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  #1  
Old 08-22-2012, 07:31 PM
cnm cnm is offline
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Brake Booster Removal Help

I finally received my replacement brake booster and I have a few questions from the directions on how to remove and install a brake booster from the W108 service manual. I understand how to remove the booster itself. However, I am having trouble with the directions regarding draining the compensating tank and bleeding the brake lines.

Step 2 states "pump compensating tank of master cylinder empty via an opened bleeding plug of the front axle and rear axle brake circuit. Then loosen brake lines of tandem master cylinder." I do not know what this step refers to, specifically what and where is the bleeding plug (not shown in the diagrams) or how to pump the compensating tank empty.

Finally, the last few steps (13 and 15) state that I "reconnect the brake lines," "bleed the brake system and check for leaks." Do I not refill the compensating tank at any time? I didn't see a step for this. Also, not sure how to bleed the brake lines.

I am doing my best to learn on my own but running into more questions than answers. Any help would be greatly appreciated.

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Old 08-22-2012, 07:52 PM
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Quote:
Originally Posted by cnm View Post
I finally received my replacement brake booster and I have a few questions from the directions on how to remove and install a brake booster from the W108 service manual. I understand how to remove the booster itself. However, I am having trouble with the directions regarding draining the compensating tank and bleeding the brake lines.
"Compensating tank" means the brake fluid reservoir that is on top of the master cylinder. I've never heard that term before - is your shop manual British?
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Originally Posted by cnm View Post
Step 2 states "pump compensating tank of master cylinder empty via an opened bleeding plug of the front axle and rear axle brake circuit. Then loosen brake lines of tandem master cylinder." I do not know what this step refers to, specifically what and where is the bleeding plug (not shown in the diagrams) or how to pump the compensating tank empty.
Basically the instructions want you to get the fluid out of the reservoir. Each brake caliper will have a brake bleeding valve. The reservoir will likely have a compartment that is for the front brakes and a compartment for the rear brakes. So if you open a front bleed valve and push a tube over it so it can drain into a jar or something, and you pump the brakes, it will pump all of the fluid out of the reservoir. Same for the rear brakes. Tandem master cylinder means that there is a pressure line that goes to the front brakes and a pressure line that goes to the rear brakes. This also could be called "duel circuit brakes".

After you have pumped the fluid out of the reservoir it's telling you to remove the hydraulic lines from the master cylinder. They want you to empty the fluid first because otherwise it will just make a big mess when you remove the hydraulic lines.

Quote:
Originally Posted by cnm View Post

Finally, the last few steps (13 and 15) state that I "reconnect the brake lines," "bleed the brake system and check for leaks." Do I not refill the compensating tank at any time? I didn't see a step for this. Also, not sure how to bleed the brake lines.
You need a tutorial on brake bleeding. Try googling it. It's not mercedes-specific, but google brake bleeding and do some reading and then come back. It's not difficult and it is easier with two people. Basically you are bleeding all of the air out of the brake lines. You keep topping off the reservoir and keep pumping more fluid through the system and out the bleed valves until there are no air bubbles left in the system. And you do this starting at the farthest point from the master cylinder and working your way towards the closest point (closest wheel).
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Old 08-22-2012, 08:14 PM
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In case you don't know, you really want to try to avoid from getting the bake fluid on painted surfaces, even within the engine bay. If it sits on paint, it'll cause the paint to peel. (I typically make a "bib" for the master cylinder by unrolling a paper towel for about a yard or so, then doubling it back, and poking a hole through it for the reservoir opening to poke through. It is the first line of defense against spills, catching any drops, and I can then wipe the surfaces under with a wet cloth afterwards.)

When removing old fluid, you can often use a turkey-baster-type device (vs your actual kitchen implement) to carefully remove most of the fluid out the top, then gravity-flow the rest out the caliper bleed screws.

If you intend to reuse your master cylinder, I would caution against using full travel when pumping, either to evacuate the system, or when bleeding. It can be tempting to use long to-the-floor strokes, but that puts the master cylinder's piston seals in to bore territory they normally don't operate in, and can damage the old seals. The pedal travel is quite limited under normal conditions, and the part of the bore that isn't used may have gunk, etc., and suddenly pushing the old seals over that area may result in a weepy master after not too long.

Good luck!

And yes, even when using a Mity Vac, it is much easier to have two people when bleeding.
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Old 08-22-2012, 11:02 PM
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Forget the Mighty Vac, use a Motive Power bleeder which pushes the brake fluid down to the caliper, when the bleed screws are opened.
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Old 08-23-2012, 01:10 PM
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Thanks! I appreciate the help. I plan to give it a go this weekend.

Quote:
Originally Posted by Palolo View Post
If you intend to reuse your master cylinder, I would caution against using full travel when pumping, either to evacuate the system, or when bleeding. It can be tempting to use long to-the-floor strokes, but that puts the master cylinder's piston seals in to bore territory they normally don't operate in, and can damage the old seals. The pedal travel is quite limited under normal conditions, and the part of the bore that isn't used may have gunk, etc., and suddenly pushing the old seals over that area may result in a weepy master after not too long.
My master was replaced about a month ago (before the car was put on the market). I assume there is no need to change it. Also, could I reuse the brake fluid assuming it is only one month old?
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Old 08-23-2012, 04:41 PM
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Originally Posted by wbain5280 View Post
Forget the Mighty Vac, use a Motive Power bleeder which pushes the brake fluid down to the caliper, when the bleed screws are opened.
I was hoping that I could get one of these locally. No such luck. However, after looking at this bleeder, it appears to be fairly easy to build on your own. I may not have much car experience, but I do have some experience with homebrewing contraptions dealing with the movement of liquid. Replace a yard sprayer handle with a spare master cylinder cap with a nipple; connect nipple to hose. Voila. A homemade brake bleeder. Such a simple idea that I figured it must have been done before. Here is a great link to building one yourself:

The DIY $20 brake bleeder
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  #7  
Old 08-23-2012, 08:06 PM
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Don't try to reuse brake fluid, unless your life is worth less than 5 bucks.

Keep brake fluid absolutely clean.

Unless I'm mistaken, the two brake circuits are not front/rear, but left front, right rear/right front, left rear.

If you've never bled brakes before, find a friend, uncle, or someone who has bled experience to help you. It's sort of an art, can easily go awry, and is way too important to be casual about.
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Old 08-23-2012, 08:16 PM
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The brake circuits are front and rear.
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Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

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  #9  
Old 08-23-2012, 09:09 PM
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When I did the job on my 300M the lines were flexible so I was able to keep the master cylinder on the car and remove just the booster.

Of course, I had to remove the wipers, cowl, strut tower brace, and some other stuff to just get to the booster

Bleeding a non-ABS system with a mityvac is easy. But if you have an ABS system you'll easily go thru over 2 quarts of fluid. Ask me how I know
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  #10  
Old 08-24-2012, 10:10 AM
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Thanks again for all the help. I successfully removed the old booster and installed the new one last night. Re-installing the master cylinder, brake lines and bleeding the system is all that's left.

Quote:
Originally Posted by overlander View Post
If you've never bled brakes before, find a friend, uncle, or someone who has bled experience to help you. It's sort of an art, can easily go awry, and is way too important to be casual about.
My friends/family that are experienced with cars are all back in Mississippi. Unfortunately, it will likely be me and a similarly inexperienced friend.
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  #11  
Old 08-25-2012, 12:56 PM
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Well, a valve broke off. Any idea how to fix this?





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  #12  
Old 08-25-2012, 01:19 PM
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You'll need a bolt extractor to get the old piece out of the caliper and a replacement bleeder nipple - if you can't find a new one, you'll need a new caliper. I don't know what size extractor you need so take the piece with you to find the best size. You may need to drill it bigger and, if you do, then you'll need to disassemble the caliper to clean out all of the bits.

VERMONT AMERICAN Screw Extractor Set, Spiral Flute, 10 Pcs - Screw-Bolt Extractor Sets - 2LKP2|21829 - Grainger Industrial Supply

Sears, Lowes, and other tool places sell these.
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Old 08-25-2012, 01:35 PM
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Crap. That sucks. I've never had that happen. Sorry for your pain-in-the-ass project before you.
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  #14  
Old 08-26-2012, 02:04 PM
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Major PITA.

Stuck/frozen bleeders will turn a 1 hour project in to a 3 day project, especially if they shear. If clearance is tight and you round off the flats, it is still salvageable.

You'll now have to demount the caliper (easy enough) and mount it solidly in a vise to be able to extract the remaining piece without damaging the caliper threads and conical seat (the sealing surface) at the bottom of the threads.

The good news is that you can now clean the calipers (may as well pop the other one off now, too) well and pop on a rebuild kit.
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Old 08-26-2012, 02:13 PM
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Regarding rounding off things - use flare nut wrenches with brake items.

Regarrding one hour --> 3 days, rebuild kit, etc.

Consider the investment in a set of new (rebuilt) calipers from NAPA or something like that.

My 2 cents...

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