tommygirl

im confused cant figure this one out i can start the truck barely mash the brake miss,miss, then stops press all the way down fine let off the brake miss,miss then if i pump the brakes it misses bad changed brake booster 3 times same thing changed check valve same thing changed egr vacuum modulator same thing sprayed ether on all vacuum hose around carburater bottom cant find no vacuum leaks. so i cant figure it out could it not be getting enough vacuum if so how do i know how much its suppose to get to check it ,and if it isnt getting enough vacuum how can i fix that. it is a 1986 toyota 4x4 22r thanks for all the advice in advance

wmayota

Does it have auto hubs?

tommygirl

no it has manul hubs

jbtvt

Did this start all of a sudden or happen right after a repair job or mud bog? Would that be a 22re or was it swapped?

It could have manual hubs and still an intact ADD system if someone converted it BTW, but not sure how a vacuum leak there would only affect the pedal when it's partially depressed, myself.

thook

ADD systems weren't on the 4rnr's or trucks until several years later than '86. So, the truck wouldn't have any ADD components on it unless someone were crazy enough to swap out the front diff/housing and install all the necessary switches and vacuum equipment. Rather unlikely.

You say "bad"? Like how bad? Enough to cause the engine to run rough vibrating the cab, etc? Any running problems when the brakes are not applied? Like even any slight misfires?

Vacuum is created by the pull of the pistons in the cylinders while the intake valves are open and exhaust valves are close. Any one or more cylinders/valves not operating correctly....like lack of compression (whether due to valves or rings) or improper combustion.... is enough to cause a drop in the total amount of vacuum/power your engine can create. And, the brakes draw on enough power from the engine that even though the brake system may be intact and proper....ie. no leaks....it can exaggerate even slight condition sometimes.

I recently had a fuel pump failure in my wife's '92 V6. Before it finally crapped out, it was causing enough of a loss of fuel pressure that engine wasn't producing as much power as it should and pressing the brakes caused the motor to run down a bit at an idle. Not too mention, a couple of the injectors weren't working right, so any misfiring was more noticeable.

So, there you have an example of what could be causing your situation......only you don't have injectors. Still......

Have you noticed any running problems, or at idle, or overall loss of power?