How To Bleed Brakes

[1970GranCoupeConvert]

Hey there,

Looking for some advice/tips/tricks/good vibes...

I am new to power brake booster brake bleeding.

I just converted from a manual master cylinder front disc/rear drum to power brakes.  The Master Cylinder is new as is the single part proportioning valve (it does not have the secondary rear wheel anti-lockup valve) and the front disc and rear drums are original.

I have already bench bled the MC by putting it in a vice and had the hoses routed up and dipped into the reservoir and pumped it until the bubbles stopped then installed it on the booster and connected up the prop valve and pipes and then pushed the brake pedal down by hand a few times.

Using a Mighty Vac I connected it up to the right side rear wheel and pumped away and cracked open the bleeder screw and only a very small amount of fluid came out but it never started to flow like it should. 

The reservoir is still mostly full so I am not getting any significant flow.

Am I missing something?

I have heard that the MC might have an internal valve or seal that can be damaged if I do the usual "pump five times and hold the pedal on the floor" routine.

Any advice is appreciated!!!

[DeathProofCuda]

There are many ways to skin the brake bleeding cat.  I've tried some, but I'm sure not all of them, but for me the standard method of holding the pedal down and cracking the bleeder still seems to work the best. I would give that a shot before looking for other problems.  If I don't have a helper around, I place a 2x6 flat against the front of my seat, then wedge an appropriately sized 2x4 between the brake pedal and the 2x6 to keep the pedal held down.  Takes a while, but its not too terrible of a way to spend an evening in the garage while listening to tunes and drinking beer.

I will say though that I had a similar problem a few years back after putting a new master cylinder on my Cuda.  Even with someone stomping on the pedal I couldn't get good flow out to the right rear wheel.  Ended up being an issue with the master cylinder.  I replaced the internals with a cheap rebuild kit and then it was good to go.

Good luck.

[Bullitt-]

Using a Mighty Vac I connected it up to the right side rear wheel and pumped away and cracked open the bleeder screw and only a very small amount of fluid came out but it never started to flow like it should. 

This does not register with me as the appropriate way.. Pumping then open bleeder.
I would think opening the bleeder before pumping, which in this case creates a vacuum, would be the order of things.... 

[Filthy Filbert]

What I like to do when I'm working by myself:

make sure the reservoir over the master is full to the brim.  Open the bleeder that's the farthest away from the master.  Let it stay open until you see fluid bubbling out of the bleeder.  Close it and move to the next fullest.

Once you go through all 4, put a weight on the pedal or wedge a stick between pedal and seat.  I like to use a piece of 1" square tubing about 18" long, and wedge a 6" long piece of 1x6 or similar wood between the tubing and the seat cushion so you don't tear up the seat cushion.  Bring the seat up to put pressure on the pedal.

Then go open the furthest bleeder to release the pressure.   Repeat 2 or 3 times or until the fluid comes out smoothly without any popping or bubbling.

Repeat through all 4.

Works every time.


When I have help, I do the open bleeder till bubbling, then have my helper pump the pedal while I go around and crack open the bleeders.

[Mr Lee]

For bleeding solo:

I attach a clear hose to the bleeder, point it up in the air so fluid is always resting against the bleeder, and then down into a clean jar on the floor.
Open the bleeder 1/8 to 1/4 turn and then continuously press and release the pedal about 10 times or as many as you can without pumping the master dry.  Refill the master and do it again.

To view what's going on:
I set up my cell phone on the brake drum and video record whats coming out of the bleeder through the clear hose. After pumping, id go back and watch the video.  When i saw that all the air bubbles came through, I'd go to the next wheel.

Once i got my borescope i would just set up the camera pointing at the bleeder hose and watch what was going on from the driver seat on the screen as I'm pumping the pedal.  Super easy. 

With this method there's no opening and closing the bleeder a million times, no jamming 2x4's against the seat, and i always get a firm pedal. 

Re-use whatever clean fluid you get in the jar.


Sent from my iPhone using Tapatalk

[Mr Lee]

How long since the car's been on the road?  Are things rusty? 
Hmm, I've never done manual brakes so I'm not sure about if everything is compatible / if you can just change the MC and that be it. 
I've never heard that about a seal in the MC potentially getting damaged by pumping and holding the pedal.  Not sure why that would be.
But, in my experience it is possible to push the pedal down to the floor so far that it got stuck on me once.  Pedal came back up but one of the springs in there was still stuck in the down position and it wasn't working right.  I had to pull the MC and pull out the guts out and reinstall.  Not sure if that helps you or not.

[1970GranCoupeConvert]

THANKS for the quick reply and the information!!!

[cuda hunter]

https://www.amazon.com/gp/product/B00CJ5DY16/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1&pldnSite=1

after dealing with a brake issue on my C body I purchased this pump above.  worked great.  Blew out some crap that I could not get to push out. 
I did replace the master cylinder and then power pumped it and everything is good to go now.

[1970GranCoupeConvert]

Oh HAPPY DAY!!!

I got the brakes bled...using the old fashioned pump three times and hold it on the floor method.

I had for many years used the Mighty Vac and vacuum bled the brakes however this time it did not work...no idea why.

So THANKS all for the well wishing...moments of silence and the positive energy flowing my way...now I need to turn some of that energy into black tire marks and burning rubber!!!

Dang...This deserves some positive energy dancing bananas!!!

[Mrbill426]

I just bled the completely new brake sytem on my '72 with a Mighty Vac but it was marginal at best up front and I got no fluid to the rear.  I put it away and got out the $4.00 one-man plastic bottle bleeder and it worked fine.

Oh HAPPY DAY!!!

I got the brakes bled...using the old fashioned pump three times and hold it on the floor method.

I had for many years used the Mighty Vac and vacuum bled the brakes however this time it did not work...no idea why.

So THANKS all for the well wishing...moments of silence and the positive energy flowing my way...now I need to turn some of that energy into black tire marks and burning rubber!!!

Dang...This deserves some positive energy dancing bananas!!!

[MoparCarGuy]

The attached pages from the 1970 Plymouth Service Manual discuss three methods of brake bleeding for disc brakes: Gravity, Pedal, and Pressure methods.
The tried-and-true Pedal Bleed method for disc brakes is not affected by the metering valve. The Pressure Bleed method using a separate hand vacuum pump (Mity-Vac or other) is affected by the metering valve. The metering valve stops flow of fluid to the front disc brakes when below 135 psi and thwarts your bleeding effort.

So what is going here? The answer is the metering valve delays application of the front discs from 3 - 135 psi in order to allow the rear drum brakes to apply first. This keeps the vehicle stable directionally when braking and, if the driver continues to apply more pedal pressure, the front brakes will apply upon reaching 135 psi to continue braking.

Great video on the disc brake valves and how they work https://www.youtube.com/watch?v=qzUk8W1-2pw.

[MoparCarGuy]

For bleeding solo:

I attach a clear hose to the bleeder, point it up in the air so fluid is always resting against the bleeder, and then down into a clean jar on the floor.
Open the bleeder 1/8 to 1/4 turn and then continuously press and release the pedal about 10 times or as many as you can without pumping the master dry.  Refill the master and do it again.

To view what's going on:
I set up my cell phone on the brake drum and video record whats coming out of the bleeder through the clear hose. After pumping, id go back and watch the video.  When i saw that all the air bubbles came through, I'd go to the next wheel.

Once i got my borescope i would just set up the camera pointing at the bleeder hose and watch what was going on from the driver seat on the screen as I'm pumping the pedal.  Super easy. 

With this method there's no opening and closing the bleeder a million times, no jamming 2x4's against the seat, and i always get a firm pedal. 

Re-use whatever clean fluid you get in the jar.

Totally agree with the jar and pedal pressure method. It is almost foolproof. If using DOT-5 silicone fluid, be careful with reusing the fluid in the jar. There can be microscopic bubbles in the silicone which are very difficult to get out. Some mechanics save the silicone in the jar separately and continue bleeding with new silicone fluid until done. That way your "salvaged" silicone can sit to let those bubbles slowly work there way to the top. If the salvaged silicone looks contaminated with rust or anything else, do not reuse it. Dispose of it at your local auto parts stores waste receptacle.

I always use DOT-5 silicone (purple) because it is does not absorb water, does not damage paint, and is virtually maintenance-free as compared to regular DOT-3 or -4 fluids. The only caveat is that you must either start with a new set of brake lines and components or completely flush every last bit of DOT-3 or -4 from your system before you can convert to silicone.