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post #1 of 11 (permalink) Old Jul 10th, 2012, 4:29 pm Thread Starter
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Exclamation Check your Brakes and Ride Safe

I suppose with an older '97 K1200 RS ABS II it was inevitable that one day I would be into the brake master cylinder, but I did not expect to find a problem this way. For a couple of years I have had this feeling that the front brake pull on the first pull is further back than it is on a second pull immediately after. I kinda got used to using two pulls to brake, instead of one and never had a problem stopping the bike.

I have just replaced the oem lever micro switches with brake line pressure switches and added a 'brake on' led in a spare location in the instrument warning lamp array. The brake switches I used come on at a higher pressure than I would like, but here is the scenario:

I am slowing gently using only the front lever and there is sufficient fluid pressure to put on my warning lamp and rear brake light. Over a few hundred yards I expected it to stay on, but it went out! I repeated the same slow down, this time pulling on more lever pressure and I could swear the lever was moving slowly towards the throttle grip - difficult to say when riding.

I have just been through the entire braking system and I know calipers/pads and unions are all OK. I get back home and check everywhere for a fluid leak and there is none. The master cylinder reservoirs are as full as when I topped them off the previous day. So, brain in gear the master cylinder must be losing pressure.

I put the bike on the stand and give a gentle pull on the front brake lever just putting on the brake light (nice to have the led now in the cockpit). I held the lever for 30-40 seconds in the same position, the light stayed on and the lever did not move. Then I put a lot more hand pressure on the lever pulling it back to about 30mm from the throttle grip. Sh*t, over 30 seconds the lever was slowly moving back till it hit the throttle grip and my brake warning led went off!

I got a fair deal on a used MC off a newer bike today and that gave me chance to look further before buying a MC repair kit to repair my original MC.

I tore down the suspect MC, pulling out the piston with its seals and return spring (see photos). The MC bore looked fairly clean apart from a couple of spots where the alochrome has taken some wear. The secondary seal at the back looked in poor condition, but that does not do all the pressure work. Even so, it could be responsible for pulling in air at the back and causing my lever to always seem soft, however much I bled the system.

The front primary seal does all the pressure work. I had a look at the seal edges under a 30X microscope and there were uneven 'flats' around the edge. That would explain the slow leak back of fluid back to the MC reservoir. I have been riding this bike nearly 2 years with annual DOT tests and never had a problem stopping. But If I had to do a long stop from high speed, I would have had the lever hit the throttle grip as the system leaked out pressure.

I can only advize you to check your front and rear master cylinders can hold pressure for at least 40 seconds or more. If either the pedal or lever changes position, or the 'feel tension' appears to change, then check your master cylinder seals. Do not assume you just need to bleed your brakes!

I don't have servo brakes, but somehow you need to hold in the brake lever or rear brake pedal and feel if the pressure is sagging over 40 seconds or longer. Perhaps you can disconnect the servo to make the check more sensitive.



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post #2 of 11 (permalink) Old Jul 10th, 2012, 10:10 pm
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Thanks Vox, I won't feel so alone when I mention doing that to just about any vehicle. Funny the pedal going down all the way as you sit in a junker someone is trying to sell you. Or my own junker, beats finding out on the road when the line breaks or MC packs it in.

I have a BMW MC here that was showing signs of corrosion under the boot at the circlip, not the first I see like that but luckily that one isn't damaged in the bore yet, like the others I have seen.

Moisture getting in there pass the boot and causing that???


So rebuilt??? My Miller's Red Grease got lost between the UK and here. The replacement showed up today so now I can weatherproof them boots properly.20+ years worth of grease for $20.00, good deal....!

I go a bit farther than the 40 seconds, I pump the brakes with the servo then tie up the lever overnight with a zapstrap. Next day I check if pressure left at the lever and also all the hoses and connectors for seeps.Yes did find one seep after my Speiglers install, very small and may have taken days to show anything from under the fairing.

Benelli 50cc at 14
Yamaha RD 200 at 16
Yamaha RD 350 at 17
Honda CB 750 F at 18
Honda V45 Sabre at 24
BMW K100RS at 27
BMW R100GS at 34
BMW K1200RS at 53

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post #3 of 11 (permalink) Old Jul 11th, 2012, 3:08 am Thread Starter
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Yes I have been using my big tin of red grease.

I can just see the beginnings of corrosion near the circlip around the edge of the MC, but not serious.

I think that secondary seal can get dirt behind it and is the first to fail. But you do not notice anything because the front seal is doing most of the work. I think the corrosion comes from some fluid getting past that seal, then air and brake fluid becomes very corrosive to aluminium.

PS: Have you ever wondered how the seals get on the piston rod? I messed around with the old one. The assembly seemed to be all one piece. The front primary seal could be slipped off towards the front, but the rear secondary seal would have to stretch an awful lot (?)



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post #4 of 11 (permalink) Old Jul 11th, 2012, 11:37 pm
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Yes a little hard to figure out what really attacks them seals/bores. Fluid seeping out certainly would attract moisture, even worse if it is "Sea Air" will bring salts in.

In/Out could be both ways. Most of it preventable with the proper maintenance and lots of "Red Lube" I'll guess. I'll just fill them boots right up and even some down the bore passed them cheap plated circlips. On that I just figured out why BMW plating seems to degrade more than in the old days, they took some of the better chemicals/heavy metals out of the plating process because of environmental concerns. If I read that right may even be a law in Germany over the plating/chemical process and what they can use.

Altough I did a quickie job of preventing corrosion on both my MCs, doing it properly has been bugging me for a little while now, got worse after I inspected the MC of the old GS and found that external corrosion. Not cheap them BMW brake parts....

We looked into finding them seals in a weird size, not BMW, If I recall they are "Radial Seals" and could be available but you'd have to figure out the profile/I.D., and for that they'd have to come out. Putting them back in that's another story. Yep always wondered how they do that, but car MCs are similar so maybe someone has the answer on the cage side.

I'll ask my friend, former chopper mechanic and now motorcycle restorer when I part with some of my Red Lube for his projects, he may know how they get them seals on.I doubt it is DIY so we are stuck buying them overpriced "repair kits" at best or at worst, new MCs.

I think lots of grease and frequent fluid flushes will be cheaper/safer in the long run.

BTW that grease used to be called "Rubber Grease" in North America, now next to impossible to find but very good to treat all the rubber bits/hoses and prevent them from cracking or degrading. I have never replaced much BMW rubber,if any since 1985.

Someone on FleaBay is/was selling it by the spoonfull.....

Benelli 50cc at 14
Yamaha RD 200 at 16
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Honda CB 750 F at 18
Honda V45 Sabre at 24
BMW K100RS at 27
BMW R100GS at 34
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post #5 of 11 (permalink) Old Jul 12th, 2012, 4:12 am Thread Starter
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I had that piston in the vise to destroy and work out how the seals came off. I twisted every part and nothing came apart.

The rear part looked like it could have been press fitted. I attacked it with an angle grinder and it seems to be turned in one piece. The rear seal would have to stretch to over 4 times its diameter, which seems far too much to me.Got a new assembly on order, but I would like to know how they put the seals on.

Everything that has gone to being eco friendly has got wors, although it seems to me you can still get the 'bad things' made in China! I wonder if you can get a stainless version of that circlip? Filling up the pushrod boot with red grease seems a good start.



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post #6 of 11 (permalink) Old Jul 12th, 2012, 10:08 am
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SS circlips.....nice unseen farkle. Maybe the marine stores??? I'll ask the Chief if I can look in the catalogues, I'd have them at home but we are out in the salt air now and hard to connect to them big marine hardware websites.

I think BMW recommends replacing that circlip anyway when doing a rebuilt???? That is either in the manual or maybe Max's parts fiche. Way too sacrificial them new friendly platings even if it may look in good shape. Yep, if it does corrode that would be introducing little bits of a dissimilar metal in the brake assembly, add a little briny moisture to that and....ooops, trouble later.

You are in there Vox, how easy is it to access/remove the boot after the lever is removed to inspect and lube. It has been a couple years since I was there and only sprayed stuff that way, did not try removing the boot. Easy enough on the older BMWs leaving the MC in place, but not sure about ours???

Benelli 50cc at 14
Yamaha RD 200 at 16
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Honda CB 750 F at 18
Honda V45 Sabre at 24
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post #7 of 11 (permalink) Old Jul 12th, 2012, 3:37 pm Thread Starter
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Easy peasy on the MC push rod boot:

It can just flop out when you pull off the lever. There is a groove in the MC ali body just above the circlip. Pull it out and to put it back, just carefully use a small electrical screwdriver to work the boot lip edge back into the groove. The center should be collapsed inwards so it looks kinda concertina shaped.

Nobody has told me yet how to fit some new MC seals if my aftermarket seal seller can source them! I am fine with replacing my own (cheaper) MC seals every 5 or 10 years, but not at the stealer price of £45. The piston rod does not wear.

The clutch side will be identical but a mirror of the MC reservoir. That has got to be next on my to do list.



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post #8 of 11 (permalink) Old Jul 12th, 2012, 8:48 pm
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Thanks Vox, that's what I tought, them MCs haven't changed much in years looks like,

Had to rebuild the one on the K100RS, maybe the piston wasn't too expensive way back then.Most of the parts weren't....way back then! I remember having to polish the bore a little. We used to do that on cars but we had hones for that, I still do but way too big for a motorcycle MC.

However the bore can be resleeved,Stainless and I think maybe even bronze. That's common for restorers to get that done as lots of the old stuff is NLA.

What I did back then for the K100RS was to use a "gun mop" of the right size and lubed it with extra fine valve lapping compound then spun it with the drill. Worked but I'd rather not recommend that and stick with BMW/Clymer on that .....do not hone. What I do in the privacy of my own shop well......!

Benelli 50cc at 14
Yamaha RD 200 at 16
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Honda CB 750 F at 18
Honda V45 Sabre at 24
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post #9 of 11 (permalink) Old Jul 13th, 2012, 5:21 am Thread Starter
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What I do in the privacy of my own shop well
My thoughts because too many look for quick answers off the web without thinking through the consequences. I am about to tear down a spare VAG ABS car pump so I can learn what is inside before I try and fix a brake pressure sensor fault on the one in my car. When you do that type of thing, you have to be aware of what test equipment the oem probably has before they put their 'ok tested' label on.

Those bores have some kind of BMW plating on them which looks like the 'alochrome' we used to get done. That kind of plating is really just a chemical etch type process and not really plating at all. I found a formula for it and have the chemicals in the workshop. It probably helps agains corrosion, but does more in telling you where the wear areas are.

A polished stainless steel liner sounds like the way to go. But you would have to ensure a press tight fit and high pressure bonding to the MC casing. Run me up a couple next time you are on the lathe!



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post #10 of 11 (permalink) Old Jul 13th, 2012, 10:00 am
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Quote:
Originally Posted by voxmagna
My thoughts because too many look for quick answers off the web without thinking through the consequences. I am about to tear down a spare VAG ABS car pump so I can learn what is inside before I try and fix a brake pressure sensor fault on the one in my car. When you do that type of thing, you have to be aware of what test equipment the oem probably has before they put their 'ok tested' label on.

Those bores have some kind of BMW plating on them which looks like the 'alochrome' we used to get done. That kind of plating is really just a chemical etch type process and not really plating at all. I found a formula for it and have the chemicals in the workshop. It probably helps agains corrosion, but does more in telling you where the wear areas are.

A polished stainless steel liner sounds like the way to go. But you would have to ensure a press tight fit and high pressure bonding to the MC casing. Run me up a couple next time you are on the lathe!
I wonder if you couldn't buy them sleeves.I don't run the lathe, Chief or Senior engineer will do that for me and I already have a couple wheel bushings for them to do. Can't do that from here but if you google motorcycle MC repairs you may get some hits, there are at least 2 outfits in the US doing that.

But that would involve boring the MC and then pressing sleeves in, best left to the experts.

Alochrome ???? The old ones were just plain Alu, no plating. An improvement...!

Benelli 50cc at 14
Yamaha RD 200 at 16
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Honda CB 750 F at 18
Honda V45 Sabre at 24
BMW K100RS at 27
BMW R100GS at 34
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