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Thread: School me on hydroboost

  1. #1
    Join Date
    Jan 2012
    Location
    Vancouver, BC Canada
    Posts
    94
    My Cars
    1985 Mercedes 300SD

    School me on hydroboost

    So having now gotten my 1983 733i running (a combination of the wrong main relay, missing coil lead, the wrong ecu, and a bad OBC relay box, and bad fuel pump. It was a hair pulling experience) I will be moving on to the next big hurdle. The brakes.

    The car was sitting for years before I got it and had several different owners try to get it running/work on it by the looks of things. The most glaring issue however is that there appears to be no brake fluid in it, none, and naturally the pedal just sinks to the floor with no resistance.

    Now on cars previous I would of course assume that it had a leaky caliper or brake line. However this being a hydroboost car, I was wondering if there was any chance the fluid could have gone somewhere else or if there was anything else special I should be aware of.

    Thanks
    1983 BMW 733i My current project (or at least one of them)
    2003 Volvo V70 5 Speed Current Daily Driver
    1993 300TE 4Matic Project wagon -sold
    1997 E290 Turbo Diesel Wagon -traded for above, an amazingly comfortable car to drive, great drivetrain, but the rust, oh my god the rust

    1992 BMW 525i -traded in
    1990 Silver 300TE -Sold Loved the wagon, hated the M103
    1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
    1979 Silver 300D "The Silver Slug" -Sold

  2. #2
    Join Date
    Mar 2007
    Location
    Quadratechtown, PA
    Posts
    741
    My Cars
    5, 7, 4x4
    probably not the boost and brake fluid are separate systems.

  3. #3
    Join Date
    Jun 2010
    Location
    TX
    Posts
    4,487
    My Cars
    1983/84/85 745i

    Thumbs up

    At this point, anything rubber should have been replaced at least twice to me.

    That being said, start with replacing all of the low pressure return lines for the system. It specified ATF way back in the 80s, but I have used power steering oil and hydraulic oil of similar weight with no issues. Use what you want. There is also a filter in there you should run, but most vehicles on the street do not use one.



    As you know, neglected brake systems kill master cylinders. My guess it leaked out of the rear seal... or a dead caliper, I have yet to see a leaky rubber hose (wheel seal... yep!). Many of us have done the E32 rear caliper and rotor upgrade from the V8/V12 cars. This puts a pair of vented rotors on the back and helps to minimize nose dive. Front is just stock four pot calipers and vented. You can pick up stainless braided hoses easily for these cars if you like that, I did.



    Pad choice is like an oil thread. Run what you want. I have run organics on my old 735i and a few W126. I like ceramics now for less dust, recently slapped Porterfield R4S on my F350 to try out. Totally quiet and seem to pull the reigns in hard when needed. I would probably slap these on my next E23 pad change.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  4. #4
    Join Date
    Mar 2007
    Location
    Quadratechtown, PA
    Posts
    741
    My Cars
    5, 7, 4x4
    HitManX is of course discussing two different fluid systems. The hydroboost, using Dexron ATF a few high pressure hoses and a few more, generally smaller, low pressure return lines to the reservoir and the larger low pressure pump feed line. The other is the brake system, might as well do the clutch system, too, you did get lucky with a manual transmission? These are obviously brake fluid systems.

  5. #5
    Join Date
    Jun 2010
    Location
    TX
    Posts
    4,487
    My Cars
    1983/84/85 745i

    Thumbs up

    Whoops! Maybe I missed the main point of the thread. If so, sorry!
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  6. #6
    Join Date
    Jan 2012
    Location
    Vancouver, BC Canada
    Posts
    94
    My Cars
    1985 Mercedes 300SD
    No manual transmission. Although I'm probably one of the few who prefers a slush box. It may get treated to a 4 speed auto at some point, but that's way down the line.

    As for the leak. So on a traditional brake system a bad rear seal on the MC would fill the brake booster. I would imagine on these it would just dribble down the firewall? If so I would expect to see peeling paint/rust under it. I'll have to take a look.

    I'll probably just fill it with brake fluid and see what happens. I was just curious if there were any known culprits with the system.

    On a side note, is there a PDF of the owners manual for those cars somewhere?

  7. #7
    Join Date
    Jun 2010
    Location
    TX
    Posts
    4,487
    My Cars
    1983/84/85 745i

    Thumbs up

    e38.org/e23

    Same on the auto, worn out manuals are a pain in the ass.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  8. #8
    Join Date
    Apr 2007
    Location
    Birmingham, AL
    Posts
    97
    My Cars
    03M3 99M3 82733i 12X5
    Had my master cylinder for my 82 733i rebuilt by Jay who I would highly recommend. See his link below. My car sat for 15 years and had to replace the "Brake Bomb" too. I rebuilt calipers and everything works great.
    https://www.bimmerforums.com/forum/s...ng-Booster-SLS

  9. #9
    Join Date
    Jan 2012
    Location
    Vancouver, BC Canada
    Posts
    94
    My Cars
    1985 Mercedes 300SD
    @Red Imola M3
    Thanks for the link. If I need a rebuild I'll look into him. Being in Canada however shipping tends to make these forum services unrealistic for me as shipping usually out costs the value of the part... if kits are available I might just do it myself.... is there a how to on the forum somewhere? I'd be curious.

    @HitmanX
    Thanks for the link, I usually try to avoid that site due to all the broken links... I'll go have a peak and troll through it though
    1983 BMW 733i My current project (or at least one of them)
    2003 Volvo V70 5 Speed Current Daily Driver
    1993 300TE 4Matic Project wagon -sold
    1997 E290 Turbo Diesel Wagon -traded for above, an amazingly comfortable car to drive, great drivetrain, but the rust, oh my god the rust

    1992 BMW 525i -traded in
    1990 Silver 300TE -Sold Loved the wagon, hated the M103
    1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
    1979 Silver 300D "The Silver Slug" -Sold

  10. #10
    Join Date
    Jun 2010
    Location
    TX
    Posts
    4,487
    My Cars
    1983/84/85 745i

    Thumbs up

    Jay is a good guy, he does my boosters and SLS pumps. I was unaware he does brake masters now too.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  11. #11
    Join Date
    Jan 2012
    Location
    Vancouver, BC Canada
    Posts
    94
    My Cars
    1985 Mercedes 300SD
    Fair enough, still I think I might give it a go myself. I think its within my wheel house. I notice rebuild kits are listed based on the metal used (either steel or Aluminium MC). Were these used interchangeably in our cars?

    Also, is there a walkthrough for a MC rebuild on these? Just curious.
    1983 BMW 733i My current project (or at least one of them)
    2003 Volvo V70 5 Speed Current Daily Driver
    1993 300TE 4Matic Project wagon -sold
    1997 E290 Turbo Diesel Wagon -traded for above, an amazingly comfortable car to drive, great drivetrain, but the rust, oh my god the rust

    1992 BMW 525i -traded in
    1990 Silver 300TE -Sold Loved the wagon, hated the M103
    1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
    1979 Silver 300D "The Silver Slug" -Sold

  12. #12
    Join Date
    Jan 2012
    Location
    Vancouver, BC Canada
    Posts
    94
    My Cars
    1985 Mercedes 300SD
    bump for info
    1983 BMW 733i My current project (or at least one of them)
    2003 Volvo V70 5 Speed Current Daily Driver
    1993 300TE 4Matic Project wagon -sold
    1997 E290 Turbo Diesel Wagon -traded for above, an amazingly comfortable car to drive, great drivetrain, but the rust, oh my god the rust

    1992 BMW 525i -traded in
    1990 Silver 300TE -Sold Loved the wagon, hated the M103
    1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
    1979 Silver 300D "The Silver Slug" -Sold

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