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Topic-icon Master Cylinder question

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3 weeks 3 days ago #3597 by dcb_wvu
dcb_wvu created the topic: Master Cylinder question
So, I traded my 99 F650 for an 88 R100RT. So far seems like a good deal. I am having a brake issue. The pads are "hanging up" on the disc, well, at least slightly. It seems to get worse over time until I have to stop and give it a little bleed. I have replaced all of the "hard" lines and have ordered the soft hoses as well. The cylinder in the master cylinder is new too. I did take it apart to see how it worked and noticed that there are two holes in the outlet port. The one towards the lever is wide open, the other seems to be partially drilled but not fully open. This one is toward the brake lines and the exit of the master cylinder. I have the Clymer manual and cannot tell if both are supposed to be open.

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3 weeks 1 day ago - 3 weeks 1 day ago #3603 by Wobbly
Wobbly replied the topic: Master Cylinder question
The most likely reason is that one or more of your flexible brake hoses are collapsing internally. This is a very common problem on OEM brake hoses across all bike brands. It usually happens to the hoses that flex the most during riding, however it can occur on any of them.

This is an excellent reason and time to convert to "stainless steel" brake hoses. They have a PTFE ("teflon") inner hose that isn't attacked by the brake fluid and they also have a stainless steel braid to support the high pressures exerted during stopping. Because they don't expand with pressure during braking, using these type hoses will increase your braking efficiency a tremendous amount. It's no exaggeration to say it will feel like you have double the braking power.

Because they cost about the same as the OEM hoses, IMHO buying the OEM hoses is really throwing your money away.

Hope this helps.

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2 weeks 1 day ago #3619 by dcb_wvu
dcb_wvu replied the topic: Master Cylinder question
An update. So the front hole was plugged and not open to the piston below. I opened it up. This allowed the brakes to "release" but still spongy. Replaced all the hard lines and hoses. Brakes started to work at about half pull on the lever but would just about go to grip. Found that the right caliper was leaking in between the halves. Rebuilt it with the kit. I will say it was difficult to get a seal, you need to tighten this like a head to the block. It took four tries to get it to seal. Now I have brakes at about 1/3 and full lock at 1/2 pull. I can probably only pull the lever back to 3/4. My guess is that I still have a little more air in there and will work to get it out in coming days. I did reroute the over tire brake line outside the fender, the under the fender just made me nervous.

This weekend is a shock rebuild with progressive springs, new fork seals and new bellows for the fairing. Then I shall be tearing up the roads of north Florida! My reason for the springs is that I feel the bike dive about 2 inches under braking and even some movement with the wind against the fairing. The fork seals are leaking so I thought I would do a full update whilst it was apart. Some peace of mind with new innards going in!

Courtney
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2 weeks 1 hour ago #3622 by Wobbly
Wobbly replied the topic: Master Cylinder question

dcb_wvu wrote: An update. So the front hole was plugged and not open to the piston below. I opened it up. This allowed the brakes to "release" but still spongy. Replaced all the hard lines and hoses. Brakes started to work at about half pull on the lever but would just about go to grip. Found that the right caliper was leaking in between the halves. Rebuilt it with the kit. I will say it was difficult to get a seal, you need to tighten this like a head to the block. It took four tries to get it to seal. Now I have brakes at about 1/3 and full lock at 1/2 pull. I can probably only pull the lever back to 3/4. My guess is that I still have a little more air in there and will work to get it out in coming days. I did reroute the over tire brake line outside the fender, the under the fender just made me nervous.


• Sounds as if you still have lots of air in the system. The natural place for air to accumulate is at the top of the U-tube connecting the 2 calipers. I find pushing fluid up from the caliper to be a better plan of attack than traditional m/c-to-caliper "bleeding". Bleeding simply doesn't move enough volume of fluid fast enough to chase out tiny air bubbles in that area. If you installed aftermarket "stainless" brake hoses, then the lever should be rock hard.

• Damage to the U-tube under the fender is simply an unfounded fear. The bike is 30 years old. If it hasn't sprung a leak so far, then what's it going to do now ?

• Several of the "stainless" flexible hose makers simply convert that layout over to dual, independent lines going back to the m/c. There's a lot to say for that design as it removes places for air bubbles to collect and hide. For the average rider it's a better design becasue the m/c then becomes the highest place in the system. In other words, no place for air entrapment. In that way the system becomes self-bleeding, and thus self-maintaining.

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5 days 22 hours ago #3653 by dcb_wvu
dcb_wvu replied the topic: Master Cylinder question
Got most of the air out, still gonna try one more bleeding but this time, with the front wheel out and kinda holding the calipers sideways. I am confident that the remaining air is in the "over the wheel" part of the line. Just have not decided which way to turn them to either go out the top or out the bleeder, we shall what space allows! I will upgrade to the stainless lines but want to collect all the part prior to doing that.

thanks all the advice. It is really helpful and gives me a different way to thinking about these things. The Clymer manual tends to over simplify some of these issues.

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5 days 18 hours ago #3654 by Wobbly
Wobbly replied the topic: Master Cylinder question
I went an bought a new pump oil can and filled it with brake fluid. Then a 2" section of battery hose was used to connect the can to the bleed nipple. That's how I pumped fluid up to the m/c. That will chase the air out.

You want the bars turned so that air can rise from the hose into the m/c reservoir. The hose needs to be lower so that air can naturally make its way out as it floats up.

Sometimes if you'll simply pump the brake lever slowly and methodically you'll see very tiny air bubbles rise in the m/c reservoir. Do this while tapping on the banjo fittings with a screwdriver handle.

Don't hide 'em, Ride 'em !!
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