Front brake Woes

[Adrian]

Hi again - having reassembled the front brake system I have a small problem
.
I have bled the system thru sucessfully - or  so it seems. The front pads are now rubbing gently against the disc thru the full rotation and the brake is either off on on -
.
Any help please ...... Adrian

[wilcom]

Adrian.................. how does the lever feel?  does it feel hard or spongy?  Does the lever compress all the way to the handle bar?

[Adrian]

Adrian.................. how does the lever feel?  does it feel hard or spongy?  Does the lever compress all the way to the handle bar?

The lever moves a small distance and then comes to a very hard stop. When I try to turn the wheel by hand with the lever pulled its rock solid and won't move.
.
Problems - problems - problems lol lol lol

[wilcom]

Adrian.....

I think I misread the issue. The brakes stop fine,  but when released,  they pads are touching the rotor slightly. If that is true,  there is some good stuff in the archive, I did a search on "brake dragging" and came up with some good info for that condition.

The seal itself seems to be the item that pulls the pads back ever so slightly to keep them off the rotor.

I must confess that your search will give you better info than I could attempt top translate. Go check it out in the archives

[Barry]

A firm brake lever is normal enough but it will be even firmer if the pads are not retracting from the disc as less piston movement is then needed to re-apply the brake. The symptoms therefore suggest sticking pistons.

To give the seal a chance of pulling the pads back off the disc the pistons need to be free to move in the caliper and that means they need to be free from corrosion and assembled using brake grease. Red rubber grease is commonly used but there are other types probably silicone based. Don't use any mineral oil based grease like copper grease or it will attack the rubber.

When you get this right you should be able to actually see the pads move back when the lever is released and there will be zero drag on the disc. If you give the front wheel a spin by hand it will keep rotating for a least 60 secs.

[georgesgiralt]

Also, if the pressure is not released completely, the pads still force on the discs.
You may check the very tiny hole at the bottom of the master cylinder reservoir to see if it is not clogged. It is through this tiny hole that the liquid goes back to the reservoir releasing the pressure...

[Bob_Roller]

Personally, if I had that situation, I would not be concerned about it what so ever  .

[mrclubike]

A slight amount of rubbing is not a big concern
The wheel should spin freely but you may still hear a slight rubbing sound
Did you install new brake pads also with the caliper overhaul

[Tony Smith]

A twist in the brake line will induce this problem.

[Adrian]

Okay thanks guys - I think I'll pull the caliper apart again and use some grease as barry suggests - I used only the brake fluid for lubrication as thw Clymer and Haynes say is okay. I use Silicon Dot 5 so it won't damage the paintwork. So back t the shed tomorrow ..........

[mrclubike]

O NO Here we go 
I would not use DOT 5
If you search this
There is just to much controversy to make a decision on its use
Not enough paint work to worry about that
If the MC was under the tank then maybe
Big paint eater is the wet cell battery any way 
My Bike gets over 10K miles per year on it so it doesn't sit enough to cause corrosion problems just  flush every year or two

All that said I don't think the DOT 5 is your problem but it could be   :-/

[mrclubike]

Like George said
Also make sure the  plunger in the MC is not sticking and not allowing full return back
 The fluid cant go back to the reservoir if the piston is not all the way back

[Bob_Roller]

I don't know if this has changed since I first used DOT 5 brake fluid when it first came out .

Unless the vehicle has a brake system that was designed to use DOT 5 fluid, I would stay away from it .

It will degrade the rubber parts in the system .

[wilcom]

I don't think the Dot 5 has anything to do with the dragging condition...........But ..................Snowbum explains why Dot 5 is not for our machines in a nice concise artical here:

http://bmwmotorcycletech.info/brakes.htm

[Barry]

Okay thanks guys - I think I'll pull the caliper apart again and use some grease as barry suggests - I used only the brake fluid for lubrication as thw Clymer and Haynes say is okay

I hadn't realise you had used DOT 5.  Provided it hasn't done anything nasty to the seals or interacted with the old fluid I would have thought DOT 5 it's better for lubing the pistons than DOT 4. The problem with using DOT 4 fluid on the pistons is it immediately attracts moisture and starts corrosion.  The DOT 5 isn't going to do that. If I was concerned about piston stiction with DOT 5 in the system I'd just remove the dust seals and squirt a little aerosol silicone grease around  the edge of the piston, wipe up any excess and refit the dust seals.

I'm open minded on DOT 5.  In a clean system with all new seals I don't see why it shouldn't work.

Whatever the problem is I hope you find it.