'99 Sienna; Is master cylinder part of ABS pump?

[vtouba]

I'm losing a small amount of brake fluid every time I brake. The leak is definitely in the vicinity of the power brake booster, not at a wheel or in hydraulic piping to a wheel. When I look at the suspect area I see a rectangular manifold with six pipes emerging on the top side and a cylindrical object towards the bottom of it. I suspect I'm looking at the "ABS pump". Question: Is there a separate master cylinder also or, is the master cylinder part of the ABS pump? (please reply only if you're absolutely sure). Any advice or tips on changing these braking system component(s) will also be appreciated.

OK, nobody responded so I dove in anyway and here's the result: First of all, the ABS pump is separate from the master cylinder and, is located directly beneath it. I found one on-line retailer that offers rebuilt ABS pumps; http://www.bba-reman.com/index.aspx but, I didn't go that route. I priced some used ABS pumps on line and found the asking price to be about $150. I was lucky enough to find one at a local junkyard (excuse me..."auto recycling center") for $100.

Replacement was fairly straightforward but, if you're new to auto mechanics, I have two tips: (1) Have plenty of penetrating oil and new brake fluid on hand. (2) To avoid damaging the brake line nuts, don't use regular open-end wrenches. Use only "flare-nut" wrenches http://www.craftsman.com/craftsman-5...1&blockType=G1

Start by disconnecting the negative battery terminal and removing the air cleaner cover and lower housing. Next, remove the air intake pipe up to the throttle plate. Besides the six brake line connections to the pump, you'll have to disconnect the large electrical connector, located at the lower front. Release the white connector locking lever but don't pull up on it to detach the connector. Gently pry the connector out and "help" it by lifting up on the lever simultaneously.

The ABS pump is secured to the vehicle by a metal bracket and three rubber shock mounts that have smooth-bore holes in their center. The bracket has three detachable "pins" that complete the connection between the bracket and the pump. Loosen the bolts holding the pins to the mounting bracket. If the pins turn with the wrench, you may have to hold the flange on the pins with a pair of pliers. Good lighting and is essential for this job!

To reduce the mess from leaking brake fluid, I completely removed the two short brake lines between the pump and the master cylinder, then plugged the master cylinder output ports. Keep the brake fluid reservoir topped off to avoid drawing air into the master cylinder.

When attempting to remove the old ABS pump, you may be stymied by a small hose-retainer bracket in front of it. Gently bend the bracket down to give yourself clearance and restore it when re-assembling.

Install the replacement pump in reverse order of removal. Be careful not to cross-thread any brake line nuts! Finally, you'll have to bleed all four brake lines. Do this with the engine off. Start the engine and check to make sure the ABS light is not illuminated on the dashboard. If it is, it may indicate a problem with your replacement pump . For the real test of the system, you'll probably have to find a nice, big puddle or an icy, empty parking lot.

I've attaches some digital images to help clarify what I've described. Good luck!