My Brake Pedal Feel is Kicking My Butt... - Page 2 - BMW M5 Forum and M6 Forums
E39 M5 and E52 Z8 Discussion 1998-2003 Advertiser's Forum

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post #11 of 158 Old 30th November 2018, 01:25 PM
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Ok, good luck on further evaluation - hope you get this sorted out soon.

Couple of thoughts: (1) there should be no tire lockup on maximum braking. It doesn't matter if DSC is on or off, ABS stays fully functional (unless you pull its fuse). Hence on a max effort braking action, you should quickly feel the pedal pulsing as ABS is active prevent one or more wheels from locking up. The tires will likely lay down a light rubber trail since they are being held to a rotation speed less that car velocity by a small amount, but it's unlikely to yield much if any tire smoke. So, no skidding, locked up wheels -- that shouldn't be happening. If you're getting tire lockup, other problems are at work.

(2) What blackknight is referring to above is that pads with a low coefficient of friction (essentially all ceramic low dust pads unfortunately) require more brake piston force to provide the same level of braking action as a "normal" pad. Hence while a set of OE type pads might require say 20lbs of brake pedal force (and the small amount of pedal travel that would entail) for a serious stopping event, the ceramic pads might need 40lbs of brake pedal force for the same braking action. The pedal travel required to create that level of force is of course a good bit more. I think that's what Paul was referring to.

It's almost impossible to relate how much of a difference brake pad coefficient of friction makes on the E39 M5; much more so than other cars I have experience with. With Stoptech BBK up front on my M5, I could run the Centric ceramic pads and be ok with the braking action, more or less. With the stock front brake setup, the same pads created a less than desirable brake pedal response (with more pedal travel required). I sold my car this summer, and I think the new owner was ready to change out those new pads right away. Dust be damned!

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post #12 of 158 Old 2nd December 2018, 01:43 AM Thread Starter
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Unfortunately I had to take care of some work at our rental property and did not have the energy to work on the Beast. I hope to work on the M5 on Monday and report my findings or success...
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post #13 of 158 Old 5th December 2018, 01:00 AM Thread Starter
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Yesterday I was able to spend some time on the Beast.
I ran the INPA program and activated all of the valves, pumps, etc... presented.
Then I ran ISTA+ program and found how to select the DSC 57 unit venting and pump activation while pressure bleeding via the 'continue' button. Need to select 1 and continue, then 2 and continue for RR, RL, FR, FL corner.

No air bubbles were seen coming out so I have to think my whole brake system is purged of air.

Went for a test drive and some drifting to work the DSC. The pedal travel still goes deep to stop. I found out about another large empty parking lot with only one light pole. I will go there and have some fun.

When I changed out the brake pads, I threw them in the trash. I will see about getting the Jurid and Textar pads and try them and see if the pedal travel is better/shorter.

In the past I used Axxis Ultimate (for the longest time they squealed like Banshees) and also Ferdo pads that felt right but with some brake dust.

To be continued...


I want to add that after looking up price and availability on the Jurid and Textar pads, I see they are both using Ceramic pad compounds. Now I am unsure if these will have the same issues as I have with my current pads????


Does anyone else have first hand experience info to add on this or other brands to try?

Last edited by mr_g_bock; 5th December 2018 at 01:32 AM. Reason: Added pad info
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post #14 of 158 Old 5th December 2018, 01:55 AM Thread Starter
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I would like to ask a question pertaining to bench bleeding the master cylinder. The master cylinder has three ports, one on each side of the cylinder bore and a smaller size at the far end. I bought the cylinder bleeding kit a a local auto parts store. I fitted the port fittings and hoses that then ran into the reservoir. With a full reservoir, I gently pumped the plunger and pumped brake fluid till no bubbles were seen going into the reservoir. Is this correct? All three lines pushing fluid back to the reservoir?



After the master cylinder was bolted to the booster and installed into the car, I reinstalled the bleed fittings and hoses to the reservoir and pumped more fluid through just to be sure before reattaching the metal brake lines (all three).


Did I do anything wrong here? Please advise.


Thanks!!!!!!
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post #15 of 158 Old 5th December 2018, 02:46 AM
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I have the akebonos, that's not the problem, keep firing the parts cannon at it, or do what I suggested in my first post,

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post #16 of 158 Old 5th December 2018, 01:13 PM
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Personally, I do not and have never liked ceramic pads. They're just . . . weird. My opinion, of course.

I like the Jurid pads very much. Economical and simple choice. If you're trying to troubleshoot a problem, try and remove variables. The Jurid pads are pretty reliable in that regard.

I've used Pagid Red (Bavarian Autosport house brand) and they worked well.

I really, really like the Carbotech 1521 Bobcat pads. They're comparably expensive and yes, they're a ceramic formulation but they're very nice.

The Centric Post-Quiet Semi-Metallic pads I just installed in my X5 are really great. Very sure stopping in all temperatures, zero noise and not as much dust as I would expect. In fact, probably less dust than the OE pads on there before which were also very good.

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post #17 of 158 Old 5th December 2018, 07:11 PM
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OP - Do you know the status of the calipers? My M5 suffered from poor pedal feel that was somewhat improved by ss lines, mutiple rounds of bleeding, etc. I still was not happy with the pedal feel, so I decided to rebuild the brake calipers. I found the piston seals bad on the rear two calipers and the piston was rusted on one of the front calipers and the seal was destroyed. I never had any external indications of brake fluid leakage, but after replacing all the pistons and seals, my pedal feel improved to where I would consider it normal. I had the same problem you're reporting, brakes would feel solid with the engine off, but the power assist from the booster with the engine running was enough to make the pedal mushy.

I think rockauto has the caliper seals and freshly chromed pistons for about $30/corner so that might be something to look into. It seems you've tried everything else.


I'll second the Carbotech 1521 pads if you're looking for a street pad. It looks like OP does a bit more that just street driving, though. They took a few hundred street miles for the pedal feel to solidify, but for a street pad I really like them. Pedal feel is good, low dust and low noise and surprisingly good rotor wear. The only real world problem I have discovered is the pad has relatively low tolerance for dust/sand, so they are not ideal for cars that operate in sandy soil areas. The pad is hard enough that the sand particles will embed in the surface, but not sink in and will quickly groove brake rotors and become noisy.
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post #18 of 158 Old 12th December 2018, 12:14 AM Thread Starter
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Well I just came from the garage and want to report in....


I set up my Motive Power Bleeder, full reservoir, wife watching the brake fluid catch bottle while I started up the engine. I opened the bleed screw and pumped the brake pedal ten times full stroke (the master cylinder is new). At the right rear caliper, she said she saw some bubbles at first, then just clear fluid. The I closed the bleed screw. I did this at all four corners ( ten strokes of the pedal) while keeping the reservoir topped up. Then while the engine is off, I pumped the pedal maybe five times and then held it. I then started the engine and the brake pedal went right down to the floor.


From what I had read earlier, the brake pedal should have only dropped maybe a quarter inch, not to the floor. Am I right in suspecting that the brake booster or vacuum line to it could be bad? Any tips on diagnosing a vacuum leak for this? Pulling the master cylinder and booster again does not make me happy along with re-bleeding the whole system if this is the problem.


All comments and suggestions are very much appreciated!!!!!!!!
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post #19 of 158 Old 12th December 2018, 02:28 AM
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Quote:
Originally Posted by mr_g_bock View Post
Well I just came from the garage and want to report in....


I set up my Motive Power Bleeder, full reservoir, wife watching the brake fluid catch bottle while I started up the engine. I opened the bleed screw and pumped the brake pedal ten times full stroke (the master cylinder is new). At the right rear caliper, she said she saw some bubbles at first, then just clear fluid. The I closed the bleed screw. I did this at all four corners ( ten strokes of the pedal) while keeping the reservoir topped up. Then while the engine is off, I pumped the pedal maybe five times and then held it. I then started the engine and the brake pedal went right down to the floor.


From what I had read earlier, the brake pedal should have only dropped maybe a quarter inch, not to the floor. Am I right in suspecting that the brake booster or vacuum line to it could be bad? Any tips on diagnosing a vacuum leak for this? Pulling the master cylinder and booster again does not make me happy along with re-bleeding the whole system if this is the problem.


All comments and suggestions are very much appreciated!!!!!!!!
Either your booster is bad or one or more of your calipers needs to be rebuilt. Start with the booster unless your calipers are high mileage, in which case they probably should be rebuilt anyway. I'm betting it is the booster. Not an entirely unusual phenomenon.

--Peter

Last edited by herrubermensch; 12th December 2018 at 02:29 AM.
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post #20 of 158 Old 12th December 2018, 02:23 PM
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[ set up my Motive Power Bleeder, full reservoir, wife watching the brake fluid catch bottle while I started up the engine. I opened the bleed screw and pumped the brake pedal ten times full stroke (the master cylinder is new). At the right rear caliper, she said she saw some bubbles at first, then just clear fluid. The I closed the bleed screw. I did this at all four corners ( ten strokes of the pedal) while keeping the reservoir topped up.]

Are you closing the caliper bleed screw before releasing the brake pedal?
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