brake drag question - The Unofficial BMW M5 Messageboard (m5board.com)

RGCRAWFORD · 28th January 2006, 03:00

I changed the brake fluid (to ATE blue) and brake lines (to StopTech SS) on my '01 beast, and now the wheels don't spin easy when raised. There is some drag on them, as if the brake calipers are not all the way open. Bled the brakes again - didn't change anything. Does not go away with time on the road.

Otherwise, the brakes function ok....I'm just concerned that it is going to wear down my pads, damage my rotors, etc.

Any experts know what is going on? Any suggestions for fixing or adjusting the brakes?

Many thanks!

Raphael

Mth_degree · 28th January 2006, 05:33

Unless the pistons / sliders are sticking there is no way to adjust the brakes. There will always be drag on the wheel from the pads as well as the friction in the wheel bearing etc. You should be able to turn the wheel fairly easily with one hand, and if you spin the wheel fairly quickly and let go it shouldnt just stop immediately. Obviously the rears will have a lot more drag due to the rotation of the diff etc with the wheel.

If you drive at fairly high speed for a while and then stop using as little brake as possible, you can touch the wheel in the centre and it shouldnt be hot. If the brakes are binding more than usual the wheel will be very hot and you will probably smell the brakes.

I doubt you have changed anything by replacing the fluid and hoses, so I would just keep an eye on it (i.e. check the rotors don't become discoloured from overheating etc)

y2km5too · 28th January 2006, 06:01

I don't want to be alarmist about this, but you mention changing to SS brake hoses. When I had my Corvette, a lot of Corvette guys had problems with the SS hoses - the hoses themselves are still rubber; only the outer covering is stainless.

For some reason I can't remember, the SS hoses are more susceptible to internal cracking that causes "1-way check valves" within the hoses, which tend to hold hydraulic pressure in and not let the brakes release.

Might be worth checking into - it sounds like your brakes are tighter on the tires than they should be.

VancouverM · 28th January 2006, 10:02

I recently added the Stoptech SS lines as well as new Axxis Deluxe + pads, along with the corresponding obligatory bleed (using OEM fluid). I have not observed this problem with the wheels at all when I recently raised my car to inspect the underside. This was maybe 700 km after my brake job. How many kms since your brakes were done?

Calling Dave Z?

RGCRAWFORD · 28th January 2006, 17:36

Thanks for all the advice.

Mth Degree - The wheels do indeed spin, but not too freely. And no off smell or excessive heat. Sure feels like its the pads creating the drag (far more pronounced with the wheels off).

y2km5oo - I agree that it is probably worth checking out next time i take in the car for service. I have put it away for the winter - in the Spring I'll have it checked out and will report back.

VancouverM - Good idea- I'll send a note to Dave and see what he thinks. I have only put about 200km on the car since I made the change.

-Raphael

DZeckhausen · 28th January 2006, 22:26

Quote:

Originally Posted by y2km5too

I don't want to be alarmist about this, but you mention changing to SS brake hoses. When I had my Corvette, a lot of Corvette guys had problems with the SS hoses - the hoses themselves are still rubber; only the outer covering is stainless.

Not true. All stainless steel braided lines use a Teflon inner core, which does not flex under pressure as much as the fabric reinforced rubber core of traditional lines.

Quote:

For some reason I can't remember, the SS hoses are more susceptible to internal cracking that causes "1-way check valves" within the hoses, which tend to hold hydraulic pressure in and not let the brakes release.

Again, not correct. Rubber lines are more prone to a flap being formed during assembly of the ends. This flap can result in some residual pressure being held under exactly the right conditions. But it's very very rare. It's even less likely during the assembly of Teflon lines. In particular, the StopTech lines (every single line) are tested by being bled, to confirm flow through the fittings, then pressure tested up to 4500 psi, then the pressure is released and the lines are not disconnected from the fixture until the pressure has dropped all the way to zero. Such testing would detect a blockage that could result in residual pressure. The more likely effect of a blockage would be the inability to achieve full braking force on a caliper.

Quote:

Might be worth checking into - it sounds like your brakes are tighter on the tires than they should be.

The brakes grab the rotors, not the tires.

DZeckhausen · 28th January 2006, 22:39

Quote:

Originally Posted by RGCRAWFORD

I changed the brake fluid (to ATE blue) and brake lines (to StopTech SS) on my '01 beast, and now the wheels don't spin easy when raised. There is some drag on them, as if the brake calipers are not all the way open. Bled the brakes again - didn't change anything. Does not go away with time on the road.

You didn't explicitly mention if you noticed this residual drag on one front wheel or on both front wheels, although you do say "wheels" as in plural. So I'll assume this behavior is the same on both sides. If that's the case, then the likelihood that it's a line problem is so close to zero as to be virtually impossible. A "1-way" effect in a line (that somehow managed to escape detection during testing) would only affect the associated caliper. To have TWO such lines on the same car is simply not possible. It would be like winning the lottery twice.

When you first jacked your car up and spun the wheels, they turned relatively freely. Then you pulled the wheels, installed the lines, and bled the brakes. When you bled the brakes, you clamped the pads tight against the rotors. So naturally, when you now reinstall the wheels and try to spin them, there will be more drag. As the rotors spin and the wheel bearings flex under load, the pads are pushed away by the rotor runout. So a wheel will always spin more freely before you bleed the brakes than after.

You said in your other post that miles don't seem to make a difference. Yet you also mentioned bleeding the brakes a second time. Well there you go! You've just clamped the pads against the rotor again, so the wheels are going to have the same resistance that they had the first time.

I expect that if you drive the car around for a few miles, then pull into the garage (without stomping hard on the brakes) and jack the car up again, the front wheels will spin freely again. This seems to be normal behavior. I woudn't worry about it.

RGCRAWFORD · 29th January 2006, 00:54

Many thanks for the detailed reply, Dave. you are correct in assuming that the problem was on both front wheels the same.

I feel much better about the situation now. As you say, with miles it will go away.

Other than that, the SS lines work great. Thanks for the original recommendation.

RC

y2km5too · 29th January 2006, 05:09

Quote:

Originally Posted by DZeckhausen

Not true. All stainless steel braided lines use a Teflon inner core, which does not flex under pressure as much as the fabric reinforced rubber core of traditional lines.

Ok, not trying to start an argument here, but what you say is not true either. Maybe all REPUTABLE SS lines use teflon, but there are others available in the aftermarket that wrap a stainless covering over a standard rubber line. They have that "cool" SS look, but are cheaper than the full-up race type. These are available for Corvettes - maybe they don't make them for BMWs; I haven't checked because I just don't care how cool my brake lines look.

Because the SS cover stiffens the lines, inexperienced people tend to kink them during installation, causing the internal "check valve" effect. I've seen this several times, and helped several fellow Vetters undo the error. I agree with you that from a purely statistical standpoint, it's highly unlikely (but not impossible) to have two lines go bad simultaneously - but if they are installed wrong, it's not only possible, it happens.

Again, not trying to start a flame war, just offering possibilities for diagnosis - it's easy to check for residual pressure (just crack open the bleeder screw and see what shoots out).

DZeckhausen · 30th January 2006, 07:14

Quote:

Originally Posted by y2km5too

Ok, not trying to start an argument here, but what you say is not true either. Maybe all REPUTABLE SS lines use teflon, but there are others available in the aftermarket that wrap a stainless covering over a standard rubber line. They have that "cool" SS look, but are cheaper than the full-up race type. These are available for Corvettes - maybe they don't make them for BMWs; I haven't checked because I just don't care how cool my brake lines look.

Well, perhaps I should have said all stainless brake lines use Teflon cores except for fake stainless steel braided lines from China. Not that I understand why anyone would care about the "look" of brake lines, since they are completely hidden when the wheels are on the car.

Do you have any links to Corvette board threads discussing which vendors are selling these rubber lines with stainless coverings? Someone needs to expose the fraud by explaining to potential victims that the stainless covering is only there to protect the fragile Teflon inner core from road debris. It has nothing to do with the firmer pedal feel. I'll be happy to jump into the fray and expose these thieves.