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Join Date: Nov 2002
Location: Cincinnati, OH
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Help removing circlip on brake master cylinder

in the process of rebuilding my master cylinder. I got it out no problem. I went to remove the circlip to pull out the piston per the rebuild instructions but the clip has no tabs with little holes to get the pliers in. not sure how to get the circlip out. it spins so its loose. i cant get anything in behind it to pry it out. looks like somebody might have broken the tabs off. Am I SOL? any other way to get it out? the instruction call for pushing the piston in using a mandrel. I can push it in but that seems to have no effect. thought it might loosen the circlip so I could get it with some pliers but no luck.

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Old 07-27-2018, 02:21 PM
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It does appear that someone has broke the ears off your circlip.

Looks like you might have a use a pick to get behind the circlip and pry it out, then while it is pried out slide a thin bladed screwdriver or a small bladed knife into the gap created and work it out.
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John Curry (Drift King) 928OC member
Grand Prix White 1994 GTS AT (The GTS)
Cobalt Blue 1989 S4 AT (The Blue Car)
Indishrot 1984 Euro S AT (The Stepson)
Black Metallic 1984 Euro S 5 speed (The Schwartz)
Old 07-27-2018, 08:52 PM
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Got it! the suggestion to use a pick was the key. Thanks. was able to get it in behind and pry it out. I don't think it was broken. looks like a clip without eyes.



wrestling the piston out was a lot of fun. also found out that when you loosen the bolt holding the lower plunger piece in there, it will shoot across the garage. but, its all apart now and ready to be cleaned up and reassembled with the new seals.

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Old 07-28-2018, 04:59 PM
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Petie3rd
 
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Its a fun exercise, to take one apart.
You will note they are not made to come apart easily.
That said if you value your time ,safety and money follow these instructions

Get a new ATE master cylinder, the one you have should be taken out of service.

A new booster , based on the back of the old MC it has been leaking brake fluid into the booster and or the booster has water in it.

A set of stainless flex lines, the brake lines should be upgraded.

a liter of ATE fluid, with fresh parts bleeding should take less than a liter.

a tube of DC 111 for the grommet bushings. Amazon sells this,

NOTE the DC111 will prevent the inlet ports from corroding.
NOTE you can wash the tank in brake cleaner,
then simple green and hot water rinses till its clean.
Then shake it dry ,
then add a ounce of Iso alcohol and shake it ,
then pour it out,
use a hair drier to blow warm air into the tank to remove the alcohol and water.
Roger has all of these parts
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Old 07-28-2018, 08:15 PM
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9fourteen,

I didn't know they even sold rebuild kits for these master cylinders.

I used to rebuilt master cylinders for MGs back in the day and never had much good luck beyond a week or so keeping the brake fluid inside the master cylinder.

I had always determined my inability to successfully rebuild a master cylinder to be my own lack of skill regarding this exercise.

I also see folks in other countries rebuild master cylinders.

I don't believe that I would attempt to rebuild a brake master cylinder for a 928. New ones are not that expensive and are readily available.
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John Curry (Drift King) 928OC member
Grand Prix White 1994 GTS AT (The GTS)
Cobalt Blue 1989 S4 AT (The Blue Car)
Indishrot 1984 Euro S AT (The Stepson)
Black Metallic 1984 Euro S 5 speed (The Schwartz)
Old 07-29-2018, 05:52 AM
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yes, the existing booster had a lot of fluid in it. probably a combination of water and brake fluid. the system didn't hold pressure. i put my bleeder on it and fluid was coming out from a few locations.

i pulled the old booster.



installed a new booster



regarding rebuilding vs replacing the MC. I do have a kit. Pelican sells one. looks to have just about all the internal guts minus the springs. the housing is rusted but i was planning on cleaning it up. wire wheel brush off the surface rust and hit it with some paint to make it look good. then thoroughly clean the internal surface. the housing doesn't appear to be damaged in any way besides rust. are the replacements designed differently that would warrant a replacement? the replacement pieces looks slightly different. maybe the difference is in the internal design that i got with the rebuild kit. all the new MCs i looked at online appear the same as mine. at least the housing looks the same unless they are just using stock images of a 928 MC.

kit

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Old 07-29-2018, 08:37 AM
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Petie3rd
 
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Wow that got to be the worst looking brake booster I have ever seen in a 928.

Please go buy a new ATE master cylinder.
The chances of getting the cylinder bore good enough to work and then making the inlet bores smooth enough for the new grommets to properly seal will not be in your favor.

And since you just spent big money for a brand new booster your going to take a chance that your reseal job wont leak fluid into that new booster, That is a folly my friend.

SRSLY I fix these cars every day,
a new master cylinder is cheap compared to time it will take you figure out that the MC you rebuilt is working properly.
I guess you could ask yourself this ,
do you think that the rebuilt master will last another 30 years?
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Old 07-29-2018, 06:24 PM
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Alright. Seems the consensus is to replace it. Didnít think rebuilding it would have been such a risk. Did a little searching on a replacement. Any difference between the MC for a 84 or newer 928 and my 83 928S? Seems like all listed on eBay are for 84 or newer. The part number is the same except the last digits. There seems to be a big difference in price for the ones listed as pre 84 vs the 84 and newer.
Old 07-29-2018, 06:57 PM
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Just ordered a new MC from here. Looks like the 83 and older is different from the 84 and newer.

EDIT: Also ordered the braided brake lines. Figured I should replace those as well as suggested.

Last edited by 9fourteen; 07-29-2018 at 07:49 PM..
Old 07-29-2018, 07:35 PM
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Three different part numbers based on year
78-83- 928-355-011-04
84-86.5- 928-355-011-23
87-95- 928-355-011-24

I'm glad you decided to buy a new MC.
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John Curry (Drift King) 928OC member
Grand Prix White 1994 GTS AT (The GTS)
Cobalt Blue 1989 S4 AT (The Blue Car)
Indishrot 1984 Euro S AT (The Stepson)
Black Metallic 1984 Euro S 5 speed (The Schwartz)
Old 07-30-2018, 08:03 AM
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Petie3rd
 
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Thats great your listening to sound advice.

Please make sure you also order the ATE brake fluid you should need 1 liter,
no sense in screwing up new parts with an off brand fluid.

Use the DC111 on the grommet inlet bores and grommets and the MC base seal to the booster
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1988 S4 Auto , Elfenbein Perlglanz, Pearl Gray
1988 S4 5 sp, Black / Black leather/ Carmel carpet
Old 07-30-2018, 04:41 PM
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I received the new MC and got it installed. I am getting all the vacuum reconnected but not sure if everything is here and I got it right. looks like something is missing. The main line is there from the booster. it has the short section then a connector with a small tube coming out that goes to a four way connector you can see in the picture below. from the fender a Y connector connects to the four way. There is a small tube that come through the firewall that looks like it should connect but its short and lose if I put it into the 4 way. for the forth connector on the 4 way I have nothing to put in it so not sure what its for. this was how it was when I started so not sure how its supposed to be. if somebody has a picture of what it should look like I could probably figure it out.



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Old 08-02-2018, 06:37 PM
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hey 9fourteen - check that 4 way and see if the unused port is plugged - it is plugged on my 84 - might have been an option i don't have - however since you have an extra vacuum line that doesn't reach maybe yours should connect some way - not much help i know but if it is plugged at least you would know your extra line doesn't go there - good luck

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Old 08-02-2018, 07:47 PM
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Here is what I have. Did a little more research and drew a better diagram so its clear.



Where it is short I think I can make it reach. The previous owner had the line tied to the brake line making it short and not connecting to anything. I cut the ties and think I can make it reach the four way.

Am I missing the vacuum check valve? This picture from honerboys and pictures I found googling show a blue and black check valve before going into the four way. When searching for parts on Pelican the brake check valve listed for my year is different from the what I have and the blue/black check valve. Pelican says the blue/black check valve may not be for my car.

This is what comes up when I search Pelican for my brake check valve. Different from my setup.


Here is the other check valve


Are there two check valves?

For the forth, unused connector on the four way I am at a loss. Can't find anything definitive on what should go there. Some pictures show it going to the intake flap actuator. I guess I can look to see if I have one of those and if the vacuum line is missing. Other pictures shows a white connector or cap on there. In honerboys picture you can see this white thing on the left appendage.
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Old 08-03-2018, 07:03 AM
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Petie3rd
 
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the 4th port is plugged and is used for testing,
it should have a double sided green plug with a rib in its center

the system also used two check valves,
one for the booster the big one,
and the the small one .
NOTE the small one takes its feed from the big valve
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1988 S4 Auto , Elfenbein Perlglanz, Pearl Gray
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Old 08-04-2018, 05:25 AM
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