Audi A4 Rear Axle Brake Failure Repair

Hello,

I have almost no braking power on the rear axle of my Audi A4.
The brake discs look like this:

Right side: Outer surface with scattered rust spots (depressions) distributed across the entire disc.
The inner surface is completely worn out except for a 0.5 cm wide ring that protrudes (there is a corresponding indentation in the brake pad).

Left side: Outside is unused, inside is used; outside is used.
Inside used, outside unused.
each at 50% (the correct edge is in the center of the disc).

Since the TÜV inspection is coming up, I probably need to do something .

On the right side, I quickly realized why the outside looked so strange: one of the guide pins in the brake caliper was heavily rusted. I then loosened it, cleaned it, and re-greased it (it now moves completely smoothly).
Furthermore, the handbrake lever was stiff and difficult to move. After some back-and-forth movement, it started working properly again. However, it will still be replaced.

On the left side, however, everything was fine. The saddle also looked like it had been replaced before. All the parts were movable and in quite good condition... But where did this strange wear come from?

I will add some pictures later to illustrate this.

After replacing the rotors and pads (including wheel bearings), I'm seeing the beginnings of grooves appearing on the outer edges after just a few braking cycles. However, the grooves are distributed across the entire surface of the rotor, not just in one area.

Where does it come from?

I suspect either worn or stuck linings (which is common), or too much play in the guide bolts, which could cause the saddle to tilt somehow (that's what the wear pattern suggests).

Make sure the brake pad alignment on the seat stay is perfectly flat and use brake grease.

To be on the safe side, you should get a new rack and a new saddle.

The brake pads are not seating properly, and the guide pins also have no play. The contact surface is fine... I'm not entirely sure what's going on. I need to get this fixed for the TÜV (German technical inspection). Normally, I wouldn't worry about the handbrake as long as there isn't a significant difference between the left and right sides.

I always use copper grease paste, mainly to prevent squeaking. I guess I'll have to go looking for a brake caliper now.

Quote:

Furthermore, the handbrake lever was stiff, but after some back-and-forth movement, it worked fine again. --> It will still be replaced.

Quote:

The pads were not tight, and the guide pins also have no play. The contact surface is fine... I'm not entirely sure what's going on there...

You already wrote the answer yourself. If everything is working now, I'll just observe the grooves for now.

Unfortunately, the fix with the handbrake lever often only lasts for a short time and doesn't explain the wear pattern.

If the brake pads are now fully engaged, I would initially just observe the formation of grooves. If you have even pressure, the grooves likely only come from the structure of the disc or the pad material...

[quote="cksIT".... brauchs halt für den tüv jetzt... normalerweise wäre mir die Handbremse egal... solange nur keine zu große differenz zwischen links und rechts herrscht.

benutze übrigends immer kupferpaste, alleine schon wegen dem quitschen. werde dann wohl mal Bremssattel suchen gehen.../quote]

Hello,
I would apply the brakes fully and evenly now, initially braking gently (frequently engaging the handbrake while it's still cool), and then checking for control.

Am I understanding correctly that it has 165 horsepower, and you only need the rear brakes for the TÜV (technical inspection)?

Regarding copper paste: Ceramic paste is all the rage right now!

Regarding saddle replacement: it's always best to replace them in pairs, and then everything will be fine!

[/quote]

Quote:

Well, as long as they don't brake too differently and still actually brake, it's okay. After all, the rear brake doesn't really contribute that much anyway... (20%).

What is the advantage of ceramic paste compared to copper paste?

I'll see if I can get a few saddles . Then I can have them painted at the same time, so I don't have to be without my car during that period }.

cksIT wrote:

[...Bitte gib mir den deutschen Text, den du übersetzt haben möchtest. What is the advantage of ceramic paste compared to copper paste? [...Bitte gib mir den deutschen Text, den du übersetzt haben möchtest.

The advantage is that the aluminum parts on the calipers don't corrode. In some new vehicle models, the brake calipers are made entirely of aluminum.

Copper paste could also cause problems with the ABS sensors (which are magnetic), as far as I know, that's the only reason.

Herr Antje wrote:

Copper paste could also cause problems with the ABS sensors (magnetic), as far as I know, that's the only reason.

Copper is not magnetic.
The text refers to the electrochemical series, and it seems that aluminum and copper are not behaving as expected ("not quite green").
As galvanic elements, copper has a potential of +0.52 volts and aluminum has a potential of -1.66 volts.
This results in a combined voltage of 2.18 volts in the worst-case scenario.
Ceramics, on the other hand, provide insulation.

Quote:

Aluminum and copper are not really "green" in terms of environmental impact!

That's correct. However, so far, I haven't found anything more effective than copper paste for the area between the brake caliper and the brake pads, as it prevents corrosion until the end of the pads' lifespan.

Quote:

Well, as long as they don't brake too differently and still actually brake, that's okay, because the rear brake doesn't really contribute much anyway... (20%)

@cksIT

In practice, and in the age of ABS, this is actually more than 20%, not to mention the potential for over-reliance on the front brakes when applying the same amount of braking force.

If you don't know what you're writing about, it's best to leave it alone.

BM wrote:

That's correct. However, so far, I haven't found anything more effective than copper paste for the area between the brake caliper and the brake pads, as it prevents corrosion until the pads wear out completely.

It's likely because an aluminum saddle wasn't used; with cast iron or gray cast iron, it won't play as significant a role.
There used to be anti-squeal compound included in the packaging with the brake pads.
I also have it in the cupboard as a spray. It is also suitable for exhaust connections.

So, copper also works... '' ...still.

PS: He urgently needs the rear brake performance! In my opinion, during full braking, there is initially no dynamic load transfer to the rear axle that would be disadvantageous. At best, all four wheels lock up briefly (or mostly the rear ones), and then the rear lifts.
As you brake more and more gently, the rear end starts to lift up more noticeably, and if it has an ALB (Anti-lock Brake System), pressure will be automatically reduced.
Is it correct that since the introduction of ABS, ALB is no longer used?
However, he's partially correct; the braking force of the front brakes is usually twice as strong as that of the rear brakes (due to a larger friction surface plus about 30%, and the point of application being further out). This means that the rear brakes don't have much work to do.

Quote:

But he is partially right; the braking force of the front VA brakes is usually twice as large as that of the rear brakes (due to the friction surface being larger plus about 30% more, and the point of application being further out) so there is little demand on the rear brakes.

Several factors are involved there, which cannot be explained in a few sentences.

Approximately 30% braking force on the rear axle is already possible, and in some cases even more, depending on the load. You cannot ignore the effect of the rear brakes; for example, if you need to brake harder in curves, the ABS will reduce the braking force because you are losing too much traction or grip, or you may experience severe understeer (like R. Schumacher). Regardless, the car will not brake properly. On older 190 models (W201), if driven aggressively, the front brake discs will overheat within 200 km if the rear brakes are only providing half or less of the potential 30% braking force.

It doesn't really matter anyway, as I want to bring the speed back down, or rather, I would say it's slowing down again now... At least, the wear and tear looks quite even so far.

"The ridges are present everywhere there are holes in the brake disc; I suspect that's where they originate from..."

Now I'm just left with the problem that the right brake caliper has a hole in the boot of the piston.
Has anyone ever rebuilt a brake caliper before? What should you be aware of when doing it? I don't want to just start taking things apart without knowing anything, maybe there are some specific tricks or techniques that one should know.

I just don't really want to spend €200 if I can simply refurbish the saddle instead.

Hello.
Do you now have new perforated brake surfaces (like those from Zimmermann), and that's why you're experiencing vibrations/grooves?
If you have a torn dust boot, it can be replaced. However, if the boot is brittle, the brake may have overheated, causing the material to become fragile.
then the inner poetry will no longer be new either.
Disassembly and overhaul are not possible; instead, we offer replacements at a reasonable price with a warranty. For example, Budweg or Caliper products.

Quote:

then the inner poetry will no longer be new either. icon_evil.gif Zerlegen und überholen ist nicht- gib es im Tausch günstig und mit Garantie ZB. Bsolution / caliper

The seal and gasket are available for at a price of 19 EUR. I don't see why you would need to replace the entire saddle if it is otherwise okay, just because the gasket is defective.

The repair process is straightforward once the piston has been pushed out using the handbrake lever.