Soft brake pedal on my E38

[voodoomelon]

Hi guys.
Long time no post! I just bought back my 2000 E38 728i Sport for peanuts (I sold it 3 years ago, still driving my E66).

Anyways, it always had a soft brake pedal and 3 years on, its still the same.
So I swapped out the master cylinder last week as I thought I might have damaged it years back, popped in a TRW one.

I pressure bled the whole system when finished and still the same - the first 2/3 of pedal travel is extremely soft and light.

So then did the 2 man bleeding system, had him work the pedal whilst i cracked and tightened the bleed valve. No difference.
I've activated the ABS pump in DIS, no difference.
I've activated the DSC pump too, no difference.

I then pressure bled the whole system again, still no difference. I see no fluid leaks or balooning lines, no evidence of bleeder leaks or brake line joiner leaks.

What in the world can cause this?

And now, only just now, have I spotted this when the brake pedal is pressed, see the video below:



There's a definite squelching noise of air or fluid around the ABS module, is this normal?

Thanks guys!

[SEVEN40iL]

Welcome back!

[voodoomelon]

Thanks man!

No help as of yet though, still stumped.

[shenofjo]

i am also feeling the soft pedal feel like you describe. I thought it was due to me swapping to carbotech brake pads, but my other car with the same pads brake very solid with normal initial bite. with the 740 with the upgraded 750 brake system for emergency braking i need to stump on it and when i do the car stops real quick. hope you figure out the problem soon! i feel like i just tag along problem threads... at least i dont shimmy anymore

History of my situation: Initially bought the car and remembered brakes being good. had the shop change the brake fluid as part of new purchase maintenance and it felt more spongy. rear pads and rotors changed, got worse, front pads and rotors changed, stayed around the same.

[Jimmy E34]

I just replaced the rotors and pads (Akebono) in my E38 and now have a very soft brake pedal too. Haven't tried a re-bleed yet, though.

[chris33]

There are two rubber lines on the firewall near the ABS module. Have you checked them? They know for dry rotting due to high temps in the engine bay.

[shanecarmaster1]

I must say, I've always questioned the brakes since I bought the car. I thought I remembered them being really good when I first drove it, but I had a brake job done a few days after bringing it home.

Long story short is that you need OEM parts. Replace your brake lines (I believe there may be some vacuum hoses behind the engine that also contribute). I know the brakes were OEM when I bought the car, which were fantastic. After 6 years of dealing with spongy pedals, repeated bleedings, stainless steel lines, warped rotors, shimmies, and nose dive... I bought OEM parts and suddenly the brakes feel best out of any car I've driven.

I must also include that I bought OEM pads slightly BEFORE I installed the OEM rotors, and they both made huge differences. I've always seen Meyle rotors as respectable and easy since they're so cheap, so I've always faulted my car for their warping. (I did have a slightly dragging front brake caliper for years). However, recently fixing the caliper still warped the rotors in no time! I recently replaced them with OEMs, still with the same new OEM pads, and wow. The car rides differently, is smooth, and the brakes feel unbelievably night and day.

All that longwinded response to say: make sure ALL parts are OEM. It even makes the nose stay flat when braking rather than that sloppy dive it used to do. Also, I've been through the Akebono thing and it felt like I was always going to rear end someone. Don't go there.

[shenofjo]

I feel very confident in my carbotech brake pads and front oem rotors, but i wonder if my rear r1 concept rotors are to be questioned. They have great reviews from supra community though... Will get it checked out by the shop and see whats up

[voodoomelon]

There are two rubber lines on the firewall near the ABS module. Have you checked them? They know for dry rotting due to high temps in the engine bay.

Yes they look in fine condition. The ones going down the right shock tower?

I must say, I've always questioned the brakes since I bought the car. I thought I remembered them being really good when I first drove it, but I had a brake job done a few days after bringing it home.

Long story short is that you need OEM parts. Replace your brake lines (I believe there may be some vacuum hoses behind the engine that also contribute). I know the brakes were OEM when I bought the car, which were fantastic. After 6 years of dealing with spongy pedals, repeated bleedings, stainless steel lines, warped rotors, shimmies, and nose dive... I bought OEM parts and suddenly the brakes feel best out of any car I've driven.

I must also include that I bought OEM pads slightly BEFORE I installed the OEM rotors, and they both made huge differences. I've always seen Meyle rotors as respectable and easy since they're so cheap, so I've always faulted my car for their warping. (I did have a slightly dragging front brake caliper for years). However, recently fixing the caliper still warped the rotors in no time! I recently replaced them with OEMs, still with the same new OEM pads, and wow. The car rides differently, is smooth, and the brakes feel unbelievably night and day.

All that longwinded response to say: make sure ALL parts are OEM. It even makes the nose stay flat when braking rather than that sloppy dive it used to do. Also, I've been through the Akebono thing and it felt like I was always going to rear end someone. Don't go there.

Yes I hear similar stories about non OEM parts. Thing is, all my discs and pads are OEM, straight from the dealer. Albeit 4-5 years old, they're in decent condition. I also have a full set of Brembo pads on the way (the OEM calipers for the 728i/735i in Europe were Brembos) as they're very close to the wear indicators.

But the thing is, OEM or non OEM shouldn't make the slightest bit of difference to a stationary car and that's what i'm describing. Sitting in one spot, not moving with the engine running, the brake pedal sinks 2/3 of the way to the floor with zero effort. The same feeling is out on the road. I can see how non OEM parts can soften braking feel and change how the pedal feels when slowing down, but not when you're parked up.

I'm worried there's something up with the ABS pump, that noise above cannot be normal.

[racer2086]

Congrats! I was surprised to see a recent post from you. Great to have you back!

I would say that in my experience, what you describe is a factor of the brake pads and rotors on the car. The lack of initial bite makes the pedal feel more spongy because it requires more pedal action to obtain the same bite/feel. I recently changed my Wagner pads to Stoptech, and it improved tremendously. I can feel the brakes grab even when I'm only lightly on the pedal. It's not OEM level, but much much better for the lack of dusting.

Now, mind you, the pedal isn't "stiff" like an M3, but the response is there. The 7 has never had a "stiff" pedal per se, and I don't think they were designed that way. But if you feel that you require too much "action" of the pedal to feel the brakes, it is your pads and rotor combination.

[voodoomelon]

Thanks for the input, but again I have OEM dealer bought pads and discs all round.
And this isn't really about pedal feel as such, as I know that can be subjective, its about the pedal going 2/3 of the way to the floor before you begin to feel anything.

It's definitely not normal, but I still have no clue what's causing it.

[srq]

I have similar problem w/soft brakes. When the car is cold in the morning for the first couple minutes of driving, brakes work really well. Slight tap on pedal stops car. As car heats up, I lose breaking power and it take a lot more pedal pressure to stop. I am guessing it is related to the power booster and or maybe losing vacuum pressure that assists braking.

How is you your brake performance when engine is cold?

[chris33]

So, like you I had been chasing a soft pedal issue. Also, like you I have flushed the fluid completely and bled the system on multiple occasions using DIS with no change. Whenever I have bled the system, the fluid always flowed clear and free of air bubbles, and when I would initially drive the car the brakes felt good and the pedal was tall and firm. But as the drive progressed the pedal became less consistent on height .e.g sometimes it was tall and other times in would go to about halfway to the floor and the foot pressure needed to stop the car increased.

I was at the point of replacing the master cylinder, but instead I decided to remove one of the calipers, and what I found in the was a gray soupy mix of fluid (this explains the inconsistent pedal height), behind the piston, I proceeded to check the other three calipers and found the same. I cleaned all four calipers, flushed and bled the system and now the pedal is firm and consistent and the brakes feel perfect.

In summary, just because when you bleed the brakes and see clear, air free fluid, does not mean there is not contaminates in the calipers.

[Aitch]

What was your procedure for cleaning the calipers? Interested to know.

[chris33]

Disassembled and cleaned with brake cleaner. Here is a good example: http://www.********s.info/general-gu...-calipers.html

[shenofjo]

that link is broken

[Greygoose82]

I'm assuming you took it apart by removing the front dust boot and rear seals to clean the insides of each? This would mean then you pretty much rebuilt them.

[Giest740i]

My fix. Parked my car, ordered all new parts that go into a caliper and SS mesh lines. Removed the calipers, disassembled them entirely, cleaned and removed rust inside and out. Drained the brake fluid lines completely. Painted the calipers red (because I'm so dope), reassembled them. Installed the new S/S mesh lines, sensor, drilled discs, and pads. Put in the recommended BMW brake fluid (just in case there was a different molecule floating around in there..you know how German engineers can overthink things), Tok it out on the road and yes they are more responsive. But listen, these things are luxury sedans, not track cars and they are heavy, so you still have a soft-like brake compared to a real M car.

[Reza713]

3 years of same Spongyniess pretty much had everything replaced

750il Caliper upgrade
OEM Portection Package Rotors
OEM Pads
SS LINES
NEW soft lines around ABS module
Rebuilt calipers again due to spongy feeling
New Master cylinder

So frustrating not sure what else to change or do any more

[tmcnall]

3 years of same Spongyniess pretty much had everything replaced

750il Caliper upgrade
OEM Portection Package Rotors
OEM Pads
SS LINES
NEW soft lines around ABS module
Rebuilt calipers again due to spongy feeling
New Master cylinder

So frustrating not sure what else to change or do any more

Did you ever find the fix? Mine is a 2000 740i Dinan Stage 2. I bled it with INPA and DIS, dealer bled it with ISTA, 2 independents tried too with no change.

Now I'm replacing pads and rotors, but doubt that's going to fix a spongy pedal.

[setconstr]

+1 with chris33 I found the 2 small brakes lines below the abs module had worn out and there was a small leak on one and a ballon on the other. Replaced all the brake lines with stainless steel bleed the brakes and no soft pedal. I have been running Akebono pads and Zimmerman drilled rotors for at least 10 years I love them, zero dust, stops Awesome and the life of the pads are unreal ........

[GeoffreyS]

Hey Voodomelon, I don't know if you're still following this but, it caught my eye because you posted on my birthday

Anyway, it sounds to me that the spring on the primary piston inside your master cylinder has failed/weakened. So, you are not getting much (if any) brake fluid moving toward the calipers until the primary piston physically contacts the secondary piston. Hence, nothing happens until the pedal is 2/3 depressed.

Replace or rebuild your master cylinder.

Hope this helps, cheers