#*$*+#* rear brake master cylinder

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LD Hack

Member
Joined
Dec 13, 2009
Messages
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0
Location
Grand Marais, MN
I've been battling rear brakes on my GL1100-sidecar rig for a long time. Problem I'm having is bleeding the rear brakes. I have two brake lines coming off the master cylinder on a dual banjo bolt, one line for the rear brakes, and one line for the sidecar brakes. It's been that way for years and worked fine. Spongy brakes, I discovered a bad line on the sidecar. I now have steel braded lines throughout the machine. Brand new on the sidecar in two locations, and another braded line on the motorcycle from 2 years ago. No sign of leakage at any of the joints.

Putting things together, I also rebuilt the master cylinder. It would not hold the circlip, so I found a used master cylinder with 11,000 miles on it, very new looking. I replaced the rubber parts and used the old plunger, since it has a "screw" on the shaft of the plunger that's between the two rubber valves inside the master cylinder brake cylinder. Not able to bleed the brakes to solid, I went with the kit plunger, which has the star shaped plate covering three bleed holes. This star shaped plate pushes against the rubber valve that's on the end of the spring. The original "screw" style plunger has no holes or star shaped plate covering the holes.

I tried bleeding brakes using the brake pedal method with speed bleeder on the motorcycle and regular bleeder on the sidecar brakes. I got some pedal out of it, but not adequate.

Eventually I tried using a vacuum pump, which under higher vacuum started pulling air at the bleeder. My guess is the air is coming in through the outer rubber valve on the brake master cylinder. What I'm referring to are the two rubber valves inside the master cylinder. One is on a spring, and the other is on the plunger. I'm referring to the one on the plunger. I don't think air is coming through the banjo fittings at the master cylinder, although that's another potential source. I replaced the banjo bolt washers, although the bottom one against the master cylinder is steel, because I couldn't purchase a copper one locally. I can't see any abrasions or signs of damage to the brake lines anywhere. No sign of fluid leakage on any lines or at no joints.

My next bleed attempt is to pressurize the brake reservoir and bleed the brakes using the pedal and the pressurized reservoir. I just set that up and haven't gone though the bleeding process.

What am I missing? How come this is so difficult?

Is there a small bleed hole in the master cylinder that needs to be cleaned with a small wire? I know of this requirement for the front master cylinder. I've looked for a hole, and I can find only one. It's the one behind the reservoir hose barb, and it's pretty good sized. There are the three holes in the plunger, behind the star piece on the end of the plunger. Those are the holes, I assume, that relieve fluid pressure and prevent the brakes from locking up when the fluid gets hot. Am I right?

The summary of my problem; I believe when I'm bleeding the brakes, that on the down stroke of the brake pedal, I get fluid to move in the brake line. My guess is that on releasing the pedal, instead of the brake system filling with only fluid from the reservoir, that it is also sucking air. I'm guessing it's the rubber valve that's on the plunger of the master cylinder. How to overcome that???

If you're with me still, congratulations. This is still a tough one to figure out. I wish I had a mechanic who is good so I can hire him to fix this for me. Unfortunately, it appears I'm on my own.
 
Rear Brakes? What is that? I dont have one on my bike :? me needs to fixxit

Wish i could help with your problem.... Welcome to the site by the way :salute:
 
dan filipi":33afjcec said:
Do you have the linked brakes LD?
No, the rear master cylinder operates the rear brake, plus the sidecar brake. The two front calipers are both operated by the handlebar brake laver.
 
Are you bleeding from the hack first and then the Rear?? Most cars say start with furtherest and work up.. You could remove the hack line and run a single line to isolate this as a master cylinder or caliper issue.. if either brake pumps up and gives you the feel you want then in the process you may have eliminated air... also on the hack is the bleeder pointing straight up?? sometimes with a slight lean in the mounting of the brake cylinder the shape of the caliper holds a minute pocket of air... removing one bolt and titling it till bleeder is up will allow excessive air to be purged.. (works for the fronts also) just some thoughts to help find the snake..
 
I am with Joe on this one. Disconnect the cailper from the bolts and tilt it up so that the bleeder screw is straight up (but be sure the caliper is still on the pads). Since you replaced the brake lines, there is a very good chance that there is air stuck in the top of the caliper. (Very common on these bikes and it is my personal experience with mine also!)
 
One of the problems I don't know how to address; the brake line from the master cylinder to the hack has a loop in it. As the braded line leaves the master cylinder, it loops back over the pivot of the rear swing arm, forward behind the battery case, then to the right and DOWN to the frame of the hack. It's one line from the master cylinder to mid way down to the fame of the hack, and then there is a steel line the rest of the way down and across the frame of the hack. The connection of these two lines is in the "down" direction, about half way from the high point of the flex line to the low spot on the hack frame. Getting all the air out of that down run is a challenge.

This one is surely a bugger. I had it working decent with the old master cylinder, but that one would no longer hold a snap ring. The snap ring came off four different times before I got the replacement master cylinder. This is a case of fix one thing (bad brake line on the hack) and it results in having to fax a second thing (master cylinder).
 
It sounds to me like the whole problem is getting the air out, I dont think air will get sucked back in at the MC.

Air will go up so that loop might be the entire problem.
Can you get the car up in the air and pressure bleed that line?
 
Car???
:smilie_happy:
It's still early, eh Dan? :smilie_happy:
It's sometimes hard to get all the air out of a system. Pressure bleeding is best, but not convenient for all. I have found that using a vacuum bleeder(like a MityVac) is good for only one thing...sucking air in past the seals on the calipers/wheel cylinders. :sensored: They're ok just to get some fluid flow to the calipers, but that's about all.
There are also some cool "injection" bleeders that will inject brake fluid in from the caliper end, there-by pushing all of the air up and out thru the master... ;)
 
Yes, Car meaning the sidecar.
They're called many things. Chair, hack, monkey seat.......... I bet LD could add quite a few others.

Sidecarsusie is a good friend of mine, she was a member before.
She was born in a sidecar.
She told me she bled the sidecar and front brake successfully herself.
I'll have her get on here, maybe she can add something we havent thought of like,,,,,you know, the girl thing. They have some good ideas somethimes :roll:
 
I am making use of a oldwing expert, a riding buddy, from FL (I'm in MN). He helped me figure out where the small relief oriface is located in the master cylinder. It's cleaned. Thank goodness for cell phones.

I'm still having problems with air/bleeding. Although there isn't any obvious leakage in the brake lines or calipers, I'm going to isolate the two brake systems and see if one or the other looses pressure. I located a single banjo bolt, which will help with this diagnosis - not the easiest thing to find in a northern, small town. I am able to get pressure using the pressure bleeding method, pumping fluid in to the reservoir line and through the master cylinder and out the caliper bleeder. The pressure doesn't hold for long though. I'll update any armchair mechanics, as I figure out more.

Thanks for the input and off handed comments. Pertaining to the off handed comments, the third wheel (on the right in my case) can be called chair, tub, sidecar, car, hack, and probably a couple other terms I don't have on the top of my head. The rider in the sidecar is more often than not called the monkey, unless it's your wife, and then you better use "passenger". I think women sidecar pilots, namely a female sitting on the motorcycle and driving, can call any sidecar passenger a monkey. Definitely, if it's her husband....

And later on... I do have success, of sorts. I have brakes on the mule, and I disconnected the brakes on the sidehack. They bled out fine on the rear of the mule, so I have some sort of problem with the lines or caliper on the sidehack. I have a little pull to the left when I brake now, but I'll declare my partial success to be complete success (that seems to be the correct political thing to do these days). Spring, when it warms up, I'll tackle the sidehack brakes. Thanks for the input and snide comments.
 
Any of us that have run this era of Honda no matter what model it is, has many ways of getting around this problem of bleeding honda brakes....hmm, that came out wrong, the bleeding of Honda brakes. One of mine is using a syringe body to "inject" clean airless fluid in, I also have one of those kits where you can fill from the bleed nipples back, used with varying success. Having said any of this I have found that seemingly very similar bikes can be very different to bleed.....

btw....it's pretty much a sidecar in the UK, never really heard of them as much else although they used to be common you hardly ever see one now except around vintage events, the trike has taken over as a vehicle to carry extra passengers, and you don't need a Motorcycle License to ride one....
 
Hi I have 83 goldwing aspencade I bought with the spongey rear brakes, and couldn't get it to work right for the life of me. But with the help of a friend we found that the guy who had it before me had cross threaded the hole the brake line went in to and had it tightened in really hard but still leaked slow .. When we found that we had to retap the hole carefully to clean the threads we then wrapped the male thread part with thread wrap in put it back together.. Well it worked for us .. It's just a thought check it out.. :music:
 
blkhot08":10yvm660 said:
... but still leaked slow ...
Thanks for the comment. I'm thinking along the same lines. How did you find your leak? A small leak is not easy to find.

Since I have the problem isolated to the sidecar, my current plan is to seal off the banjo fitting with a bolt and copper washers, then pressurize the system with air through the brake bleeder on the sidecar caliper. I'm not sure how easy pressurizing the system will be to accomplish though. I hope I'll be able to find a leak somewhere in the system.

This all started when I replaced the rubber sidecar lines with braded lines, because of spongy brakes. It could be that my spongy brakes were due to seveal factors, or who knows right now, until I do some more diagnosis. It's cold in the garage right now...
 
I dont see that you've tried this so I'll mention it.

When I bleed brakes I put a rubber hose on the bleeder and the other end in a clear jelly jar sized container with brake fluid.
Keep the end immersed in fluid, break the bleeder loose, now pump the brakes repeatedly til no more bubbles come out then tighten the bleeder and move on to more funner things like riding.
 
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