I recently had a chance to change the lines on an MCS and replaced the fluid with ATE. I did the standard bleed of all 4 corners as well as the clutch. Fluid was clean after the brake bleed with no air bubbles at all. I actually used up more than 3/4 of the bottle just to be sure their was nothing trapped.

I did notice that when doing the bleed of the back brakes, the master cylinder (or some component near it) made a "swooshing" sound when the brakes were pressurized via the pedal. This was not the case when doing the fronts.

When I completed the job, the brake pedal did feel marginally firmir, but not as expected when changing to braided lines.

Anyone have any thoughts as what the problem might be?

Thanks,
Boris

 

The "swooshing" sound is the noise made by power brake booster, nothing to worry about. You may need to re-bleed the brakes once more to get everything cleared out.

You won't feel a remarkable change between braided steel and stock lines, but overall you will have better control under heavy braking, This extra control gets noticed when really pushing hard in the corners such as auto-x and rally driving, and you dont get quite as much spongey feel when the brakes and lines get hot.

 

Later this week, I'll be upgrading to braided lines, bleeding the brakes, and replacing with Motul 600. I'm interested to learn more about this topic as well. :smile:

 

You cannot get "firmer" lines than those that come from any OEM. For one thing, OEM lines must bre pressure tested while after market ones don't have to be. Both rubber and braided ss hoses share one thing in common, the inner core is made of teflon which, in the end, is what holds the pressure. If you look at a Semi, which has air brakes, you will see it has just teflon lines. A professional test driver who spends hours upon hours behind a wheel MIGHT be able to tell the difference in firmness and if he did he would probably come down on the side of the SS hoses giving a softer pedal.
If you have a mushy brake pedal, you did not do a good enough job of bleeding, possibly if you ran the master cylinder dry and sucked in some air, it is going to take you a couple of bottles to get it out....

 

Greatbear,

Why would the brake booster make noises when bleeding the rears only? I have installed lines on many other street vehicles as well as track cars. The mini, but far seem to have the softest intial pedal feel of all. I do agree that threshold modulation is greatly improved, its that initial mush that I don't really care for.

I will try another complete bleed, maybe there is a small bubble what is stuck? Who knows.

On a side know, anyone have thoughts on the Mintex 1144 compound for primarily street use? I've used it before on other BMW's with good results.

Thanks.
Boris

 

Usually the booster will make noises (with the engine off) until it's residual vacuum is depleted, then it's more or less quiet. Some boosters will make noises without vacuum when bleeding the brakes because of the increased piston travel (the pedal usually gets near the floor when bleeding). I would not worry about the swooshing, though I dont know why it would happen with the rears only (did you start the engine between doing the fronts and rears?).

Did you change pads before or when you did the bleeding? If so, you need to go through a break-in period of the new pads to seat them. You will have a somewhat soft pedal feel until they bed in. Also, force the ABS into operation a couple times (make a few hard stops) before re-bleeding. this will help free up any air trapped in the ABS valving. In some stubborn cases, tapping on the lines, fittings and calipers will help dislodge stubborn bubbles.

 

pocketrocketowner: You are SO WRONG about not getting firmer lines than oem. SS Braided lines a much better and don't expand like rubber OEM brake lines. The inner core of most all oem lines are not made of the same material.
Boris: That swooshing sound you heard may have been the master cyl sucking air. I'd bleed with the key on so the ABS pump is working and make sure you don't let the fluid level get to the point that would allow the master cyl to suck air.
It's not unusal to have to bleed the system several times to get all the air out.

 

I just bled my brakes to ol' fashioned way - pump pump hold

Used ATE Super Blue, used 3/4 litre - flushed my '03 MCS completely of the stock fluid. Blue at all four corners, no bubbles, so I'm confident that the system was bled correctly.

Still spongy pedal feel, longer travel than I'd expect. If I stomp on it, the pedal goes almost to the floor - I don't feel like that's right. What am I missing?

 

You still have air in there.
Check your lines for leaks and I assume you have help bleeding and haven't let the reservoir run dry...

 

You think so? We were extremely careful - I had one guy cracking the bleeders, another topping off the reservoir, and all four corners are blue, with no bubbles...

 

What pads did you install? I did the brake flush, bushing install and Hawk HPS front, Mintex redbox rear. My brakes feel a little mushy I did not bleed them, and they felt mushy, near went to the floor after a track day. Then installed Speedbleeders and bled all four corners, and brought the pedal back somewhat. I think in my case it is hard rotors (brembo and hard pads).

 

No pads - just a fresh brake bleed. My car is 4+ years old and only has 29k on it - I'll bet it never had a flush. Front pads and rotors appear to be recent, though I doubt they're anything nice - could be Autozone or something, as I think the dealer I bought them from put them on. They snapped the head off the rotor set screw - I'll have to extract it at some point. The rotor is just loose in there.

I did a skid school/autox today, brakes seemed to work fine, just longer pedal travel than I expect I suppose.

 

If you have some hose that fits snug over the bleed valve and a cup/bucket you can bleed he brakes better.

Put some fluid in the cup, put the hose on the bleed valve and let it sit in the cup so that the end is under the fluid.

Pump the brakes, once the air is out of the the hose, you dont have to worrie about getting more air in the system because there is no were for the air to come from. you can use this system by your self if you have enough hose.

Just my $.02

 

+1 ^

 

Holy heck! I finally let myself be convinced that there had to be air left in the lines, and last night I threw the car on a lift (I work at a dealership) and performed a 'gravity bleed' - ie - pop open the bleeders 2 at a time, let the reservoir run down to a certain point, refill, repeat (in my case, I did it 3 times for the rear and 3 times for the front) and do the same for the clutch.

First off, it's very easy - though time consuming, it's just a matter of cracking the bleeders and letting gravity suck out the fluid. Once I finished the rears, I moved to the fronts, let the reservoir drain to the min level, then finally did the clutch. I hadn't done the clutch the first time around either.

And I repeat - holy heck! What a difference! The pedal feel is like a rock compared to the squishiness of before, and the clutch has a noticeably firmer pedal feel - confidence inspiring. All in all I'm 100% more confident this time around than I was the last time around - I recommend everyone do it this way as opposed to the pump, pump hold method!

 

Thanks for the update. I've heard a few people say the gravity bleed method works well on the MINI.

 

Glad you sorted it out. I just knew there had to be some air in there.

 

I like to bleed the brakes once - then let the system sit for 15 minutes, and then bleed again (per Randy Webb's original FAQ on bleeding the MINI's brakes, so the credit goes to him).

We've found that when installing new calipers and/or lines, sometimes the 'ol Power Bleeder will let you down - we've started suggesting doing the initial bleed with a Power Bleeder, and then doing it the old fashioned way on the 2nd pass. On new calipers especially, it's really, really tough to get all the air out without compressing the pistons (e.g. the ol' fashioned way).

 

Glad you posted this response, I'm having the same trouble. I change the pads and fluid, and the pedal is actually worse than before. I suspect the master Cylinder is possibly bleeding pressure by the piston seal, as the pedal seems to go down slightly after I hold pressure on the pedal. I bled the brakes with the wife's help (pedal pumper) and I used aquarium air hose into a bottle over the bleeder valve. I'm sure no air was sucked back in, but I dont know how the pedal would get worse than it was before.

Any advice would be appreciated.