Gravity Brake Bleeding
12-23-2006, 03:22 PM
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Join Date: May 2006
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Gravity Brake Bleeding
Gravity Bleeding
Many of you, especially those with early less complicated cars, can bleed your brakes easily in less than 30 minutes without an assistant, and without spending more than $5 on equipment. My 73 911 lacks a hydraulic clutch so I don’t know if this procedure can be adapted for use with non-mechanical clutches.
You will need: brake fluid, six or seven feet of plastic tubing sized to fit snugly over the nipple on the brake caliper (mine uses 3/16” internal diameter tubing but check yours), and an appropriate small box wrench to open & close the bleed valve. (Sears makes small 6 sided combo wrenches which are useful for recalcitrant cases; the bleed valves on my car are 7mm but some I believe are 8mm.)
Here’s the procedure: jack the car up, support it on jack stands or wood blocks, and pull the wheels so you can get at the calipers. Or do one wheel at a time if you want.
Loosen the brake fluid container cover in the trunk.
At the first wheel, position the plastic tubing so it hangs straight down (from your garage roof or door or even a stick or spouse) to the caliper. Slide the box wrench over the nipple, slide the plastic tubing over the nipple, and open the nipple a quarter turn with the wrench.
Watch the fluid rise in the tubing until it reaches the height of the brake fluid reservoir in the car, maybe 15 inches. This will take 3-4 minutes. Tap the caliper with a rubber hammer or block of wood if you want. Watch the tubing for bubbles, especially when you start. It helps to hold a flashlight behind the tubing. If they keep on coming after the level in the tube has risen 12-15 inches, close the nipple, remove the tubing, drain it into a paper cup, and repeat. Assuming you are bubble free after 2-3 inches of fluid have drained, however, do this just once; tighten the wrench, pull the tubing off while holding a paper cup to catch the fluid, and move on to the next wheel.
Keep an eye on the fluid container and replenish the brake fluid when it's down more than an inch.
Do all four wheels & again replenish the fluid.
You are done. Gravity has done all the work. You cannot damage your master cylinder with this technique, and you don’t need a helper (if you have a garage or a tree or can rig a stick to hang the tubing from.) This should take you a maximum of 5 minutes per wheel once the car is up and the wheels are off. Forget the idea that there are bubbles all thru your lines and that pressure will somehow push them out but not the fluid. A pressure bleeder only moves any bubbles and fluid thru the lines more quickly. But they travel together. So gravity will do the job perfectly if time isn’t the object.
This process works because nearly all the bubbles generated by driving around and heating the brakes excessively are found at the very top of the caliper near the bleed valve…in effect where the heat is.
Depending on how much fluid you withdraw each time, you will find that the fluid is fully replaced every 10-15 bleedings. I track my car 5-6 times per year; bleeding pretty much replaces all the fluid over a couple of years, as recommended by many experts.
Many of you, especially those with early less complicated cars, can bleed your brakes easily in less than 30 minutes without an assistant, and without spending more than $5 on equipment. My 73 911 lacks a hydraulic clutch so I don’t know if this procedure can be adapted for use with non-mechanical clutches.
You will need: brake fluid, six or seven feet of plastic tubing sized to fit snugly over the nipple on the brake caliper (mine uses 3/16” internal diameter tubing but check yours), and an appropriate small box wrench to open & close the bleed valve. (Sears makes small 6 sided combo wrenches which are useful for recalcitrant cases; the bleed valves on my car are 7mm but some I believe are 8mm.)
Here’s the procedure: jack the car up, support it on jack stands or wood blocks, and pull the wheels so you can get at the calipers. Or do one wheel at a time if you want.
Loosen the brake fluid container cover in the trunk.
At the first wheel, position the plastic tubing so it hangs straight down (from your garage roof or door or even a stick or spouse) to the caliper. Slide the box wrench over the nipple, slide the plastic tubing over the nipple, and open the nipple a quarter turn with the wrench.
Watch the fluid rise in the tubing until it reaches the height of the brake fluid reservoir in the car, maybe 15 inches. This will take 3-4 minutes. Tap the caliper with a rubber hammer or block of wood if you want. Watch the tubing for bubbles, especially when you start. It helps to hold a flashlight behind the tubing. If they keep on coming after the level in the tube has risen 12-15 inches, close the nipple, remove the tubing, drain it into a paper cup, and repeat. Assuming you are bubble free after 2-3 inches of fluid have drained, however, do this just once; tighten the wrench, pull the tubing off while holding a paper cup to catch the fluid, and move on to the next wheel.
Keep an eye on the fluid container and replenish the brake fluid when it's down more than an inch.
Do all four wheels & again replenish the fluid.
You are done. Gravity has done all the work. You cannot damage your master cylinder with this technique, and you don’t need a helper (if you have a garage or a tree or can rig a stick to hang the tubing from.) This should take you a maximum of 5 minutes per wheel once the car is up and the wheels are off. Forget the idea that there are bubbles all thru your lines and that pressure will somehow push them out but not the fluid. A pressure bleeder only moves any bubbles and fluid thru the lines more quickly. But they travel together. So gravity will do the job perfectly if time isn’t the object.
This process works because nearly all the bubbles generated by driving around and heating the brakes excessively are found at the very top of the caliper near the bleed valve…in effect where the heat is.
Depending on how much fluid you withdraw each time, you will find that the fluid is fully replaced every 10-15 bleedings. I track my car 5-6 times per year; bleeding pretty much replaces all the fluid over a couple of years, as recommended by many experts.
12-23-2006, 10:22 PM
#2
James,
You should be careful with your suggestion here. Later Porsches have to be bled under a couple bars of pressure. Fortunately, a pressure bleeder is only about $50 and makes the job extremely easy.
You should be careful with your suggestion here. Later Porsches have to be bled under a couple bars of pressure. Fortunately, a pressure bleeder is only about $50 and makes the job extremely easy.
12-28-2006, 09:57 PM
#4
Our tech requires flushing the fluid if it is older then 3 months before tracking the car. While this may seem excessive the fact is that most brake fluid will accumulate moisture over time and the boiling point lowers making brake fad a real possibility under hard braking.
