vadim

Sorry if this has been discussed elsewhere.

I will be installing StopTech SS braided brake lines soon; here are my questions:

I am planning on using Motul 600 brake fluid. Do I have to drain the entire system or can it be mixed with whatever stock brake fluid is left in the system? Both are DOT4.

Also, what is the best way to drain the brake fluid in this car?

And, finally: how much brake fluid is needed for this, considering that some will be wasted on bleeding?

TIA.

nukblazi

I used two bottles to flush the system, I am not sure how to get all the fluid out, I'd have someone do it...

vadim

Tom, did you do it yoursef? I take it as you mixed Motul with the MB brake fluid, or am I wrong?

SUNILP

eaisest way is to open the caliper bleeder valve and have someone pour it in the resivour and someone keep pumping the pedal. That is the cheapest and eaisest way to do it.

vadim

Well, I have a better way - power bleeder! My concern was whether it is ok to mix different brands of brake fluid, as you can't replace 100% of the old content by pumping the new fluid through (I guess it is possible if you pump a lot of it through, though). I guess it is ok, otherwise I would have found something on the 'Net by now. So, in goes Motul 600 and new SS brake lines!

StopTech

It's ok to mix the two fluids. Motul RBF 600 is compatible with DOT 3 fluids which are probably in your car. If you haven't flushed out the system in a while, i'd suggest doing that. A brake system usually holds 1 liter, however we recommend having 1.5 liter (3 bottles) just in case since spillage and accidents do occur.

tommy

Vadim, did you end up doing this yet? Has brake feel improved? This is one of those "I'm not sure if it's worth it on my non-track-use girly 2.3L equipped car" mods. Any feedback would be great.

If not installed, damn, you're lazy!

vadim

Not installed - I am still waiting rotors from StopTech to do it all at once.

TNblkc230wz

MB's use a DOT 4+ brake fluid which is actually pretty good. It is a standard glycol based fluid. If the Motul is a glycol based DOT 4 or 4+ fluid, they should be mixable. If it is not glycol based, it can't be mixed and I don't recommend using it.

I don't recommend using Motul if it is only a DOT 4 fluid.

vadim

Motul 600 is designed for racing and has a much higher boiling point compared to "conventional" brake fluids. It certainly is not inferior to the stock brake fluid in any way. The downside of using Motul is that being extremely hygroscopic, it needs to be changed more frequently (at least once a year). I have not heard anything about side effects of using Motul from people who have put it in, including those who track on a regular basis.

lars

That downside is not restricted to Motul. With regular (non-silicone) brake fluid, the higher the boiling point the faster it absorbs water. For this reason, I don't think a brake fluid formulated for racing is all that useful in a street car.

vadim

True. I just happen to have bought Motul 600 that is sitting around which coincided with my car needing the brake fluid changed I will keep using the regular MB-recommended brake fluid after that. Well, maybe after one or two track events

TNblkc230wz

Not sure what hygroscopic is? Also what is the wet boiling point of Motul? Otherwise, you will be changing your fluid often.

nukblazi

I am sorry I had not seen this earlier. I had asked Tim (from StopTech) to send me enough fluid to flush the whole system with. I had this done at a highly regarded shop. Before this season starts I am going to completely flush the system again then alternate blue then amber to ensure a complete system flush. I am also going to change pads (from Porterfield R4S to something with a little more bite at Autocross temps)

FYI- I've been running the Motul on the street for some time. I love it, though I scare family members and friends. The setup I got from StopTech is insane. Now that I am used to it, I am freaking other people out regularly. :v

vadim

Thanks for words of reassurance, Tom! While I do understand that Motul 600 is great for tracking, it sure looks like it is a bit of an overkill for the street use, no?

C230 Sport Coup

I had considered replacing stock fluid with Motul, but too much of a pain in the ****. And I will say, I have driven my car pretty agressively on backmountain roads with the AMG brakes up front, and those things just kick ***. It would take a lot to heat those
35 lb rotors enough to boil the fluid in a street application.

I have heard to truely bleed the brakes of the stock fluid you need some electronic device to pulse the ABS.
I have read that mixing IS bad, but maybe Motul is OK.
In any case, in the course of my warranty service they've bled the brakes twice replacing the fluid, without me knowing in advance.
So another reason to just leave it alone and stick with the stock MBZ product, which can only be purchased at MB dealer, as it is
DOT4+ which has a slightly higher boiling temp than plain DOT4.

Unless you plan on driving on the track I wouldn't worry about it.
And if you do drive on the track, I read of people who cooked those AMG brakes completely here somewhere. And it had nothing to do with the fluid.
I find it hard to believe they could do that....
my commute is like a rally race...and I use the brakes plenty.

vadim

--> Hygroscopic

Motul RBF 600: dry boiling point: 594F(312C); wet boiling point: 421F(216C).

TNblkc230wz

That's really good. Why does it only have a DOT 4 rating?

vadim

I guess - just to emphasize that it is not silicone-based (as DOT5 fluids ought to be). If water finds its way into a brake system with DOT 5 fluid, it will not get absorbed by the fluid, but will roll down to the lowest point (usually calipers) due to gravity. This may potentially lead to much worse vapor locks than in case of DOT 4 or even DOT 3 fluids.

TNblkc230wz

Thanks for the info.

nukblazi

I suppose it is (?) Though I can say that with stock fluid, I could put my brake pedal to the floor. I hated the stock brakes on this car being that I came from '00 325xi. On the street it's a comfort level, I will say that I think the brakes have helped me avoid accidents in the Baltimore commute for SURE.

vadim

Was it track or street? Before or after you installed the SS lines/StopTech rotors/new pads? Any hydraulic fluid should provide the same type of response when cold (a typical volume change figure for hydraulic fluids under pressure is ~0.4% per 1,000 PSI). Usually mushy brake pedal is an indication of a serious contamination of the fluid.

nukblazi

Off the boat, out of the dealers lot. Then again after bleeding, then after flushing, then after flushing again.

Cured it with the brake set up I have.

vadim

I bet it is the SS lines that did the trick! My slotted rotors are in the mail (finally), so hopefully next week I'll be able to compare.

nukblazi

Definately, the SS lines are a big factor. In conjunction with the new fluid. I don't know, I can "test" these brakes and post numbers, but they FEEL better then a BBK up front