Types of brake flushing

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We used to call it "gravity bleeding". It works fine as long as there isn't any air trapped in the system. BTW, a better way is to first clean out as much of the old fluid out of the reservoir as possible. Then add new fluid and loosen the bleeders. No need insert the bottle upside down and risk fluid flying all over everything. Some systems will readily flow fluid using this method and some wont. Also, this method wont flow fast enough to bleed much trapped air. So if you're looking to correct a soft pedal it's best to use the old "5 pumps and hold it" method.
 
I guess you could tear up a Master Cylinder Piston seal by the pump to bleed method, but it hasn't happend to me yet in over 40 years of bleeding brakes.

If the master cylinder bore was bad enough to tear up the seal, I would want it to happen while I was bleeding the brakes instead of some day when I had a brake problem going down a mountain road and used more pedal than normal
shocked.gif


Someone who thinks their master cylinder is in bad enough condition to damage the seals if the piston is moved too far and doesn't fix the potential problem needs to be removed from the gene pool. Preferably without taking anyone else with them.

A big advatgage to the pump the pedal to bleed method is that the high fluid velocity you get does a better job of washing out the lines.
 
I use vacuum bleeding on all my cars these days: one hand-crank vacuum pump + PVC tubings and a nylon fluid reservoir.

The trouble is, it took me a lot of practice before I could get the bleeder nipple settings right otherwise it would not work for air will rush in through the thread section due to design and that introduces more air into the hydraulic system.

I have been able to purge out micro air bubbles with this method with great satisfaction. However, I have the obsession of using excessive amount of fresh fluid during the purging stage so as to flush the lines (usually 2 bottles of Valvoline Syncpwr DOT4 for regular 4-banger cars, 2-and-a-half bottles for those who share hydraulic brake fluids with clutch).
 
Quest, how DID you get the vacuum bleeding method to work without getting air past the threads? I've never been successful using this method.
 
I had the BG brake service done. I didnt notice a difference. I wanted to try it for my self to see if it was worth it. It didnt make a too noticable of a difference. I dont know if it was worth it for the car or not, but I wanted to see if there was a difference.

[ January 05, 2005, 01:58 PM: Message edited by: JMG ]
 
quote:
Originally posted by XS650:
I guess you could tear up a Master Cylinder Piston seal by the pump to bleed method, but it hasn't happend to me yet in over 40 years of bleeding brakes.

If the master cylinder bore was bad enough to tear up the seal, I would want it to happen while I was bleeding the brakes instead of some day when I had a brake problem going down a mountain road and used more pedal than normal
shocked.gif


Someone who thinks their master cylinder is in bad enough condition to damage the seals if the piston is moved too far and doesn't fix the potential problem needs to be removed from the gene pool. Preferably without taking anyone else with them.

A big advatgage to the pump the pedal to bleed method is that the high fluid velocity you get does a better job of washing out the lines.
Click to expand...
I tend to agree for the most part altho I've only been at it about 30 years.....I vote we chalk this up to yet another solution to a problem that doesn't exist except in an auto-neurotic's overactive imagination.

As said earlier, the danger of getting brake fluid in places where it shouldn't seems rather large here, and I do know brake fluid is an excellent paint solvent.
 
the gravity bleed method may have flow restricted somewhat on a system that uses a residual pressure check valve.

I prefer the pedal bleed and flush method when I do it but that may be influenced by the lack of equipment for some of the other methods.

I have tried using a hand vacuum pump to bleed with limited success.

As to the air coming in around the bleed screw, coating the outside base of the screw with sil-glyde may help.

JD
 
quote:
Originally posted by kenw:
... and I do know brake fluid is an excellent paint solvent.
Click to expand...
I have always heard this, and decided to try it.
I got a steel wheel at a recycler for snow tires, and the identifying information was written across it in yellow paint marker.

I scrubbed it off using brake fluid and a toothbrush/ cloth.

It worked, but it was not magic. The underlying paint on the wheel was not damaged by this. No bare metal.
 
quote:
Originally posted by Kestas:
Quest, how DID you get the vacuum bleeding method to work without getting air past the threads? I've never been successful using this method.
Click to expand...
If I use a vacuum pump on brakes, it is to flush old fluid out, not to bleed the system. The final bleeds should be using master cylinder pressure and maybe 5 iterations at the bleeder screw. But as far as air getting back into the brake lines is concerned, it may not be as big a deal as it appears (little air bubbles). It's the plastic vacuum hose that's under vacuum. If you leave the cap of the master cylinder off, assuming there is no great restriction in the brake line, the air will go to the place of least vacuum, which is the vacuum pump hose, not the brake line. I don't chance it - I pressure bleed anyway.
 
I tried vacuum bleeding because I heard it's better with respect to the fact that any air bubbles in the system will expand under vacuum and are more easily drawn out that way.
 
The other option, which my dad has had to use on his Saabs is "Pressure bleeding"; a special master cylinder cap is used that has a fitting for an air line and the reservoir is pressurised to force air/fluid through the lines.

The old Saab Sonetts have the master cyl on the floor of the engine compartment, with the reservoir at the top of the engine compartment and an 18" rubber hose connecting them. It is next to impossible to bleed the air from the connecting hose by gravity or pumping the pedal.

The clutch is even worse, as the fluid has to go back uphill through an inverted "J" hose to get to the slave cyl. on top of the trans case, so you have 2 air filled hoses to bleed out. Once the air is out, it bleeds out fine, but getting the air out after we rebuilt it took forever.
 
Thanks for the info guys. The tearing up the o-ring sounded a bit too conspiracy theory to me. The pedal to the metal flush still sounds like the best way to go, aside from the whole ABS system junk.
 
Motive sells a product that will flush your brake system. It is a bottle that you pump upto 10 psi and the new brake fluid is hooked upto your resv. and your whole brake system will be at about 10 psi and you open the bleeder vavle. the fluid will keep coming out. I think this is the best method.
 
Shaman, the damsge you heard about probably is very rare. Other sites describe the cause as being: normal brake pedal travel is only 3 to 5 inches. When you bleed, the pedal travels much farther and there is a tiny chance that a slightly corroded part of the piston, at the very end of the travel, might abrade the seals.

In other words, the problem could be caused because the master cylinder wasn't designed to have the pedal go all the way to the floor. Parts that haven't been rubbing and polished in normal use, now rub against each other.

The solution (they say) is to put a wood block under the brake pedal so that it only goes down 80% +/-, instead of the full 100%.

XS650's logic is sound too. But I wouldn't think the failure would be catastrophic - no brakes at all, instantaneously.

Again, not my knowledge, just something I read.

My .02 cents worth!
 
The don't push the pedal to the floor caution has been around a long time. Nobody worried about it at the brake shop I worked in for a while. I am having troubling remembering, but it seems to me that most of the pitting in master cylinder bores was near the resting area of the piston rather than the far little used area. I wonder if the problem is less where the piston goes, than asking too much of a tired old cup or O-ring? If you ruin the master cylinder, maybe it was on its last legs anyway.
 
quote:
Originally posted by Kestas:
Quest, how DID you get the vacuum bleeding method to work without getting air past the threads? I've never been successful using this method.
Click to expand...
I use Teflon tape to keep air from going around the threads.
 
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