jjyoda_86

so the other day I noticed I had no power brakes after racing past this moron on the road the other day after passing him I needed to make the next turn hit the brakes and had no power assist until rpms dropped to 4500 or less. I then decided to smoke test the brake booster and it and it was leaking so I replaced it with another one, used but it was working good on the truck it came off. still I have a rock hard pedal at high rpms. trying to figure out if im supposed to be using the 3.4 booster or not.

JasonYota

iTrader: (1)

Your brakes work off of vacuum. The engine vacuum is greater at lower rpm or when your not pressing the gas. When you push the pedal to the floor the engine doesn't create enough vacuum for power brakes.

aztoyman

Do you have a check valve between the vacuum source and the booster? It will maintain the vacuum in the booster even though your intake vacuum will drop off when you punch it.

My donor 99 3.4 4Runner did not have one in the line like my 88 22RE did. Maybe built in the booster of the 99?

I took the check valve off my 88 and put it in my booster line.

jjyoda_86

no I do not have a check valve in between the booster and intake. that was my next solution just have to go pick one up and see what happens. thanks for the intel.

jjyoda_86

I installed the one way check valve and it fixed my brake problem.

MechanicTony

+1 on this solution, I used the 3.4 vacuum hose and spliced in the check valve from the 3.0:

NWLS

where did you pick up the check valve from?

aztoyman

Just grab one from a truck that has one or buy a generic one from a parts store that fits the line.

MechanicTony

Mine came off my 91 Toyota Pickup with a 3.0 - make sure to put it in the right way or you'll have no power brakes.