So I just did a big brake kit on my 55 suburban and my mechanic and I were talking and he says the cam is to aggressive and doesn't create enough vacuum for the brakes. Can someone explain this to me. I see how it's logical but don't know how it technically works.

when driving when it can't idle and brake and turn all at the same time due to there not being enough vacuum. I just don't know the technical side of it.

eric L, allmotor? Anyone?

Vaccum is created during the intake stroke of the cylinder. 4-stroke motor (4cyl)... there are at least two cylinders in some portion of this phase at all times. That's the 'sucking' sound you hear on the intake! Even at idle... there is enough vacuum to support the brake system. If your car is a auto... put in neutral and turn the car off before bringing it to a stop... you'll notice the brakes getting very touch. The power-steering is not vacuum-assisted.. its hydraulic. The brakes are actuated in a hydraulic fashion... but assisted by vacuum pressure.

In the olden days there were cars where the windshield wipers were vacuum driven... so when you are idling.. it runs slower and when you speed up they go faster!


If there is significant overlap due to very aggressive cam lift/duration... sure there might be problems at idle.... so don't cruise at idle if you need to stop the car

yea our 58 caddy windshield wipers are vacuum driven. Thanks for making it all make sense man. I appreciate it.

As usual, Allmotor is dead on.

The solution is to get a larger vaccum reservior. In the early 70's, some of the cars had a tough time generating vaccum with the smog motors. Cars that had a ton of vaccum operated items like the Caddys used vaccum reserviors to store vaccum. It's similar to having a 30 gallon tank on your air compressor - it give you some reserves.