Replace Master Cylinder and Brake Booster At Same Time?

15239 Views 11 Replies 7 Participants Last post by Drunken Elvis, Jul 12, 2021

kc27

Discussion Starter · Apr 19, 2017

My 2005 Town and Country van has over 250,000 miles on it. Yesterday, when I went to back it out of the driveway, I stepped on the brake pedal, heard a pop, and the brake pedal went to the floor.

None of the lines going to any of the calipers are leaking. I looked near the master cylinder and saw a brake fluid. I am not sure the brake booster or the master cylinder are bad, but with the amount of miles and the age of this vehicle, should I have both parts replaced?

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LEVY

· #2 · Apr 19, 2017

Hello,

Brake booster would not leak brake fluid, so if it is leaking, your problem shouldn't be the master cylinder. Not need to replace booster unless it is full of brake fluid and it is not holding vacuum.

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kc27

Discussion Starter · #3 · Apr 19, 2017

I will take another slower, more detailed look tonight. I did a quick look at the flexible lines that connect to each caliper last night, and did not see any leakage. The brake line connection area of the master cylinder looked wet, that is what got me considering it to be a master cylinder problem. That and the popping sound seemed to come from right under the hood.

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nate95366

· #4 · Apr 19, 2017

Sounds like a bad master cylinder from what you have said. On a 250,000 mile vehicle, I wouldn't go replacing parts "just because (it's old)." You're liable to replace the whole van! If the booster holds vacuum it's fine, and I think it's far more common for the vacuum hose that connects the brake booster to the intake to dry rot and fail than it is for the booster itself to fail.

Nate

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kc27

Discussion Starter · #5 · Apr 20, 2017

You are right about the replacing the whole van comment. I am going to take a second look tonight to see if I can locate the leak. Besides this latest brake episode, I need to replace a passenger side lower control arm, and inner and outer tie-rod ends on both sides.. That, and I have an oil leak to track down. It is our "utility" vehicle for taking yard waste to the recycling center, materials from lumberyard, etc. I am thinking of searching for another van to use for those types of tasks, but one that has around 100,000 miles on it. I applaud some of the really high mileage van owners on this site. They really must stay on top of their vehicle maintenance to have a high mileage vehicle that is dependable.

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BillGrissom

· #6 · Apr 21, 2017

I suspect there is a vacuum seal between the MC and booster (sealed w/ flat O-ring) since my M-B cars have a similar-looking pancake booster. If true, a rear fluid leak from the MC will flow fluid into the booster (as my M-B). On older Mopars, there was a "drip gap" between MC and booster, and the booster had an inner bellows around the output shaft. That made the boosters thicker. So, when you change the MC, look for fluid inside the booster. You might stuff in rags to get it out w/ capillary action. Normal glycol brake fluid absorbs moisture to cause rust, so you probably don't want any sitting inside your booster. It should be much easier to replace just the MC. The booster requires crawling under the dash, which is always fun. Bench-bleed the MC to get all air bubbles out, and flush new fluid thru all the tubes after install. You should do that every 4 yrs or so, regardless just to fight moisture, especially for those living in the East. I use silicone fluid (DOT 5) in most of my cars so no rust. I even put it in my 1996 Voyager last pass, even though it says "not for use in ABS systems". I just had to test that lawyer-speak. The brakes work normally and I get the proper ABS "chatter" when I skid in a wet parking lot. I suspect they simply didn't qualify the system w/ DOT 5.

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kc27

Discussion Starter · #7 · Apr 22, 2017 (Edited)

Thanks everyone for the help on this. I had time this morning to take a closer look, I removed the battery and battery tray to for a better view. There are two small metal mesh hoses under the master cylinder. The lower of the two hoses burst. Photos below.

Can anyone identify these two lines so I know what part I am looking for? And if you have any advice on remove and replace of these lines, that would be appreciated, too.

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kc27

Discussion Starter · #8 · Apr 23, 2017

OK, these are the primary and secondary lines from the master cylinder to the hydraulic control unit. Has anyone replaced just these lines before? If so, do you have any advice?

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NICKELSMUG

· #9 · Jul 11, 2021

LEVY said:
Hello,

Brake booster would not leak brake fluid, so if it is leaking, your problem shouldn't be the master cylinder. Not need to replace booster unless it is full of brake fluid and it is not holding vacuum.

So, I have a buick century with 300k miles on it with NO fluid leak but pedal goes to floor with air sound. Also, it seems that pressing the pedal must introduce air to the engine as it seems to screw with the idle.

I'm thinking brake booster. Wondering if I also might as well replace master cylinder given car age

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beat_truck

· #10 · Jul 11, 2021

NICKELSMUG said:
So, I have a buick century with 300k miles on it with NO fluid leak but pedal goes to floor with air sound. Also, it seems that pressing the pedal must introduce air to the engine as it seems to screw with the idle.

I'm thinking brake booster. Wondering if I also might as well replace master cylinder given car age

A bad brake booster shouldn't make the pedal go to the floor. Sounds more like a bad master cylinder or a leak somewhere in the system. Also, pushing the pedal far down and / or repeatedly will affect the idle some.

By the way, this is a Chrysler minivan forum. Seems kinda odd that your first post would be about a Buick Century. 🤨

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LEVY

· #11 · Jul 11, 2021

NICKELSMUG said:
So, I have a buick century with 300k miles on it with NO fluid leak but pedal goes to floor with air sound. Also, it seems that pressing the pedal must introduce air to the engine as it seems to screw with the idle.

I'm thinking brake booster. Wondering if I also might as well replace master cylinder given car age

How do you know it is not leaking?

Seems like you have a bad booster, and maybe also a bad master cylinder.

When master cylinder goes bad, many times it leaks brake fluid into the brake booster. This brake fluid then destroys the brake booster diaphragm.

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Drunken Elvis

· #12 · Jul 12, 2021

Assuming everything was working before the failure. Then likely only one thing has failed. A line, a leak, or a master cylinder. There is no reason to think the booster has failed provided the information given.

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