Front brake issues

David Toll

Reliving my youth?
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Of all the jobs I've attempted over the last 4 years, bleeding the brakes has proven to be the most frustrating and time consuming. I followed the advice of many of our experienced members and managed to get the rear brakes working without too much grief. The front brakes are proving to be another matter.
The bike is a '78 Special. I purchased a master cylinder from an XV 250 Virago, rebuilt it with new parts and put it in place, I also rebuilt the callipers - new piston, seals, rubbers and pads. The system has braided brake lines from Banggood.
First attempt at bleeding resulted in no pressure at the handle. There are a plethora of suggestions here on how to deal with that situation and I have tried them all. I have filled the callipers, line and cylinder with fluid and tried to bleed with no result. I have removed the system, filled it with fluid, hung it vertically and tempted tp back bleed with limited success. I have rebuilt the master twice trying to ensure that the piston rubbers are not folded or otherwise distorted in the cylinder. I have replaced all crush washers and banjo bolts with new items and pumped the handle until my biceps rival Stallone. Still, the bloody thing won't work.
I took a thread of stainless wire to the air hole in the bottom of the cylinder and ensured that it was clean. The diameter of the wire was smaller than the hole so I don't believe it caused any enlargement. I took a horse syringe to the beed outlet and managed to draw air and some oil through the system but not enough to provide a constant flow - it just keeps bubbling air out. The banjos are tight and there are no leaks, that I can see, at those junctions or at the calliper
I do notice the, when I put my thumb over the cylinder outlet, it builds pressure and eventually shoots fluid around the garage. I also notice that it builds an element of suction at the outlet as well. The cylinder appears to pump the fluid on the in stroke and suck it back on the release. I am about to tear it down again today but I don't know what else to look for.
Any suggestions??
 
Yes WA, the vacuum pump is probably my next step. I started pulling the system down this morning and thought I would video the cylinder action first. As you can see, it's trying to pump fluid and if I filled the cylinder through the banjo opening, it would squirt the stuff all over but, at the moment, very little. I'm assuming the new piston assembly is somehow compromised.
 
Squeeze the lever then put your thumb over the hole then release the lever while keeping your thumb in place, wait a second then take off your thumb. Repeat a few times this should draw fluid through the piston assembly.
Hope it helps.
 
This has worked at times.. depends on the angle of the h/bars…. wrap a rag around the banjo bolt on the master... pump lever up.. and crack open the banjo... I've found a small air bubble.. repeat once..twice.. it has worked in the pass.
 
In the past month I have changed my fluid twice in testing a different size MC and rebuilding calipers on my Virago which is basically the same setup as the SH I had which was a cow to bleed without suction, same with the Virago. My technique is to open the bleed nipple about 1/2 turn, connect a length of plastic tubing about 1 meter long and start sucking while at the same time pump the brake lever. As soon as fluid starts to come out into the tubing I stop sucking and just pump the brake lever until the job is finished. Works for me but you may think I suck at it.

Never used a vacuum pump but seen it demonstrated and they are excellent.
 
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Yes WA, the vacuum pump is probably my next step. I started pulling the system down this morning and thought I would video the cylinder action first. As you can see, it's trying to pump fluid and if I filled the cylinder through the banjo opening, it would squirt the stuff all over but, at the moment, very little. I'm assuming the new piston assembly is somehow compromised.
how about you lay out the MC parts as assembled and snap a pic, mebbie someone assembled wrong at factory? Grabbing at straws perhaps, but that MC SHOULD flow fluid out the banjo just sitting, with fluid in the reservoir.
PS a goto for me is; install the caliper piston just in past the seal, fill caliper with brake fluid by pouring inthe banjo bolt hole. Assemble the lines all the way to MC then grab a c-clamp and push the caliper piston all the way in. That forces fluid all the way up to reservoir and usually results in good lever immediately.
 
When pumping on the brake lever I place a cloth over the top of the open reservoir because some little drops of fluid often shoot out and can damage paintwork. I also cover the tank with a big plastic bag and a thick cloth on top - who knows where those little drops will end??
 
I swear by the Mighty Vac but I wish it had a flat bottom so you could set it down. In any case, it sounds like you may have assembled the piston incorrectly.
Been there, done that.
 
I also swear by my MityVac, been using it for years. To put it down while in use, I rest it on my little mechanics stool, letting the fluid cup hang off the side .....

ziNpcTN.jpg


This tool alone doesn't do the bleeding operation 100%, I have to finish with a few old fashioned hand pumps, but it makes short work of filling an empty system and getting some pressure to start building.
 
My method is similar to Gary's. Hold the caliper horizontal with the piston out. Fill it with fluid and then push the piston in until it just passes the seal. Now rotate it until the line is on top so air will "gravitate" out the line... give it a few raps with a piece of wood to dislodge any bubbles stuck in there. Slowly push the piston all the way in 'till it bottoms. that should have the fluid up in the reservoir. Top it off with fluid and put it all together. Pump the piston back out adding fluid as required. Works every time if everything is assembled correctly.
 
Did 3 hours of pumping and bleeding yesterday based on the principle that I simply wasn't trying hard enough. I am getting air bubbles at the bleeder but no fluid which leads me to suspect that there is a leak in the system. Have a bag of crush washers so, I am replacing those with each assembly and trying not to twist the threads off the banjo bolts when I tighten. Tilted the MC so that the fluid ran down into the line. Pumped and bled ad infinitum and managed to build a little pressure. Levelled the MC up and left the handle tied back last night and will revisit this morning to see if the Tooth fairy has given me a brake, (if you'll pardon the pun).
Piston came assembled from the manufacturer and, really, can only go in one way with the spring first and the rubber cups facing forward. I was concerned that those "cups" may have folded over during assembly but I have put it together three times now and paid special attention to feeding the cups into the bore correctly. I was concerned that I may have damaged the air return hole that Tom T describes above although, I have read warnings on threads here, about taking care when cleaning that aperture and used a thin diameter strand of wire that shouldn't have enlarged the passage. I don't seem to get any air coming out of that opening which, I assume, functions to release air from the cylinder as the plunger descends. The repair kit I am using, ('95 XV Virago 250), has a washer that fits under the circlip. I don't recall removing one from the original assembly when I first dismantled the MC. The parts list shows it in place so, I have installed it.
As usual, the Forum has provided excellent advice which I will put into play today, (a holiday in this state). This is a simple system that uses a plunger to motivate fluid to flow down a line and compress a piston against a pad. The problem must be air. I have found, with the XS, that the solution often presents itself when repeating the procedures carefully step by step - often for no easily identifiable reason. If I find that I do have to strip it down again, I will document what I'm doing to facilitate your analysis of the issue. I know it's there, I just can't put my finger on it yet.
Your time and advice is, of course, greatly appreciated.
Cheers
 
Still no success. Am about to throw myself on my torque wench. These front brakes are the dizzy limit. Stripped them down again and took some photos. Photo one shows the state of the bore - you can't really see it but it's good. Pic 2 shows the unblocked holes in the MC. Pic 3 shows the layout of the piston assembly organised as they go into the cylinder spring first. Pic 4 is a close up of the new assembly. Pic 5 shows the piston in place. Had little trouble getting the rubbers to go into the bore but managed to coax them with a fine flat head screw driver. Piston functions and when I put my thumb over the hole it builds pressure straight away. When I connect it all up - good and tight....... nothing! 200 pumps and no pressure build up. Bleeder releases air but no fluid.
There must be a leak in the system that is stopping it from pressurising. The banjos are tight and not leaking fluid. The bleeder seems to seal when I close it. Is it possible that there is a leak around the piston in the calliper?
 

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You need to get some suction on the bleed nipple. I am guessing you have an air bubble stuck somewhere. The first time I did an XS front brake I pumped for an hour easily without anything happening, this is why people have their own little tricks to get the job done. Even when I use a piece of tubing and suck it takes about a minute to get the fluid flowing then the handle does the rest. Those Virago MCs do not seem any different to work with compared to the XS Special MCs.
 
Tried sucking on the bleed tube, (no offence) and all that happened was that I spun out. Started to fret about brake fluid poisoning. Just tried Gary's reverse bleed method. Got bubbles and even a jet of fluid at the MC when I applied the clamp. Took the clamp-off and pumped the lever - nothing. No leaks around the calliper piston seal,(least ones that carry fluid). This has got me screwed! Will start over again after a bit of a sabbatical courtesy of Queensland Health. I know you're right Paul. It's a challenge! Mityvac next.
 
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I looked through several Virago circa. 1995 images and the piston assembly you have is correct:
MC250.jpg
Like you said, the 2 rubbers were pre-installed.
 
Try this: 1- open bleeder, 2- finger on bleeder with light pressure remember that you want to let fluid and air out but not back in, 3- gently stroke lever with finger on bleeder, 4- after only fluid comes out hold the lever squeezed and tighten the bleeder.

There are bleeder screws available that can perform the above method but they cost more than using your finger, search the interwebs for "solo-bleed brake bleeders"
john
EDIT- make certain the M/C is level.
 
There is another way I do it sometimes. Use an oil can the type with a pump on it, fill it with brake fluid, fasten the oil can to the open bleed nipple with clear tubing, start pumping, watch the fluid go into the system through the clear tube. Pump until clear fluid going in fills the master cylinder reservoir, you may need to recover excess fluid from the reservoir, once happy close off the bleed nipple, should be good to go.
 
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