MC bench bleed problem
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MC bench bleed problem
I looked in the FAQ and did some searches, but cannot find the answer to this problem.
My '67 non-power brakes will only work if pumped, and even then not well. I believe the MC is bypassing internally. It has a non-correct MC already, so I am going with a parts-store rebuilt unit.
I put the MC in the vise (clampling on the flange) and bench bled according to the instructions. This MC came with threaded plugs for the output ports to use on the bench. Put the fluid in, and started slowly moving the piston as instructed, 3/4" to 1" strokes. The bench bleeding instructions say you should get to a point where the piston only moves 1/8". They do not specify how many strokes this may take. I have actuated the piston 300 times (I counted), and it still moves 1/2". There are no bubbles coming out though. When I move the piston, I see fluid squirting up through a hole in the bottom of the front reservoir, making a ripple but no bubbles. Edit: to clarify - this MC did bubble, unlike the first one.
I've already taken one MC back that never changed stroke length and also never bubbled significantly. Is this one bad too, or are the instructions just bad?
My '67 non-power brakes will only work if pumped, and even then not well. I believe the MC is bypassing internally. It has a non-correct MC already, so I am going with a parts-store rebuilt unit.
I put the MC in the vise (clampling on the flange) and bench bled according to the instructions. This MC came with threaded plugs for the output ports to use on the bench. Put the fluid in, and started slowly moving the piston as instructed, 3/4" to 1" strokes. The bench bleeding instructions say you should get to a point where the piston only moves 1/8". They do not specify how many strokes this may take. I have actuated the piston 300 times (I counted), and it still moves 1/2". There are no bubbles coming out though. When I move the piston, I see fluid squirting up through a hole in the bottom of the front reservoir, making a ripple but no bubbles. Edit: to clarify - this MC did bubble, unlike the first one.
I've already taken one MC back that never changed stroke length and also never bubbled significantly. Is this one bad too, or are the instructions just bad?
Last edited by L79vette; Nov 7, 2009 at 06:53 PM. Reason: unclear
Burning Brakes
Joined: Jun 2000
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I prefer using the tubes method (method B), always works for me;
http://www.performanceonline.com/blo...ench-bleeding/
http://www.performanceonline.com/blo...ench-bleeding/
Le Mans Master
Joined: Nov 2008
Posts: 5,691
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From: columbus oh
on dual chambered m/c's you must engage both ports and 3/4 inch wont do it...you must go almost to the limit of travel and yes the tube method is best and a lot neater as it captures fluid....i dont trust re built m/c's although others may disagree.....ss brake company makes a neat brand new unit with a 1" cylinder for your car and it comes with tubes for bench bleeding which i feel is somewhat over rated ..jmo ..good luck
Le Mans Master
Joined: Feb 2008
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From: NJ Hockey beer league
You can't judge a Master cylinder by the number on bubbles you get on the bench. If the air is out, then install it and proceed with bleeding the calipers. You will know soon enough if there is anything that requires further attention. Sounds like you might be over analyzing this a bit. 
Pilot Dan
Pilot Dan
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You can't judge a Master cylinder by the number on bubbles you get on the bench. If the air is out, then install it and proceed with bleeding the calipers. You will know soon enough if there is anything that requires further attention. Sounds like you might be over analyzing this a bit. Pilot Dan
Pilot DanIs it OK to have the piston stroke 1/2" after bleeding? It seems that it would not work.
Last edited by L79vette; Nov 7, 2009 at 09:50 PM.
Team Owner
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From: Washington Michigan
2. Just use the $5.00 blister-packed kit with the plastic adapter fittings and hoses (see photo below) and stroke it until you don't see bubbles in the fluid exiting the hoses, and you're done. The stroke length won't change - never heard of that either. I've only done this about 100 times over the years.
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John - The 1/8" stroke deal is because the outlet ports are plugged off. With tubes connected like you have there, you get a full stroke and the fluid is pumped out through the outlet ports and back into the reservoir. But with the plugs in place, the fluid cannot go out the outlets, which is supposed to give you a 1/8" travel when actuating the piston manually after the air is out. Since the plugs and instructions to go with came with the MC, I've been using their method. Since the travel does not do what they say it should, I must again conclude the MC is bad.
Another set of instructions I found online said to use the method in your picture and then install plugs to test the MC. With the plugs in, they also said you should only see 1/8" travel. Since it is traveling way more than that, I can only conclude the pedal woud be very low.
Here is a link to the instructions I am using:
http://www.cardone.com/English/Club/...es/Bleeder.asp
Another set of instructions I found online said to use the method in your picture and then install plugs to test the MC. With the plugs in, they also said you should only see 1/8" travel. Since it is traveling way more than that, I can only conclude the pedal woud be very low.
Here is a link to the instructions I am using:
http://www.cardone.com/English/Club/...es/Bleeder.asp
Last edited by L79vette; Nov 8, 2009 at 02:51 PM. Reason: added link
Burning Brakes
Joined: Feb 2008
Posts: 916
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From: prescott arizona
Master cylinder bleeding
1. I've never heard of bench-bleeding a master cylinder with the outlet ports plugged.
2. Just use the $5.00 blister-packed kit with the plastic adapter fittings and hoses (see photo below) and stroke it until you don't see bubbles in the fluid exiting the hoses, and you're done. The stroke length won't change - never heard of that either. I've only done this about 100 times over the years.
2. Just use the $5.00 blister-packed kit with the plastic adapter fittings and hoses (see photo below) and stroke it until you don't see bubbles in the fluid exiting the hoses, and you're done. The stroke length won't change - never heard of that either. I've only done this about 100 times over the years.
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I agree with John too - I'm familiar with his work, and understand that he has done this many times.
Auto parts stores do not seem to carry the tube-type bench bleed kits any more. So I am following the directions that came with the MC. Since it is not behaving as specified, this one is going back too.
Auto parts stores do not seem to carry the tube-type bench bleed kits any more. So I am following the directions that came with the MC. Since it is not behaving as specified, this one is going back too.
Le Mans Master
Joined: Nov 2008
Posts: 5,691
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From: columbus oh
do you have outlets on both sides of the m/c??.....why would you plug them??....if you have them on both sides then yes plug one side only and use the tubes from the open side....after 300 pumps wow ....it usually takes 10 or 15
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Yahoo! Success at last.
With the tubes I was able to flush out the air. It still took many pumps. I also started pinching the hose (especially on the rear reservoir) before letting the piston back out, which led to more bubbling. Got lots of small bubbles, 100+ strokes again. The good news is that once all the bubbles stopped, when I put the plugs back in there was only 1/8" of piston travel. This is like bench bleeding followed by a bench test with the plugs in place. I do not know why the bleed-with-plugs-in-place procedure did not work as advertised, but it certainly did not. I think what is supposed to happen with the plugs in place is that the air comes up through holes in the bottom of the reservoir. Some certainly did, but there was a lot left.
Now that I have the correct piston travel, I will install with confidence.
Thanks JohnZ and everyone else for the advice.
With the tubes I was able to flush out the air. It still took many pumps. I also started pinching the hose (especially on the rear reservoir) before letting the piston back out, which led to more bubbling. Got lots of small bubbles, 100+ strokes again. The good news is that once all the bubbles stopped, when I put the plugs back in there was only 1/8" of piston travel. This is like bench bleeding followed by a bench test with the plugs in place. I do not know why the bleed-with-plugs-in-place procedure did not work as advertised, but it certainly did not. I think what is supposed to happen with the plugs in place is that the air comes up through holes in the bottom of the reservoir. Some certainly did, but there was a lot left.
Now that I have the correct piston travel, I will install with confidence.
Thanks JohnZ and everyone else for the advice.
Melting Slicks
Joined: Dec 1999
Posts: 2,262
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From: Goldsboro NC
I'm replacing the MC on my 67 now also.
1. The MC that's on the car has bleeder screws like JohnZ's picture. The rebuilt MC from Advance is not the exact design, and no bleeder screws. Is the new one the correct application?
2. Where did you find the bleed tube kit? I can't find one at Advance or Auto Zone.
1. The MC that's on the car has bleeder screws like JohnZ's picture. The rebuilt MC from Advance is not the exact design, and no bleeder screws. Is the new one the correct application?
2. Where did you find the bleed tube kit? I can't find one at Advance or Auto Zone.
Last edited by Jeff Garner; Nov 9, 2009 at 07:56 PM.
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