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86-95 Trucks & 4Runners 2nd/3rd gen pickups, and 1st/2nd gen 4Runners with IFS

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Old 03-01-2012, 07:41 AM   #1
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Brake pedal rock hard when turned off and now...

Put a v6 booster and master on my truck 2weeks ago. Everything worked great but the truck had a really stiff pedal when turned off. To the point to where if i was on a hill i can not push my clutch in and brake and stop my truck until i start it. So it just rolls back. Other than that it worked great until now. On my way to school my pedal got as stiff as it did when turned off. Could not stop my truck. would let off and press again then pedal felt better but woulds shoot back and be hard again.

Everything is bleed
worked perfect for 2 weeks other than at start
line is hooked up to the booster
drums are adjusted
calipers are v6 and still pretty new
booster and master are used but came off the same truck.
if your saying its the booster or master please give me a way to test it.
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Old 03-01-2012, 07:49 AM   #2
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I changed my booster and MC a while ago and was having similar issues lots of air in lines. If you did not bleed the master after install you'll want to do it. also if your truck still has the proportioning valve and you didn't bleed that you'll want to do that after the MC bleed. then bleed brakes again. PIA to bleed brakes..
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Old 03-01-2012, 07:50 AM   #3
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Nice looking rig.. btw
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Old 03-01-2012, 07:51 AM   #4
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ran through all those issues bleed the master 2 times and did the LSPV too.
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Old 03-01-2012, 07:59 AM   #5
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FYI, air in brake lines does not cause a hard pedal. I don't know where that came from. If anything sticking calipers and misadjusted drums can cause that. MAYBE a failing LSPV. A bad master can cause this too, and I have seen new masters be bad right from the store.

Another thing to look for is if you put the check valve that is in that vacuum line to the booster in backwards, you won't be getting vacuum assist. I would lean towards that first.
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Old 03-01-2012, 08:03 AM   #6
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If you have a hard pedal while the engine is running then you have a booster/vacuum issue. Not sure about your clutch pedal statement....
Air in the lines will not cause a hard pedal.
Check your vacuum line from the engine to the booster. Kinked, blocked internally. Did you install the one-way check valve at the booster ?

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Old 03-01-2012, 08:07 AM   #7
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Will have to check the valve. what i mean about the clutch is. I can not stop or hold my truck until i start it. the pedal is so hard before i start that i can not stop it from rolling back until the truck starts. everything worked great until just now.
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Old 03-01-2012, 08:17 AM   #8
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E-brake is still functional.....
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Old 03-01-2012, 08:20 AM   #9
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no its not
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Old 03-01-2012, 09:01 AM   #10
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HMM.. funny because my brakes were hard as a rock when i first put in my MC and booster. drove around a bit and they just kept getting stiffer and my brakes were heating up as the air expanded as it got hotter. Bled them 3 times and was fine. However, as MY87runner's brakes are not functional until startup- I agree probably not air in brakes. sound like almost something is up with the booster itself.
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Old 03-01-2012, 11:45 AM   #11
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Its for sure not air in the brakes, I am not so sure where you got that assumption but standard science will tell you gasses can be compressed and air is a gas, that is why you get a spongy pedal when there is air in the lines, liquid cannot be compressed which is why it is used in hydraulics because it applies equal force in all directions when compressed.

Your problem is most likely what others have suggested being a booster or vacuum problem, if you put your foot on the brake and then start the truck the pedal should move downward. You could have gotten a bad booster

Here is some reading on checking the booster and the check valve, it also explains how the booster works.
http://www.autoshop101.com/forms/brake05.pdf
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Old 03-01-2012, 12:10 PM   #12
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Makes sense why politicians are so spongy...
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Old 03-01-2012, 03:01 PM   #13
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Bad booster or check valve. A hard pedal as you described is from the engine and booster vacuum levels being the same. This can only happen from a tear in the booster diaphragm or a bad check valve. If it was only with engine off. it would be a bad check valve.

One more time, just check that you are getting vacuum by wiggling the vacuum hose at the check valve on the booster to confirm a hissing sound when the seal is broken.

My guess is that you had a small tear that has gotten worse.
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Old 03-01-2012, 03:01 PM
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