Brake pedal sometimes loses pressure - Toyota Nation Forum : Toyota Car and Truck Forums
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post #1 of 9 Old 12-11-2017, 08:36 PM Thread Starter
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Brake pedal sometimes loses pressure

Brake pedal sometimes loses pressure

I've noticed this a few times. I'll be sitting at a stop light. And the pedal loses pressure sometimes and goes further in. But then I'll let off the brake pedal and then back on and the pressure is back to normal.

My truck is not under very hard braking, just normal street driving.

Any quick diagnostic ideas?

Btw, it's a 1987 22R manual 4x4.
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post #2 of 9 Old 12-11-2017, 08:46 PM
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Could just be vacuum as the brake booster; did you check the fluid level in the reservoir?
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post #3 of 9 Old 12-12-2017, 12:09 AM Thread Starter
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Just checked the fluid reservoir level. It's full, almost to the max line.
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post #4 of 9 Old 12-13-2017, 09:39 AM
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My '88 pickup had the same problem. It was a worn brake master cylinder. Replaced the master cylinder.
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post #5 of 9 Old 12-13-2017, 03:03 PM
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Quote:
Originally Posted by roadsterred3 View Post
My '88 pickup had the same problem. It was a worn brake master cylinder. Replaced the master cylinder.
Totally agree!
Sounds like the fluid is bypassing the valve in the master cylinder.
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post #6 of 9 Old 12-13-2017, 07:47 PM
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If it sinks to the floor under pressure , then comes back when you pump it a little, it probably is the MC.
Be sure to bench bleed the new MC before installing, the thoroughly bleed the entire system.

_No THANKs necessary !
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post #7 of 9 Old 12-14-2017, 03:17 PM Thread Starter
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Thanks guys! I'll look into replacing the MC.
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post #8 of 9 Old 02-12-2018, 10:48 PM
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Quote:
Originally Posted by davebigtruck View Post
Thanks guys! I'll look into replacing the MC.
So was that it?
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post #9 of 9 Old 05-28-2019, 02:05 AM Thread Starter
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Quote:
Originally Posted by sc2dave View Post
So was that it?
This response is very delayed. But I got the MC replaced recently with a new oem unit. And yes that was it, brake pedal feel and pressure are now normal and working great!
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