Author Topic: Brake Master Cylinder replacement  (Read 4738 times)

1974450SEL

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Brake Master Cylinder replacement
« on: 31 January 2011, 11:13 AM »
Hello all.  I've read the Library articles on how to do this but it looks easier than I suspect it will be.  My current master cylinder has recently started to leak everytime the car is not driven for a couple days and I've never replaced it since I owned the car.  I can get a remanufactured one off Rockauto for 45.00 which seems very reasonable.  Any advice, thanks.

koan

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Re: Brake Master Cylinder replacement
« Reply #1 on: 31 January 2011, 12:12 PM »
Hello all.  I've read the Library articles on how to do this but it looks easier than I suspect it will be.

Should be am easy job but preparing for problems is wise

Quote
My current master cylinder has recently started to leak everytime the car is not driven for a couple days and I've never replaced it since I owned the car.

Unusual that it leaks after standing, I would expect to leak when under pressure - foot on pedal.

Where is the leak from? Only possible places are the grommets where the plastic reservoir attaches, the two (or three) brake line connections, or from the rear where it mounts to the brake booster.

A rebuilt master cylinder should come with new grommets for the reservoir mounting and a new O-ring for brake booster mounting.

The brake line fittings are usually very tight and to undo them a flare nut spanner in needed, like a ring spanner but with a gap in the ring to pass over the pipe. Using an ordinary spanner will almost certainly round off the corners of the fittings and not do the job anyway.

Brake fluid is not good for paint, you need to empty the reservoir by opening a front and rear bleed nipple and pumping out brake fluid by repeatedly pushing the brake pedal.

Disconnect any reservoir level switches and pull the reservoir straight up to remove it.

Disconnect and remove any brake failure switch screwed in to the master cylinder body.

Undo the pipe fittings with a flare nut spanner, a few light taps with a hammer on the flats of the "nuts" often helps loosen stubborn fittings.

Remove the nuts attaching the master cylinder to the booster. Take care not to dislodge and lose the small rounded end piece of the push rod and the associated washer(s).

Use a new O-ring between booster and master cylinder and new grommets for the reservoir. Attach the brake lines. A little brake fluid on the grommets will help when pushing home the reservoir. Don't install the failure switch (if there is one) until the system has been bled.

Bleed the brakes, check for leaks, test the brakes by running up the engine in "D" against the brakes, if OK go for a slow drive until confident brakes are working as they should.

koan
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WGB

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Re: Brake Master Cylinder replacement
« Reply #2 on: 31 January 2011, 04:46 PM »
Adding to Koan's comments.

1) You presumably have an earlier style of master cylinder if your car is a 1974 model.

I believe they are not easliy interchangeable with the later model that is on my car shown here due to different pipe positioning on the master cylinder - but certainly the later model is quite inexpensive new and comes supplied with all the necessary new seal and nuts and a new plastic reservoir for the newer type is also quite inexpensive.



2) The use of flare nut wrenches - pictured below - is essential or heartache will follow rounded off hex couplings. If you do not want to lash out on a whole set at least purchase the 11mm one as that is the common brake coupling size.



3) Get a good seal between base of master cylinder and booster or you will have varying pedal pressures.

4) Keep your greasy fingers away from the fluid and the inside of the reservoir or your hard work will not last for long.

Bill

1974450SEL

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Re: Brake Master Cylinder replacement
« Reply #3 on: 01 February 2011, 11:50 AM »
Excellent advice from both replies.  Thanks Koan and Bill.  I was going to ask for a photo of the Spanners but you've answered that question.  I will take heed to all advice when I tackle this project on a slightly warmer day than we've been having as of late. 

Koan - You maybe right about the leak coming from the booster/master cylinder junction and not the master cylinder itself.  The puddle of fluid is right at the front wheel well area.  I will recheck this tonight. 

Bill-  Correct 74 model, car manufactured 11/73.  Yes my master cylinder is the older rectangular type compared to the photo of yours here, the filler caps look similar though. 

I'll keep you posted on progress.  Thanks again.

Squiggle Dog

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Re: Brake Master Cylinder replacement
« Reply #4 on: 01 February 2011, 12:41 PM »
I bought my W116 with a "new master cylinder", which was actually the original and rusty one. The rubber grommets were dried up and leaking so the reservoir wouldn't hold fluid. I was lucky and got a master cylinder with reservoir and booster that looked like they were brand new for $12 at the local wrecking yard! They came off of a 1985 W126, but they were identical to the ones in my 1980 W116 and worked great.
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mswcpt

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Re: Brake Master Cylinder replacement
« Reply #5 on: 01 February 2011, 11:57 PM »
I recently had an experience with my breaks loosing resistance when the car is stationary and the breaks applied. The master cylinder was removed and inspected and found to have small corrosion "pits" on the inside. My mechanic took it to a place here that actually reconditions these, and for a small sum had the old one re-conditioned and guaranteed to last for another 50 000kms.

1974450SEL

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Re: Brake Master Cylinder replacement
« Reply #6 on: 22 February 2011, 03:28 PM »
Well,
 I've finally had some extra cash to order the re-manufactured Cardone Master Cylinder from www.Rockauto.com and a "one man" bleeder kit, both about $50.00 US with shipping.  I'll be going to Autozone to get the Spanner set and begin work as soon as the parts come in.  I'll take step by step pictures and post them upon completion by this weekend.

hans moleman

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Re: Brake Master Cylinder replacement
« Reply #7 on: 22 February 2011, 07:23 PM »
I just replaced my master cylinder last night, it went very well. I cleaned my reservoir out with soapy water (GASP!!!)dried then swished alcohol around then dried once more. I used a bit of silicone lube on the big o-ring and just a tiny bit on the reservoir grommets. Do yourself a favor and install the reservoir last as access to the interior 13mm nut is much easier with it out of the way. Nobody was around to help with the bleeding so I gravity bled at each corner, brakes work great. With a helper and above freezing temps job should only take 2 hours max with multiple beer breaks, good luck.

thysonsacclaim

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Re: Brake Master Cylinder replacement
« Reply #8 on: 22 February 2011, 10:53 PM »
Good pointers Bill, Koan et al.

My seals are also leaking, very slightly. They are moist, but the fluid level seems to stay up so it appears it is in the early stages of deterioration. The brakes also worked very well when the car was in service.

With this in mind, and since I'm removing the booster anyway, I'll probably undertake this job when I begin to put the top end back together. Peace of mind is worth it, and the price is really not so bad.

With our crazy drivers here, I'd prefer not to find out my brakes aren't working what some joker pulls out in front of me
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calvin streeting

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Re: Brake Master Cylinder replacement
« Reply #9 on: 23 February 2011, 12:28 AM »
My seals are also leaking, very slightly.

With our crazy drivers here, I'd prefer not to find out my brakes aren't working what some joker pulls out in front of me

This happend to me once in a vauxual viva HA. I stamped hard on the brakes and brake fluid was shot all over my legs. it was at that point i thought "i am going to die".... but managed to avoid everything and used the kurb to slow down. :)

1974450SEL

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Re: Brake Master Cylinder replacement
« Reply #10 on: 27 February 2011, 03:25 PM »
I've, successfully installed the replacement master cylinder, bleed all four corners, test drove and she's good as new!  I want to post photos of the steps I took to do it but I am at a loss on how to do that on this forum.  Can someone assist? 

WGB

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Re: Brake Master Cylinder replacement
« Reply #11 on: 27 February 2011, 04:50 PM »
Post your pictures onto a web provider - I use www.photobucket.com.

Then you press the "picture"button and place the web address between the square brackets.

There is a problem with this web site once you get past a certain point in a larger posting where the cursor will jump back to the top of the page.

I get around this by posting all my pictures first and then write the text afterwards.

AFIK teh preview button still doesn't work so you have to post it and then edit from the post itself.

Bill

1974450SEL

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Re: Brake Master Cylinder replacement
« Reply #12 on: 27 February 2011, 05:15 PM »

Removing reservoir, took some careful prying with screw driver

about to remove old one with spanner wrench

old one out without too much fuss

view of new one

new one installed

reservoir installed on new master cylinder

bleeding left rear wheel with self bleeder (this helped immensely)

sensors hooked back up



view of car after being test driven after a month of sitting, man how I miss driving this car!
« Last Edit: 27 February 2011, 05:49 PM by 1974450SEL »

WGB

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Re: Brake Master Cylinder replacement
« Reply #13 on: 27 February 2011, 07:02 PM »
Good on you and thanks for posting the pictures.

Well done - must be a good feeling.

Bill


1974450SEL

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Re: Brake Master Cylinder replacement
« Reply #14 on: 27 February 2011, 07:19 PM »
Bill, thanks a lot.  It is a good feeling.  I look forward to further projects as the Spring/Summer come here.