I am still a lurker but I find myself thinking what should I do to prepare. As to bleeding brakes, I have been old school, one of the boys pumping the pedal while I crack the bleed valve. If I am going to build a car, what would I do? I find 3 types of solutions, vacuum at bleed valve, pressure at MC reservoir, reverse flow pressure at bleed valve. What has been the experience of the forum members. The cars that we discuss are generally not ABS equipped but my everyday vehicles are and am concerned that reverse flow might be a problem for them. Interested in your response. Thanks.
Bleeding Brakes
- Thread starter Mike Giblin
- Start date
PeteB
GT40s Supporter
I've tried all three methods and prefer the reverse bleeder. The old pump the pedal method takes forever when you're starting out with new, totally empty brake lines. The pressure at the reservoir method tends to make a mess at the reservior and I don't think I'd want to try it with a remote reservoir. The reverse bleeder contains the mess at the calipers and fulls up empty lines quickly. The downside is it will not work with speed bleeder valves.
After many years of rebuilding braking systems on a large range of cars, I'll share the following few thoughts.
1. Don't do the pump-the-pedal routine. Why? Because a fair amount of the time you end up with a leak at the master cylinder after doing the brake job....because the mc seals just had to go into new territory in the mc bore (all the way down the bore) with such territory perhaps corroded or rough. It's OK if you just put in a new mc however.
2. Pressure bleeding works well. Although there's the risk of spraying some brake fluid at the reservoir, pressure bleeding does a good job of removing the air completely from the system. It's also efficient....pressurize and open the bleed nipple, close when she runs clear of bubbles. Works well when there are sneaky little places for air to hide in the system.
3. Vacuum bleeding works well too. IMHO not quite as good as pressure bleeding but it works well. Watch out for air leak right at the nipple creating the impression of air in the brake lines.
4. When you're stumped, use both. If you're having trouble with soft brakes then use both pressure and vacuum. I recently rebuilt the brakes on my rolls corniche and that is the most complicated braking system you'll see on a car...six calipers, enough brake lines going everywhere to make a bowl of spaghetti look like parallel lines...and the only way that system can be completely 100% bled is with both pressure and vacuum.
5. Pre-filling the mc on the bench can be helpful. Also, at the slave end, if the slave is sloped down one direction or another you'll likely get a bubble there and this bubble can be tough to eliminate if the nipple isn't properly positioned. Take the slave out (but still connected to the flex line) and bleed it with the nipple up and oriented to best eliminate the air.
Be patient. A couple good beers or a martini helps.
1. Don't do the pump-the-pedal routine. Why? Because a fair amount of the time you end up with a leak at the master cylinder after doing the brake job....because the mc seals just had to go into new territory in the mc bore (all the way down the bore) with such territory perhaps corroded or rough. It's OK if you just put in a new mc however.
2. Pressure bleeding works well. Although there's the risk of spraying some brake fluid at the reservoir, pressure bleeding does a good job of removing the air completely from the system. It's also efficient....pressurize and open the bleed nipple, close when she runs clear of bubbles. Works well when there are sneaky little places for air to hide in the system.
3. Vacuum bleeding works well too. IMHO not quite as good as pressure bleeding but it works well. Watch out for air leak right at the nipple creating the impression of air in the brake lines.
4. When you're stumped, use both. If you're having trouble with soft brakes then use both pressure and vacuum. I recently rebuilt the brakes on my rolls corniche and that is the most complicated braking system you'll see on a car...six calipers, enough brake lines going everywhere to make a bowl of spaghetti look like parallel lines...and the only way that system can be completely 100% bled is with both pressure and vacuum.
5. Pre-filling the mc on the bench can be helpful. Also, at the slave end, if the slave is sloped down one direction or another you'll likely get a bubble there and this bubble can be tough to eliminate if the nipple isn't properly positioned. Take the slave out (but still connected to the flex line) and bleed it with the nipple up and oriented to best eliminate the air.
Be patient. A couple good beers or a martini helps.
Thanks for the comments! I have added a phoenix reverse bleeder to my list for Santa. Just have to get by that "been good" thing.
I have tried many methods. Gravity bleeding works best. It takes more time, but it works. When I see the fluid come out of the bleeder solid, with no air, I then tap on the caliper and it frees up any air that may be trapped in the caliper. (an old Corvette trick) Works for me every time.
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