MC brake fluid leak?

[steely]

I refurb'ed the pedal cluster and noticed some ATE blue brake fluid around this plastic sealed nipple under the dash board.

It is located under the MC.

I inspected the rear of the MC and am not sure if I see some 'wet' deep down there.
I read about the MC seals, can only see one but it looks dry. The original rubber/cloth lines are dry too.

Am I going to have to go in there?

I was getting all set to bleed my new slave/master clutch cylinders too darn it.

Thanks

[steely]

FWIW, I think I am looking at the same problem as described here.

Brake fluid in driver's footwell - Master Cylinder leak?

Will have to wait until tomorrow evening to verify.
I pulled the trunk carpet and the cover over the rear brake pressure regulator and saw some tell-tale wetness in the trough. need to see how much went into the smugglers box and if any got onto anything (like the steering rack).

What is that thing in my first picture?

[KTL]

There is a well underneath the brake booster in the front trunk. If fluid leaks in the trunk, it seeks the well under the booster and then drips thru the hole in the well if i'm not mistaken. Grab a paper towel or small catch cup and remove that plastic plug. I bet you get a small stream of brake fluid.

[steely]

Thanks Kevin.

So that thing is a plug? Can I assume it pulls off/down?
instead of doing my planned clutch MC and slave cylndr bleed, I will probably spend this evening removing the stuff around the brake MC to see what I can see - order parts in parallel.

[steely]

I took some pictures tonight as I tried to determine the extent of my brake Master Cylinder leak. I believe the leak to be coming from the rearward Master Cylinder Brake Lamp Switch. I saw no leaks from the reservoir or its lines, or the brake line or the MC seals / reservoir line bushings, or the junction of the MC at the vac boost.

I did see the front Master Cylinder Brake Lamp Switch to be dry and the rear most one to be wet. I also saw that there was fluid residue under it and forward to the through that the brake line/rear brake pressure regulator lies in. Any fluid that leaked down this trough was stopped at the foam pad that is located under the smugglers box lid.


I also saw some wetness under the vacuum booster and the top of the 'drain' plug. I shoved a paper towel and a long cotton swab under there and verified the presence of fluid.

I will try to clean this up before paint damage if any gets worse. I will order a 2 prong Master Cylinder Brake Lamp Switch and replace it, and plan to do the entire MC later.

if you think my plan is short-sighted or disagree with my diagnosis, I'd appreciate any feedback.

Thanks


rear brake line pressure regulator/ trough - some wet evidence


A shot of the MC looking good


A shot of the brake switches - hard to get pic but there was a big difference in the condition of the front and rear in terms of dryness.


front switch


rear switch


under the brake booster - wet - you can see the top of the plug / knurled edge

[KTL]

Yep checked my car this AM and it is indeed a plug/hole to drain the well. I suspect the thought in providing that hole is the drip in the driver floor area would reveal itself much sooner than if the leak was allowed to pool in the well and find its way somewhere else?

Note that the warning switch threads are pipe thread style. They don't have a sealing ring, so that means they seal by thread interference. Point being is, when you tighten them you want to make them nice & snug. Don't want to be too loose or too tight to invite boogering the threads in the MC and cause a leak that requires the MC replacement!

[Nickshu]

Yep. Been down this road....the linked thread that is up above is mine. Brake fluid in driver's footwell - Master Cylinder leak?

Most likely the hose/nipple seals as photographed in my thread. Pull everything out of the way so you can see the area clearly. Swapping out the hoses, seals, and nipples with new was not a difficult job.

[steely]

Hiya Nick - yes I know it was your thread - it was of great help, thank you.
Sorry I didn't mention your name.

- I saw your seals and looked for the same external clues, but mine are dry.

Last night I caved and decide to just do the whole thing, so I bought a new MC with the switches and rubber line. "ships tomorrow"

After I bleed my new clutch master and slave cylinders, I will replace the brake MC, and flush everything. I don't feel like going back in there again for the next switch or seal leak.

Then I will do an autopsy and let you know what I find one the switches, seals etc.

[gregwils]

I did mine one winter purely as a preventive measure. I figured 20+ years is long enough. It's not too difficult IIRC.

[KTL]

Not a bad idea just to change the MC completely. Local friend Mark recently had his original MC go south in his nice '86. Pulled it out of the garage a few months ago and pedal went to the floor. Had to pump it up multiple times & use hand brake to get it to stop. No warning. Just decided one day it wasn't going to make pressure any more.

[steely]

Thanks Kevin / Greg

Yeah, the more I thought and read about it, the more I figured I should do that.

My new brake MC arrived yesterday.

Would anyone know the torque value for the single MC mounting bolt under the dash? I don't see it in the Bentley manual.




PS - I still remember/appreciate your bailing me out with that front torsion bar Greg :-)

[steely]

this entry is more like a blog. I am now trying to negotiate the vac booster/MC sub-assy out around the goofy defroster fan (not the correct name) hardware. The dash fan arrangement has some diverter control cable woven in between the booster and the MC fluid reservoir to MC feedline. I used a pump and small diameter rubber line to suck out the fluid so I wouldn't leak it allover the place when I then I cut the braided cloth /rubber feed lines so I could clear the dashboard/windshield fan stuff w/o damaging anything.

Now I am trying to remove/maneuver out the booster/MC from under the dashboard fan hardware. LOL always something.

I seem to remember reading something about that, so I am back online in research mode.

[steely]

I am trying to remove the MC/vac booster as a unit per bentley.
This pic showing the interference offered by the fan gizmo (some ventilation item that forgive me escapes my mind right now not that it matters).
The booster is at the bottom of the pic. The pic bottom is front and the perspective is looking down n the MC.
The ventilation item hardware is on top of the MC flange where it mates to the booster, preventing me from lifting the MC/booster assy out.

You are supposed to lift the assy out and separate the MC and booster on a bench. I am having some fun. I did try to separate in situ, but the ventilation hw is blocking the access to an MC-to-booster nut.

[john walker's workshop]

be very careful not to break off the heater cable bracket from the plastic valve assembly in the process.

[KTL]

Disconnect the pesky cable over to the left at the central big air box assembly

That MC mount bolt under dash is basic M8 spec 18 ft-lb. Snug is plenty

[steely]

Thanks Kevin and John

I will go with 18 ft#s or snug - I really do appreciate the feedback.

I found that I could simply unsnap the spring metal cable keeper and that was a big help in clearing the path for MC removal.

jumping ahead, I cleaned the trunk floor and POR'ed the spot under the booster. I taped off a 5 x 5 in square.
The booster itself, while in good shape, showed evidence of paint bubbling underneath, so I wiped it down with damp cloths, dried it, sanded the bubbly paint surface, and POR'ed her too.

Then I assembled everything and realized I forgot to replace the little white plastic hole plug - kicking myself dagnabit - so I will resume in the morning. In other news, I wish weekends were 5 days long.

on edit: just a note, the brake master cylinder did not come with brake fluid nipples inserted into the feeder seals, unlike my new clutch master cylinder. Am so glad I did not damage or destroy the originals, but am a bit bugged that I didn't get new ones shipped with the MC. such is life - excellent Saturday otherwise