Wimpy Front Brakes K75

[White Dog]

I recently replaced the front pads on my K75 and blocked the brake lever from operating.  Once the pad job was completed, I pulled on the brake lever several times to get a "full lever".  I now have about a half pull of free play before feeling any braking power.  I read somewhere that no adjustment exists for front brake lever.  What do you suppose is causing this?  Do I have air in the lines?

[BrickMW]

I now have about a half pull of free play before feeling any braking power.

Is the free play in the lever? or the piston?


In other words, is the piston fully retracting and staying in contact with the lever? or Does the lever have a gap before it starts pushing the piston?

[White Dog]

I have just over 1" free play in the lever before any braking resistance is felt.  Compared to my R1100RT (which also has ABS brakes) that lever has just over 1/2" free play.  My Honda cycles have less than 1/2" free play, both non-ABS.


The K75 resovior is full and the front brakes do not feel spongy.


Is the amount of free play I have normal for a K75?

[MarcoK75c]

I recently replaced the front pads on my K75 and blocked the brake lever from operating.

How did you block your lever from operating?
How much free play did you have before replacing the pads?
Where are you measuring free play?

Sounds like your master cylinder piston is not moving freely and taking up fluid from the reservoir as it should. I would suggest some DOT4 fluid and a flush. You might have dislodged some crud and it's keeping the piston from moving freely.


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[White Dog]

How did you block your lever from operating?  Block of wood between grip and lever with wood taped to grip.
How much free play did you have before replacing the pads?  Unknown
Where are you measuring free play?  End of tape measure to outer front edge of lever ball end, then pulled lever and measured where resistance was felt.  Recently replaced linings on my R1100RT and bled the brakes and got a "tight" lever as a result.  I have good braking power on the K75 front brakes, but the lever has too much free play, as compared to the R1100RT.

Sounds like your master cylinder piston is not moving freely and taking up fluid from the reservoir as it should. I would suggest some DOT4 fluid and a flush. You might have dislodged some crud and it's keeping the piston from moving freely.  Any recommendations about the ABS unit?


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[K1300S]

did you change the pads and not change the fluid?

how old is the fluid?

flush it.  full process.  including the ABS.

[White Dog]

did you change the pads and not change the fluid? no

how old is the fluid?  no idea but it looks clear in the handlebar resovoir.  The rear master cylinder was replaced by BMW about a year ago.  They may have changed fluid in the front at the same time.

flush it.  full process.  including the ABS.

Which do you suggest I do first--the calipers or the ABS pump?  Since this bike has the intergrated brake system, would the rear caliper and pump need purging also?

[White Dog]

Hmm.  Since my owners manual shows the ABS pumps to be linked to one electronic controller (on page 21), I guess I assumed the brake lines were linked, as well. Should have paid more attention to what I was reading.  Duh!  So, this is good news.  Now, I can just focus on the front system.


How much brake fluid are we talking about to purge the pump and calipers?  My rear master cylinder was replaced within the past year at BMW.  They may have changed the fluid in the front at the same time.  It looks clean.

[White Dog]

Well, there you go confusing me.  The pictorial on page 21 shows each pump connected to the controller but the front hoses and rear hoses are  shown as separate units. The pump on the left side has two (2) hoses running to the front of the bike.  Looks as if one goes to the caliper, the other to the front reservoir.

[K1300S]

No confusion...k75s have the first abs on a bike.  Nobody had even thought of integrated abs yet.  Two separate systems front and rear.  Flush the both.  Abs module first.  Maybe a pint of fluid.

Should do this every year anyway.

Does not sound like you have one...Get a shop manual asap.

[White Dog]

I have a shop manual.  The problem I have with it, however, is the technical language.  It appears to me the writers of repair manuals assume that proficient mechanics are the only users.  Some things I can follow, others I cannot.  Brakes are a classic example.  The Clymer gives instructions for ABS and non-ABS but says "if you have an ABSII system, have your BMW dealer bleed the ABS pump."  How do I know what ABS system I have?  Where can that answer be found?  I need a repair manual "BMW Repairs For Dummies."

[White Dog]

Thanks, Johnny, for the clarification.  I will proceed with the assumption I have 2 separate brake systems, but they are both controlled by a single electrical controller.


What did you mean with the statement about rubber hoses?

[White Dog]

Update.  Flushed the front brake system today until we saw clear fluid in the lines.  Lever is now firm and stops on a dime.  Quite surprised to only find one (1) bleed valve on the front left caliper--none on the right side but they are connected with a metal pipe which runs across the fender.  Pretty simple system to bleed.

[Laitch]

It seems like you've got it under control, White Dog. That's a good outcome.  :clap: