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Discussion Starter · #1 ·
81 gl500 (dual disc dual piston) decided to change brake pads...my obvious thought was to open the m/c and compress the calipers...they wouldn't budge. so i decided to open the bleeders and compress that way...they compressed smoothly. i reinstalled and assembled, pumped the brakes and the calipers came back out as i expected. topped off m/c. now my brakes are dragging. i find it odd the calipers wouldn't back flow to the m/c but the will forward flow to the calipers, and i get the impression they are not fully releasing the discs...do my pads need to wear in for the drag to subside or do i have a bigger problem...i'm trying to repair on a budget...thoughts/help?
 

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Having just rebuilt my rear dual piston caliper, I decided prior to replacing the pads (which were badly worn down) that I would do a complete caliper rebuild. After all the caliper seals may be shot - after nearly 30 years anything is possible. I removed the pistons and replaced the piston seals (two seals per piston), and they NEEDED REPLACING! One was almost not existant. I also replaced the caliper seal and grommets, lubed the caliper pins and of course installed the new brake pads. I learned that you really need to have the sliding part of the caliper, well, SLIDING....easily. Be sure it is well lubed.



If you still have issues, then you may be a candidate for a rebuild. Your seals may have worn down (were they ever changed in the 30+ years of their life?), or given the amount of time your brake pistons were extended (exposed) whilst driving with your thinner worn brake pads, they may have suffered from the elements and corroded on the sides, which if you pushed them back into their cylinder without removing and polishing them, may now make it difficult for them to completely "release" after letting off the brake. Did you see the condition of your pistons prior to pushing them back in?
 

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Did you check to see if the tiny little hole in the MC is plugged. I know mine did that when the hole was plugged, not allowing the pressure to bleed back into the MC reseviour when the brake lever was released.
 

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Discussion Starter · #4 ·
Did you check to see if the tiny little hole in the MC is plugged. I know mine did that when the hole was plugged, not allowing the pressure to bleed back into the MC reseviour when the brake lever was released.


I just tried the "paper clip" method of clearing the tiny hole, once i found it...i didn't drain the cylinder to do so, just fished around...i rode it around the neighborhood a little bit, it seemed like it may have helped some, but i can't be sure...i'm gonna try putting a few miles on the pads to let them "wear in" but i'm skeptical...after my last test ride, they were still squeeling, but it didn't seem as difficult to walk as earlier in the day. over all, i realize it's a 30 year old bike, and the front brakes haven't been serviced in the last 3 years i know of...and they're due for a complete overhaul, but i just got it back on the road friday from a 2 week teardown for carbs, tank, and fork springs, and i'm a little beaten down on the fact that i haven't been able to enjoy a solid week of riding since i got it...i would have prefered to just get all new calipers, lines and a master cylinder...but at least the beginning of that list is un-gettable...otherwise waiting on another payday to get the caliper rebuild kits, a quote for my hoses, and the cb400 m/c swap seems the easiest...mind you i haven't even gotten to put 10 miles on the new pads yet...
 

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I just tried the "paper clip" method of clearing the tiny hole, once i found it...i didn't drain the cylinder to do so, just fished around...i rode it around the neighborhood a little bit, it seemed like it may have helped some, but i can't be sure...i'm gonna try putting a few miles on the pads to let them "wear in" but i'm skeptical...after my last test ride, they were still squeeling, but it didn't seem as difficult to walk as earlier in the day. over all, i realize it's a 30 year old bike, and the front brakes haven't been serviced in the last 3 years i know of...and they're due for a complete overhaul, but i just got it back on the road friday from a 2 week teardown for carbs, tank, and fork springs, and i'm a little beaten down on the fact that i haven't been able to enjoy a solid week of riding since i got it...i would have prefered to just get all new calipers, lines and a master cylinder...but at least the beginning of that list is un-gettable...otherwise waiting on another payday to get the caliper rebuild kits, a quote for my hoses, and the cb400 m/c swap seems the easiest...mind you i haven't even gotten to put 10 miles on the new pads yet...
take the calipers and master apart-clean well & replace "OLD"rubber parts.
GJ
 

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Old rubber brake lines can work as a one way valve when the inner lining swells or starts to break up.



The MC generates more pressure to push the fluid down the line than the calliper does to send the fluid back and this will cause brake drag.



If clearing the MC return hole hasn't done the trick and the pistons weren't dirty or corroded this is another possible cause of your problem.



How old are the brake lines?
 

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I just tried the "paper clip" method of clearing the tiny hole, once i found it...i didn't drain the cylinder to do so, just fished around...i rode it around the neighborhood a little bit, it seemed like it may have helped some, but i can't be sure...i'm gonna try putting a few miles on the pads to let them "wear in" but i'm skeptical...after my last test ride, they were still squeeling, but it didn't seem as difficult to walk as earlier in the day. over all, i realize it's a 30 year old bike, and the front brakes haven't been serviced in the last 3 years i know of...and they're due for a complete overhaul, but i just got it back on the road friday from a 2 week teardown for carbs, tank, and fork springs, and i'm a little beaten down on the fact that i haven't been able to enjoy a solid week of riding since i got it...i would have prefered to just get all new calipers, lines and a master cylinder...but at least the beginning of that list is un-gettable...otherwise waiting on another payday to get the caliper rebuild kits, a quote for my hoses, and the cb400 m/c swap seems the easiest...mind you i haven't even gotten to put 10 miles on the new pads yet...
The paper clip is way to large. You need an .080" drill bit or a perhaps a guitar G string. Almost clean doesn't cut it.
 

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81 gl500 (dual disc dual piston) decided to change brake pads...my obvious thought was to open the m/c and compress the calipers...they wouldn't budge. so i decided to open the bleeders and compress that way...they compressed smoothly. i reinstalled and assembled, pumped the brakes and the calipers came back out as i expected. topped off m/c. now my brakes are dragging. i find it odd the calipers wouldn't back flow to the m/c but the will forward flow to the calipers, and i get the impression they are not fully releasing the discs...do my pads need to wear in for the drag to subside or do i have a bigger problem...i'm trying to repair on a budget...thoughts/help?




IMHO....because you were able to get the pistons to go back in after you opened the bleader the problem is either your brake hose or the return hole in your MC (like others have mentioned on both accounts).
 

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Discussion Starter · #9 ·
take the calipers and master apart-clean well & replace "OLD"rubber parts.
GJ


the pads appear to be "wearing in" and the drag has subsided...however, to the best of my knowledge the entire front brake system has never had any extensive service and i am beginning to lay out plans for an overhaul...i've been in touch with JDA about new brake hoses...for the price i can pick up a new cb400 m/c (which i've read to be a suitable replacement, although i would rather find a round alternatice) i think i'm just goint to replace the m/c versus do the rebuild...leaving me at my final hunt...finding an all-inclusive overhaul kit for the calipers...also...i broke a bleeder screw...if this was a car, my acetylene torches and an easy out would make this an easy fix...any words of wisdom/caution with these (this) caliper? ...thanking my stars it's only one of the two...after this is done, i'm a fan of never-seizing bleeder screws...



on a side note, having cleaned and lined my tank, thoroughly cleaned my carbs, swapped out the monoshock and fork springs, changed fork fluid, replaced plugs/caps, and wires, greased and lubed my driveline...i think this should be my last hurddle for the season...
 

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Did you say your front brake was dragging and SQUEALING? I would check and see if the disc was getting hot. If not I would not worry about it. Just my 2 cents.
 

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Discussion Starter · #11 ·
Did you say your front brake was dragging and SQUEALING? I would check and see if the disc was getting hot. If not I would not worry about it. Just my 2 cents.


the disc was getting hot, mind you i'm still within my first 50 miles on the new pads...they are now down from a squeal to a squeak, and the drag seems to be subsiding...i'm going to take it to work again today and will feel the discs when i get there (about 10 miles)...



in my experience, at least with cars brakes dragging creates heat which creates brake fade...the fade seems to be subsiding also...i have intentions to to the whole overhaul, i think my 30 y/o lines are going to prove to be the culprit, but if i'm going to open the system, i'm doing it all...
 

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the disc was getting hot, mind you i'm still within my first 50 miles on the new pads...they are now down from a squeal to a squeak, and the drag seems to be subsiding...i'm going to take it to work again today and will feel the discs when i get there (about 10 miles)...



in my experience, at least with cars brakes dragging creates heat which creates brake fade...the fade seems to be subsiding also...i have intentions to to the whole overhaul, i think my 30 y/o lines are going to prove to be the culprit, but if i'm going to open the system, i'm doing it all...


Let us all know what you find. There can never be to much information passed around on this forum. Billrod
 

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Discussion Starter · #13 ·
Let us all know what you find. There can never be to much information passed around on this forum. Billrod


For grins, I Pulled the M/C off an old suzuki GS250 that's been sitting around here for years...i attempted to reverse bleed through the bleeder screws with my pressure bleeder tank...for the pressure i applied, i got really poor return flow out of the m/c...after hours of trying to bleed in both directions, i got a relatively firm grab and test rode...and low and behold my problem is more pronounced than ever...almost to the point of full brake lock...i got it in the drive, and grew tired of fighting to walk it...that's when i had a eureka...i cracked a bleeder and instantly all the pressure was off and i had free roll...closed bleeder and pumped...brakes held and locked again...cracked the bleeder and brakes were off...one bleeder seemed to get both calipers...i'm liking the hose diagnoses...most likely from the m/c down to the splitter, but i think once my new JDA lines come in, the story should turn. my stock m/c is leaking between the can and m/c...i doubt the m/c off the Zukini 250 is going to be enough to be realistic being it's single disc single piston...but it was a free trouble shooter...expecting to be rebuilding/replacing the stocker...really liking the wemoto setup, but if the suz's cylinder proves to provide decent stopping power, it does provide minimally the round can i want...we shall see in a few weeks when the new lines arrive...
 

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The problem is much more likely to be the clogged return port in the master cylinder. If you got a paper clip thru it, you didn't find the very tiny second hole. This is the one that closes up and actually becomes difficult to even find, and then difficult to punch open. It's in the bottom of a dimple farther forward than the larger hole. Your symptoms are very classic of this tiny port being closed. I wouldn't waste time with other possibilities until you have confirmed you have the second (tiny) hole open. Been there, done that, as have many others. I'll buy you a beer at the Amish Rally if I'm wrong on this.
 

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The problem is much more likely to be the clogged return port in the master cylinder. If you got a paper clip thru it, you didn't find the very tiny second hole. This is the one that closes up and actually becomes difficult to even find, and then difficult to punch open. It's in the bottom of a dimple farther forward than the larger hole. Your symptoms are very classic of this tiny port being closed. I wouldn't waste time with other possibilities until you have confirmed you have the second (tiny) hole open. Been there, done that, as have many others. I'll buy you a beer at the Amish Rally if I'm wrong on this.


I'll buy a six pack if Rich is wrong. Hell, I'll buy one if he's right too.



99.9% of the time those symptoms are a blocked orifice tube. I took a master off a GL parts bike, couldn't clean the hole to save my life. Gave it to a machinist friend who makes medical devices, he found a broken sewing pin tip wedged inside the hole.
 

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Discussion Starter · #16 ·
I'll buy a six pack if Rich is wrong. Hell, I'll buy one if he's right too.



99.9% of the time those symptoms are a blocked orifice tube. I took a master off a GL parts bike, couldn't clean the hole to save my life. Gave it to a machinist friend who makes medical devices, he found a broken sewing pin tip wedged inside the hole.




ok,thought before i try, how risky would it be to try ab blow it out from the outlet in with my air compressor?
 

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Discussion Starter · #17 ·
ok...i made some decisions...SS Brakes lines c/o JDA and a M/C off an 04 cb600rr (11/16 bore over our standard 5/8 bore) I have bled, and come up with a decent pedal, but i do have a question...i've read a little about tying the handle back over night to firm it up more...can somebody elaborate as to the why and how of this? i've gone ahead and tied it back for the night, and will cut the zips loose tomorrow and ride it to work...if i've already figured out that it works then...well cool...but otherwise, i would at least like to hear a technical break down of the how and why....but otherwise, good brakes, and NOT DRAGGING woohoo!....the down side is this m/c leaves no provision for a mirror, but i'll either hunt down some after market clamps, or better yet, find the fairing mirrors for this thing and negate the issue altogether....but...i digress...
 

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I think the reason for tying the lever back overnight is to allow those very tiny bubbles to float up the lines and out of the system. That, and it keeps you from messing with it for 10 hours.
 

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Discussion Starter · #19 ·
I think the reason for tying the lever back overnight is to allow those very tiny bubbles to float up the lines and out of the system. That, and it keeps you from messing with it for 10 hours.


where's the fun in not messing with it for ten hours....lol...otherwise i'll find out in the am...
 

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ok...i made some decisions...SS Brakes lines c/o JDA and a M/C off an 04 cb600rr (11/16 bore over our standard 5/8 bore) I have bled, and come up with a decent pedal, but i do have a question...i've read a little about tying the handle back over night to firm it up more...can somebody elaborate as to the why and how of this? i've gone ahead and tied it back for the night, and will cut the zips loose tomorrow and ride it to work...if i've already figured out that it works then...well cool...but otherwise, i would at least like to hear a technical break down of the how and why....but otherwise, good brakes, and NOT DRAGGING woohoo!....the down side is this m/c leaves no provision for a mirror, but i'll either hunt down some after market clamps, or better yet, find the fairing mirrors for this thing and negate the issue altogether....but...i digress...
That strikes me as odd going up on the bore size of the m/c. Normally going smaller is the way to improve lever feel and controllability on these vintage bikes. I would have thought that a 9/16" (14mm) master cylinder would have been a better choice. As far as that goes, I'm surprised that and 04 CBR had a 11/16" m/c.



From everything that I have read, going to a larger m/c should have given you a very wooden feeling brake lever.



I'd be interested in hearing how this works out for you.
 
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