Why would brakes effect RPM

[2001LC]

I've noticed my RPM drops slightly when I depress the brake peddle. I do this with engine at operating temp, in gear and parking brake set.

Any opinion as to why? and is their anything I can do to reduce this effect keeping RPM more stable?

 

[OregonLC]

I don't know that it would effect it, but it might affect it.

Is the pump coming on? Alternator draw typically will have a slight decrease in rpm.

 

[2000UZJ]

Brake booster kicking in, it pulls a lot of power and can drop RPM's. Any time it ices over in Atlanta and my ABS/booster kicks in on ice the RPM drops.

 

[2001LC]

Yeah it is when pump comes on. I've only recently noticed it drawing power and reducing RPM. I've noticed because I'm tracking down the "D" vibration and this is adding to it.

I'm wonder if electrical contacts might be improved with some electrical spray or a if a new battery with more amps would help?

I don't know that it would effect it, but it might affect it.

Is the pump coming on? Alternator draw typically will have a slight decrease in rpm.

I know it is affecting the RPM, and wondering if I can reduce the effect.

 

[Trunk Monkey]

Has nothing to do with the wiring or the battery. You're adding a load to the idling motor, that's it. Same thing if you turn your AC on while you're sitting. It's not harming anything, but it is another random thing to worry about needlessly.

 

[2001LC]

So aging electrical connection or brand-new; I'd still see an RPM drop of what?

 

[APKhaos]

With battery and alternator in top shape you may not notice any RPM drop.

 

[2001LC]

That's what I was wondering.

I replaced OEM with a walmat EverMaxx 24FN 750 CCA battery 3 years ago, it had 3yr wty. Its OK but was wondering if a higher AMP one would make any difference or is that just effect cranking power?

BTW; does Toyota or anyone make a rebuild kit for the alternator?

 

[Trunk Monkey]

You'll still see an RPM drop. I don't get why this is so hard to understand. The engine is idling at "x", you increase the load on the motor with something - anything - the RPMs are going to drop. AC, brake booster, etc. All cars do this. The only way to compensate is to increase RPMs. So, next time it does it, just press down on the gas pedal a little. Problem solved.

 

[Manhattan]

The reason it seems odd, is that the 100's brakes are essentially electric. The ABS pump/booster is pulling lots of juice - not vacuum. Oh, and that assembly costs $2,300... plus labor

 

[OregonLC]

But the electric part comes from the engine spinning the alternator, right? And when a large load is put on the alternator it will slow the engine down. I've never paid attention, but watching it this morning mine does drop 25 rpm or so when the pump kicks on. Completely normal.

 

[2001LC]

You'll still see an RPM drop. I don't get why this is so hard to understand. The engine is idling at "x", you increase the load on the motor with something - anything - the RPMs are going to drop. AC, brake booster, etc. All cars do this. The only way to compensate is to increase RPMs. So, next time it does it, just press down on the gas pedal a little. Problem solved.

I appreciate your feedback TM, and I do understand. I realized long ago even running the heater fan puts a load on engine by taxing the alternator, which BTW drops MPG by about 5%. I was under the false impression our brake system had a vacuum line, as-well as booster pump motor.

That said I've notice over the years in various vehicles the heater fans speed up and lights get brighter as RPM go up. This becomes more apparent with age of vehicle.

So IMHO aged alternator, aged copper wires, corrosion on electrical connections and aging Booster Pump Motor may draw more power (AMPs) than new, which increases load.

With battery and alternator in top shape you may not notice any RPM drop.

This is what I'm thinking.

But the electric part comes from the engine spinning the alternator, right? And when a large load is put on the alternator it will slow the engine down. I've never paid attention, but watching it this morning mine does drop 25 rpm or so when the pump kicks on. Completely normal.

I also only recently noticed this. Only have dash tachometer to go by, it looks like ~25 to 50 rpm drop.
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So we've all agreed here; brake booster pump drops RPM when engaged. It seem we've a difference of opinion if aged will draw off more RPM's than new.

So let us assume for a moment, that and aged system will increase draw:

Will new healthy battery draw on alternator less than aged battery?
And
Will battery with higher amp rating = less initial draw on alternator?

 

[Cfbrenton1]

That's what I was wondering.

I replaced OEM with a walmat EverMaxx 24FN 750 CCA battery 3 years ago, it had 3yr wty. Its OK but was wondering if a higher AMP one would make any difference or is that just effect cranking power?

BTW; does Toyota or anyone make a rebuild kit for the alternator?

The problem is that you put something bought at Wal-mart into your precious Land Cruiser! It is mad at you!