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Old 03-30-2021, 02:16 AM   #1
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Default Brake Master cylinder leak

About 4/5 months ago the brake fluid reservoir was half empty, so I topped the brake fluid reservoir without properly inspecting everything (dumb thing to do I guess).
This week had some time so was doing a general inspection and noticed that the reservoir is missing about 20% of the fluid.

Noticed that the brake master cylinder has a small leak on the back, and the lower part of the brake booster is rusted, so I guess it has been leaking for a good while. Ordered a rebuild kit with the pistons and seals (Seiken brand 48 USD), since a new cylinder (Nabco brand OEM) costs 340 USD in here, waiting for it to be delivered.

The brakes work fine, and the brake booster pressure appears to be fine. Did some simple tests, like pressing the brake pedal until it becomes hard with the engine off, then turning on the engine while pressing the pedal. The pedal goes down slowly while doing that, so I guess it's working fine. It does squeak a bit when i press the pedal tho. The squeak gets louder the harder i press the pedal. If i press it softly it doesnt squeak that much, so don't know if it's related to the booster or not.

Not sure if the brake fluid entered the booster too. Is there a way to drain the fluid from the brake booster, or should I just let it be since it appears to be working fine? A new one costs more than 400 USD, and used ones aren't available.

Since i'm replacing the piston and seals of the brake master cylinder, should I go ahead and replace anything else?

It's a ’88 4x4 Crew cab with 207.000 km (128 miles?).

EDIT: Fixed the brake master cylinder leak using a repair kit for the cylinder (pistons, springs and washers), sprayed some WD-40 on the brake pedal springs and now everything is working perfectly. Don't know if it's useful, but I used the repair kit 205-51751 (Seiken brand) for Nabco master cylinder.
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Last edited by PFDSA; 04-13-2021 at 06:18 AM. Reason: grammar
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Old 03-31-2021, 02:02 AM   #2
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Bump.

I want to know too.
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Old 03-31-2021, 04:33 AM   #3
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Originally Posted by jp2code View Post
Bump.

I want to know too.
You have the same problem?
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Old 03-31-2021, 10:25 AM   #4
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You have the same problem?
No. Just curious what to do if brake fluid gets inside.
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Old 03-31-2021, 11:58 AM   #5
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Quote:
Originally Posted by PFDSA View Post
About 4/5 months ago the brake fluid reservoir was half empty, so I topped the brake fluid reservoir without properly inspecting everything (dumb thing to do I guess).
This week had some time so was doing a general inspection and noticed that the reservoir is missing about 20% of the fluid.

Noticed that the brake master cylinder has a small leak on the back, and the lower part of the brake booster is rusted, so I guess it has been leaking for a good while. Ordered a rebuild kit with the pistons and seals (Seiken brand 48 USD), since a new cylinder (Nabco brand OEM) costs 340 USD in here, waiting for it to be delivered.

The brakes work fine, and the brake booster pressure appears to be fine. Did some simple tests, like pressing the brake pedal until it becomes hard with the engine off, then turning on the engine while pressing the pedal. The pedal goes down slowly while doing that, so I guess it's working fine. It does squeak a bit when i press the pedal tho. The squeak gets louder the harder i press the pedal. If i press it softly it doesnt squeak that much, so don't know if it's related to the booster or not.

Not sure if the brake fluid entered the booster too. Is there a way to drain the fluid from the brake booster, or should I just let it be since it appears to be working fine? A new one costs more than 400 USD, and used ones aren't available.

Since i'm replacing the piston and seals of the brake master cylinder, should I go ahead and replace anything else?

It's a 88 4x4 Crew cab with 207.000 km (128 miles?).
It's probably NOT the booster. That runs off engine vacuum and fluid might enter the engine somehow, and then you would know looking at your exhaust.

Squeaks most often come from the springs at your pedal. If the noise isn't coming from inside the cab, then it could be your brake pads up front, or your drum brakes in back. Dust, grease, whatever. Check for brake fluid leaks starting from your brake master cylinder and work it back all the way to the back brakes.

If you have no leaks, good. But leaks don't cause pedal squeak on brakes. That's either your brakes units themselves, or your calipers or drums. Or your brake pedal springs.
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Old 03-31-2021, 11:13 PM   #6
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Quote:
Originally Posted by XoXSciFiGuy View Post
It's probably NOT the booster. That runs off engine vacuum and fluid might enter the engine somehow, and then you would know looking at your exhaust.

Squeaks most often come from the springs at your pedal. If the noise isn't coming from inside the cab, then it could be your brake pads up front, or your drum brakes in back. Dust, grease, whatever. Check for brake fluid leaks starting from your brake master cylinder and work it back all the way to the back brakes.

If you have no leaks, good. But leaks don't cause pedal squeak on brakes. That's either your brakes units themselves, or your calipers or drums. Or your brake pedal springs.
Thanks for the answer!

The squeak appears to come from inside the cabin, will check the springs like you said.

So far only found a very obvious leak on the back of the master cylinder. The repair kit (piston/springs and seals) just arrived today, so will atempt to stop that leak on the weekend. Will check all the way to the back brakes too like you said.

Would be great if someone could give me some insight on the brake booster, how to check if brake fluid entered, if it's dangerous to keep running with brake fluid inside it, and if it's possible to drain it.
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Old 04-01-2021, 02:25 AM   #7
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My guess is your brake booster is fine. If your squeaks are coming from inside the cab when you push the brake pedal, it's time to get down under that dashboard with a good flashlight, some grease, and/or a can of WD40. Watch out what you spray. Try to stay off the electrical connections with the spray.

The grease can be spread along where the springs make contact with metal, or where the cotter pins live, etc. Work the pedal, spread the grease. Do it on the clutch pedal too, as long as you are down there.
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Old 04-05-2021, 01:48 AM   #8
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Replaced my master cylinder's pistons, seals and springs and it doesn't leak anymore!
Bled the cylinder in the truck, with my girlfriend pressing the brake slowly while I covered the brake lines holes in the cylinder with my fingers (read about that method in the manual), and also bled all 4 wheels. Not sure if the wheels are properly bled, but the brakes are working fine so far. Pedal feels kinda soft, but it always did since I bought the truck.

Lots of debris and rust around the brake booster, tried to take a look at it but honestly can't see how brake fluid would enter the brake booster from the master cylinder.

Some photos:




Next thing to do is greasing the brake pedal, like SciFiGuy suggested. Will update.
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Old 04-13-2021, 06:11 AM   #9
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Update: Used WD-40 on the brake pedal springs (clutch pedal too) and had no squeaks since the last week, so I guess that for now the brake booster is fine
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Old 04-13-2021, 12:20 PM   #10
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My clutch pedal in the truck squeaks like door in a horror movie lol
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