brake pedal too stiff at freeway speeds

i have an 04 trd 150,000 miles x cab, with a scary brake issue. i was driving on freeway, luckily leaving a big gap , and traffic stopped abruptly so i stomped on the brakes. the brake pedal was really stiff like there was no vacuum(like when engine off) and little to no braking, and then it seemed to settle and brakes slowed the vehicle. the brakes work fine otherwise. took at least two seconds off braking reaction time. .and maybe two yrs off my life. seems to happen at speeds above 45 mph. any ideas out there? vacuum leak?pinhole in booster? super clean truck no rotten hoses blabla, did visual, loks good . thx

 

That sounds like ABS brakes at work. Does your Truck Have ABS brakes

Is this only with a hard brake application?

Vacuum leaks or booster problems seldom are intermittent but strange things do happen.

The booster is simple to test.

 

Sounds like either the brake booster is failing or the vacuum check valve on the booster has failed.

 

delayed braking , scary late like no brakes, coasting till pedal settles in and gets downa couple inches and works different than my oo taco, both have abs, i ll test booster , and check vlv, thx guys. i ll give update.

 

It really sounds like a ABS computer issue.

Good luck!

 

When was the last time you serviced the brake system?

Replaced front pads, rotors, calipers?
Have you ever replaced your brake fluid?
How are the rear brakes- ever replaced the shoes or had the drums turned?
Do you use the e-brake when you park the truck (setting the e-brake adjusts the shoes)?
How are the parking brake bell cranks? Depending on road conditions and use (or non-use of the e-brake) they can seize and prevent correct shoe adjustment.

 

check valve seems to test good, i think booster is bad, ran engine for a few n shut it off, no assist happening after shut off . i guess theres supposed be a couple pumps left if engine quits . gonna change it . we ll see.

 

That's cool that you're chasing the smoking gun and all, but as my previous post eludes to, make sure the various up keep items are indeed kept.

I can tell you that replacing the booster is not "simple". You're going to have disconnect the MC- take your time and get a rebuild kit for it. Make sure it's properly bench bled before attempting to reinstall it. Then completely flush the system of the current fluid. The calipers are also rebuildable- That's far more preferable than an returb aftermarket (parts store reman) solution.

The Motiv power bleed system is worth it's weight in gold. I spent 18 years saying I didn't need one because manually bleeding should be just as good.. and yeah, it's not. My well kept brake system never felt better after it's first motiv bleed.

 

changed booster, brakes work normal. can hear tires at friction breaking threshold immediatly upon stomping the pedal. i cheated by pulling master cylinder forward and turn sideways, after disconnecting lines from firewall. barely had to flex lines. theres a nice coil of line below that allowed it. thnx. dm93 nailed it