brake bleeding

[nevets]

I realize this topic has been covered many times...apologies for covering well trodden ground.

My usual 2-person method to bleed brakes is to have person-A in the car pump the pedal until it is firm and then hold it there, applying pressure. Person-B then opens the appropriate bleed valve, which has a tube attached extending into a jar of clean brake fluid. As soon as the valve is opened, the pedal falls to the floor and hopefully air is expelled from the brake line along with a small amount of brake fluid. Person-B then closes the bleed valve, and person-A raises his/her foot. This process is repeated until no more air is expelled, and done at each brake in the appropriate order. Throughout the process the master cylinder reservoir is checked and brake fluid added as needed.

Another method, which I haven't actually tried, is this: Again a tube is attached to the bleed valve extending into a jar of clear brake fluid. Person-A pumps the pedal as before, BUT with the bleed valve open, which I assume will expel any air along with brake fluid, as well as pull in some fluid from the jar on the pedal upstrokes (?) Then with the pedal held to the floor, person-B closes the bleed valve. Process is repeated at all four corners of the car, while keeping an eye on the fluid level in the MC reservoir.

My question is this: Which method is better?

I have used products like EZ Bleed, and a German pump-up canister pressurizer with some level of success, but my problem with those gadgets is I always seem to get brake fluid where I don't want it and then cleaning /drying/ storing them is pain.

Thanks!

 

[vette]

Hi Nevets, IMHO I believe the first method is the most fail safe. With the bleed valve closed before the up stroke of the pedal is the safest way to preclude any air being sucked back in. The second method is one that has been encouraged since I was a kid when there is only one person to do the job. Theoretically with the tube immersed in the fluid in the jar air can not be drawn back in.
A couple of points I might mention that might help. It has been quite awhile since I have bled my Healey's brakes but on many cars that I work on I am able to gravity bleed the brakes. That is just open a bleeder screw and let it drain. The only time that this method may not work is when part of one of the lines goes higher than the reservoir holding the fluid. On the Healey I think this works on the brakes but will not work on the clutch because the clutch line from the MC to the Slave Cyl goes up along the firewall. One tool that has worked for me when the gravity method does not work is from Groit's Garage. It uses shop air pressure to siphon the fluid thru the lines. It is much better than the vacuum tools because it uses shop air. Sometimes pressure up into the 70 psi range. Here is the web page: https://www.griotsgarage.com/produc...eeder.do?sortby=ourPicks&refType=&from=Search

One more idea. If the bleeder screws are opened to much, air is drawn in around the threads.

 

[roscoe]

One problem I've had with the second method is that the bleeder screw threads can let some air by so when you think you are sucking fluid only back up into the system, you are really pulling in a bit of air. I have managed to eliminate this by the use of teflon tape on the bleeder threads, which may have been worn but it is a tedious method.

 

[steveg]

I like the Dorman bleeder syringe for simple effectiveness and easy cleanup. Pulls the juice out through the screw. Amen to the use of teflon tape on the screw threads. Packing grease around the screw where it meets the caliper or cylinder also works.

 

[nevets]

Thanks everyone...couple of questions:
Regarding gravity bleed - one wheel at a time or all wheels at once? And how long are the bleed screws left open...presumably with a catch container below?
Regarding the Dorman syringe - What happens if the plunger is fully withdrawn and still no air appears? Do you detach the tube, empty the syringe and repeat?

 

[dklawson]

If I may add a comment....

The steps in method 2 as described above are not quite the sequence I have used for years. In the method I learned it is still a two person method requiring a tube and a catch jar and coordination between the two people. However, as I learned brake bleeding, you do not leave the bleed nipple open.

The second method as I practice it is sometimes referred to as brake flushing since all the fluid is typically replaced. Person A is at brake hub, person B is in the driver's seat. Person A connects a bleed tube from the nipple and places the other end of the tube in a catch jar. Person A then opens the bleed nipple about 1/2 turn and calls "DOWN" to person B. Person B pushes the pedal all the way down and holds it to the floor. Person B then calls "DOWN" back to person A who closes the bleed nipple. Person A then calls "UP" to person B who releases the pedal slowly. When the pedal has reached the top, person B calls back "UP" to person A.

This UP/DOWN OPEN/CLOSE sequence is repeated until no air bubbles are seen exiting the tube in the jar. When flushing the fluid, it is repeated until no more dirty fluid enters the catch jar. Of course... the level of the reservoir is checked frequently.

It does not hurt to apply a layer of heavy grease round the base of the bleed nipple to prevent any tiny bits of air from being sucked in around the threads during the pedal's "UP" stroke. Those tiny bubbles typically make it look like there is still air in the pipes when there really isn't. No... the grease does not risk contaminating your brakes or brake fluid. The grease is always on the discharge side of the bleed nipple and not inside the wheel cylinder or caliper.

A modern, 1-person variation of this bleed method can be done with either 1) a check valve in the bleed tube, or 2) modern Speed Bleeders. Speed bleeders are available in most parts stores for about $10 a pair. They are bleed nipples with built in check valves and thread sealant on their threads. I have several bleed hoses with check valves in them. I also have used a MityVac to vacuum bleed/flush brakes when necessary.

The first method described above (pump, pump, pump, hold, open nipple) was alien to me until a few years ago. Apparently that method was/is very commonly used on American cars. While it works, there are certain British and foreign cars where I would not recommend it. In general, if the car has a proportioning valve of any type for the rear wheels, method 1 can make it very difficult or impossible to bleed the rear brakes.

The question was asked above, "which method is easier". For me, the 1-person method using grease around the nipple threads and a bleed hose with check valve is by far the easiest as you don't need a second person or need to coordinate steps with them. Vacuum bleeding is my second choice. Method 1 would be my third choice. Some people swear about using the Eezibleed kit. I have no experience with that method but it seems like a lot of kit and a lot of expense to handle what should be a simple job.

EDIT: Sorry, I overlooked your question about gravity bleeding and the Dorman syringe.

I have only resorted to gravity bleeding once. I suggest to use that method only if you have bench bled the master cylinder to get it primed. Then bleed the wheels one at a time working your way from furthest from the MC to closest. In fact... you may want to move downward from the MC and crack each fitting "open" and leave it open until fluid starts to drip out, then tighten that fitting and move down the line. When you get to the wheel cylinders and calipers, proceed as long as necessary to get a continuous flow of fluid without new bubbles in the discharge hose. Keep your eye on the reservoir.

On the Dorman syringe bleeder, treat that the way you would any bleeding operation. If they syringe (catch jar) is getting full... stop, close the bleed nipple, then remove the hose and empty the syringe. Like the MityVac and check valve bleed tube method, a layer of grease at the base of the bleed nipple to prevent air from getting sucked in around the threads is advisable.

 

[RAC68]

I have used the 1-person procedure for at least 20 years on a number of cars including my Healey with NO issues. I do not open the bleed screw to the extend that it is so loose that air could be drawn up into the system and have not noticed any problems. I use a tube and empty water bottle with the tube outlet sitting below the surface of an initially small amount of fluid in the bottle. I often secure the bottle to a level platform and drill a hole through the cap the size of the tube to have the tube as stable and properly positioned. Without the help of a second individual, this is my preferred approach.

Ray(64BJ8P1)

 

[vette]

Thanks everyone...couple of questions:
Regarding gravity bleed - one wheel at a time or all wheels at once? And how long are the bleed screws left open...presumably with a catch container below?

Nevets, Dk covered it pretty good, but to answer your question, When I gravity bleed I have always done it one wheel at a time. DK makes an interesting point I believe in that he suggested opening all the bleeders at the same time to facilitate gravity pushing the fluid from the highest point (the reservoir) to the lowest. I have never done that but it might help, just keep a sharp eye on the fluid in the reservoir. Also a catch can and tube would be beneficial at each wheel unless you want to oil your garage floor. You let each bleeder open until there is steady fluid coming out with no visible bubbles. Here a clear tube is most beneficial especially to keep the fluid away from the braking surfaces. I would still do one wheel at a time if it were me. Depending on the brake system layout you might have to wait a minute or two for a steady flow.
You might find it interesting to know that at most professional shops where they do routine brake work as new linings, rebuild or replace calipers or wheel cylinders, the mechanics usually have very little brake bleeding to do per sea. If they are going to replace a caliper or wheel cylinder they get the new piece close at hand, take the brake line off the old one and very quickly thread it into the new one. Without touching the brake pedal, no air is drawn in. They may allow a little drip to facilitate a wee bit of gravity bleed. Then a check of the reservoir to top it off and they're done.

 

[steveg]

Thanks everyone...couple of questions:
Regarding gravity bleed - one wheel at a time or all wheels at once? And how long are the bleed screws left open...presumably with a catch container below?
Regarding the Dorman syringe - What happens if the plunger is fully withdrawn and still no air appears? Do you detach the tube, empty the syringe and repeat?

Syringe: typically bleeding the left rear first, I may still be getting a couple of bubbles at the end of the plunger stroke. I close the bleeder valve, empty the syringe into a jar and start over. Most of the air comes out the first bleed. The other three wheels - very little air comes out.

When I installed my Fiat dual master cylinder - rather than bench bleeding it before installation, I relied on the syringe to pull fluid through the MC. which it did with no problems.

 

[bob hughes]

I bought a Gunson Ezee bleed unit for mine, I some times use it, but my one person method suites me better. - a Lighting stand to a height just above the level of the car (so it will be above the level of the hydraulic reservoir), a long length of thin clear poly tube mated to a slightly thicker one, to fit over the bleed nipple and a jar. The jar is placed at the bottom of the lighting stand, the thin clear poly tube is draped over the stand with one end in the jar and the mated thicker end fixed onto the nipple. Crack open the nipple and pump the brake and watch the fluid climb up the tubing, you can see the air bubbles coming up and when they stop, tighten up and move on to the next.



Bob

 

[dklawson]

... Crack open the nipple and pump the brake and watch the fluid climb up the tubing, you can see the air bubbles coming up and when they stop, tighten up and move on to the next.
Bob

That is very clever. I like it.

 

[nevets]

Bob Hughes
I'm intrigued by the description of your apparatus. Is my sketch accurate? I am assuming the thin tube is used to keep the volume of brake fluid to a minimum and to speed up the flow? You keep pumping the brake pedal until you stop seeing bubbles? And no concerns sucking in air around the nipple threads? Thanks

 

[dklawson]

I cannot answer for Bob but your sketch is what I envisioned from his description. I don't think you would have to worry about sucking air in around the nipple threads if you operate the pedal slowly as there will always be head pressure from the column of fluid pressing "out" at the bleed nipple.

Incidentally, the only thing I question in your sketch is the orientation of the bleed nipple. In every instance I am familiar with the nipples are either horizontal or vertical pointed up. If they point down it will be difficult to get all the air out of the caliper/cylinder.

 

[nevets]

Oh yes, sketch is sketchy, nipple should be pointing up...