Newbie question on power bleeders for brake

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Hello everyone,

I've recently bought a Mityvac MV6840 power bleeder to make my bleeding operation a one man job. This is was my first bleeding on a car and first use of power bleeder.

I followed this video as a reference since they are using the same bleeder: http://www.youtube.com/watch?v=tBNWMWNAXQU#t=85 and I did the following:

1. Removed old fluid from reservoir

2. Topped reservoir to max using new DOT 4 fluid

3. Hooked Mityvac filled with new DOT 4 fluid (2 liters) to reservoir via special adapter

4. Pumped 15 psi of pressure

5. Hunged Mityvac to be at the top of the hood so that it will be the highest point

Once I started to bleed on the caliper I decided to let it go for a while since I really wanted to flush the system. I bought the car recently and I was not sure when the previous owner changed the fluid.

Anyway, after 100 ml bleed from the caliper imagine my surprise when I saw a compressed air going out from the bleed valve
frown.gif


I closed the valve and took I look at the Mityvac. I saw that it was pumping air and fluid into the reservoir. So I guess since my reservoir is really tiny it went dry and compressed air was pushed through the master cylinder.

I wonder, if this a normal thing? I saw a couple of videos of featuring Motive bleeder, and they all say that it is normal to have some air in tube, e.g.: http://www.youtube.com/watch?v=miv3jjN95ok#t=175

How come it works for everyone but I got air in MC?
 
While this is not normal, fact is, you have (by chance) introduced air into your brake system when your reservoir runs out of fluid.

Now, you have to re-do the whole process all over again, starting from the brake master cylinder (make sure your reservoir is full before you proceed) and re-purge the whole system (to be on the safe side).

Q.
 
Motive Bleeders like a KD Tool use a single pressure tank and only pump air in a system if it runs out of fluid, if air is in the tube when you hook it up it will go to the top of the reservoir and stay there it will not go in to the system. You should get a sold flow out of bleeder when flushing system or when bleeding is done. I did add a valve in line with both my bleeders so all I do is hook up bleeder and turn on valve to charge system so I am pumping it up before I put bleeder on car and hose purges once valve is turned on.
 
Hello everyone,

Thanks for all your replies. To answer your questions:

The Mityvac did not run out of brake fluid. I put 2 liters and the problem started to happen when the bleeder had 1.9 l in the tank.

I notice another thing when using the thing. If I pump say 15 psi the fluid starts to flow from pressure bleeder to reservoir. At some point the flow stops and I do not see any fluid coming through the hoses. If I put more pressure nothing will happen (bear in mind that I cannot pump pressure infinitely since I am afraid to damage reservoir). I had to drop the pressure to 0 in the pressure bleeder tank and again pump to 15 psi.

If I don't drop the pressure the bleeder effectively pushes air through reservoir and the system runs dry. I checked on youtube more detailed videos on power bleeders and I found this: http://www.youtube.com/watch?v=-GggWPGKm3w#t=290 . (the video should be watched since 4.50). As you can see the guy is pumping the pressure and he has some air in the tube as well. He managed to solve the problem by ticking on the hose and waiting until each bubble is moved out from reservoir to pressure tank (see video further).

This video inspired me and I decided to do the same, so I changed my algorithm to the following:

1. Pump 15 psi of pressure and straighten the hoses

2. Tick on hose for a while until all air bubbles are gone from reservoir to pressure tank

3. Open bleed valve on caliper for a short time (max 30 seconds) and close it again

4. Check the pressure tank hose and see if there any bubbles in the line

5. If there are, drop pressure to 0 psi and repeat the sequence from # 1

I spent around 6 hours total yesterday doing the flush. On a first run I introduced air in the system since I was naivly told pressure bleeder is a tool which you hook up and forget - just open the bleeders. On a first run I used the following order:

Left front
Right rear
Right front
Left rear

However after I introduced air I changed my behavior according to video https://www.youtube.com/watch?v=-GggWPGKm3w#t=290 so I again topped the reservoir and started to bleed in the following order:

Right rear
Left rear
Right front
Left front

After so many hours of slow bleeding I finally managed to get out air from the system and now pedal is firm and breaking is very efficient.

However, I am still lost what did I do wrong on the first bleed?
 
Maybe 15 psi is too much for bleeding. Whenever I open my brake system to change a caliper, I let the system gravity bleed to fill the new caliper. It takes about 5-10 minutes for the head pressure from the MC reservoir to push the air out of the caliper, but I get a solid brake pedal afterwards. I just make sure that the reservoir doesn't run out of fluid.
 
A_Harman,

Originally Posted By: A_Harman
Maybe 15 psi is too much for bleeding.


Believe it or not, but during these 6 hours of removing air from system I had come to the same assumption as well, so I gradually tried to decrease pressure from 15 psi to 10 and see if it changed anything. It did not. I also tried 18 psi - same result.
 
I just went through Motive bleeder instructions at http://www.motiveproducts.com/frame-instruct.htm and I found this:

9. If fluid remains in the Power Bleeder tank when through: tip the tank away from fluid pick-up tube and open bleed valve closest to the master cylinder. Allow air to flow into fluid reservoir until fluid level falls just to the maximum fill level on your reservoir. Close the bleed valve and tighten to specified torque.

Is this sentence more or less describes my problem?
 
I can bleed the brakes or flush them myself with just an empty bottle and a piece of tubing. I noticed that, with the bleeder open and a tube attached to it, if you partially pump the pedal and release it fairly slowly at first when the tube is empty, only part of the fluid pumped out, will retract when the pedal is released.

So, I can do the slow pumping action at first to prime the tube, and once the tube is full of brake fluid, you can start pumping faster and all the way to the floor if you wish. It makes for an easy and fast brake bleeding or flushing job.
 
"all the way to the floor" seems quite likely to damage the master cylinder on an old system. I assume this is because its beyond the normal travel, and there's perhaps a wear ridge that chews the seals up, though I don't really know.

I made myself a simple brake-pedal-holder-downer thingy with a bit of aluminium channel shelf support (any stick or tube would do) notched for a rope at one end. Stick goes through the steering wheel onto the brake pedal, rope is tied with a clove hitch on the steering wheel rim.

I initially had an adjustable depth stop at the pedal end by tying the stick to the pedal lever so that part of the stick projected below it, but I found I didn't need one.

If you used bungee cord, or hung a weight on the end of the stick, you could probably get more brake pedal travel when you opened the bleed nipple and the bleed job would go quicker, but then you'd need a depth stop anyway to avoid master cylinder seal damage from over-travel.

I know you can get various gadgets in the UK to make this a one-man job, but they arent readily available here in Taiwan.

I tried using a Taiwanese girl for this purpose (and have used a Scottish girl in the distant past) but the stick is simpler, more reliable, and much cheaper.
 
Originally Posted By: volodymyr
Thanks guys for your responses.

Any pressure bleeder DIY here?
smile.gif



See stick-thingy, though its not a pressure bleed, other than from limited brake pedal pressure.

For DIY pressure bleed, any reason you couldn't do this the other way around? i.e. backflush the system, perhaps after an initial downward flush?

I'm assuming there aren't any non-return valves etc that would prevent this.

I'm thinking empty and rinse out the reservoir with "turkey baster" style pipette, then maybe do an initial low volume downward bleed with the stick thingy, then back-flush it with a hypodermic syringe through the bleed nipple

You'd have to watch you didn't introduce any air, of course, but so do doctors, and they don't kill all that many people, AFAIK.

A syringe is cheap, should give you complete control over the volume delivered, and I'd expect brake fluid would be compatible with its piston seal.
 
Last edited:
Turns out, unsurprisingly, that isn't a new idea

https://www.youtube.com/watch?v=lBk00597EyE

Apparently pretty tolerant of air entrainment, since he fills the syringe in an unusually kack-handed way which probably introduces loads of it, but the method still works.

I'd want to do a bit of a downward flush first though, to reduce the amount of [censored] blown back through the master cylinder.

You could presumably also suck with the syringe, but I suppose that'd increase the chance of drawing air into the system.
 
Last edited:
Catch being, gravity bleed takes time. And I suppose if you walk away to get a cup of coffee, there is the chance you'll forget what you're doing and not come back for a couple hours. At which time the system has fully drained and let lots of air in.
 
IIRC, gravity bleed does not solve the main problem: letting air via bleed valve.

Which is at least been solved by pressure bleed (since liquid is being pushed out of value) or vacuum bleed (air is not going inside the bleed valve due to vacuum).
 
I have a vacuum bleeder, still use it sometimes. Also the speed bleeders. On both I would take the bleeder screws out and put some thread sealant paste on them or I had problems with air getting sucked in around the threads.
 
Hello everyone,

Some update on my Mityvac MV6840 pressure bleeder. Few days ago I hooked it up to my Nissan Qashqai (this is an European version of Nissan Rogue) and I got exactly the same result.

I use the kit using the following way:

1. Remove old fluid as much as possible from master cylinder (MC) reservoir

2. Top up the MC reservoir with new brake fluid (to max level)

3. Fill Mityvac MV6840 with 1 liter of brake fluid

4. Connect Mityvac MV6840 to MC reservoir and make 15 psi of pressure

5. Once I start to bleed the calipers I see that the level in MC
reservoir is dropping, but the fluid does not flow from Mityvac MV6840
to MC reservoir. If I do nothing, the level in reservoir drops and air
is entering the system thus causing a major problem

In order to fix the problem I need to relief the pressure and pump again to 15 psi - once I start pumping the fluid flows well, but then once I start to bleed it does not and I need to repeat the process.

I wonder if this is normal?

Originally Posted By: volodymyr
Hello everyone,

I've recently bought a Mityvac MV6840 power bleeder to make my bleeding operation a one man job. This is was my first bleeding on a car and first use of power bleeder.

I followed this video as a reference since they are using the same bleeder: http://www.youtube.com/watch?v=tBNWMWNAXQU#t=85 and I did the following:

1. Removed old fluid from reservoir

2. Topped reservoir to max using new DOT 4 fluid

3. Hooked Mityvac filled with new DOT 4 fluid (2 liters) to reservoir via special adapter

4. Pumped 15 psi of pressure

5. Hunged Mityvac to be at the top of the hood so that it will be the highest point

Once I started to bleed on the caliper I decided to let it go for a while since I really wanted to flush the system. I bought the car recently and I was not sure when the previous owner changed the fluid.

Anyway, after 100 ml bleed from the caliper imagine my surprise when I saw a compressed air going out from the bleed valve
frown.gif


I closed the valve and took I look at the Mityvac. I saw that it was pumping air and fluid into the reservoir. So I guess since my reservoir is really tiny it went dry and compressed air was pushed through the master cylinder.

I wonder, if this a normal thing? I saw a couple of videos of featuring Motive bleeder, and they all say that it is normal to have some air in tube, e.g.: http://www.youtube.com/watch?v=miv3jjN95ok#t=175

How come it works for everyone but I got air in MC?
 
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