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Old 04-10-2012, 08:39 AM   #106
Fritzie
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Master Cylinder Rebuild

Greetings,
I'm new here and facing the dreaded master cylinder rebuild myself. I am looking for the o ring between the reservoir as well. Any help would be appreciated. My bike is a 9/1975 (year model 1976) Daytona Orange r90s w/41k on the clock. I've had it since 1980 and the brakes just failed. Ordered the rebuild kit from A&S since the main seal was leaking, not the reservoir seal, but I had to take it all apart and am suspect reusing the old o ring. Thanks in advance.



Quote:
Originally Posted by _cy_ View Post
thanks my R90S has really come together. starting to feel road worthy.
looks like yours is on the way...



got my kit from Bobs BMW, which was suppose to be as supplied from BMW. NO seal under reservoir provided. not available (except with new BMC $375) according to feedback from several folks way more experienced than me. ended matching seal up with brake fluid resistant rubber at a local industrial seal company.

where did you order your BMC kit from that included the reservoir seal?



I've got the Fox too... sure make things easier if mine was adjustable
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Old 04-11-2012, 10:02 AM   #107
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Quote:
Originally Posted by Fritzie View Post
I am looking for the o ring between the reservoir as well.
Is the o-ring damaged? Was there a leak at the reservoir? If no leaking or no damage to the o-ring... re-use the o-ring. Need more info.
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Old 04-11-2012, 10:06 AM   #108
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If you need a new o-ring, check with http://www.mcmaster.com/#o-rings/=h27lun .
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Old 04-12-2012, 10:43 AM   #109
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Originally Posted by craydds View Post
Is the o-ring damaged? Was there a leak at the reservoir? If no leaking or no damage to the o-ring... re-use the o-ring. Need more info.
Yes the o ring is toast. When I tried to remove it with a toothpick it cracked in 4 pieces. It did not seem to be leaking before the removal, but now needs to be replaced. The MC is 17mm, anybody know the correct size to spec a replacement ? Also, is the current consensus to replace brake lines when a rebuild job is done ? If so, when the new lines are made up, what about the in line rubber grommett ? I don't think it will fit over the end fittings. Does it come installed on the new lines?
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Old 04-12-2012, 11:30 AM   #110
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Originally Posted by Fritzie View Post
anybody know the correct size to spec a replacement ?
Also, is the current consensus to replace brake lines when a rebuild job is done ?
If so, when the new lines are made up, what about the in line rubber grommett ? I don't think it will fit over the end fittings. Does it come installed on the new lines?


1) I don't know the size. I'll measure mine but probably won't get at it until Saturday. Hopefully another inmate will know the size or carry the correct replacement o-ring.
2) Some have said to keep the stock brakes lines, that they last forever. Unless they are damaged, you can keep them. Oak recommends using only the stock BMW brake lines. However, several inmates make and sell brake hoses. I made my own. (pictures to come, soon)
3) Grommet does not come with new lines. It is a separate item. The small end of the brake hose will slip through the grommet.
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Old 04-12-2012, 11:37 AM   #111
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I wonder what Oak says now that some BMW's come stock with steel braided teflon lines? I know from first hand experience many times over that the stock rubber lines do not last forever. Steel braided teflon lines last a long time! Way longer than rubber and they work ten times better in between.

The rubber grommets will stretch over. #3 braided has a smaller OD than the stock rubber lines. I have been using the same stock grommets for decades with no problems. I went to steel braided lines in '88 I believe it was. I would never have rubber lines on my own bike.
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Old 04-12-2012, 12:11 PM   #112
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Originally Posted by supershaft View Post
I wonder what Oak says now that some BMW's come stock with steel braided teflon lines? I know from first hand experience many times over that the stock rubber lines do not last forever. Steel braided teflon lines last a long time! Way longer than rubber and they work ten times better in between.
+1 on the braided/teflon hoses. I think they are better - my opinion - I've used them for them for over 30 years. Plus, one can make their own (I did) or purchase a pair for slightly more cost than the price of one stock hose. Ask the inmates who make 'em.
I just read an article by Oak about the brake hoses, but I think he was referring only to the older models that came with rubber hoses. He recommended using only the stock hose... curious. Don't think he mentioned the new bikes at all.
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Old 04-12-2012, 02:07 PM   #113
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Question

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Originally Posted by craydds View Post
+1 on the braided/teflon hoses. I think they are better - my opinion - I've used them for them for over 30 years. Plus, one can make their own (I did) or purchase a pair for slightly more cost than the price of one stock hose. Ask the inmates who make 'em.
I just read an article by Oak about the brake hoses, but I think he was referring only to the older models that came with rubber hoses. He recommended using only the stock hose... curious. Don't think he mentioned the new bikes at all.
Just got back from the Beemer shop here in NorCal. The recent rebuild kit for the 17mm Master Cylinder (#34311234927) comes with the o ring. Nice. Now I'm not sure how the MC piston stack goes back together. Any pictures out there? The wrench at the shop got one caliper piston out with air, the other is frozen. I need to put the system back together and pump that frozen piston out. Arrg. Two OEM rebuild kits for the calipers on order. This is getting spendy, but it is good to be able to stop.
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Old 04-12-2012, 02:41 PM   #114
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Originally Posted by Fritzie View Post
Now I'm not sure how the MC piston stack goes back together. Any pictures out there?
Look at post #42, see if that picture helps you.
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Old 04-12-2012, 03:54 PM   #115
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Quote:
Originally Posted by craydds View Post
+1 on the braided/teflon hoses. I think they are better - my opinion - I've used them for them for over 30 years. Plus, one can make their own (I did) or purchase a pair for slightly more cost than the price of one stock hose. Ask the inmates who make 'em.
I just read an article by Oak about the brake hoses, but I think he was referring only to the older models that came with rubber hoses. He recommended using only the stock hose... curious. Don't think he mentioned the new bikes at all.
Oak is a great guy. I have met him personally a number of times but man he can get hard headed stuck on the wrong side of many a subject. Why would you only recommend the stock hoses? They are junk compared to some alternatives.
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Old 04-12-2012, 10:43 PM   #116
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Quote:
Originally Posted by Fritzie View Post
Just got back from the Beemer shop here in NorCal. The recent rebuild kit for the 17mm Master Cylinder (#34311234927) comes with the o ring. Nice. Now I'm not sure how the MC piston stack goes back together. Any pictures out there? The wrench at the shop got one caliper piston out with air, the other is frozen. I need to put the system back together and pump that frozen piston out. Arrg. Two OEM rebuild kits for the calipers on order. This is getting spendy, but it is good to be able to stop.
nice... good news new BMC kit now comes with Oring.

I had to match up correct oring at a local O ring supply house. finding correct size is no big deal... getting correct rubber compound that will withstand brake fluid is critical.

all the information with part numbers is in my bringing R90S back to life thread if oring doesn't work
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Old 04-13-2012, 08:42 AM   #117
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Quote:
Originally Posted by Fritzie View Post
Just got back from the Beemer shop here in NorCal. The recent rebuild kit for the 17mm Master Cylinder (#34311234927) comes with the o ring. Nice. Now I'm not sure how the MC piston stack goes back together. Any pictures out there? The wrench at the shop got one caliper piston out with air, the other is frozen. I need to put the system back together and pump that frozen piston out. Arrg. Two OEM rebuild kits for the calipers on order. This is getting spendy, but it is good to be able to stop.
Put together the rebuild MC and hooked the pipe directly to it to pump out the stuck piston. Used bleeder screws to plug extra hole on MC and caliper. NO go. The MC won't pressurize. It pumps, but doesn't pressurize. No noticeable leaks, although I am concerned that the stoplight switch uses a crush-able washer, and I am reusing that. Is it common for the MC to not pressureize after a rebuild ? The bore was clean, and only very slightly rough in the middle under the intake hole.
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Old 04-13-2012, 09:57 AM   #118
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Originally Posted by Fritzie View Post
Is it common for the MC to not pressureize after a rebuild ?
You have to bleed the air out of the entire system in order to generate hydraulic pressure. Elevate the caliper above the master cylinder, open the bleeder screw on the caliper, squeeze the hand brake lever, close bleeder screw, release brake lever. Keep master cylinder full of fluid. Repeat, again, and again. It's nice to have a helper, but you can do it alone. Bleed 'em.
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Old 04-14-2012, 08:12 AM   #119
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Fritzie, any luck getting that piston out? Let me know. There are several ways to remove a stuck piston. Here are some suggestions:
1. Remove the caliper; remove the external dust seal.
2. Soak the caliper in diesel.
3. Use a hammer and a drift; knock the piston inward. This may break the rust "bond".
4. Heat the piston with a torch.
5. Try the grease gun method as supershaft, et. al, have described.
6. Use curse words as needed.
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craydds screwed with this post 04-14-2012 at 08:58 AM
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Old 04-14-2012, 01:39 PM   #120
Fritzie
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Piston Still Stuck

I'm working on the grease gun method. Do you guys braze a zerk onto a bleeder screw ?
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