Master Cyllinder Bench Bleed Methods

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Does the plug method of bench bleeding a MC have more of a chance of damaging seals than the recycle fluid method? I used the plug method on the last MC and took an hour to bleed and ended up defective with the pedal going to the floor after several bleeds. Maybe a coincidence but...
 
I've always done bench bleeding with the master cylinder on the car, using a kit like the one linked by Quest. Thread in and snug up the fittings, attach the hoses, fill the reservoir with brake fluid, use the little clips in the kit to hold the hose ends below the fluid level, slowly work the brake pedal, and the air is out of the master cylinder in a minute or two (usually after just 4-5 strokes). I like to have a helper watch the reservoir to tell me when there are no more air bubbles.

I've only had occasion to do this on GM vehicles with a very common master cylinder. I don't know if there's a reason this wouldn't work well on other vehicles.
 
Here's one more tidbit to share RE: master cylinder bench bleeding.

After you are satisfied with the bench bleeding of your master cylinder and installed on the car, do get a helper to bleed all the calipers/brake cylinders at least 1 round (2 rounds, to be on the safe side). This will ensure that there's 100% no air trapped within your hydraulic braking system.

While I've seen ECG on one episode RE: using hand/finger to cover the master cylinder connector hole while bench bleeding and then also mentioned that no need to perform individual caliper/brake cylinder bleeding of air once the replacement master cylinder installed (I believe it was an integra or similar), fact is: he may not be 100% right in this case, for there's still the potential possibility of introducing air into the system as he swap the fitting ends during the installation.

Play it safe. Afterall: properly functioning braking system is your last saviour on the road if every other things go wrong.

Q.
 
Quest is right on. While usually the lines at the MC are at the high point and a minuscule amount of air, if any, gets in, any amount of air is a problem. I'm only satisfied after I've checked at all four wheels, found no air bubbles, and have a firm pedal.
 
I have always done it This way. Master cylinders use to have the bleeder kits in the box.

Never done the gravity bleed way in the first part of This video, but I will next time around. Little bit more messy, but no tubing to have to play with.
 
Good advice, I always do a bleed at all four corners with a MC replacement. In this case I replaced all the hard lines and the front calipers, then did a bleed before and after the MC replacement. I will do a bleed at all corners again after the 2nd MC replacement.
 
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Originally Posted By: BigD1
I have always done it This way. Master cylinders use to have the bleeder kits in the box.

Never done the gravity bleed way in the first part of This video, but I will next time around. Little bit more messy, but no tubing to have to play with.


I did it the 2nd way - plug/gravity bleed for the 1st mc replacement.
 
Originally Posted By: jr047
I've always done bench bleeding with the master cylinder on the car, using a kit like the one linked by Quest. Thread in and snug up the fittings, attach the hoses, fill the reservoir with brake fluid, use the little clips in the kit to hold the hose ends below the fluid level, slowly work the brake pedal, and the air is out of the master cylinder in a minute or two (usually after just 4-5 strokes). I like to have a helper watch the reservoir to tell me when there are no more air bubbles.

I've only had occasion to do this on GM vehicles with a very common master cylinder. I don't know if there's a reason this wouldn't work well on other vehicles.


Why do they call it "bench bleeding" when it's on the car while you're bleeding it ?
 
Originally Posted By: Merkava_4

Why do they call it "bench bleeding" when it's on the car while you're bleeding it ?


Exactly this. Some firewalls have the MC pointing uphill and away, and you have to get fluid in the far corners so there isn't a big bubble you can't force down a line nut and out. My firebird MC came with the bench bleeding hoses presumably b/c it's a design that needs it. Bench bleed it, level, before you put it in, then bleed it again through the wheels.

I don't think you can blow a seal just using your thumbs on the pushrod plunger thing no matter how you try.
 
I am using the plug /gravity method shown in the 1 Napa video. I am only getting fluid out of one reservoir - RF/LR with gravity. The is a diagonal split system with 4 ports. Can I still cycle the piston without damage from no brake fluid to the seal?
 
Originally Posted By: Merkava_4
Why do they call it "bench bleeding" when it's on the car while you're bleeding it ?


My shop manuals show mounting the MC in a vise, on a bench, so that would be bench bleeding.

I don't own a vise so I have had success with putting the MC on the booster on the car and using the brake pedal to pump it. Again, this is just my experience on '70s and '80s GM cars with a very common master cylinder; I do not claim it will work for every car in every situation.
 
Originally Posted By: edge10
I am using the plug /gravity method shown in the 1 Napa video. I am only getting fluid out of one reservoir - RF/LR with gravity. The is a diagonal split system with 4 ports. Can I still cycle the piston without damage from no brake fluid to the seal?


If you really get stuck, get a dishpan from dollar tree and a gallon of DOT3 from walmart, dunk the thing, and pump away.

I think they have a "brake fluid gel" they use as assembly lube for the seals.
 
Originally Posted By: jr047
My shop manuals show mounting the MC in a vise, on a bench, so that would be bench bleeding.

I don't own a vise so I have had success with putting the MC on the booster on the car and using the brake pedal to pump it. Again, this is just my experience on '70s and '80s GM cars with a very common master cylinder; I do not claim it will work for every car in every situation.


AH HA!! I knew there was a story behind it .... that's why I called you out on the carpet.
grin2.gif
 
This is the last time I try to be helpful, to share something that has worked for me, because now I know I will be "called on the carpet" just so someone else can be entertained.

I have better things to do than play word games with someone on the Internet.
 
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I ended up using my Mityvac very slow at less than 5 psi vac to draw the fluid out of the two ports. There was definitely an air bubble before the fluid came out,but it bled pretty quick after the Mityvac .

I see how the in car bleed at the wheels go.

Your right, it look like it has some assembly lube when I checked the piston bore and reservoir.
 
Originally Posted By: jr047
This is the last time I try to be helpful, to share something that has worked for me, because now I know I will be "called on the carpet" just so someone else can be entertained.

I have better things to do than play word games with someone on the Internet.


Wait a minute, LOL! I brought it up because I thought I was doing it wrong all these years. If I can just pump the pedal like you did, that'd be a lot easier than stabbing it with a #3 Phillips screwdriver.
grin2.gif
 
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