250 Bleeding Dry Line Tips

RageD

RageD

Hi guys,

Back with another question... Maybe I should just open a single thread for all things related here lol :)

The other day while riding I noticed my front brakes were getting spongy (ok, really spongy). If I gave the lever a hard pull, I could bring it all the way back to the grips.

Knowing the previous owner never did more than replace the pads on these brakes, I've opted to do a full rebuild of my front brakes. The brake line is the rubber OEM line from about 20 years ago and by the look of the caliper seals, they're probably about as old. I just cleaned up the caliper and pistons and replaced the seals. My master cylinder rebuild kit and new front brake line are coming in on Wednesday (there was a mixup at the shop :( killed my riding for the weekend).

Anyway, I was thinking about this problem: I've never bled a dry line :) Anyone have any tips on this? I did run out and buy a hand-powered vacuum pump for the job, but I'm wondering if I should be doing anything else? Do I need to pay any special attention to bleeding the master or basically make sure the reservoir stays full and pump away?

I have changed the brake fluid before using the traditional crack and slow lever pump method, but I never let the reservoir get too low. Now that there is air in the system, just want to make sure there is anything special I should be doing.

Thanks!

**EDIT:** I've also read quite a few things about bleeding bottom up. Is this better than using the vacuum pump to bleed down? Anyone have experience to compare the two methods? :)
 
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SRAD97750

SRAD97750

Moderator
Staff member
Once a decent amount of fluid is in the line, I crack the bleed nipple with a hose submerged in a bucket, and pump the lever (refilling the reservoir) until the fluid coming out the nipple is clear. Any haze in the fluid is bubbles.
This uses a bit of fluid, and takes some time, but works for me every time.
I have a linked brake system on my sport bike which consists of probably 20+ft of brake lines. This method works there as well. - BIG DAN:thumb:
 
O

ossagp

I have the hardest time using the master cylinder to do any of the work. If you cant find your vacuum pump and drive a company car, or have a brother inlaw who parks on your place you can easily use a vacuum port off the manifold of said vehicles to hook up to your bleed port on your caliper. simply fill the master cylinder and pour some fluid in as you open the bleed valve. you can flush and bleed one in minutes this way, and cleanup is all done for you. Remember, brake fluid is hard on paint, but also don't forget, and DON'T use your car.
 
M

MikeinFresno

you can also push the caliper to one side to push the piston(s) in. This pushes the fluid and air up the line and back into the master where the air is supposed to be. I use this on the trail or while riding if I have an issue. The other thing for over nite that works well is to tie the lever all the way back to the bar, or as close as you can get it, turn the bars to the left so the master is the high point and also check the hose-it may have to be pulled down a little so it is not the highest point. This allows the air to slowly bubble up to the master. I tap the line a little a couple of times and gets the bubbles headed up the line.
 
O

ossagp

On another forum, a man from england posted a pic years back of him running a line from the rear master cylinder bleedout to the front caliper bleedout, thus doing a great bottom fill. I haven't tried it yet, but I thought how smart people can get when they don't have as much to work with.
 
O

ossagp

MikeinFresno:
you can also push the caliper to one side to push the piston(s) in. This pushes the fluid and air up the line and back into the master where the air is supposed to be. I use this on the trail or while riding if I have an issue. The other thing for over nite that works well is to tie the lever all the way back to the bar, or as close as you can get it, turn the bars to the left so the master is the high point and also check the hose-it may have to be pulled down a little so it is not the highest point. This allows the air to slowly bubble up to the master. I tap the line a little a couple of times and gets the bubbles headed up the line.
Click to expand...

Floyd leaves street bikes like that quite frequently. (second suggestion)
 
RageD

RageD

Alright, so I actually spent all of Wednesday night rebuilding the master cylinder and was busy Thursday; had the day off today so took a crack at this.

After 2 bottles of brake fluid and several hours of bleeding, I feel a bit defeated :) Where I sit today: the brake pads will grab and release the rotor but the lever is super weak. What I would consider a "normal" handful of brakes takes me all the way to the bars :(

I started with the dry line and the bottom up approach. I initially wasn't paying much attention and made a mess on the garage floor with the reservoir overflowed :( That aside, I was excited to feel the brakes. At first, there was no lever. After pumping the brakes up I realized I got to a point where the pads grabbed the rotor, but it felt the same as it does now.

At this point, I began to alternate between the traditional "pump, crack, pull, close, release" method of bleeding and the vacuum pump. I never noticed any air bubbles coming out with either method: just fluid. I also tried various ways of reorienting the hose to make it easier for air to travel through including making the caliper higher than the master: no luck.

Right now, I've got the bike sitting with the lever zip tied to the bars. I'm sure that won't do much though as I'm feeling confident there is probably air hidden in that hose (or somewhere) still. Do you guys have any ideas? I just rebuilt the caliper and master cylinder. I reused the pistons because they didn't have any noticeable scoring. Similarly, I triple-checked that I put the seal cups on properly on the piston for the master cylinder. Any other areas that may be causing problems!

I'm going to check again tomorrow but one of my pistons looked a bit wet (though I just replaced the seals... and the other way bone dry) but I also spilled some brake fluid in that area. I'm going to let it dry off and check again, but is it likely a loose fitting seal could be the problem?

Thanks!
 
Mihylo33

Mihylo33

RageD:
Alright, so I actually spent all of Wednesday night rebuilding the master cylinder and was busy Thursday; had the day off today so took a crack at this.

After 2 bottles of brake fluid and several hours of bleeding, I feel a bit defeated :) Where I sit today: the brake pads will grab and release the rotor but the lever is super weak. What I would consider a "normal" handful of brakes takes me all the way to the bars :(

I started with the dry line and the bottom up approach. I initially wasn't paying much attention and made a mess on the garage floor with the reservoir overflowed :( That aside, I was excited to feel the brakes. At first, there was no lever. After pumping the brakes up I realized I got to a point where the pads grabbed the rotor, but it felt the same as it does now.

At this point, I began to alternate between the traditional "pump, crack, pull, close, release" method of bleeding and the vacuum pump. I never noticed any air bubbles coming out with either method: just fluid. I also tried various ways of reorienting the hose to make it easier for air to travel through including making the caliper higher than the master: no luck.

Right now, I've got the bike sitting with the lever zip tied to the bars. I'm sure that won't do much though as I'm feeling confident there is probably air hidden in that hose (or somewhere) still. Do you guys have any ideas? I just rebuilt the caliper and master cylinder. I reused the pistons because they didn't have any noticeable scoring. Similarly, I triple-checked that I put the seal cups on properly on the piston for the master cylinder. Any other areas that may be causing problems!

I'm going to check again tomorrow but one of my pistons looked a bit wet (though I just replaced the seals... and the other way bone dry) but I also spilled some brake fluid in that area. I'm going to let it dry off and check again, but is it likely a loose fitting seal could be the problem?

Thanks!
Click to expand...



The calipers hold a lot of air and depending on the design yo may have to to turn the caliper so the bleeder is higher than the piston pockets. At which point you pump that lever until it feels solid hold it and release the bleeder.
 
timoyz

timoyz

I've also had luck with pulling the reservoir and master cylinder unit off so I can hold it higher than the bike and get the hose as straight as possible. Also laying the bike over then with the reservoir lid off you can see the bubbles working their way out of the top. Those banjo fittings also trap air, it sometimes also helps to tap on them as you're actuating the lever.
 
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RageD

RageD

I'll run out and grab some more brake fluid today and try these. This morning after ripping the zip ties off, the lever felt about the same (as I expected).

One thing I did notice, however, was when I cracked the bleeder a small amount of fluid came out, but a lot of fluid from the master reservoir was sucked down into the line (seemingly more than leaked out). Does this indicate anything to you guys? Maybe totally irrelevant, but seems like space freed up somewhere.

Would pushing the pistons all the way in help remove air from the cylinders?
 
Mihylo33

Mihylo33

RageD:
I'll run out and grab some more brake fluid today and try these. This morning after ripping the zip ties off, the lever felt about the same (as I expected).

One thing I did notice, however, was when I cracked the bleeder a small amount of fluid came out, but a lot of fluid from the master reservoir was sucked down into the line (seemingly more than leaked out). Does this indicate anything to you guys? Maybe totally irrelevant, but seems like space freed up somewhere.

Would pushing the pistons all the way in help remove air from the cylinders?
Click to expand...


Yes. It means you are getting the air out.
 
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