I went fourwheeling recently and I had a problem in 4wlow. The brakes would go out. The vacum booster seemed to go die on me. This was only when the truck was idling around(not needing to press the gas when I was climbing hills). When the rpms went up the power would return or if the truck was just sitting there in neutral. The weird thing is that the brakes work perfectly fine in 4wdhigh. No problems at all. I am thinking either vac. leak or bad pump but what difference is there in vacume between low and high. I assume there is more brake pressure to slow the truck in low because of the torque. Any suggestions?

 

Someone correct me if I am wrong but I thought our trucks had a hydraulic brake booster that works off of the power steering pump.

 

Not until '97.
It's a common problem, low idle rpms just don't put out enough vacuum to keep up with repeated brake use. Dealer fix is a $125 vacuum tank and some hose for extra storage.
My fix would be to buy a $10 vacuum tank or to make my own with a piece of pvc pipe and two caps, run some hose and tee it into any part of the vacuum system.

 

A vacum tank is a good idea, I never thought of that , thanks for the tip!

 

I stand corrected.