So this week this problem started and it's intermittent. It feels exactly like when you pump your brakes 4 or 5 times and it gets harder and harder to push the pedal down. Needless to say this a serious safety concern. Everyone I've talked to seems to think it's the master cylinder but from what I've read the mc just goes bad once and for all, not just kinda every once in while like mine. What do you guys think?
Brake pedal hard to push down
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LittleCaesar
New member
Brake booster for starters.
For starters? Is there any way to figure out what the problem is before I start just replacing things?
Magmotor
New member
any codes being thrown? here's a list of items to check for Hard Pedal....
http://tacoma.site40.net/4Runner_96...toypdf/02rmsour/2002/024runne/br/trou/pst.pdf
19963.4lsr5
New member
There is a check valve in a grommet in the brake booster that the vacuum hose attaches to. It fails and causes a hard brake pedal and barely adequate brakes
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bad master pedal to floor
bad booster high hard pedal.
17 yrs old my guess is booster leak.. when you shut off engine [no vacuum] if the booster is good the brakes should work normally 2-3 times then hard pedal.
the check valve holds vacuum in the booster so when engine dies you still have some braking. if the valve fails this will not cause you problem.
the booster has a rubber part that over time will leak. usually 200K miles and 10-15yrs ...
very easy to check with a vacuum gauge.
bad booster high hard pedal.
17 yrs old my guess is booster leak.. when you shut off engine [no vacuum] if the booster is good the brakes should work normally 2-3 times then hard pedal.
the check valve holds vacuum in the booster so when engine dies you still have some braking. if the valve fails this will not cause you problem.
the booster has a rubber part that over time will leak. usually 200K miles and 10-15yrs ...
very easy to check with a vacuum gauge.
I don't know about Florida, but a bad check valve can cause a hard brake pedal in colder climates.
19963.4lsr5
New member
When the check valve sticks closed it prevents vacuum from going into the brake booster. And the exact explanation of hard pedal etc happened when my check valve failed. And it was intermittent. And really didn't like cold weather. But once it opened after pushing brakes a few times the brakes were fine till it sat overnight.
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I never seen one plugged up usually they stay open /leak down .but a check valve plugged up would do it.
could also be booster guts plugged it up .. then need both or just blow out the check valve.
19963.4lsr5
New member
Trust me. I tried everything before replacing it. I got lucky and my wrecked 96 parts truck had one that I robbed to get my wife back on the road. A new one was around 50 dollars.
Spraying it with brake cleaner and blowing it out and then shooting a little spray lube had me thinking I fixed it. Then a few days later it happened again in the morning. (She almost hit the tree at the garage) So I just took the one out of the 96. Sadly the bad one only had 125,000 miles on it and the 96 had 230k miles and sat for a year. But, problem never came back after changing it to this day. It's been 2 years now.
A few threads here pointed to the check valve and that info pointed me in the right direction.
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Thanks everybody.
So clearly living in Florida this isn't a check valve issue related to freezing cold temps, but how likely is it that it could still be the problem part? Either way for under $50 I guess it's worth a try.
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19963.4lsr5
New member
Do you have a friend with a 4Runner? Borrow his.
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Ok just tried this with my truck that's been off for about eight hours. First couple brake pumps were normal and the third was hard. So that means the brake booster is ok and the check valve is ok too?? Sorry, kinda confused by how you worded it. Thanks
I do actually. The problem is that this is so infrequent (maybe once a day) that I'm not sure how long I could borrow it to make sure that it's the problem. But I will ask him, good idea.
White Stripe
New member
If your truck is off that is normal. The booster stores a few assisted brake applications when the engine is off. Once the engine is started the engine will resupply vacuum to the booster.
so your booster and the check valve is good.
since it can occur intermittently then possible it is a brake caliper/hose /pad as the brakes heat up.. check that all the brakes are evenly at the same temp.
hoses do collapse internally at this age . fluid gets blocked hard to stop .. binding calipers/pads also. the hottest one is most likely the bad one. if all are the same temp when it messes up possible the master cylinder is binding but never seen that.
your wording also confused the hell out of me.
so if he got all hard pedals with the engine off, thats a test confirming a bad check valve?
Reservoir is good.
For the three weeks leading up to this I had the rear axle seal leaking pretty good. My buddy helped me get that replaced and he did a good job of cleaning out the gear oil from the drum and other parts that got leaked on. He assured me that the leak wouldn't have any effect on the brakes though, which is why I didn't mention it.
