2nd gen 4runner brakes issue

[smaddock]

Hey,

Just after some advice as to what may be the problem in my 4Runner.

Basically the brakes appear to be working fine, except for when I've just been accelerating then jump straight on the brakes, the pedal feels bloody hard and the car doesn't pull up as well as normal. I'm assuming this may be booster related? I've checked the one way valve from manifold to booster and it appears to be working fine and is installed the correct way. This has only started happening in the last couple of weeks, but is scary in peak hour traffic when morons in front of me jump on their brakes...

As said, under normal driving they are fine with good pedal feel, its only when I've just been accelerating then jump on the brake.s

Cheers guys

[berad]

Spot on, hard brakes/lack of stopping power is the lack of vacuum assist from the master.

By the sounds it is petrol, and because when your accelerating in a petrol there is no vacuum and in a diesel there is a pump producing it for you, are you sure the 1 way valve is fine as this could cause the lack of vacuum in the master with a quick stab on the brakes after accelerating.

Is it diesel or petrol, and auto or manual. If it's diesel check the vacuum canister etc, or the vac pump on the back of the alternator (early) or late model on the front of the alternator, pull the air vac hose off the canister and crank the motor and listen to the end of the hose for air being sucked in.

If its petrol, you COULD have a leak in the brake booster line, or worse a busted master cylinder (unlikely). Have you bled the brakes lately, or if you have changed the pads, if so there may be some air in the lines.

[smaddock]

Its a petrol, actually a 3rz conversion from a 22R I only tested the 1-way valve by blowing thru it one way then the other, and I only could one way. When blowing thru it the correct way, it felt like it was 'sticky', and took a little pressure before it let my breath thru, if that makes sense.

The brakes were bled with all new fluid pumped thru last september or so, and the pads were replaced at the same time. Has been fine up until a few weeks ago...

[smaddock]

Tested the one way valve today, its fine so that doesn't appear to be the issue.

One thing I forgot to mention is that I've had quite a few gas backfires over the last 6 months or so, could this have caused damage to the booster at all?