Bench Bleeding M/C ?
Thread Starter
Intermediate
Joined: Nov 2007
Posts: 34
Likes: 1
From: Gardner Kansas
Bench Bleeding M/C ?
Okay, I got a question.... or two.
I am not a mechanic so please take these ?'s with that in mind. I have replaced the calipers and all the hoses. I'm waiting on a replacement brake line so I have focused on the Bench Bleeding the M/C. I've never done this so I have read a couple of techniques and frankly I don't get it.
First of all why does it have to come off the car?
The purpose is to remove air from the M/C, when you reconnect the brake lines don't you just put air back into the M/C?
When you bleed the whole system aren't you also bleeding the M/C in the process?
I have seen two techniques. One involves a Syringe. As far as I can tell a vacuum bleeder and a piece of hose accomplishes the same thing.
the second involves two hoses inserted into the brake line ports and resubmerged into the top of the M/C into each resevoir. This one I wonder what happens when you pull the hoses out of the brake line ports?
I apologize if these are "stupid" questions but I have to ask them.
If an easier technique is out there... I'm listening.
Thanks in advance.
I am not a mechanic so please take these ?'s with that in mind. I have replaced the calipers and all the hoses. I'm waiting on a replacement brake line so I have focused on the Bench Bleeding the M/C. I've never done this so I have read a couple of techniques and frankly I don't get it.
First of all why does it have to come off the car?
The purpose is to remove air from the M/C, when you reconnect the brake lines don't you just put air back into the M/C?
When you bleed the whole system aren't you also bleeding the M/C in the process?
I have seen two techniques. One involves a Syringe. As far as I can tell a vacuum bleeder and a piece of hose accomplishes the same thing.
the second involves two hoses inserted into the brake line ports and resubmerged into the top of the M/C into each resevoir. This one I wonder what happens when you pull the hoses out of the brake line ports?
I apologize if these are "stupid" questions but I have to ask them.
If an easier technique is out there... I'm listening.
Thanks in advance.
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
When you connect the hard lines fluid is seeping out and air is not let in in any significant amount. Once connected, minimal air will remain, and a standard bleeding will take care of that.
Your syringe idea is fine, and any other variation will work as well.
Bench bleeding in the car is okay so long as you have nipples with rubber tubes leading back up into the reservoirs so fluid is circulated and air can be released. Just make sure everything is tight and air is not being sucked in around the threads.
Every now and then, stop pumping to tap the master with a wooden handle of some sort to loosen any air bubbles hanging on.
Once your lines are all intact, do a gravity bleed to get the calipers filled, and then bleed at each wheel like usual. The tapping method works great with calipers too.
Your syringe idea is fine, and any other variation will work as well.
Bench bleeding in the car is okay so long as you have nipples with rubber tubes leading back up into the reservoirs so fluid is circulated and air can be released. Just make sure everything is tight and air is not being sucked in around the threads.
Every now and then, stop pumping to tap the master with a wooden handle of some sort to loosen any air bubbles hanging on.
Once your lines are all intact, do a gravity bleed to get the calipers filled, and then bleed at each wheel like usual. The tapping method works great with calipers too.
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 38
From: Fremont CA
I don't know about the previous answer but, I ALWAYS "bench bleed" a new master cylinder by putting fittings into the outlet ports and submersing the ends back inside the resivoir (it will take several strokes and you will be SURPRISED by the amount of air you see in a new master cylinder.) Keep the ends of the hoses or old brake line submerged and pump several times waiting if you see a lot of foaming in the brake fluid. I don't know how you could get all the air out of the MC unless this method is used. After bench bleeding, you can gravity bleed the brake system by opening the furthest away bleeder screw (right rear outer) and proceed to get a firm brake pedal. I see many posters on here struggling with their brake systems, maybe this is one of the reasons why so many have to "fight" their system. I use Ford brake fluid for racing Vettes and Castrol LMA for street Vettes.
Le Mans Master
Joined: Oct 2000
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From: Austin TX
Race Director
Joined: Dec 2006
Posts: 13,172
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From: West Chester OH
2020 C6 of the Year Finalist - Unmodified
Cruise-In IX Veteran
St. Jude Donor '08 thru '13
We used to bench bleed all the new MC's when I was a kid working in the neighborhood gas station.
After we installed the MC we'd crack the lines coming out of it and bleed it there. You might get a little air out, rarely had to bleed the entire system.
After we installed the MC we'd crack the lines coming out of it and bleed it there. You might get a little air out, rarely had to bleed the entire system.
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
I don't know about the previous answer but, I ALWAYS "bench bleed" a new master cylinder by putting fittings into the outlet ports and submersing the ends back inside the resivoir (it will take several strokes and you will be SURPRISED by the amount of air you see in a new master cylinder.) Keep the ends of the hoses or old brake line submerged and pump several times waiting if you see a lot of foaming in the brake fluid. I don't know how you could get all the air out of the MC unless this method is used. After bench bleeding, you can gravity bleed the brake system by opening the furthest away bleeder screw (right rear outer) and proceed to get a firm brake pedal. I see many posters on here struggling with their brake systems, maybe this is one of the reasons why so many have to "fight" their system. I use Ford brake fluid for racing Vettes and Castrol LMA for street Vettes.
That's just what I said. I just pointed out that you CAN bench bleed a master while it's in the car. You just connect run rubber tubes from the bungs to the reservoirs.
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Melting Slicks
Joined: Dec 2006
Posts: 2,669
Likes: 3
From: Kingston Ontario
ZIP has a detailed description of MC bench bleeding;
http://www.corvettemagazine.com/content/view/85/
Go to step 33.
http://www.corvettemagazine.com/content/view/85/
Go to step 33.
Racer
Joined: Aug 1999
Posts: 466
Likes: 71
From: West Chester PA
I think the idea of being out of the car was to ensure the MC was level. If the MC is not level, air pockets will remain after bleeding. The MC must be level, not the car being level. The best way to check would be to put a level on top of the MC. This may require you to raise one end of the car higher than the other.
Melting Slicks
Joined: May 2007
Posts: 3,246
Likes: 4
From: Bay Area CA
You gotta pull it and put it in a vice (easily). With it's front up, in the car, you will never get all the air out of the thing. Got to get it level. Use full strokes if it's new. I bench bled mine and it took a good five minutes to get this or that little bubble out,, just keep bleeding it untill "No" air comes out. experience.
Burning Brakes
Joined: Aug 2004
Posts: 856
Likes: 2
From: Tyler Texas
My 73 GM Service Manual states that for bench bleeding the MC (off the car) in a bench vice, you should (1) "have the front end of the MC tilted slightly DOWN" when you are pressing in on the primary piston to compress the piston return spring. Then, (2) "reposition the MC in the vice so that the front end is tilted slightly UP and repeat the bleeding procedure."
Purpose of the tilting in the vice is to deal with the air pocket issue.
Anyone ever bench bleed their MC in a vice using the Motive Pressure Bleeder instead of manually pressing in on the piston?
Purpose of the tilting in the vice is to deal with the air pocket issue.
Anyone ever bench bleed their MC in a vice using the Motive Pressure Bleeder instead of manually pressing in on the piston?
Race Director
Joined: Apr 2003
Posts: 19,346
Likes: 654
From: Tampa, Florida
the easiest is to purchase plastic master cylinder fittings and rubber hose from any auto parts store.
I'm looking for a 'kit' like the one that come with new M/C.
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Yeah, but you usually have to ask for them. They come with new or reconditioned master cylinders and usually they will just take one out and sell it to you separate.
Racer
Joined: Jan 2007
Posts: 385
Likes: 3
From: RTP NC
I just bought a new (reconditioned) MC and there are directions stating: NOTE. New MC bench bleeding process. There are 2 plugs in each line opening rather than the plugs with hoses going back into the MC. Otherwise, the process is the same.. Just FYI. Bought mine at Advanced Auto for $20.00...
Burning Brakes
Joined: Aug 2004
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From: Tyler Texas
Drifting
Joined: May 2005
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From: BETHEL PARK PENNSYLVANIA
our m/cyls came with the hose kits before. now they give you plugs for the 2 fittings on the m/cyl. and you just pump it till the bubbles are gone in the resivor. just did 1 on a 78
vc
vc
Race Director
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From: Tampa, Florida
Team Owner
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From: Springfield MO
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