Vague braking feel?? - The Unofficial BMW M5 Messageboard (m5board.com)

atomic80 · 17th February 2002, 19:32

Last night I was driving back from Portland on the "superhighway" with my beast. It occurred to me that the M5 doesn't have a very good "braking feel" compared with most of the cars I've driven in the past. Even my Tundra pickup has a better braking feel. It almost feels "mushy" at times to the point where I'm not even sure that I can stop.

I went about 125 mph and when using the brakes to slow down it didn't "grab" as fast as I'd like it to have.

Any idea what I can do to improve the braking performance? I should also mention that I do have the euro braking ducts + grille/splitter in place and no, it wasn't raining last night either.

This made me want to seriously reconsider going with an aftermarket braking solution but I'd like to hear from you folks before I go for this expensive upgrade. Maybe something as simple as changing the brake fluids would improve matters some? What do you guys suggest?

TCM · 17th February 2002, 20:16

Jason:

I am surprised to hear this. Every BMW that I have driven has had good brake feel, at least better then a pick-up. Maybe you are running low on brake fluid? I would suggest opening up the brake ducts and switching to a higher boiling point brake fluid (Super Blue and ATE600? I beleive are up there). If I remember correctly, the opening of the brake ducts is a minor job that is cheap. These mods will improve your barkes without costing an arm and a leg. I think you must be running low on brake fluid because even my '97 540 has great brake feel and I am running normal DOT4 fluid at the moment. Check it out, good luck.

atomic80 · 17th February 2002, 20:35

Do you know how I can check the brake fluid levels?

atomic80 · 17th February 2002, 20:49

For that matter....should I go with Super blue or ATE600? And also, how much of either one should I order? 2 or 3 quarts? I don't want to try bleeding the braking system myself if I can avoid it. From what I hear it's not for the faint hearted especially a newbie one at that too.

Finally, I took a look under my hood. I can't see a place to check the brake fluid levels anywhere. I saw a place for the ATF right next to where the oil filter goes.

greg · 17th February 2002, 21:25

I have no trouble modulating the M5 brakes. There IS more pedal travel than, say, in the Porsche - but less than in, say, a cadillac. But I know how hard to stab to get rapid braking initiated, and I feel I can control the mount of braking very well. You may prefer a different feel, though -

Squishyness can come from:

1) Air in the lines. Make sure your system has been properly bled.

2) Slight stretching of rubber hoses. Steel braided lines can reduce this, but I understand they also increase mechanical stresses on the ends of the hoses, so they require more frequent inspections.

3) Mechanial flexing of the pedal assembly and the caliper aseemblies. I seriously doubt either of these are a major factor here.

ATE super blue has a higher boiling point, and boiling fluid can create gasses in the lines that reduce pedal feel. However it would be just about impossible to boil the fluid in the M5 unless you're on the track pushing very hard - in which case you might want to investigate a more complete brake upgrade.

alpywhite · 17th February 2002, 21:31

One thing I am noticing in the rainy season is, if I drive on the highway for a prolonged period in the wet stuff without braking, there will be a very brief (but unnerving!) delay in grip when they're applied.

It feels like they're "slick" for a microsecond and need to dry out via friction before they bite with full power.

Anyone else feel this???

TCM · 18th February 2002, 00:51

Jason:

Your brake fluid container (master cylinder) is located under the driver's side air cabin filter. You have to remove the filter and black housing and you will see the master cylinder underneath. There should be a line on the side marking the full line. Usually you just fill it up to the top of the container and then begin to bleed the system. If you are not technically inclined, bring the car to a technician who can perform the service for you. As Greg stated, you may just have air in the lines. As far as the brake fluid, you are not going to boil it unless you are really going at it at a track but upgrading to SuperBlue or another high end brake fluid makes sense IMHO. Does not cost much and will improve your cars braking abilities if you ever do go to the track. I am not even sure if the other stuff is ATE 600, I know there is a product out there that is as good as Super Blue but I forget the name of it. Dave Z. should be able to help you out a lot. He is big into brakes and higher temp fluids. Good luck.

greg · 18th February 2002, 00:59

Alpy - I have felt that too - though I don't think I always do (or more likely, I'm just not being observant enough.) I truly think it IS just water lubricating the pads, but it dries off so incredibly fast that I doubt it would ever make much of a difference in stopping time. Of course if it is wet out I always leave more room, go slower and maneuver more gently as a matter of course.

atomic80 · 18th February 2002, 01:22

I'll take my car to the dealership to have them check to see if there's air in the tubes. I suspect that's the case. From what I can recall, driving the M5's at the DE, it wasn't like this by a long shot. There IS definitely wrong with my brakes. It doesn't like to "bite" as easily..it feels squishy by nature. I don't think that I need to "upgrade" to ATE600 or Super blue. I think that once I check for bubbles that should do the trick. I recall having very good braking feel when I first picked the car up. Any idea what could have caused the bubbles to get in my tubes in the first place? I'm trying to recall if this happened before or after I had the brake ducts put on.

In any case, I'll see what happens after I take it to the dealership.

Thanks, you guys.

MEnthusiast · 18th February 2002, 01:26

Alpy,
Ive had the same thing, but it goes away very fast- if Im alone on a highway in the rain, I gently apply the brakes for 2 seconds every 10-20 minutes.

Jason,
I havent had that sensation- I agree, its worth the hastle factor to take it to the dealer, way better to be safe than sorry.