Brake thought for the month.

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Re: Brake thought for the month.

Postby fv22 » December 28th, 2017, 10:10 am

Is there a reason wheel cylinders are placed vertically at the 9 or 3 o'clock position? Obviously makes it hard if not impossible to bleed properly when mounted like that. Seems to me they should always be at the top with bleeder up at highest point but I have seen them in different positions on different cars.
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Re: Brake thought for the month.

Postby BLS » December 28th, 2017, 3:05 pm

I'm assuming you are asking about the rear regarding location, since they can be relocated while the fronts cannot.

I'll guess that many locate the rear from the original upper position thinking it is more aerodynamic. I don't think it matters.

The top position is the better one to properly bleed the brakes.

On the fronts, I will initially bleed them without the shoes and by turning the cylinder to place the bleeder at the top. Clamp the pistons. This gets all the air out. I don't think many people do this, believing all the air will get out anyway. I've bled the brakes the normal way, then done this and found a tiny bit of air. YMMV.

If the rears are not mounted at the top I would do the same thing.
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Re: Brake thought for the month.

Postby FV80 » December 28th, 2017, 3:52 pm

The rears are 'normally' mounted at the top. The fronts are not. I have not had any problems bleeding the fronts at the 3 and 9 positions. If done right, it is not an issue. Bleed the brakes by installing a bleed tube that is immersed in brake fluid (standard 'bleeding' container - if you make your own, make certain that the tube extends deep into the bottom of the bleed container enough to be below the level of fluid in the container). Open the bleeder screw enough to allow fluid to escape, but not enough to allow AIR to get back in (takes some 'touch' - using CLEAR tubing allows you to SEE any bubbles and tell if they are being drawn back towards the wheel cylinder). Then slowly depress and release the brake pedal several times until no more air can be seen coming from the end of the tube in the container. Close the bleeder and 'bang' the pedal several times, then press and hold the pedal while releasing the bleeder screw until fluid comes out. Watch for bubbles. If you don't see any, you are done. Also, if you have clear bleeder tubes (and you SHOULD), make sure they exit the bleeder UPWARD, so that any air will be visible immediately. If the wheel cylinders are in good condition and this process is done correctly, the internal WC seals will almost touch each other in the center at full release of the brake pedal. There really should be no place for air to be trapped. Banging the pedal a couple of times should ensure that there is no trapped air. Visually confirming that there is no air remaining in the tube should be adequate. If in doubt, repeat the process.

For both front and rear, it's best to JACK the car so that the wheels being bled are above the master cylinders. That should endure that any air that is in the system will gravitate to the bleed screw. Make sure you always bleed enough fluid to purge the entire line from the master to the wheel cylinder each time. That will ensure that only CLEAN fluid remains in the system. To minimize fluid waste, I generally dump almost all of the fluid in the master cylinders before starting the bleed process. Dump as much as possible without getting it below the input valve at the bottom. (If there is any residue in the master cylinder reservoir be sure to CLEAN It thoroughly before proceeding, even if it means exposing the port in the bottom. CLEAN fresh fluid in the system should be your primary goal.) . Then add enough fluid for a couple of pumps.. allow the fluid to get down to the bottom but NOT expose the input port. Add enough more fluid and repeat the process at least twice. Just be sure to flush enough fluid to make SURE that any air trapped at the MC has had enough time to make it to the wheel cylinder and get out.

OH.. one more thing.. as a start, I generally open BOTH rear bleed screws that the same time to ensure that there is no air trapped at the splitter between the rears. Then close both and proceed with bleeding of one, then the other. Not much of a problem in the front since the line is split right at the master cylinder instead of several feet away.

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Re: Brake thought for the month.

Postby BLS » January 3rd, 2018, 5:40 pm

Almost forgot about this.
You should read and listen to Steve of course.
One thing I remember I discovered later - I was using one of those bleeder devices with the check valve. Works pretty good. However, my report of a bit of air left in the front wheel cylinder was actually a problem with this. I found that while the check valve worked just fine, when you released the pedal a very small amount of air would get sucked back around the threads of the wheel cylinder bleeder screw. That doesn't happen when you open and close the bleeder screw with the stroke of the pedal. I actually didn't have any problem once I realized that.

They make bleeder screws with the check valve in them. Those have a bit of sealant on the threads to prevent the air from going by the threads. I have not tried them but they are cheap enough that they might be worthwhile.
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Re: Brake thought for the month.

Postby FV80 » January 3rd, 2018, 6:50 pm

BLS wrote:...I was using one of those bleeder devices with the check valve....

I have tried those 'auto-bleeders' as well and also found that they leaked air back into the system.
Follow the process and DOUBLE CHECK using CLEAR bleed tubing. You won't regret it.
Also, make sure to apply a small amount of hi-temp lube to the shoe contact areas on the backing plates... and make sure to CLEAN and reapply every time you inspect the shoes.
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