Unknown brake part

[Snowturtle]

What is the canister that hangs off the front of the big brake booster and below the master cylinder on my '03 Yukon XL? It looks to be attached to a vacuum line. Before the brake system is warmed up, that unit hums when I press and release the brake pedal and the brakes are kind of soft. After driving a little while, the humming stops and the brakes act normal.

 

[Mechahead]

It is a vacuum assist pump. For the life of me I can't remember exactly what it is called.

 

[YukonXL04]

Is it a silver canister to the left of the master cylinder? If so it's the power booster for your brakes that runs off the power steering pump

 

[Snowturtle]

it's black but the description sounds logical. I'll check to see if it's connected to the power steering pump. Do you know what it's called so I can order a new one? The brake system diagrams I have found don't show anything attached to the big booster.
Thanks!

 

[SLCHOE]

Check your power steering fluid level.

 

[Snowturtle]

Power steering fluid and brake fluid levels are both fine. I've looked for diagrams and through parts lists and I can't figure out what this vacuum canister is called or how to buy one or what it does. The large vacuum hose goes to the intake manifold. I would guess that it's just a vacuum pump but what does it have to do with my brakes? It is attached to my booster, it hums when I press the brake pedal, and the brakes are soft until this part is warmed up enough to stop humming. I can't figure out why I can't find it in brake system diagrams. Can anyone help me?
Thanks.

 

[Gatorlac]

flush the power steering fluid

http://www.duramaxforum.com/forum/diy-tech-discussion/9081-how-power-steering-hydro-boost-flush.html

just did mine even though I didn't have any problems but it did make the brake pedal firmer. Might wanna give it a try before you start replacing parts lol

 

[Snowturtle]

If my power steering is involved, why isn't it acting up too?

---------- Post added at 11:16 PM ---------- Previous post was at 11:15 PM ----------

Oops, just saw the bottom part of the post - I'll give it a try, it can't hurt. Thanks.

 

[Gatorlac]

yea its only 20 bucks for a gallon of PS fluid and it took me 15-20 min. I'd be willing to bet it'll work

 

[big_b_in_PA]

From the pic shown, it looks like he doesn't have hydro boost steering, so flushing the power steering will not help him out.

After a little research, that part is called an auxiliary vacuum pump, apparently when it goes bad, it acts like what you're describing.