Brake Discs Overheating: Causes & Solutions

Hello,

"First of all, I've tried searching, but unfortunately, I couldn't find anything relevant."

Now, regarding my problem:
I have an AUDI 80 Avant TDI, manufactured in April 1994, with 357,000 kilometers on the odometer.
"I felt a pulsating steering wheel when braking (the front brake discs have a warp). When I checked the tires at the beginning of the week, I noticed that the rims were warm and the discs were painfully hot. I assumed the brake pads were stuck, so on Saturday I installed new brake discs (Jurid) and pads (ATE)."
The brake pistons could be retracted without any issues, and the guides were also working properly. The old rotors were worn down approximately 1mm on each side, and the brake pads were worn down to about 2/3 of their original thickness.

Despite replacing and cleaning the brake calipers, both brakes are getting hot. To test, I drove five kilometers without braking, at a maximum speed of 70 km/h, and let the car coast. The brake discs were cold. Then, I got on the highway, braked briefly once, drove 15 kilometers at 170 km/h without braking, and let the car coast to a stop in a parking lot. When I touched the brake disc, it was burned (no blisters). It seems to me that the pads are constantly rubbing after I brake even once.
I then looked through the service booklet and saw that the previous owner had replaced the brake discs, pads, and calipers at 329,100 kilometers. So, the brake discs and pads only lasted 28,000 kilometers.
Upon contacting the previous owner, it was revealed that the brake calipers had been replaced because the brakes were overheating (!).
My question is: Is it normal for the brakes to get hot during the first 200-300 kilometers (break-in period), or do I have a bigger problem? My concern is that the new pads and rotors will be worn out again after 28,000 kilometers because something is preventing the pads from releasing from the rotors after braking.


Regards,
Michael.

MichaelJ wrote:

My question now is - is it normal for the brakes to get hot during the first 200-300 kilometers (break-in period), or do I have a bigger problem? My concern is that the new pads and rotors will be worn out again after 28,000 kilometers because something is preventing the pads from releasing from the rotors after braking.

Hi,

Unfortunately, I share your concern... In my opinion, it's also not entirely impossible that the ABS system is malfunctioning.

Tip: Disable the ABS (by pulling a fuse or similar) and try again.

Furthermore, you can often identify brakes that are dragging by observing the car's rolling behavior: Brake until just before coming to a complete stop, and then let it roll freely for the last ~3 km/h.
If the vehicle comes to a stop with a slight jolt, at least one brake is likely dragging.

If this test runs without any issues on your vehicle, then, in my opinion, the suspicion of an ABS problem is strengthened. -> It brakes at higher speeds and disengages the system almost completely.

Hi,
It sounds more like a master cylinder issue.

Hello,

Thank you for the answers.

"@ Ulf - There was no jerking when deploying it; it simply rolled out. I'll test the ABS later tonight, but if the ABS is malfunctioning, then all four disc brakes should get hot. Only the front brakes are getting hot. Also, my understanding of the ABS function is that it redirects the pressure in short intervals just before the wheel locks up, thus preventing it from locking. Therefore, it releases pressure, rather than building it up."
But maybe I'm wrong about that.


@ Christians - Oh no, please don't let it be the master cylinder. What could be broken, and how can I rule it out?

"Something else I've noticed is that when I let the car roll in neutral (idle) and press the brake pedal three or four times, the brake assist function is lost. Then I have to press the brake pedal fully, like in the old Beetle."


Greetings.
Michael.

MichaelJ wrote:

I have previously understood the function of ABS in such a way that the ABS redirects the pressure in short intervals just before the wheel locks, thus preventing the wheel from locking.

Therefore, it releases pressure rather than building it up.
If the ABS only releases pressure until the wheel starts rolling again, it could potentially release too much pressure, thereby wasting braking force – especially if the road surface becomes more grippy again within the next meter.
So, it alternately builds up pressure until the wheel (almost) locks up, then releases the pressure, builds it up again, and releases it again... that's why you feel the pulsing in the pedal, even when the ABS is active and the pedal doesn't sink down.

Therefore, in my opinion, the ABS may still not be working – especially if the wheels are spinning freely at low speeds.
Since the ABS controls each wheel individually, a defect can sometimes only affect the rear wheels.

"@ Ulf - well, it seems ABS is probably not the cause. I had a friend put the car on a lift at her truck repair shop, and the front wheels are turning much more slowly (the brakes are dragging slightly) than the rear wheels."

The master and apprentice couldn't figure it out. They examined the wheel brake cylinders and ruled them out as the cause. According to them, the problem could be with the brake hoses or the master cylinder. The recommendation, for cost reasons, is to first replace the hoses on the front axle, and if that doesn't solve the problem, then replace the master cylinder.

If I replace the brake hoses, can I bleed the brakes normally, or does that only work in a workshop?
The AUDI repair manual only distinguishes between brakes without ABS and brakes with ABS and ESD (Electronic Stability Program). For brakes without ABS, bleeding can be done without a pressure device. For ABS and ESD systems, bleeding requires a pressure device AND a VAG ABS tester.
My Audi 80 only has the "standard" ABS system.

Greetings.

Michael.

Hi,
It can be achieved with just ABS. However, the main brake cylinder can develop a leak if a layer of rust has formed at the end of the normal piston stroke, which can then scratch the rubber seal of the piston.
I built a device from a container lid I found at a scrapyard to connect to a tire valve, following a tip I saw here, but I haven't tested it myself yet.

Hi,
The master cylinder has a so-called equalization hole, which ensures that the fluid can flow back into the reservoir after being displaced, or that it is transported there by the brake pads due to minimal disc movement.
I once had a Passat (from around 1977) that had the same problem after 230,000 kilometers. I then replaced the hydroboost unit with a used one from a scrapyard, and the effect of the "self-applying" brake disappeared; the rotors remained cold.

If it were the hoses, the braking performance would also be poor.

P.S. Regarding the lack of power steering assistance at idle after 3-4 braking events: Don't worry too much, the vacuum pumps aren't really great. Even new pumps exhibit this effect after a short period. However, it might still be worth checking the hose connection to the power brake booster.

Regards,

Olli.

@everyone - First of all, thank you all for your responses.

The solution to my problem is quite drastic.
The previous owner had the master cylinder "fixed" at a mechanic's shop four years ago.
So, a new one has been installed.
After comparing the part number on the invoice, it's clear why the pads have been causing problems for four years.
and the front brake discs would always wear out after approximately 30,000 kilometers.
Die kompetente VAG-Werkstatt hat den falschen Hauptbremszylinder eingebaut. For my...
Audi offers two different types of brake boosters: one with ABS and one without ABS. In my Audi 80...
With ABS, these "experts" installed the HBZ (hydraulic brake system) without ABS.
I've now installed the correct part, and lo and behold, the front wheel brake no longer overheats.

"As the repair manuals so eloquently put it: 'Work on the braking system should be performed by..."
"to be carried out by qualified personnel."

Greetings.

Michael.

MichaelJ wrote:

As the repair manuals so beautifully state: "Work on the braking system should be performed by qualified personnel."

Hi Michael,

very well said... I'm already crying with laughter .

It just goes to show that everything in Germany fails because of the education system. So, you just have to do everything yourself.