A tip for bleeding brakes

[Normk]

Teflon tape or other methods of sealing the bleeder nipple threads are not necessary although a good seal there can help to identify if air is still being removed as the bubbles will not be by-pass air pst the nipple threads. I never bother with this but home users sometimes do. That's the thing with hobby work, it allows lots of time to do things.

The various tips in the Mityvac (and other kits) aren't usually applicable to brake bleeding but rather for connecting to various vehicle hoses for evap. system service, etc. One usually just pushes the bleeder hose over the nipple but if the nipple and hose are of different size, use one of the adapter cones to connect to a short length of hose which fits tightly over the bleeder nipple.

Others do things differently but as long as you are getting the air out, go for it!

Perhaps the most important aspect of brake bleeding is to make sure that the bleeder nipple is able to open and that the passage through the bleeder is clear of deposits. Bleeder nipples are frequently blocked solidly so that nothing can flow. I have seen many which would hold brake pressure without leaking through the deposits back when I thought I could clear nipples by blowing out the crud.

Relocating the caliper can be useful, depending on the configuration but in normal operating position, the bleeder is placed so that the bleeder passage leads into the top most area of the caliper bore. Having seen some calipers on the wrong sides, it was no wonder they couldn't get the air out.

HIH

Norm

[bccap]

When I did mine. I got the air out by constantly pumping. If I am reading the directions right, its supposed to work while not pumping ? You pump when the bleeder is closed, and the vacuum sucks out the air and fluid. when the bleeder is open. When I tried this it didn't work and I assumed it was because air was leaking past the bleeder threads. I got the air out by constantly pumping. However, not sure how it's going to work when I install my new braided lines. I never considered just using the hose on the bleeder instead of one of the fittings { dumb! }

[Normk]

There's nothing quite so funny as when we do something which we later recognize to be obviously wrong!

Sharing those events is great fun for those of us who wear similar shirts and lets the smugly superior laugh but who cares about them? Most of what we believe is intellegent discretion is simply unthinking trained action. Some of the most enjoyable experiences I have had were attending motorcycle and car shows with a young lady I knew through work. She would ask questions of the display staff who would answer in a most condescending manner as she gradually lead them to paint themself into a logical corner. Somehow the fact that she was young, attractive and female lead them to the conclusion that she wasn't a journeyman automotive machinist with an IQ higher than their entire neighborhood.

As for using the hand pump type bleeders, they need a reservoir between the pump and fluid source to avoid inhaling fluid into the pump. The reservoir also assists in maintaining a vacuum by providing volume so that the bleeding can continue without constand pumping. Professional bleeders use a powered vacuum source and larger reservior so are easier to maintain fluid flow.

A practical problem with motorcycle brake systems is that they have small diameter brake "piping" (lines & hoses) and a significant difference in elevation between master and slave cylinders. Both factors make it difficult to move air bubbles downward which can result in the air bubbles simply shuttling up and down or remaining stationary. Try bleeding some of the older cab-over trucks if you want real joy!

Brit sports cars like my wife's Midget encourage one to become bi-lingual (English and foul langages). I mentioned the need for the bleeder passage to lead into the highest point in the caliper or slave cylinder or air will simply remain in the highest volume. Cruise the sports car groups and one will read frequently about the need to disconnect the clutch slave cylinder on some cars to allow the slave to be turned so that the bleeder is upward. They simply will not bleed all the air out with the bleeder positioned at the bottom of the cylinder- seems like basic physics?

The problem in many of these cases is that someone has connected the clutch hose to the top hole and put the bleeder into the bottom one. Switch the hose to the bottom and bleeder to the top and bleeding is much easier.

From time to time one sees a case where a caliper has been installed from another bike which positions the bleeder lower than the highest part of the caliper. If having big bleeding problems it is worth considering especially if the caliper was just installed. Swap some dual brake calipers from side to side and problems can occur for the same reason.

When bleeding with the use of a vacuum bleeder, the bleeder nipple is usually left open and the pump cycled until air is cleared. In some cases stopping to check or add fluid provides time for bubbles to rise back upward and the situation can repeat over and over.

One trick used by old timers is to add a larger reservoir in series and connect that to engine intake manifold vacuum in order to provide continous action.

Not sure if that covered all the points but HIH,

Norm

[AJ]

It will be easier to move fluid if the lever is in the released postion rather than pulled in. When the lever is released, it moves the master cylinder piston back and clears the compensating port so that there is an opening between the cylinder bore (and also the line) and the reservoir. That's the small hole in about the center of the reservoir which is sometimes covered by a deflector.

So nice to have another poster that writes long, detailed technical postings. I was afraid I was boring everybody to death!

[Suzuki_Don]

Thanks for the postings guys, very informative.

[koolaid_kid]

I do it like Normk. I use a MityVac and leave the bleeder nipple open. I also put a loop in the line to the reservoir. This lets the bubbles rise to the top and the fluid stays at the bottom, since it takes a finite amount of time to close the nipple. I then refill the master cylinder reservoir and test the brake to see how firm it is. Takes a bit of time, but a firm brake is worth the time and effort.

[jwhelan65]

I use a Mity Vac and pre-fill the calipers and lines with fliud with a seringe before i start.

[bccap]

What is the procedure for emptying the old lines, when installing new ones. I have anti dive. Just open the screws and pump the break lever ?

[koolaid_kid]

I would flush the lines and m/c first, then drain the lines by opening the bleeder valve. I would not empty the master cylinder. It can be a pita to prime again. Be sure and put down protection for anything painted, or the brake fluid will remove it for you.

[Normk]

+++ on Koolaid's post regarding clean and flush.

One of the biggest problems when reacting to a post is to differentiate between including what is obvious and that which is very important. I use a small bristle brush and syringe to clean out the "crud" in the master cylinder before any other service, especially bleeding.

One should change brake fluid each year in motorcycle systems in order to avoid corrosion and formation of deposits. Brake fluid absorbs moisture and also oxidizes which cause problems with system operation and lifespan.

The amount of fluid needed to clean out the system is tiny while the cost of replacing a caliper of master cylinder is huge. This doesn't even begin to address ABS components which I service.

Do not use silicone based brake fluids, change the fluid every year, clean and suction the reservoir and you will reduce brake system problems by 99%.

HIH

Norm

[Heintz]

A high digis coppa pregitar seems to be very effective as well.....as long as the skim gootie is in order......

[bccap]

Thanx guys.