WHat are your thoughts on a vacuum style pneumatic bleeder that uses a venturi to pull a vacuum on the other end rather than pressurizing the MC?
https://www.harborfreight.com/brake-fluid-bleeder-92924.html
I bought one of these recently and as cheap as it is it worked great.
That adapter is the only one they have for 90s GMs.
https://www.motiveproducts.com/coll...ts-power-bleeders-classic-car-and-marine-kits
No shut off valve in the pressure hose. At least not on the model I bought.
The reason I had to use a pressure bleeder is because it had to be a one man job, and I couldn't wait for help.
What would you recommend using in the future, aside from a professional level bleeder? Gravity bleeding seems like it would take a while...or no?
Brake Bleeding Styles/Tools
There's five different methods of bleeding brake systems, with some variations within some major categories:
1. Pump-the-pedal
2. Pressure bleeding from an external tank
3. Gravity bleeding
4. "Reverse Injection" bleeding
5. Vacuum bleeding
Pump-the-Pedal bleeding is usually done with an assistant. If you can get a Victoria's Secret model to help you, so much the better. One person pumps the brake pedal, one person opens and closes the bleeder screw. It's best if the person pumping does so gently, rather than vigorously. And ONE pump, please, not half-a-dozen which does little except aerate the fluid. The person working the bleeder screw needs to close the screw before the pedal sinks all the way. And then one more pump, open the screw, close the screw, one more pump...
There are "automatic" spring-loaded bleeder screws (Russell "Speed Bleeders", for example) that make this a one-man job, that of "pumper". The screws self-seal when not under pressure. At the end of the procedure, the automatic screws are either removed and replaced with normal screws, or manually tightened in place so that the pressure is held and the brakes work again.
Pump-the-pedal bleeding requires no special tools other than the helper or the spring-loaded bleeder screws.
Pressure bleeding using an external reservoir requires special equipment, and the good stuff is expensive. In addition, there are a multitude of special adapters needed to connect the pressure reservoir to the vehicle's master cylinder.
Once the pressure tank is connected to the vehicle's master cylinder...bleeding is exceptionally fast. This method is good when flushing fluid, or filling an empty system after major work.
The good pressure tank has a rubber diaphragm between the compressed air used for pressure, and the brake fluid chamber. The brake fluid does not come in contact with the air, so the humidity in the air can't contaminate the fluid. "Garden-sprayer" bleeders have no diaphragm, the air with it's humidity is in direct contact with the fluid. This is a very compromised bleeder system.
It is possible to pressure bleed with enough pressure to close the metering (hold-off) valve in a disc-drum brake system. The front brakes won't bleed until the metering valve is forced open with a special tool. In actual practice, I've NEVER needed to dick with the metering valve, because I pressure bleed at 10--15 psi--not enough pressure to close the metering valve. Bleeding at high pressure--as with the "pump the pedal" method creates enough pressure to pop the metering valve open again. This high pressure isn't recommended, and maybe not even possible with a pressure bleeder.
Gravity bleeding is as simple as it gets. Fill the reservoir, open a bleeder screw, let the fluid trickle out into a drain pan. There's no special tools needed, and since there's essentially no pressure, the metering valve won't close. The only downside is that it takes a while for the fluid and air to slowly dribble out. You do have to remember to top-off the reservoir now and then. Gravity bleeding doesn't work well on old cars that have the master cylinder under the floor, instead of up on the firewall.
Reverse Injection bleeding is fairly "new", at least when using "special tools" to do it. The theory is that it's easier to push air "uphill" towards the master cylinder, than to make it flow downhill towards the wheel cylinders. There are three problems with Reverse Injection bleeding: You have to flush the system in the normal direction first, or you're pushing old, contaminated fluid back through the ABS valves, With the bleeder screw (fluid entry point) of the wheel cylinder at the highest point of the wheel cylinder, there's always going to be a bubble of air in the wheel cylinder until you finish the "reverse injection" bleeding by bleeding in the normal direction for a moment. And it's easy to over-fill the master cylinder so that it leaks out the reservoir cover.
I've used the principle of "Reverse Injection" bleeding simply by pushing a big ol' caliper piston BACK INTO THE CALIPER BORE, which moves a heap of fluid up to the master cylinder.
IF (big IF) you have an empty system, or no ABS, Reverse Injection bleeding makes sense. Otherwise, you have to flush the system with clean fluid first...and by the time you've done that, you've already bled the brakes. Doesn't make any sense to buy expensive tools to revere-bleed brakes. I've seen it done with an inexpensive (LARGE) syringe having a rubber tip. And no reason you couldn't fabricate an adapter to use a pressure bleeder and hose connected to some sort of "bleeder screw".
Vacuum bleeding is popular. I have done it, but I quit vacuum bleeding years ago. You have to seal the bleeder screw threads or you'll never know when you're done--you'll have indications of air until the end of time. And while generally not a problem with disc brake seals, drum brake wheel cylinders are designed to keep fluid in, not to keep air out. So applying a vacuum can cause air to seep around the wheel cylinder cups and seals. Again, you can bleed until the cows come home, you'll always have air in the vacuum tool. The tool itself can be any source of vacuum, from a hand-pump, an electric pump, or a compressed-air "venturi" pump. Most pumps will not tolerate brake fluid in the pump itself, so you need a reservoir to catch the bled fluid before it enters the pump.
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pressure bleed for major work, or to flush fluid.
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gravity bleed for minor work near the wheel cylinders.
