Installed new master, now brakes aren't very good? - UPDATE

Maritime

Maritime

Over 10,000 Posts
OK, on my ride to and from Mid Ohio this year my 30+ year old Front brake master shit the bed and started leaking fluid. I made it home with the brakes still working but ordered a new aftermarket for the bike as the rebuild kits were 2-3 times as expensive. It arrived the other day so I got it swapped out last night:

Removed old, swapped in new, added fluid, pumped a couple times untill air stopped coming out the return hole. All seemed good. went for a short ride and the brakes locked up on the front and got hot. Came home blead some fluid out, then the master wouldn't pump at all? So I pulled the line, drained it, drained the line, reattached filled and blead and it seemed to work ok, except it now pulls all the way to the grip and stopping power is reduced to about half. So my question is, did I not get all the air in the line and do I need to just keep pumping the handle and working the air out? or is the aftermarket MC crap and I should have bought a rebuild kit for the oem honda. 79 GL1000 dual setup similar to all the same generation Honda dual disk single piston caliper setups. One hose to a divider at the forks then 2 to the calipers. I have blead this sytem successfully once to change out the old fluid this spring, I may try that again tonight to see if it improves it and gets any trapped air out.

cheers,

Maritime
 
Re: Installed new master, now brakes aren't very good?

It sounds like you are on the right track. It would worry me that the older, larger calipers, especially in a dual set up, would take a lot of fluid volume from the master to move them accordingly. I imagine if you were running only one caliper you would have no issues and perhaps you require a larger diameter master. Can you try to isolate and bleed one caliper and see if it works properly? That may answer your question. I suspect you either need a larger master, rebuild your original, or always a chance you still have air in there somewhere. Good luck with it.
 
Re: Installed new master, now brakes aren't very good?

Thanks, I bought one spec'd the same as OEM bore and piston etc. Actually 2 other members have the same one and liked it. The quality seems decent, not Honda but not crap either. I hope it is air in the main line as I had to pull it and pump the master until fluid came out to get everything working right. and there is a slight loop in the line as the lower bars I have make the line longer than it needs to be. So air may be trapped in the loop. I may pull the master off and set it higher on the bike overnight to get the line strait. I think the first time when the brakes locked I had to much fluid in the system and after a bleed etc, everything seemed to get better except the handle went from only moving a little and locking the brakes to soft and pulling all the way to the grip and only putting 50% of the pressure needed to stop? I will play with it some more tonight and see what I can do.

Maritime
 
Re: Installed new master, now brakes aren't very good?

Getting every last bit of air out of the system can be difficult. Air bubbles tend to rise up the line, but we are trying to pump them straight down to the caliper. Between pumps, the bubbles float back upward. When there is a manifold/splitter to go to two calipers, air sometimes gets trapped there. As you suspect, there may be air trapped in a loop of excess line.

Sometimes the best way to get those last pesky bubble out is to pull a caliper, then give a few pumps to move the piston out a bit. Then put a "C" clamp on it, and press the piston back into the caliper. The reverse flow of fluid will push the air bubbles back to the master cylinder.

Sometimes it's just a little air trapped right at the banjo bolt on the master cylinder. You can crack it loose there and burp out the air. Another even easier trick that sometimes works, is to pull back the brake lever, and tie it back with a bungie cord. Tap the lines to help any bubbles rise. Then release the lever. That will sometimes allow the bubbles to move back into the master cylinder.
 
Re: Installed new master, now brakes aren't very good?

All that is is a catch bottle. It doesn't resolve the floating bubble problem.

I was recently bleeding the brakes on a dual caliper bike, and just couldn't get all the air out. I was using this device, and it still was not moving the brake fluid fast enough to get all the air out.
http://www.harborfreight.com/brake-fluid-bleeder-92924.html

Finally, I had to use the "C" clamp reverse flow method.

Another good method is to pump fluid in from the calipers. An ordinary pump type oil can will do it. Attach a small hose to the oil can and to the open caliper bleeder, and pump the fluid in from the bottom.
 
Re: Installed new master, now brakes aren't very good?

Yes, likely a bubble problem. ADC is spot on, the splitting systems can be hard to bleed completely.


An air bubble also affects the way the calipers release the rotor. With air in the system, they will not release correctly and the resulting drag will heat the rotor and make things grabby and unhappy.


Once you get all the air out, things should behave as they are supposed to.
 
Re: Installed new master, now brakes aren't very good?

Thanks guys, I will try the brake lever tied to the grip first then work the hoses. I think I am close. rode it home at lunch and i am at about 60% of full power. Brakes will stop the bike but not as fast or hard as they should, rears are good though so if i have to stop quick I can still stop faster than a car, but not much. If that doesn't work I will try the c clamp method to get the air out. I am going to rebuild the calipers this winter anyway but I want them to work well enough to get through the next 2 months of riding I have left before the roads ice up. Then I will pull them, rebuild and I think I will order 2 lines and a double banjo bolt to go straight from the MC to each caliper and eliminate the crossover, also go stainless and get a little more improvement.
 
Re: Installed new master, now brakes aren't very good?

OK I got them better but still not 100% and after reading a bunch of conflicting data, the bore may be too small. So I went back to the seller to see what they say. If it is too small I will sell this one off and rebuild the old one as it is the same price, just more work. IF the bore is right I have one more process suggested by NGW fella's I will try and see if it works.
 
Re: Installed new master, now brakes aren't very good?

Well, I tried all the tricks, I don't think there is air in the lines, i think the bore is wrong and the seller listed wrong. I contacted them to find out what they will do or I will leave negative feedback, I bought it because it was listed for a GL1000, GL1100. Then I read a little more and it states 14mm bore which 4-5 other aftermarket sellers list for the GL, so maybe it is right but then I went to Randakks and he says 5/8" is required and that would be 15.5-16mm bore so I think this is my issue. I can pull the lever to the grip before it puts enough pressure to stop the bike. He says the original unit is a 11/16" which is approx 17mm so I am not sure now at all.
 
Re: Installed new master, now brakes aren't very good?

Not to make light of your ordeal but I wish my current issues were as simple. I am trying to figure out why a 900 triple wont rev over 5000 rpms under load. I have to pull the carbs out again and make adjustments then try again and its about a three hour job and a real pain in the butt. I have a 2 page stream on the triumphrat.net site with people that are way smarter than me trying there best to help.
Regarding your brakes, You can get brembo masters w the square bottle fairly cheap on ebay and they are hard workers. I use brembo as often as possible with my bike builds, they are pretty solid parts. Unless you are trying to keep it looking stock.
 
Re: Installed new master, now brakes aren't very good?

Dont care about stock. Just want a working master. Pissed the seller listed it as gl1000 when the specs, now that I double check them, are for a single caliper bike. I am going to return it or sell it and get a suitable possibley brembo dual disk mc. Shitty deal is to ride in the mean time i have to put my leaky original back on.

Sent from my MB525 using Tapatalk 2
 
Re: Installed new master, now brakes aren't very good?

Look on ebay for any 90s up 900 models. Both the ss and the monster came with dual front discs and the masters are readily available. My 79 Bonneville build I am using Brembos from a 1098 and installing a hydraulic clutch as well. Found them both for around 300 but those 90s masters with the square reservoir is much cheaper and bullet proof.
 
Re: Installed new master, now brakes aren't very good?

http://www.ebay.com/itm/Ducati-M750-M900-16mm-Brake-Master-Cylinder-Front-/320874251006?hash=item4ab59882fe&item=320874251006&pt=Motorcycles_Parts_Accessories&vxp=mtr
 
Re: Installed new master, now brakes aren't very good?

Thanks Autotek, the seller is sending a replacement and in a different style, looks just like the oem, if it is shit too I will definatley go the route you suggest. I at least am happy with the seller as it is hit or miss with China, they have a huge positive rating and after checking with a few members here that have the same master they said some of them have shitty pistons and they tend to send better units the next time. That Duc master though is the exact bore suggested by Randakk. If this next replacement is still shit, I will nab that next pay.

Thanks again

Maritime
 
The replacement master came in last night. Bench bled the air out, installed it and now have proper front brakes. Not sure why the first was bad but the replacement, slightly different style works fine. Thanks for all the help.

Cheers,

Maritime
 
HerrDeacon said:
Great to hear Maritime. At least you now have some piece of mind when braking.
Click to expand...

Yep, did like 3 practice panic stops and the disks will lock before I run out of travel on the lever. Feel is about the same as the OEM, which makes sense, it is a brand new copy. They even sent a rebuild piston for when time comes to freshen it up. Good customer service from a ebay China seller. weihuaie is the name.
 
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