Brake Booster Failure.......................Confirmation, Please?

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LFD2037

LFD2037

TEXAS LEXUS!
10 Year
Joined
Oct 22, 2013
Threads
183
Messages
3,889
Location
Wax., TEXAS
History: Replaced pads & rotors, bled entire system about 15K miles ago. Has worked normal for the past 15K miles so I really don't think it has anything to do w/those parts.

Was pulling into a parking place yesterday, w/the steering wheel turned, & applied brakes. They were hard as a rock & I went right past where I planned to stop. Tried brakes again once I stopped, w/steering wheel straight, & they acted completely normal. Acted normal for the rest of the day.

This morning I was backing out of a parking space, w/the wheel turned, & same rock hard pedal & barely stopped in reverse. Pumped pedal & worked as normal. Drove to store w/brakes working normal. Pulled into parking space at store, w/the wheel turned & pedal hard as a rock & almost went thru the front of the store!!! Pumped them after stopping & pedal felt normal.

Driving home the issue was intermittent. It seems on the first attempt to use the pedal it doesn't work but if I pump them they work almost as good as normal (normal has never been really good but doable).If I just stay standing on the brake, after about 5 seconds, it'll get softer, pedal will sink & brakes work.

I did the brake booster tests I found online multiple times. Sometimes it passes, sometimes it fails.

Seems the problem is quickly becoming progressively worse.
I'm living in an apartment right now while my new house is getting built w/all tools in storage & no place to fix it. I can make it happen if I must but is there anything else that can be the issue other than replacing the booster?

What problem does this sound like to y'all?
 
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It does sound like booster symptoms but, the booster does not know you are turning the wheel when your braking. Have you tried engine off and pump the brake until pedal goes hard, then rest foot on brake and crank engine, the pedal should be pulled down from under your foot, regardless of the steering wheel position.

regards

Dave
 
Dave 2000 said:
The booster does not know you are turning the wheel when your braking. Have you tried engine off and pump the brake until pedal goes hard, then rest foot on brake and crank engine, the pedal should be pulled down from under your foot, regardless of the steering wheel position.

regards

Dave
Click to expand...
Yes I tried that twice. First time, pedal didn't move. 2nd time, pedal sank down like normal.

I added the steering wheel in case there was some weird vacuum situation going on but just remembered these pumps are completely hydraulic so it doesn't matter.
 
I would check the vacuum lines from the manifold to the booster, if they are leaking you will lose vacuum. On gasoline engines, if the engine is running and you expose the leak, the idle normally climbs. Diesels have a separate pump. Also as an asides check your brake fluid level, the master can leak down the plunger and it ends up in your booster.

regards

Dave
 
Dave 2000 said:
I would check the vacuum lines from the manifold to the booster, if they are leaking you will lose vacuum. On gasoline engines, if the engine is running and you expose the leak, the idle normally climbs. Diesels have a separate pump. Also as an asides check your brake fluid level, the master can leak down the plunger and it ends up in your booster.

regards

Dave
Click to expand...
I checked all lines for leak but will check again. The fluid is at the same level it was when I finished flushing it 15K miles ago. Thanks.
 
No vacuum leaks.
Just did the "w/truck not running, pump pedal a couple times to remove vacuum, hold down on the last pump & start truck" & the pedal sank down a couple inches (meaning it passed this test). BUT it failed this test earlier?!?!?!?!
 
Most times we have seen, when the valve in the booster dies, it's random, becomes more prevalent until it totally fails. Sounds just like what you are experiencing, if so, time for a new booster. If it's the booster, the brakes still work, can make full power, just requires a huge amount of effort, pedal pressure.
 
Tools R Us said:
Most times we have seen, when the valve in the booster dies, it's random, becomes more prevalent until it totally fails. Sounds just like what you are experiencing, if so, time for a new booster. If it's the booster, the brakes still work, can make full power, just requires a huge amount of effort, pedal pressure.
Click to expand...
Just did more drive testing. It's like I get one chance for the brakes to work for each braking 'session':
Driving and hit brakes & they work normal but progressively work stronger as the brake is held
Let off the pedal & immediately apply brakes again & pedal is significantly stiffer w/less braking ability
3rd time let off brakes and immediately apply then they are even stiffer than the 2nd attempt w/even less braking ability
Let off brakes for 10+ seconds & the cycle repeats itself (they work, then work less then work even less w/each apply & release of pedal).
It's like it's running out of vacuum though there's no vacuum leaks & the booster check valve proved to be functioning properly (can't blow into it but can suck out of it).
 
Toyota dealer just told me that the vacuum hose that goes from the booster to the manifold is no longer available

44773-12081

Anyone happen to know the inside diameter of that hose ?
 
GBinAZ said:
Toyota dealer just told me that the vacuum hose that goes from the booster to the manifold is no longer available

44773-12081

Anyone happen to know the inside diameter of that hose ?
Click to expand...

10mm, so 3/8" ish.
 
LFD2037 said:
Just did more drive testing. It's like I get one chance for the brakes to work for each braking 'session':
Driving and hit brakes & they work normal but progressively work stronger as the brake is held
Let off the pedal & immediately apply brakes again & pedal is significantly stiffer w/less braking ability
3rd time let off brakes and immediately apply then they are even stiffer than the 2nd attempt w/even less braking ability
Let off brakes for 10+ seconds & the cycle repeats itself (they work, then work less then work even less w/each apply & release of pedal).
It's like it's running out of vacuum though there's no vacuum leaks & the booster check valve proved to be functioning properly (can't blow into it but can suck out of it).
Click to expand...

Sounds like the booster valve dying.
 
Tools R Us said:
Sounds like the booster valve dying.
Click to expand...
That's what I'm figuring so going to replace the brake booster. Anybody know the length of external protrusion (into the master cylinder) the pushrod should be adjusted to when I install the new (re-manufactured) brake booster?
Thanks for all the input!
 
LFD2037 said:
That's what I'm figuring so going to replace the brake booster. Anybody know the length of external protrusion (into the master cylinder) the pushrod should be adjusted to when I install the new (re-manufactured) brake booster?
Thanks for all the input!
Click to expand...

There is a spec for that in FSM, if not right you could end up with the brakes not releasing when they warm up or long pedal travel.

regards

Dave
 
LFD2037 said:
That's what I'm figuring so going to replace the brake booster. Anybody know the length of external protrusion (into the master cylinder) the pushrod should be adjusted to when I install the new (re-manufactured) brake booster?
Thanks for all the input!
Click to expand...

If you are not changing the master, set it the same as your old booster.
 
Did this not too long ago. Push/pulled brakes lines/master cylinder towards the front end of the truck.

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Key is to pull out brake booster and turn it towards the passenger side so that it clears the manifold.

image.webp


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Most will say that this is a one man job. Unfortunately for me the plate inside the cabin that holds the booster sagged a bit.

image.webp



So when I was trying to pull the booster out and when I tried to push the booster in the holes were not lining up making it an issue. I needed the help of another mudder @FJRanger to line up the holes to make the job possible.

Good luck.
 
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I just replaced mine. Exact same symptoms as you, and a new booster fixed it. You set the push rod depth using a special tool which basically just makes sure that it's set so that there is just barely no clearance between the push rod and the master. I didn't have a tool. I did it by putting a tiny dab of grease on the tip of the push rod, putting the master in place, and then pulling it off to see if I got any grease on the inside of the master. I just repeated that, adjusting the push rod every time, until I got just a little grease on the inside of the master. Everyone says to set it the same as your old one, but my old one was definitely set too shallow and resulted in excessive brake pedal travel. My brakes are great now.
 
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