Brake problems

[redhot91gt]

Hello everyone,

My name is Stu and I have had a 07 M coupe for about 6 months now and am enjoying it.

Unfortunately I have a brake issue with it that I cant figure out. The brakes seem to be underassisted on some stops but then all the sudden grab and feel overassisted. It only happens maybe 30% of the stops and sometimes the grabbing feels less than other times.

I replaced the rotors and pads when I first bought the car because they were definitely bad. However, the problem is still here. (has been here since I bought the car)

I don't know if its a caliper sticking problem because they don't seem to be sticking in the applied position. (no hot brakes) Also, The car does not veer to one direction when braking. I have no codes or lights either.

Any Ideas?

Sorry my first post had to be a question. Hope I can contribute more to the board in the future.

Quick pic of the car when I bought it.


Thanks!
-Stu

[Finnegan]

The car has a "dynamic brake assist" feature. If you notice this while jumping off heavy throttle or jumping off throttle to heavy braking, the car interprets that as an emergency braking situation and ramps up the braking force. More about that here. Could you be using pretty heavy braking and then noticing that light "traffic level" braking seems to require more pedal to get the same braking force?

What are the conditions under which this braking issue occurs? Does it follow along with what is described above?

[redhot91gt]

Originally Posted by Finnegan

The car has a "dynamic brake assist" feature. If you notice this while jumping off heavy throttle or jumping off throttle to heavy braking, the car interprets that as an emergency braking situation and ramps up the braking force. More about that here. Could you be using pretty heavy braking and then noticing that light "traffic level" braking seems to require more pedal to get the same braking force?

What are the conditions under which this braking issue occurs? Does it follow along with what is described above?

To tell you the truth, If I am using heavy braking the problem really doesnt show up much. Its when I am light braking. I will lightly press the brakes and the car will start stopping but once I get down to say 15-20 mph the brake pedal will pulse once. Almost as if the abs was actuated at that moment and the car brakes really hard.

It seems to happen more when I am lightly pressing the brakes. Also during this light braking period sometimes I can feel the car braking inconsistently. A very slight jerking. (a friend could not feel it but I am pretty in tune to what the car is doing)

Edit: I also have the software to read codes and monitor sensors etc. Though some of it is over my head.. Unless anyone has any ideas on what I should be watching.

[Finnegan]

I'm not where I can look at my scanning software. Depending on what you have available (P.A. Soft, Bavarian Tech, INPA/NCS) I'd scan for braking system module faults and see what you find. Doesn't sound mechanical, sounds like a faulty ABS sensor or assist module. But that's pure guesswork w/o running a systems test.

[mtrhed]

I don't have the exact same issue but I do have the weirdest, inconsistent braking and shifting on this car than any other car I have ever owned. If I rev-match, downshift and hit the brakes it's like hitting a brick wall. I also get some weird issue with the rear brakes when trail braking, maybe just pad knockback, but unlike any other car I've driven. It's also one of the most engaging cars I've ever driven......

[the dink]

I am going to throw this out there as a suggestion. How are the tires and tire pressure? I have seen on other makes with worn tires or over inflated tires one wheel can lose traction momentarily and cause the ABS to go a little crazy. If you feel jerking when braking I would check runout on rotors, That jerking or pulsing can cause ABS confusion.

[StickMon]

Originally Posted by mtrhed

... If I rev-match, downshift and hit the brakes it's like hitting a brick wall. ...

"Hyper-brakes"
I get that all the time downshifting on off-ramps coming off the freeway.
I don't heel-toe, but I'm pretty fast on the pedals.
I think the computer is too slow, or the throttle return, so it thinks I'm still on the throttle and wants to make sure the brakes win the battle.

I've pretty much gotten used to it, but it's a shame I have to work around it.

[mtrhed]

Originally Posted by StickMon

"Hyper-brakes"
I get that all the time downshifting on off-ramps coming off the freeway.
I don't heel-toe, but I'm pretty fast on the pedals.
I think the computer is too slow, or the throttle return, so it thinks I'm still on the throttle and wants to make sure the brakes win the battle.

I've pretty much gotten used to it, but it's a shame I have to work around it.

OK, so it's not just me...and I think you are right that it's a computer issue. I wonder if the "brake assist" can be can be coded on/off or adjusted?

[gas-can]

Hi Stu,

Just to clear the obvious, can you guarantee that the brake lines are completely free of of air? (ie have you completely bled the system?). This can lead to rather inconsistent braking....

Another place to check may be the master cylinder...though with that, once it starts leaking, you will feel the brakes reducing in force, and the pedal will usually sink all the way to the floor... which doesn't sound like what's happening here.

I've seen this behaviour with older trucks that have drum based brakes. The wheel cylinder seals will often deteriorate after a while, causing exactly what you described here, but I highly doubt the M's have drum brakes

The pulse you mentioned would make me also check those wheel speed sensors for the abs. Should be a simple matter to hook up a scanner to look for codes..

good luck-
gc

[redhot91gt]

Thanks for all the replies. My tires are in good shape and pressures are good. I think gc might be onto something with air in the lines. I will probably do a full system flush and bleed the lines properly.

I have the bmtechnic software which is basically INPA/DIS/TIS etc. I am still a novice at it though, so it will probably take some fiddling around.

Is there a procedure for proper brake bleeding? Considering this car can probably get air in the abs module and such. I will do a search and see if I come up with any DIY's.

Thanks again
-Stu

[The HACK]

Originally Posted by StickMon

"Hyper-brakes"
I get that all the time downshifting on off-ramps coming off the freeway.
I don't heel-toe, but I'm pretty fast on the pedals.
I think the computer is too slow, or the throttle return, so it thinks I'm still on the throttle and wants to make sure the brakes win the battle.

I've pretty much gotten used to it, but it's a shame I have to work around it.

When I drove an e46 M3 for the first time, it shocked me how much "engine braking" the car does. Even in higher gears. Letting off the gas in the first 3 gears almost feels like you're slamming on brakes. Took a while to get used to this sort of ultra-high compression ratio gas engines that runs on 6 massive cylinders. It was almost embarrassing to watch the car buck as if I don't know how to drive a manual, when the car had SMG...

In fact, just yesterday I had someone flash their lights at me when we were in moderate traffic, I was in 4th gear, he/she was tailgating me, and when I let off the gas he had to "panic" stomp on his brakes.

The Veloster Turbo on the other hand...Polar opposite. Takes some getting used to swapping back and forth between the cars.

[StickMon]

Originally Posted by mtrhed

OK, so it's not just me...and I think you are right that it's a computer issue. I wonder if the "brake assist" can be can be coded on/off or adjusted?

Unlikely, at least not with something simple like Progman. I think it's a safety feature to keep old farts like us from accidentally mashing both pedals and driving through store fronts.

Originally Posted by The HACK

...In fact, just yesterday I had someone flash their lights at me when we were in moderate traffic, I was in 4th gear, he/she was tailgating me, and when I let off the gas he had to "panic" stomp on his brakes. ...

I drive to work and back every day in stop-and-go traffic.
I leave a car-length or two in front of me and mostly engine brake.
Every once in a while I'll tap the brakes to tell the person behind me "Yes, they do work, I'm just not using my brakes."
Most people get it, or just don't care, but about once a week I get some tailgater honking and holding his finger out to tell me I'm number one.

[StickMon]

But I've jacked Stu's thread, so back to Stu.

My guess is if the rotors and pads were bad, the original owner never flushed the brakes.
The fluid is hydroscopic, and will collect water over time. There might be air in there as well.
You should bleed them, and flush plenty of fresh fluid through. Search for a DIY. You have to be careful to not let the reservoir level get too low while bleeding.

[redhot91gt]

Originally Posted by StickMon

But I've jacked Stu's thread, so back to Stu.

My guess is if the rotors and pads were bad, the original owner never flushed the brakes.
The fluid is hydroscopic, and will collect water over time. There might be air in there as well.
You should bleed them, and flush plenty of fresh fluid through. Search for a DIY. You have to be careful to not let the reservoir level get too low while bleeding.

No worries on the thread jacking. All info is good info to me.

I am going to do the flush and bleed. Hopefully it solves the problem. I will report back.

Thanks