BMW K1200, K1300, and K1600 Forum banner

1 - 11 of 11 Posts

·
Registered
Joined
·
33 Posts
Discussion Starter #1
Hey all, owned my '93 75 brick for second season now, and noticed it was time to replace rear brake (pad non-existant) I was also leaking from pedal side of master cylinder (boot), so that replacement came shortly after pads. But here was my process

Ordered pads, and decided to renew o-rings and seals in rear caliper. Noticed a loss in pressure to brakes, so I renewed master cylinder piston. Bled brakes from caliper and reservoir side. rode for a 100 miles and repeated bleed.

My issue is i've noticed the pads weren't retracting from rotor completely so as I spin wheel i heard almost metalic squealing caused by outboard pad rubbing on rotor.

I can fix this by pushing the pad away from rotor with finger or screw driver- but then I lose pressure to pedal until a few pumps where pressure returns and the pad sticks again slightly rubbing rotor, causing rotor to get super super hot from any riding let alone at highway speeds.

I've disassembled, and cleaned piston cups, and re assembled, bled and re-bled, and I can't figure out a solution to this. All insight is appreciated, especially as I will probably be renewing front caliper components similarly within the next 1000miles.
Thanks
 

·
Registered
Joined
·
1,792 Posts
Whern they stick try opening the bleeder. If fluid under some pressure comes out and the pads release you may have a bad hose. Internally degraded then acts as a one way valve, keeps the pressure on.

You said you replaced the MC piston but....How was the bore? Shouldn't have any wear or corrosion marks.
 

·
Registered
Joined
·
33 Posts
Discussion Starter #3
outside of the MC had corrosion from leak, but I didn't notice any issues on the inside of the cylinder.

Other issue was that I didn't soak parts in brake fluid before installing. realizing this issue I disassmbled components and soaked them (except for orings in rear caliper) (everything was pliable enough to install without rupture) could this be a cause for concern, or will they be exposed to fluid and soak naturally.
 

·
Registered
Joined
·
1,792 Posts
Oh...I am very surprised the caliper pistons went in without lube if that's what you mean. Doesn't take much to make those stick and not fully release. I have done quite a few of them over the years, always lubed them and even at that they'd need a good push to sit in there. Dry that's asking for trouble.

Did you really clean the groove inside the caliper, doesn't take much corrosion or crud in there to bind things????

I don't like that method of lubing parts with brake fluid. It does work but you have to wipe any residual on the outside. If left there will attract moisture and cause corrosion.

There are special "brake mounting lubes". I use the "red rubber grease" but that's hard to find in North America.

As for the MC...there is a tiny hole in the cylinder, brings the fluid back up to the reservoir when you release the pedal. If plugged well brakes won't release. Crack that bleeder open with the brakes stuck that will give you the clues.

Adjustment rod??? It does need some play.Even a tiny pressure on the piston is enough to keep the brakes on and then heat builds up, things expand and binding gets worse.
 

·
Registered
Joined
·
33 Posts
Discussion Starter #5
I cracked the bleeder and didn't notice the fluid to be under pressure. I'm going to check the master cylinder again now,
any ideas on whether to look on mc or caliper for problem, Im guessing fluid isn't a problem, wouldn't seem as hose was issue with the bleeder test.
 

·
Addict
Joined
·
3,750 Posts
If the pad on one side is releasing and the other one isn't, I would rule out the MC for now.

My money would be on sticking pistons. Like H I have spent happy hours with old Brembo calipers. In some cases you just have to put in a new piston/seal.

I test mine with an airline, calipers off the bike and the pads removed. I set for a max pressure of no more than 10 psi, then see what air pressure is needed on each piston to push it forwards. The lower the better, but around 4 psi on every piston tells me they are o.k.

These Brembo calipers unlike car calipers have no method of retracting pistons when the MC releases pressure which is why you sometimes do get the pads just touching the rotor. But there should be no force.



Never pay again for live sex! | Hot girls doing naughty stuff for free! | Chat for free!
 

·
Registered
Joined
·
1,792 Posts
I never used the air pressure method to push the pistons out. But interesting...I push them out with air then push them back in and thumb pressure is my gauge.4 PSI, could be just about right. :) If they stick no way my thumbs will push them in.

Whatever you do...DON'T split them calipers. Altough some have been successful and did that without causing a leak at the o-ring, too many out there haven't had such success and had to buy a new($$$$) or good used caliper. :(

It takes very little to make a caliper stick....a little forgotten corrosion under the seals or same unpolished on the pistons and that is if it can be polished, wear marks etc....and maybe even a little spray of brake cleaner can swell the seals.

What I'd like to know is if they are even sticking. Is the rotor getting hot even without using the brake??? If not may have to do with the pads, some (too many) have chunks of brassy metal imbedded in the pad. Depending on the pad quality/brand, them chunks can be substantial in size and may curl out a little and cause the metallic noises.I won't get into the brands here but the pads with very tiny specks of metal or none at all seem to do much better against the BMW rotors. And that's a lesson I learned expensively. :(
 

·
Registered
Joined
·
33 Posts
Discussion Starter #9
Hey guys. I'm at wits end. Rear brake wont retract aftrr releasing. Ive been pushing pads out after stops, lose pressure for couple of depressions. Did 1600mi. Trip and found that inboard pad worn to shoe and outboard pad glazed.
Swapped pads, cracked caliper cleaned o-ring joint surface, wiped out puston cups lubed piston seals and reassembled.
Diconnected brake line and cleared. Checked MC for return after depression and it returns.

Checked to see if pushed fluid with bleeder cracl ed with no brake and no fluid expeled. Fully bled. And pads still rubbing,
I backed out foot pedal actuator stud and foot pedal sags until contact with MC. Am I missing a spring to hold up brake lever? Is this pressure enough to cause pads to rub?


To add to this, I checked front,swapped fluid and bled and now front left caliper outboard (left pad) is rubbbing in front with new fluid in system?
I know the error is mine, but what am I f#&!ing up?!
Ive got a rear brake line on order but I suspect it wont resolve issue (solely based on my luck)

Look above and you'll see I had replaced caliper components and MC cup seal within last 5k.
 

·
Registered
Joined
·
33 Posts
Discussion Starter #10 (Edited)
Hey guys. I'm at wits end. Rear brake wont retract aftrr releasing. Ive been pushing pads out after stops, lose pressure for couple of depressions. Did 1600mi. Trip and found that inboard pad worn to shoe and outboard pad glazed.
Swapped pads, cracked caliper cleaned o-ring joint surface, wiped out puston cups lubed piston seals and reassembled.
Diconnected brake line and cleared. Checked MC for return after depression and it returns.

Checked to see if pushed fluid out of bleeder whike cracked with no brake and no fluid expeled. Fully bled. And pads still rubbing,
I backed out foot pedal actuator stud and foot pedal sags until contact with MC. Am I missing a spring to hold up brake lever? Is this pressure enough to cause pads to rub?


To add to this, I checked front,swapped fluid and bled and now front left caliper outboard (left pad) is rubbbing in front with new fluid in system?
I know the error is mine, but what am I f#&!ing up?!
Ive got a rear brake line on order but I suspect it wont resolve issue (solely based on my luck)

Look above and you'll see I had replaced caliper components and MC cup seal within last 5k.
 

·
Addict
Joined
·
3,750 Posts
Although I have a K12RS with Brembo brakes, I'm assuming yours are similar.

I'm surprised you are still on this with no solution.

When you say the pads don't retract, do you mean there is still sufficient pressure on the rotor for them to bind? Because pads do NOT retract. The fluid pressure is released but the pads may still make some contact with the rotor but there should be hardly any friction. However, if you mean the pads are holding on such that you can hardly turn the rear wheel by hand or the pad wear is uneven, then that is an issue to do with lack of free play adjustment on the rear brake slave cylinder push rod or stuck pistons.

You can confirm this problem by slowly opening the caliper bleed nipple. If fluid spurts out under pressure, then the rear master cylinder push rod has insufficient free play OR due to corrosion around the circlip in the end, the push rod and piston is not returning all the way back to its stop, it only needs to be short by a millimeter to get this problem.

I am afraid you cannot easily see this problem until you get the rear master cylinder off the bike and look end on. Carefully remove the boot and circlip. Clean up its groove and any rust on the circlip. Then put it in a vise and push/pull the push rod making sure it moves easily in and out and the back of the piston comes right back to the circlip with a nice click. When you slowly open the rear caliper bleed nipple you should just get a dribble of fluid out and not under pressure.

If you release the bleed nipple and the pads are still binding when you rotate the rear wheel, you have to investigate stuck or sticking caliper pistons or sticking pads. You should be able to easily push each piston back. Similarly, the pads should be free to move in the caliper slots which sometimes get rusted or full of crud. Use a needle file to clean up the pad slots and make sure there are no wear steps. If one or more pistons are very hard to push back, then you need to replace the piston and seal. One thing that catches some out is Brembo have used pistons with slightly different diameters. Get the wrong piston back in the wrong hole and it might jam! Have you swapped the caliper pistons about?

There is a strong spring on my K12RS foot pedal, but you have to make sure the bushing is kept greased. Check the Realoem parts fiche for your bike and make sure you have all the right parts, from what I can see, there is no return spring on your pedal but there is a return spring part 9 for the pushrod shown on the fiche.

http://www.realoem.com/bmw/showparts.do?model=0573&mospid=51743&btnr=34_0620&hg=34&fg=31

Even more reason to keep the pedal bushing oiled and free.



Never pay again for live sex! | Hot girls doing naughty stuff for free! | Chat for free!
 
1 - 11 of 11 Posts
Top