I was cruising along on the freeway when suddenly my 94 Blazer started speeding way up-without my permission- when I tried to brake the pedal was real hard to push and the brakes were barely responding- I took the next exit and after combining my foot tromping with down shifting then throwing it into neutral I managed to get it slowed down enough to throw it into park andshut off the screaming engine-shook me up a bit- I called a friend of mine who looked it over quickly and drove me home- it seemed to run (and stop) just fine for him but I did see the brake warning light start to come on a couple times when he was stopping- does anyone know what could cause a vehicle to act like that? it was scary!

 

well- I guess it wasn't a demon after all- my neighbor checked some lines and told me that one was split near the master cylinder-(vacume line)- he cut the worn end off and reattached it- it seems to be running fine now-but- my brake pedal is hissing-actually it has been hissing ever since my husband replaced my heater core about 2 months ago- but everything seemed to work ok so I wasn't that worried about it- now I'm wondering if that is something I should be worried about- how serious of a problem does that noise indicate?- and is the noise problem related to my runaway truck experience?- if anyone canlet me know the most likely problems- I would really appreciate it- pleeeze answer -

 

You should try to locate the hissing. If it's a vacuum leak it may cause the engine to rev higher. If it is at the brake booster, then you could certainly lose your power assist. The power brakes are assisted with the use of engine vacuum.
That's a scary thought to have your engine wanting to rev and the brakes not behaving at the same time.
There is a large diameter hose from the intake to the valve on the brake booster, if there is a leak there, replace the complete hose. Don't take any chances.
If you hear the hissing on the inside of the truck, it may be the rubber diaphram in the booster has developed a leak and you need to replace the booster.

I use a piece of heater hose, hold it up to my ear and use it as a stethescope to locate vacuum leaks and noises like that.
Let us know, we want you safe!

 

I hear the hissing on the inside of the truck-coming from just in front of the brake pedal-behind that panel-I think I'll try replacing the power assist & get a new line-I NEVER want to go thru that again-thanks for responding -I will let you know what happins next- as soon as I can - shan- p.s.- even though she is a pain sometimes-this is my all time favorite ride- fun to drive, not too bad on gas, usually gets me there and back, and comfy to sleep in on those (rare) occasions that I am not catching any fish and have a desire to nap.