78 Eldorado Brake Master Cylinder

[Jakes]

When I got my car last Oct. the first thing I did was flush out the old, dirty brake fluid.  It was so contaminated that some of the fluid coming out of the caliper bleeders was like mud.  But the amazing thing was that the brakes worked just fine and didn't become even better with the fluid change.  I'm a stickler when it comes to this all important safety feature so I'd draw out some fluid from the MC from time to time to check it...looked fine with a transparent, tan color.  I've put about 1400 mi. on the car by doing twice weekly, 30 mi. combined local/highway exercise runs in which the brakes are "exercised" as well.

To make sure all (most) impurities were purged from the system, yesterday I had my mechanic F/F the brake system again.  When I got home I popped the cover off just to make sure the fluid level was correct (trust, but verify...) and looked down through the clear fluid and didn't like what I saw.  I put my finger into both sections of the reservoir to touch the bottom and literally churned up this mushy stuff which quickly turned the fluid brown.  So, using my trusty cooking baster, I sucked up debris from the bottom along with the fluid until the fluid level was just above the point of air entry, put in new fluid and repeated the process.  I also wrapped a paper towel around a piece of doweling and "dredged" the bottom of the reservoir several times to remove what wouldn't be sucked into the baster.  After a while I could look down through the fresh fluid and the bottoms looked a heck of a lot better than before, but rusty...........BUT did I mess myself up by letting some of this mush get down into the cylinder section which could interfere with braking action??

Well, I took the car out today for a test run and she passed with flying colors... brake action/response identical to what it was before... in fact there were a couple of short stops (the dreaded yellow light) and she was fine.  Nevertheless, I'm wondering what the cylinder wall and the pistons look like with all that previous contamination.  I thought of doing a MC rebuild, but I think the best thing overall as a preventive measure, not knowing the condition of the MC, is to replace it altogether.

After a lot of online investigating I came upon the ACDelco 18M123, a new unit, being sold on Amazon for about 70 bucks, about $30-40 cheaper than other sources (including Rock Auto).  Judging from all the info I went through online I have a feeling it's made by Raybestos (and probably made you-know-where), but since it's listed in the ACDelco online catalog (for 76-78 Eldo) I would guess it's a good part.

Your comments, criticisms, suggestions, etc. are most welcome and appreciated, as always.

[Dave Shepherd]

Avoid nos parts, new only in this case.

[Scot Minesinger]

I replaced my booster and master cylinder together as a unit, so that probably is advisable.  Mine is a Cardone, and not thrilled.  It just does not have a nice feel when using the brakes, a little too much effort for power brakes.  The booster relies on a rubber diaphragm now 37 years old, so probably is a good idea to replace it. 

[76eldo]

I'd just keep flushing and cleaning.
Over the years I have read many posts from people chasing down brake problems after installing new or rebuilt parts. If the car stops well, I'd leave it alone.

If you are really concerned, the most I would do is have your master cylinder removed, cleaned, and put back together with new seals.

Good luck,

Brian

[joecaristo]

Yes- it its not broke, don't fix it.
Joe

[76eldo]

That's the saying.

In my case it's usually "If it's not broke, don't break it!"

Brian

[Jakes]

Thank you, gentlemen, for your analysis and advice.  I went ahead and ordered the Raybestos MK772 rebuild kit from Rock Auto.  But I couldn't resist; the price on Amazon for the new ACDelco 18M123 (OE part no. 18030365) was so good ($70) and so much cheaper than anywhere else, I bought that too and just received it today, and guess what... stamped on the casing is "Made in USA" (I almost fainted..) although the box says assembled in Mexico -- go figure.  But, I'll take your advice and leave well enough alone as long as the brakes work well, but the minute I feel something odd, I'll start by trying to rehab the MC that's on the car and if I find the cylinder bore is badly corroded I'll put on the new part.  Many thanks again for your help.

[bcroe]

I once opened up a brake system that had been sitting a couple years, and I could
hardly believe the stuff occupying the wheel cylinders (no discs then).  I've had
problems with hoses that didn't leak, but didn't pass fluid unrestricted either.  I've
tried to keep changing out fluid in the master cylinder, but it never seems to clean up. 

My conclusion: by a couple decades just about everything touching brake fluid needs
to be replaced.  It seems to be a lot worse if the car sat for some time.  Exceptions
would be parts that don't rust, like stainless lines or the new cop-nic alloy lines, brass
fittings, masters not made of cast iron.  I replace a lot of brake parts.  Bruce Roe