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Thread: DIY Brake booster 5-oring and shaft seal

  1. #1
    Join Date
    Nov 2010
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    Santa Ana, CA USA
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    1988 m6

    DIY Brake booster 5-oring and shaft seal

    I just up dated this DIY, I added a new shaft seal and a how to replace the seal.

    NEW WEBSITE LINK ADDRESS : https://www.bimmerforums.com/forum/showthread.php?2341013-Jay-Stratton-JCS-master6-here-are-10-of-my-current-websites

    Read the written captions at the bottom of each photo.

    This repair needs to have the booster removed from the car.

    Tools needed: Dremal, vise, bench grinder, battery drill motor with reverse, 1-1/8 inch deep socket, 13mm 1/4 in drive socket with an extension into the drill motor, blade screw driver, 10mm drill bit or 3/8 inch metal drill bit, electric drill motor with 3/8 chuck.
    Last edited by master6; 08-27-2018 at 04:55 AM. Reason: new website address
    Jay
    '88 M6 Cinnabar Red / Nappa Natur Highline Interior (10-87) Santa Ana, California. USA

    My NEW Website, Link : https://www.jaysbmwparts.com

    Booster repair
    https://www.jaysbmwparts.com

    A/C Wingcell Compressor leak repair
    https://www.jaysbmwparts.com

    e31 Door Handle Fix,
    https://www.jaysbmwparts.com

  2. #2
    Join Date
    Jan 2005
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    Japan
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    11/88 E32 750iL+98 E36M3
    thank you very much, very good pics and explanations.
    Shogun tricks and tips for the E32 series are HERE!

  3. #3
    Join Date
    Jul 2008
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    Northern WA USA
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    91 850i +++
    Nice pics and descriptions. Were you able to incorporate the teflon seals and aluminum cone I sent? Were you able to source the input shaft o-ring and split washer that seems to be unique to the earlier cars? A technical note to anyone who may be trying to use boosters from other models; the input shaft on the earlier e32s (and maybe others) is larger, 7/8", than the later e31 units, 5/8". The early ones also used an o-ring and backing washer for the input shaft; later ones have a single u-cup, which is very difficult to source and replace. The o-ring and washer is an easier install, tho I don't sell them in my kits at present. Otherwise, the internal components of all the boosters I've seen to date are virtually identical. There is some variation in the rounded ends of the MC pushrod, but it doesn't affect the seals. And the diameter of the primary piston extension out the back of the MC is bigger on e32s, even though the piston diameter is smaller than on e31s.
    How come the middle half of any project always takes the most time?

  4. #4
    Join Date
    Jan 2005
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    Japan
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    11/88 E32 750iL+98 E36M3
    Max, not all piston diameters on the brake booster H31 on E32 are smaller than on E31.

    We have checked that here in Japan. We assume, the difference is/might be:
    E32 750 with standard brake calipers,and E32 750 with the 4-caliper piston brakes in front= usually used on EURO version E32 750 from

    for example lets take my 11/88 750:
    Caliper housing left 34 11 1 160 363 ATE
    Caliper housing right 34 11 1 160 364 ATE
    Brake servo unit 34331161772 ATE till December/1990

    then we use a 03/1994 EURO E32 750:

    Bridge caliper without brake pads left 34 11 1 159 775
    Bridge caliper without brake pads right 34 11 1 159 776
    For vehicles with: National version Germany
    from January 1990

    Brake servo unit 34331161772 ATE from December 1990

    strange enough, same part number, but ETK has the built/year month limits

    But if there is also a difference in U.S. spec cars before and after 12/1990. then there are other reasons that they changed the piston diameter, as the 4-pod brake calipers were not supplied to USA.
    Early built E32 735 with the H31 brake booster might always have the smaller diameter piston, maybe they first used these also on the E32 750 and when they found probs on the 750, they enlarged the diameter, that is another theory.

    Thanks for your special efforts with regard to clarifying this mystery and making these sets available.
    Last edited by shogun; 02-14-2012 at 05:33 PM.
    Shogun tricks and tips for the E32 series are HERE!

  5. #5
    Join Date
    Aug 2009
    Location
    IN
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    1990 735il, 1997 740il
    whats the symptoms of needing to do this, I am thinking mine needs a master cyclinder I only have braking to left front and right rear wheels.

  6. #6
    Join Date
    Nov 2010
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    Santa Ana, CA USA
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    1988 m6

    Repair 533,535,m535,m5,633,635,m635,m6,735

    Max,


    Thank you for the aluminum cup and teflon seals, that you sent me.

    If I get someone who needs a replacement for their black plastic cup, I will give them your information. To purchase your aluminum version.

    I do not want to intrude on your 8 series repair business.

    My repair kit, I have been selling for a year now. And I just recently added the shaft seal.
    Last edited by master6; 12-11-2012 at 01:09 AM.
    Jay
    '88 M6 Cinnabar Red / Nappa Natur Highline Interior (10-87) Santa Ana, California. USA

    My NEW Website, Link : https://www.jaysbmwparts.com

    Booster repair
    https://www.jaysbmwparts.com

    A/C Wingcell Compressor leak repair
    https://www.jaysbmwparts.com

    e31 Door Handle Fix,
    https://www.jaysbmwparts.com

  7. #7
    Join Date
    Jan 2005
    Location
    Japan
    Posts
    54,613
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    11/88 E32 750iL+98 E36M3
    Quote Originally Posted by ryan77 View Post
    whats the symptoms of needing to do this, I am thinking mine needs a master cyclinder I only have braking to left front and right rear wheels.
    Ryan, this is not related to your E32, it refers to early E32 735 with H31 hydraulic brake booster units instead of the vacuum operated brake booster as on your E32 735 from 1990, and all E32 750 as well as E31 850 and the others mentioned above with H31 hydraulic brake booster units.
    They start to leak.

    Breakdown of the H31 brake booster
    http://bmwe32.masscom.net/maxf_websi..._breakdown.htm

    http://bmwe32.masscom.net/maxf_website/booster.htm
    Shogun tricks and tips for the E32 series are HERE!

  8. #8
    Join Date
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    Location
    IN
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    1990 735il, 1997 740il
    ok, thanks.

  9. #9
    Join Date
    Jul 2008
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    Northern WA USA
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    91 850i +++
    No worries, Master6. I sell any of the internal bits that anyone wants, starting at $6 for the oil seal and o-ring for the black cone. Often that's all that is needed to fix the universal leak at the MC joint. The aluminum cones are a backup against breaking the plastic; they're aluminum because that's the only feasible way I could do it and they look cool 8^)

    The functional internal seals for the hydraulic actuators are the same on all the boosters, including most Audi and Citroen units. The part numbers don't make much difference except for minor details on the casing; some early ones were iron, later e31 units have 3 mounting bolts, etc. The kits I sell should work on virtually any booster, except for the input shaft seal situation, and I'll have all types of those shortly. I sold the o-rings that you have for several years, but it took a long time getting the teflon parts made and even longer for the input shaft seals. It would have been much better if ATE had never gone to the small diameter input shafts with the one-piece seal; it's kinda twitchy to deal with when rebuilding.

    Shogun, thanks for that info, and all the other research that you share. The first diameter I was referring to was for the input shaft to the booster, over the brake pedal. It is 3/4" on some boosters; in my experience, it was on a booster listed for an e32. All the e31 boosters I have seen have had 5/8" shafts. My knowledge on earlier e28, 24, etc cars is nil.

    I misspoke on the other diameter; "And the diameter of the primary piston extension out the back of the MC is bigger on e32s, even though the piston diameter is smaller than on e31s." It's the other way around, and I got in trouble because of it early on. When I made up the aluminum cones, I was using an e32 master cylinder/booster assembly as a model. The stub of the primary MC piston that sticks out was "X" diameter, and the cone was sized to clear "X". Unfortunately, the stub on e31s was "X plus 2mm" or so, and it wedged on the inside diameter of the cone a few mm shy of the end. As a result, the brakes would drag on some cars because the MC piston was pushed in slightly by the inside of the cone against the end of the stub. Major PITA.

    In general, e31 MCs are 1 1/16" and e32 MCs are 1". Some e31s are stepped diameters, like 26/20mm, some are not; don't know on e32s, think the ones I've seen are 25mm/1". The diameter of the stub that engages the booster rod doesn't necessarily reflect the working brake piston diameters. Also, the actual dimensions of all this brake stuff is all over the map. Brakes are still referred to in SAE measures, except when they're not. ATE marks some things metric, some SAE. Lots of stuff isn't marked at all but is not what you'd expect. The little rod with the rounded ends that goes between the two cylinders is 3/8", for instance, but some of the seals for it are marked 9.52mm.
    Last edited by Max Lumens; 02-19-2012 at 01:33 AM.
    How come the middle half of any project always takes the most time?

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