BMW K bikes (Bricks)


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1Back to top Go down   Front brake woes, help please Empty Front brake woes, help please Mon Jun 19, 2023 6:14 am

KiwiK100

KiwiK100
Gold member
Gold member
Hey all, I’m helping out a mate who’s having problems with his front brakes. Ok, it’s an 84 boxer, but the brake system is very much the same as a K bike with identical parts used. 
The problem is that the front brake pads start to tighten up against both rotors while riding with very little use of the brake lever and takes about 10 minutes to occur. The bike will be forced to a standstill but releasing the banjo at the mc resulting in a squirt of brake fluid fixes the problem for the rest of the ride, only to reappear the next day. Also, if left to cool down the callipers will release their grip on the rotors,  it will reappear later. Note that BOTH rotors are hot indicating (in my mind) that the problem lies in the master cylinder. Work so far includes a master cylinder rebuild kit, both callipers have been stripped with new seal kits installed, and the bike runs braided lines albeit the lines were fitted some years ago. The calliper pistons are bores are all good. The only thing left is the master cylinder itself although it seemed fine when I fitted the new piston with no scouring. The return hole to the reservoir is clear. What have I missed? All help and advice much appreciated.


__________________________________________________
Current rides:
2020 R1250RS. Metallic black with all the fruit
1983 K100C. Red. Krauzer fairing.
1984 K100RS. Madison silver.
2002 K1200RS. Owned from new. Pacific Blue, Ohlins, Speiglers, Fiamms, HID. 186,000km SOLD Crying or Very sad
1991 K1. Schwartz metallic black, 18 month frame off restoration. 74,000km SOLD Crying or Very sad
1987 K100RS Style. Black, Ohlins, Race Tech springs, Braided lines. Fully restored. 53,000 miles. SOLD Crying or Very sad
The family history:
1951 AJS 500 single - my Dads ride
1953 Triumph Terrier - my Mum's ride
1916 Triumph Type H, Battle of the Somme, France WW1 - my Grandads ride
    

2Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Mon Jun 19, 2023 6:48 am

92KK 84WW Olaf

avatar
Life time member
Life time member
A few things, since I have a 1983 K100RS and a 1984 RT and more recently also a 1984 Sprint that started out as a naked K100.

When I got the 83 RS it had sat for 17 years so needed to do the obvious. Brake hoses, caliper overhaul, master cylinder overhaul.

Having lots of parts for the 84 RT I thought simples. Not so. Transpired the 83 was different from an 84K. So we are told there are early K100 and later K100. Not so, there is super early, 83 RS did have same calipers as the boxer but mounted opposite way around so left on the boxer is right hand on the K100, but they were rapidly changed to a bigger diameter piston which is what you will be given for the early caliper that takes the 55mm pad. The later ones take the 57mm sintered pads. There were other niggles too, so in the end I just replaced the front and rear master cylinders and left the repair kits I had back in my shed. Before I did that I noticed the master cylinder also had some minor differences. It is possible your repair kit is not allowing the pressure to be released after using the brakes. Are the brake hoses replaced?

Now another thing I had recently on my 83 when I was changing the pads....I bought 55mm pads for it. But they did not fit properly. Since I have done all the work myself I knew something was wrong and its a bunch of pads that the backing plate is marginally bigger than 55mm [I have a few Ks and buy in bulk]. I had to grind them down to get them to fit freely. What was happening was they were jamming inside the caliper and not retracting. Both left and right discs affected. Symptoms exactly as you describe...if I used the brakes, coming from cold, pads would not retract properly. Then friction heated them up so that they expanded and increased the braking effect and of course heating it even more. But it also heated the fluid significantly which might overwhelm the return. The system relies on very little pressure to release the brakes and will never release them if there is the slightest restriction on the pads returning to their rest position.


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011157 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 58,200 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 51,800 miles.
1983 K100RS 0004449 Odette R100 colours 58,000 miles. Sprint fairing now 63,390 miles

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

3Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Mon Jun 19, 2023 7:53 am

Point-Seven-five

Point-Seven-five
Life time member
Life time member
It sounds like the liner in the brake line from the master cylinder is collapsing and needs to be replaced.  It is also possible that there is a bunch of crap in the line and is blocking the movement of fluid.  I had the same problem with one of my bikes.

Front brake woes, help please Dscn3019

About pads sticking, I have found that there are two different pads used during the run of K bikes and one is  about 1mm larger than the other.  They look the same and unless you measure them you will never see the difference.


__________________________________________________
Present: 1991 K100RS "Moby Brick Too"
 
Past:
1994 K75RT "Ilsa, She Wolf of the SS"
1988 K100RS SE "Special Ed"
1994 K75S "Cheetos"
1992 K100RS "Moby Brick" R.I.P.
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

4Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Mon Jun 19, 2023 11:32 am

92KK 84WW Olaf

avatar
Life time member
Life time member
Point-Seven-five wrote:It sounds like the liner in the brake line from the master cylinder is collapsing and needs to be replaced.  It is also possible that there is a bunch of crap in the line and is blocking the movement of fluid.  I had the same problem with one of my bikes.

Front brake woes, help please Dscn3019

About pads sticking, I have found that there are two different pads used during the run of K bikes and one is  about 1mm larger than the other.  They look the same and unless you measure them you will never see the difference.

The reason I asked about the brake hoses is exactly the point you mention, they break up and will block holes like this. If replaced, the brakes need to be bled on the side stand too.

You are right on the brake pads sizes, the difference is 2mm, 55mm and 57mm. The 55mm pads are normally organic/green/non sintered and only these fit the early calipers. The 57mm pads are also sintered, so they are wider for the later calipers and will only fit in them. You can buy these as green/organic too, but they dont fit early calipers.

But the pads I ordered were sold as 55mm pads and labelled 55mm, for the early calipers and were made slightly too large for them so they were sticking. I just ground the sides back a little to fit.


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011157 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 58,200 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 51,800 miles.
1983 K100RS 0004449 Odette R100 colours 58,000 miles. Sprint fairing now 63,390 miles

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

5Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Mon Jun 19, 2023 1:05 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member
One problem I have found over the years is that some aftermarket(non OEM) pads are made with old punch press tooling that is worn out.  Worn out tooling makes oversize punchings that will need tweaking to fit.


__________________________________________________
Present: 1991 K100RS "Moby Brick Too"
 
Past:
1994 K75RT "Ilsa, She Wolf of the SS"
1988 K100RS SE "Special Ed"
1994 K75S "Cheetos"
1992 K100RS "Moby Brick" R.I.P.
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

6Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Mon Jun 19, 2023 6:26 pm

KiwiK100

KiwiK100
Gold member
Gold member
Thank you both very much for your in outstanding informative advice. As mentioned in my opening post the lines have all been replaced and these are stainless aftermarket items so should be good, however it did occur to me that these might be the problem. I’ll chat with the owner and see when the pads were fitted.


__________________________________________________
Current rides:
2020 R1250RS. Metallic black with all the fruit
1983 K100C. Red. Krauzer fairing.
1984 K100RS. Madison silver.
2002 K1200RS. Owned from new. Pacific Blue, Ohlins, Speiglers, Fiamms, HID. 186,000km SOLD Crying or Very sad
1991 K1. Schwartz metallic black, 18 month frame off restoration. 74,000km SOLD Crying or Very sad
1987 K100RS Style. Black, Ohlins, Race Tech springs, Braided lines. Fully restored. 53,000 miles. SOLD Crying or Very sad
The family history:
1951 AJS 500 single - my Dads ride
1953 Triumph Terrier - my Mum's ride
1916 Triumph Type H, Battle of the Somme, France WW1 - my Grandads ride
    

7Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Thu Jun 22, 2023 6:30 am

KiwiK100

KiwiK100
Gold member
Gold member
Spent some time on my mates R series today and have discovered the following. The pads were a little tight so ran the grinder down the sides to make movement easier however when the pistons were pushed out a little via a squeeze of the front lever, they would not retract when weapon of choice was inserted between the pads in the usual manner to retract them. This was only overcome by cracking a banjo resulting in the immediate retraction of the pads. So something is preventing brake fluid from travelling back up the lines to the master cylinder. The banjo on the same calliper we were working on was cracked so that’s a no brainer that the pads retracted easily so the next step is to repeat the exercise but crack the banjo at the master cylinder and see if the same results occur. If so, then the problem lies in the master cylinder - which has a new piston kit in it.  Please note that  ALL lines are braided stainless and less than five years old. 
Here’s a question - there is a modification with one line from the master cylinder to the right calliper and then a line over the mudguard to the left calliper with one bleed nipple on the left calliper to bleed both callipers. Not perfect I know. So, each calliper has two nipples, on the right calliper the feed from the mc enters the calliper via the outside nipple, and the crossover line runs from inside nipple to inside nipple on the left calliper with bleed nipple on the outside. Confused? Me too, but does it matter? There are no one way valves within the calliper so shouldn’t matter but ya never know… To add to the issue, I asked when this problem first occurred and he said after we installed the calliper overhaul kit. Great, but prior to that the brakes were so ineffective they were dangerous, so overhauling them has simply revealed an issue that was possibly previously hidden. Any thoughts?


__________________________________________________
Current rides:
2020 R1250RS. Metallic black with all the fruit
1983 K100C. Red. Krauzer fairing.
1984 K100RS. Madison silver.
2002 K1200RS. Owned from new. Pacific Blue, Ohlins, Speiglers, Fiamms, HID. 186,000km SOLD Crying or Very sad
1991 K1. Schwartz metallic black, 18 month frame off restoration. 74,000km SOLD Crying or Very sad
1987 K100RS Style. Black, Ohlins, Race Tech springs, Braided lines. Fully restored. 53,000 miles. SOLD Crying or Very sad
The family history:
1951 AJS 500 single - my Dads ride
1953 Triumph Terrier - my Mum's ride
1916 Triumph Type H, Battle of the Somme, France WW1 - my Grandads ride
    

8Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Thu Jun 22, 2023 6:38 am

Dai

Dai
Life time member
Life time member
That's a setup I've seen before but I class it as 'non ideal', mostly because it makes bleeding the brakes a RRPITA. To me it sounds as if you have bled the brakes correctly and I'm going for a problem in the master cylinder. Specifically, it wouldn't surprise me if you found that one of the o-rings got pinched on reassembly and it's holding the piston in place.


__________________________________________________
1983 K100 naked upgraded to K100LT spec after spending time as an RS and an RT
1987 K100RT
Others...
1978 Moto Guzzi 850-T3, 1979 Moto Guzzi 850-T3 California,1993 Moto Guzzi 1100ie California
2020 Royal Enfield Bullet 500
    

9Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Thu Jun 22, 2023 7:43 am

KiwiK100

KiwiK100
Gold member
Gold member
Interesting Dai, I’m at the point of going back into the master cylinder anyway and seeing what’s going on. As mentioned previously, I’ll try cracking the mc banjo and if that allows the pads to retract immediately then that’ll confirm the issue is there and not further down the lines.


__________________________________________________
Current rides:
2020 R1250RS. Metallic black with all the fruit
1983 K100C. Red. Krauzer fairing.
1984 K100RS. Madison silver.
2002 K1200RS. Owned from new. Pacific Blue, Ohlins, Speiglers, Fiamms, HID. 186,000km SOLD Crying or Very sad
1991 K1. Schwartz metallic black, 18 month frame off restoration. 74,000km SOLD Crying or Very sad
1987 K100RS Style. Black, Ohlins, Race Tech springs, Braided lines. Fully restored. 53,000 miles. SOLD Crying or Very sad
The family history:
1951 AJS 500 single - my Dads ride
1953 Triumph Terrier - my Mum's ride
1916 Triumph Type H, Battle of the Somme, France WW1 - my Grandads ride
    

10Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Thu Jun 22, 2023 8:00 am

Point-Seven-five

Point-Seven-five
Life time member
Life time member
It might be worth spending a little time flushing the lines with the banjo bolts disconnected at the calipers and draining into a container.  A pint of fluid pumped through would confirm whether or not the problem is debris in the lines or something else.  If it is debris, it should flush it out.  Also, the resistance you will feel will tell you how bad the lines are plugged if they are.  Flushing with the banjos disconnected should have little lever resistance. 

From what  know about master cylinders, I am doubting that is where your problem is.


__________________________________________________
Present: 1991 K100RS "Moby Brick Too"
 
Past:
1994 K75RT "Ilsa, She Wolf of the SS"
1988 K100RS SE "Special Ed"
1994 K75S "Cheetos"
1992 K100RS "Moby Brick" R.I.P.
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

11Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Thu Jun 22, 2023 9:32 am

Laitch

Laitch
Life time member
Life time member
KiwiK100 wrote:Here’s a question - there is a modification with one line from the master cylinder to the right calliper and then a line over the mudguard to the left calliper with one bleed nipple on the left calliper to bleed both callipers. . . . Not perfect I know
Dai wrote:That's a setup I've seen before but I class it as 'non ideal', mostly because it makes bleeding the brakes a RRPITA.
It seems that was a factory assembly on late model Bricks. Images of 1992 Bricks show that setup on Standard, S and RT models. On my '95 Standard, the brake line runs directly to the right caliper passing through a fender-mounted wire keeper on the way. The rear half of the fender has a notch on each side for the bridge line to pass through; a split grommet surrounds the pipe and the grommet perimeter is grooved to nest it into the notch's edges.

It might seem to be a RRPITA (PITA in the USA) but all I do is open the left bleed screw and flush with ≈60mm of fluid. Of course, I use a piston retractor which some might consider a PITA (R, RR or non-R) also, but that's life. The brakes on my Brick have been functioning well on the flats and on the mountain roads here for 65 thousand miles; I don't take it to the track. Laughing


__________________________________________________
1995 K75 90,000 miles
    

12Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Thu Jun 22, 2023 2:42 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member
I had that setup on my K75RT and outside of having the bleeder on the opposite side from the brake lever I found bleeding to be pretty easy and wish I had the same setup on my K100RS.  No problem at all pushing old fluid and air out of the front calipers.


__________________________________________________
Present: 1991 K100RS "Moby Brick Too"
 
Past:
1994 K75RT "Ilsa, She Wolf of the SS"
1988 K100RS SE "Special Ed"
1994 K75S "Cheetos"
1992 K100RS "Moby Brick" R.I.P.
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

13Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Thu Jun 22, 2023 6:26 pm

lucki

lucki
Silver member
Silver member
My 1987 rescue bike had front brake problems. Flushed a!! Lines, used a litre of dot4. Problem was the rubber boot in the master cylinder disintegrated and the bits clogged the lines. Only about 40 percent of the boot was visible when the top of the master cylinder removed the 60 percent was in bits blocking the lines! Working good now. Got 200 km on bike since refit. Hope this helps someone.

    

14Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Thu Jun 22, 2023 8:35 pm

MartinW

MartinW
Life time member
Life time member
I normally vacuum bleed my brakes with a home made setup. However I saw a one way valve brake bleeder online for around $3.50 Au and purchased three. One has gone to a mate and the other in stock. I pumped all the fluid out of the calipers using it and then removed both calipers and cleaned and painted them. After refitting them fitted the one way valve cracked the bleeder and bled them by just pumping the lever. The process was easy and quick and I had no problems with air pockets at all. I was impressed with how easily it worked, easier and quicker than the vacuum bleeder. During the cleaning process the sealant around the bleed nipples was replaced with PTFE pipe sealant. The plastic hose supplied to go over the bleed nipple was too small so a plastic hose was slid over a short piece of it to upsize it. I had previously looked at speed bleeders which are expensive in OZ $ 50.00 Au a pair plus freight and hard to get.
Regards Martin.
Front brake woes, help please Brake_12
Ignore the valve core tools.
Front brake woes, help please Brake_14


__________________________________________________
1992 K75s
    

15Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Thu Jun 22, 2023 10:34 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Martin!  That is some nasty looking DOT4 in that bottle!!!  Hope that wasn't your bike.

I just open up the bleeder, put a long piece of tubing on it going to a milk jug half filled with water to keep it from falling over.  Push the tubing into the handle so it won't come out and dump brake fluid all over the place.

With the clear tubing I can see the fluid flow in the tube and adjust the lever return speed to minimize the back flow.  Then I just work the lever until I pump through an appropriate amount of fluid.  Easy peasy and CHEAP!


__________________________________________________
Present: 1991 K100RS "Moby Brick Too"
 
Past:
1994 K75RT "Ilsa, She Wolf of the SS"
1988 K100RS SE "Special Ed"
1994 K75S "Cheetos"
1992 K100RS "Moby Brick" R.I.P.
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

16Back to top Go down   Front brake woes, help please Empty Re: Front brake woes, help please Thu Jun 22, 2023 10:43 pm

MartinW

MartinW
Life time member
Life time member
Thankfully not my fluid I change mine regularly. I was also starting from scratch with no fluid in the system. The valve allowed me to pump as fast as I liked.
Regards Martin.


__________________________________________________
1992 K75s
    

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