Thread: Bleeding multi piston front brake calipers

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I have my front disc brake kit installed. It has 4 pistons per caliper, and four bleeding ports as well. Is there anything special required for bleeding this type setup, or is it just starting at one corner of the caliper and working around? Master Cylinder is new also and below the cab, so gravity bleeding is out. I did a search and read previous posts on brake bleeding in general, but am asking about the calipers specifically.
Thanks.

Purge them at the lowest point first, to get rid of the most air quickly.

Here is some info for ya.


In order for your braking system to function properly the system must be properly balanced. This is accomplished through the use of the correct valves. Below is a description of what types of valving may be used on your system.

VALVE TYPE DESCRIPTION
METERING The metering or hold off valve is used in the brake system to better balance the front to rear brakes. The valve does not allow the pressure to rise at the front disc brakes until the pressure at the rear drums has risen sufficiently to overcome the brake shoe springs. At this point the valve opens to allow full pressure to build at the front brakes.

PROPORTIONING The proportioning valve modulates the pressure to the rear brakes. The modulation is necessary to minimize rear wheel lock up found in heavy braking and to compensate for the differences in braking conditions in front disc / rear drum systems. As pressure is applied to the system full pressure is allowed to the rear drums up to a certain point. Beyond that point the pressure to the rear is reduced preventing rear brake lock up.

RESIDUAL There are two different residual valves. A ten pound residual valve will maintain a line pressure to the rear to keep the drum brake shoes out close to the drums giving a higher firmer pedal. Without a ten pound residual pressure to the rear you will experience a spongy pedal. A two pound residual valve is required whenever the master cylinder is lower than the calipers to prevent backflow of fluid from the calipers to the master.

COMBINATION A combination valve incorporates metering and proportioning into one valve. These are available for disc/drum or drum/drum systems.

ADJUSTABLE PROP VALVE The adjustable proportioning valve is used when you have a special rear condition that requires higher or lower pressure than a normal condition. You sould always use a metering valve to the front when using the adjustable proportioning valve.

Pressure bleeding is the best method with multi-piston caliper unit's.

Excellent post, Thunderbucket.

Thanks for the input. I have all the valves the system called for. It did not say anything however about the metering valve referenced by Thunderbucket. There is an adjustable proportioning valve for the rear, as well as the two residual valves. I'm going to go bleed the system tomorrow. For the caliper bleed, will start with the bottom inside to bottom outside port, then top inside to top outside port. Seems to make the most sense. There is only one input to each caliper that feeds all four pistons.

Sometimes it can help to tap on the calipers with a rubber
hammer it releases tiny air bubbles that might be stuck inside
the caliper. Do this right before you open the bleeder!!

Denny W, thanks for the pic. I have the 10 psi on rear and 2 psi on front (residual valves). I have never seen a set of 4 piston calipers other than these, but there are 4 identical bleed valves, one at each corner. Maybe the ones on the bottom aren't meant to be used for bleeding, but they are all the same. The fluid inlet to the caliper is directly in the middle, on the motor side of the caliper, equally spaced from the front to back. These were made by Wilwood, and are aluminum, if that makes a difference.
randywrench, good idea.

Mike

Yea the MC is below the floor, so the 2 psi residual is cool. I've got everything covered I think. But you know how you can think something to death? Well Wilwood said to make sure to use DOT 3 fluid only, and theirs only, which has a high boiling point of 500 degrees or more, dry. Figured I would go with Prestone DOT 3 synthetic, that had 470 or 480 degrees boiling point dry. Tonight I got to thinking that with the aluminum calipers, heat transfer to the brake fluid may be the issue and reason the company specifies their fluid only. So, it will be a week before I can get the stuff shipped.
Thanks for everyone's help.
Mike
P.S. For anyone planning on installing their own brake lines. If you are going to cut and double flare your lines, get a GOOD double flaring tool. I had two cheapos that both failed to get the job done. One wouldnt keep the line clamped in place for the first flare. The other would always angle off to the side on the first flare. It drove me a little crazier.