Unexpected revs while braking???? (1 Viewer)

[Jman]

I was coming down a hill approaching a stop light, going maybe 35 mph, shifted out of third into neutral, started to apply the brake, suddenly the engine revved from 1500 to 2500 without me touching anything but the brake, then cut back down to idle after about a second. I *don't think* it was my throttle stuck--it seemed to be in response to me hitting the brakes. And no, I haven't been drinking.

WTF?

Anyone know what dreadful disaster this portends? This has never happened before, but I've come to learn it's best not to simply ignore this kind of stuff until something breaks.

 

[60wag]

Brake booster leak?

 

[vtcruiser60]

Perhaps you are looking at a simple carb adjustment. I recall reading something about a secondary idle switch that engages when decelerating. Might be sticking....

Someone must know this around here.

 

[cahilc]

Double check your motor mounts ...

Cahil

 

[swank60]

First, check your blinker fluid...

Actually, I had this very problem with my TR6. What caused it was a leak in the brake booster. The leak in the brake booster was caused by a leak in the master cyl. that was leaking back into the booster and killing the seals.

The booster runs directly off of your intake manifold vac, and when you hit the brakes, you open up that system to outside air.

Do you hear any air/hissing inside the truck near the pedals? Any brake fluid in your footwell?

Try blocking off the hose that runs to your brake booster and see if the revving stops. Make sure it doens't leak when you do block it off though.

 

[Jman]

Ahhh, interesting. Okay, I'll start checking out brake booster/MC leak. And my blinker fluid.

Cahilc, how would bad motor mount cause higher revs???

 

[swank60]

Cahilc, how would bad motor mount cause higher revs???

I think that was just his way of saying that he thinks you're gay. Not that there's anything wrong with that.

Bad MMs can wreak a lot of havok on day to day engine ops. Keeps stuff moving around that shouldn't be moving...braking could tilt the motor forward and move your throttle linkage - stuff like that.

 

[cahilc]

...
how would bad motor mount cause higher revs???

My thought when you hit the brakes there was enough jarring of the motor to cause it to lift from a broken mount. Slightly binding the throttle linkage cause a momentary high rev.

Just a thought,
Cahil

 

[cahilc]

I think that was just his way of saying that he thinks you're gay ...

Well, that was suppose to be the subliminal message ...



Cahil

 

[swank60]

Okay, I've got a lot to check out now:

1) Brake booster/MC?

2) Idle cut off solenoid?

3) Maybe I'm gay?

4) Motor mounts?

Great, thanks!

I don't think there's any question on #3...