RE: IML: Some more questions

What you broke is called the “Check Valve”, its purpose is to prevent vacuum leaking back into the intake manifold from the vacuum reservoir when the engine stalls, so that you still have brakes when the car stalls (at least for a couple of stops).

The thingy under the fender is that reservoir tank – it is just like a steel bladder, it simply provides a chamber with less than atmospheric pressure so that should the engine stall, there will still be vacuum to operate your brakes.

The reason your pedal got firm when you disconnected the vacuum hose is that you removed the source of power to the power brake booster, thus you didn’t have power brakes anymore. If you had been driving and this happened, you’d find you’d have to stand on the pedal with all your might to stop the car.

The reason the engine speeds up when you disconnect the hose is that you are introducing excess air into the mixture, leaning it out so the combustion process gets much hotter (to where it can burn the valves in the engine if you keep driving it that way) and it also revs up the engine from the lean mixture.

The hose you need to replace is a power brake booster hose – it comes in bulk from any auto parts place. Bring in the old hose for a size comparison, and make very sure the guy behind the counter knows it’s for the power brake system, because it must be special hose that will not collapse under vacuum. Most hose is designed to operate under pressure, not vacuum.

NAPA probably has a check valve which will fit your car (you don’t say what year car you have, so I’m only guessing here). But you may have trouble finding one with a built in “T”, you may have to buy a separate “T” to make all your connections (intake manifold, reservoir, and booster).

I hope this is clear enough, if not feel free to ask again.

Dick Benjamin

From: mailing-list-owner@xxxxxxxxxxxxxxxx [mailto:mailing-list-owner@xxxxxxxxxxxxxxxx] On Behalf Of JosephStil@xxxxxxx
Sent: Wednesday, March 09, 2005 5:19 PM
To: mailing-list@xxxxxxxxxxxxxxxx
Subject: IML: Some more questions

Evenin', and how's everybody?

I don't mean to sound ignorant about the following topic, but I just don't understand something that I think y'all can help me with.

In tryin' to figure out why the power brake booster isn't working, I disconnected the vacuum line from the booster. It was connected to the booster by a length of some sort of hose and separated by a "T" which I thought was just a splicing "T." Well, it turns out this "T" acts as some sort of valve because on the side of the "T" goin' to the engine, there was, inside, a spring and I-don't-know-what-one-calls-it but when the engine vacuum sucks it remains open but it can "close." Anyway, I broke this "T" so I will be needing a replacement but I don't know what to call it.

Here are a couple of things I noticed about this whole situation. When I plugged the hose going to the engine, the idle (RPM) slowed considerably. When the hose was freed the RPM for the engine audibly increased. Also, without the vacuum hose connected to the brake booster, the pedal was much firmer. Lastly, the other end of this "T" goes off somewhere into the front fender well just ahead of the front left wheel but I can't seem to find out to where it goes.

There is no doubt there is good vacuum. But my ignorance as to how this whole process works with the engine leaves me stumped as to why the brake pedal is different, why the RPM/idle changes by plugging or unplugging the hose from the engine, and what is the purpose of the hose that goes over to the front left fender.

Lastly, if I were to replace these hoses (along with the valve do-hicky), what sort of hose would I buy?

Anyone have some good advice for me?

Thanks,

Joe