing MOT last week (the MOT system does not fully test the ABS/TCS hydraulics and control module ECU) the issue remains as a dragging and heat and I dare not try a test of ABS for fear of a third event of a fully locked brake (even though the smoke/steam is exciting!). While the main culprit is predicted to be corrosion and deposition of metals in the hydraulic block of the ABS unit there is another theory which may have relevance to this thread and has not yet been mentioned. Very high pressure is applied through to the piston under braking. Very little force exists for retraction. The flexible brake hoses can be outwardly perfect but act as one-way valves restricting the return flow of fluid. Two syndromes can cause this. One is deterioration of rubber inside the bore. The second is the rusting of connection components on the outside of the hose the build-up of which reduces the bore. Brakes work perfectly when applied but the pads remain in contact with the disc. This may be undetectable in a static test when the parts are cold. The other thing I have leant over the recent days is that there is a huge difference in quality in the metallurgy of discs from different sources with many on the market having inferior performance. I don't know if the suggestion of faulty hoses applies to our A2s but this thread seemed painfully familiar to me and I thought I should 'share'!! atb all