Brake bleeding issues | GTAMotorcycle.com

Brake bleeding issues

W

woot

Well-known member
I have been trying to flush my brake fluid for nearly 1 week. Fluid does not seem to be getting from the reservoir to the master cylinder.

Backstory: 2005 sportster with dual front brakes.
-over the winter I replaced the handlebars and fork seals. during this time I had the front brake system laying in a pile.
-the new handlebars are lower causing an S-shaped loop in the brake line similar to the trap under a sink
-I noticed this spring that the front brakes were nearly non-existent and the brake light was sticking on.
-The brake fluid looked pretty brown so I decided to try giving it a flush. looked pretty easy via youtube.

-tried the usual pumping and opening the bleed valve but very little came out. Also, no matter what it would eventually suck air back in on the second of third bleed.
-tried letting it sit with the bleed valves open and have gravity do its thing and in the last week have gotten maybe 1/2 cup of brake fluid out.
-tried vacuuming which does get fluid out but it seems like air just gets pulled back into the caliper as soon as I'm done.
-tried putting about 15psi of compressed air on the bleed screw thinking there could be a blockage somewhere. no plugs. fluid shot out of the master cylinder (luckily dot5 silicone based because it was everywhere)

-pulled the brake line off of the master cylinder and there was almost no fluid in the cylinder.
-I was not able to pump up pressure as there was no fluid coming into the cylinder and not air bubbles coming up into the reservoir
-I sprayed brake cleaner in every orifice I could access and I started to get some small bubbles in the reservoir when pumping the lever so I reassembled and still can't pump up any pressure on the lever or get fluid out of the caliper without pulling air back in.

I'm about to order a master cylinder rebuild kit from Harley but its 2 weeks out. Does the master cylinder make sense?
 
It doesn't sound like a master cylinder problem if its pumping back okay out the reservoir.
Try elevating the calipers - let them hang for a while, remount them and see if after that you can get the air out after that.
 
Push the pistons all the way back and hold them there, add brake fluid from the bottom bleeder with a syringe, if it doesn't start filling the reservoir (that you should empty first) you have a problem with the brake master cylinder. .... don't spill it all over the place! have lots of cleanup supplies ready.
 
A couple of things to note (sorry if these sound silly, they are mistakes that seasoned mechanics sometimes make):

1) Are the calipers installed on the correct sides? bleed screws should be facing up. If they are facing down, swap caliper sides.
2) From the master to the caliper, everything must be on a downslope -- if that "s-curve trap" elevates any point of the line level or above a southbound part of the hydraulic circuit air will accumulate at the high point and make it near impossible to bleed. You can leave the trap in place however you need to wiggle it around during the bleed process so it's all downhill.
3) Be sure the copper crush washers are in place, one on each side of the brake line ends.
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Bleed procedure:

1) Remove filler cap from master cylinder
2) Fill the reservoir
3) Slooooowly squeeze the brake lever 3 times, on the last pull hold full brake.
4) Crack open the left side caliper bleeder, then close it, then release the brake lever and the master should draw hydraulic fluid. If you release the lever while the bleeder is open, the master will draw air back thru the bleeder.
--- repeat steps 2 through 4 until there are no air bubbles coming through the bleeder hose (may take a dozen or more cycles)
5) Repeat steps 2-4 on the right side caliper,
6) top up and close reservoir.

This can be tough to hold the brake lever and crack the left bleeder at the same time, it's easier with a 3rd hand on the brake.
 
Make sure your helper knows to UNDER NO CIRCUMSTANCES let go of the lever when you're cracking the bleeder open and closed - firm constant pressure, and be sure to tell them to expect it to bleed down/move on them.

Even a momentarily relaxation of the pressure on the lever will cause air to get sucked in at the bleeder, thereby sending the process backwards.

Be sure to open the bleeder in small spurts as well so that the lever doesn't bottom out and also cause air to be introduced.
 
Tonight I pulled the master cylinder apart. Overall it looked good. The second smaller hole in he reservoir took a bit of of poke to get clean.

put it all back together and tried to bleed at the bolt and nothing. No fluid coming out. No lever pressure and No fluid leaving the resevoir.

I went to town vacuuming from my The caliper and I now think that the brake lines literally empty and still a full reservoir.

im really not sure how that piston works. When the lever is not pressed shouldn’t the brake fluid flow from the reservoir down into the master cylinder and lines.
 
"When the lever is not pressed shouldn’t the brake fluid flow from the reservoir down into the master cylinder and lines ?"

Yes, BUT when you release the lever it will flow back up. Keep the master cylinder full, pump and release, pump and release (slowly) until you start to see bubbles coming out the caliper bleed screws. As has been suggested before, then zip-tie the brake lever to the bar, let it sit overnight and hopefully a lot of the air will come up to the top and vent to atmosphere. Its a slow process.
 
woot said:
Tonight I pulled the master cylinder apart. Overall it looked good. The second smaller hole in he reservoir took a bit of of poke to get clean.

put it all back together and tried to bleed at the bolt and nothing. No fluid coming out. No lever pressure and No fluid leaving the resevoir.

I went to town vacuuming from my The caliper and I now think that the brake lines literally empty and still a full reservoir.

im really not sure how that piston works. When the lever is not pressed shouldn’t the brake fluid flow from the reservoir down into the master cylinder and lines.
Click to expand...
This will work:
Trials said:
Push the pistons all the way back and hold them there, add brake fluid from the bottom bleeder with a syringe, if it doesn't start filling the reservoir (that you should empty first) you have a problem with the brake master cylinder. .... don't spill it all over the place! have lots of cleanup supplies ready.
Click to expand...
otherwise you still have a problem with your brake master cylinder.

... you are thinking about how brake fluid will leak down the tiny hole, it don't work good that way.
My way you are pushing all the air up and out that tiny hole.
 
What you describe is pretty much what I would expect. When you squeeze the brake, the fluid goes into the piston, when you release it goes back. You need to create vacuum down stream, you do this by compressing the air in the system, neutralizing the pressure by opening the bleed screw. Closing the bleed screw then releasing the brake lever causes negative pressure in the line which stops the master from returning all the fluid into the reservoir.

Air compresses a lot and doesn’t create huge negative pressure in a brake system, Thats why it takes so many cycles to bleed empty brake lines.
 
Try a reverse bleed. It’s sounding like you’re having the exact same issue I had when I replaced the master cylinder on my old VTX. I spent hours trying desperately to bleed things, even a vacuum bleeder. Nothing worked.

I finally got a syringe and some latex tubing to fit over the bleeder Nipple, reverse bled the system from bottom up until all the air was forced out at the master cylinder versus the bleeder, then bled normally one or two pumps the normal way, and was done inside 10 minutes.
 
I've finally got some feeling in my brake lever. I think that my issues was allot of air and a lack of patience.

Mad Mike said:
A couple of things to note (sorry if these sound silly, they are mistakes that seasoned mechanics sometimes make):

3) Slooooowly
Click to expand...

Trials said:
add brake fluid from the bottom bleeder with a syringe,
Click to expand...

Thanks guys
 
PrivatePilot said:
...
I finally got a syringe and some latex tubing to fit over the bleeder Nipple, reverse bled the system from bottom up until all the air was forced out at the master cylinder versus the bleeder, then bled normally one or two pumps the normal way, and was done inside 10 minutes.
Click to expand...
The best way to fill hydraulics is hydraulically, exactly what you would do if you needed to bleed your brake 10 minutes before the start of a competition, you wouldn't have all day and 2 people to do it ;) just get er done and try not to get any on you.
 
Boyoboy is probably right air bubble at master cylinder end of the brake hose. Bleed the banjo bolt at the top. Same procedure pump pump pump crack the banjo bolt loose at the top of the line until it starts to sound like you’re opening a pop bottle
 
Is it fixed yet?
 
PrivatePilot said:
Try a reverse bleed. It’s sounding like you’re having the exact same issue I had when I replaced the master cylinder on my old VTX. I spent hours trying desperately to bleed things, even a vacuum bleeder. Nothing worked.

I finally got a syringe and some latex tubing to fit over the bleeder Nipple, reverse bled the system from bottom up until all the air was forced out at the master cylinder versus the bleeder, then bled normally one or two pumps the normal way, and was done inside 10 minutes.
Click to expand...
This.

I hate bleeding brakes. Best thing i ever did was get a syringe and force the fluid up through the master to the resevoir. So fast. So easy.
 
^ And when you do that, find a way to hold the master cylinder so that the vent hole to the reservoir is at the highest spot. Usually this requires unbolting it from the handlebar, sometimes you can get away with bike on sidestand and a 2x4 under one of the wheels with the bars turned all the way to the left.
 
JFD said:
I hate bleeding brakes. Best thing i ever did was get a syringe and force the fluid up through the master to the resevoir. So fast. So easy.
Click to expand...
Brian P said:
^ And when you do that, find a way to hold the master cylinder so that the vent hole to the reservoir is at the highest spot. Usually this requires unbolting it from the handlebar, sometimes you can get away with bike on sidestand and a 2x4 under one of the wheels with the bars turned all the way to the left.
Click to expand...
Or just get Speed Bleeders. I’ve had 4 of them on my ST for about 12 -15 years and they make bleeding the 3 calipers and the clutch dead simple and quick.
 
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