Bleeding Dual Disc Front Brakes
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Road Master
Joined: May 2012
Posts: 1,161
Likes: 653
From: Potter County, PA
Bleeding Dual Disc Front Brakes
I never had dual disc brakes up front before. How is the best way to bleed these? Should I alternate each series or do one side and then the other, or what? These need bled BAD, absolutely won't pump up. The Master Cylinder is bench bled and ready; appears to make good pressure. I will be doing this manually, pump and dump.
When brakes are this bad I usually just actuate the Master Cylinder without pumping up; blowing a small amount of air out each actuation. Or should I pump up a few times? I generally pump when I get a little progress and make a little pressure.
When brakes are this bad I usually just actuate the Master Cylinder without pumping up; blowing a small amount of air out each actuation. Or should I pump up a few times? I generally pump when I get a little progress and make a little pressure.
Seasoned HDF Member
Joined: Jan 2009
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From: WACO
I do good with "reverse" bleed. A kit is made just for this purpose. Cost about $25.00. Go to Tractor Supply and get a large syringe for vaccinating cows for $5.00. Same thing. Fill it with brake fluid, hook it up to bleeder nipple with hose. Open nipple and push brake fluid in with syringe back into brake reservoir. Works great. Start with brake away from reservoir. Once that is done you can do a "conventional" bleed if needed.
Seasoned HDF Member
Joined: Jul 2012
Posts: 9,511
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From: Pa.
Yep, no sense making it harder than it has to be. Do one at a time until you get clean fluid running out. Now getting fluid into brand new empty lines is another story, lol.
Road Captain
Joined: Jul 2021
Posts: 605
Likes: 441
From: BRIGHTON, ENGLAND
I find if new, it takes time to get the fluid down the hoses, so I fill them with fluid first using a syringe with a finger over the lower end as I fit the hose, yes you lose a bit, but get enough in to start ya in the right direction,,
then I vaccume bleed them,
one trick I do when bleeding, is to use a small sprung hose clip to make sure the bleeding pipe isn't sucking air & to stop it pulling off 1/2 way through,
& use Hylamar around the base of the bleed nipple before I crack it open,
I have found when vaccume bleeding you seem to get a lot of air sucked in past the threads of the nipple, defeating the vacumes efficiancy,
never get it in the threads on the caliper or you run the risk of contaminating the fluid, just around the caliper & nipple joint is enough to stop air getting in,
I tried using PTFE tape, but once cracked open it would still suck air past the tape,...
then I vaccume bleed them,
one trick I do when bleeding, is to use a small sprung hose clip to make sure the bleeding pipe isn't sucking air & to stop it pulling off 1/2 way through,
& use Hylamar around the base of the bleed nipple before I crack it open,
I have found when vaccume bleeding you seem to get a lot of air sucked in past the threads of the nipple, defeating the vacumes efficiancy,
never get it in the threads on the caliper or you run the risk of contaminating the fluid, just around the caliper & nipple joint is enough to stop air getting in,
I tried using PTFE tape, but once cracked open it would still suck air past the tape,...
Last edited by magnum45pete; Feb 14, 2022 at 08:06 AM.
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Road Master
Joined: May 2012
Posts: 1,161
Likes: 653
From: Potter County, PA
Lots of good advice here. If I get near a Tractor Supply or similar, I may look into the syringe. I am very rural in the mountains and am not driving 36 miles to buy a $5.00 item for a one-time use. Probably will try to fill the lines and then bleed conventionally one at a time. It is frigid yesterday and today. I don't like to work in my unheated garage too much when the high is in the low teens or single digits. The twenties are coming tomorrow. I will just have to wait a bit. I only have a few minor, yet tedious jobs left on this bike, my new to me '77 FXE. I still need a few items as well. Nothing close to me as far as aftermarket / custom parts. We do have a Harley Dealer 5 miles up the road, which still has a fair amount of Shovelhead parts in stock.
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Road Captain
Joined: Jul 2021
Posts: 605
Likes: 441
From: BRIGHTON, ENGLAND
Lots of good advice here. If I get near a Tractor Supply or similar, I may look into the syringe. I am very rural in the mountains and am not driving 36 miles to buy a $5.00 item for a one-time use. Probably will try to fill the lines and then bleed conventionally one at a time. It is frigid yesterday and today. I don't like to work in my unheated garage too much when the high is in the low teens or single digits. The twenties are coming tomorrow. I will just have to wait a bit. I only have a few minor, yet tedious jobs left on this bike, my new to me '77 FXE. I still need a few items as well. Nothing close to me as far as aftermarket / custom parts. We do have a Harley Dealer 5 miles up the road, which still has a fair amount of Shovelhead parts in stock.
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Seasoned HDF Member
Joined: Jun 2012
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From: CT/FL
When I first filled the brakes on my 79 fxs, the first side took longer than I expected, but when I went to the other side, it was already filled. The fluid finds its way and the air rises. I bled one side at a time too.
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