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I couldn't put the grungy brake fluid reservoir back on top of my shiny new master cylinder, so I decided to clean it. First step, search RL! Took a few tries but I found this thread: https://rennlist.com/forums/928-foru...back-help.html
I'll quote the pertinent posts here:
"I just went through the same problem. I found that the brake fluid dirt/varnish built up in the in the master cylinder reservoir not only had attached it self to the site walls and bottom but also had clogged the fine mesh screen that are in the drains of the reservoir going in to the brake cylinder and thereby starving the brake fluid supply. I used BB’s and brake cleaning fluid to shake around until all the junk was gone and I had a clean reservoir. I have everything re-installed and it work fine. I have a manual 5 speed so the reservoir has a 3rd outlet for the clutch and the reservoir has a build in baffle for the clutch side supply. I got a few BB’s stuck in there and had to drill some small holes to push them out. The attached pictures should tell the whole story. If you have more questions than let me know." - Herman K
and:
"Hi if your into cleaning the fluid resivour try this , first remove the res from the brake master, it pulls straight up, after this drain it out get some brake clean and spray into the res as best you can shake the res with gusto drain it repeat. Then get some simple green and hot water fill the res and shake with gusto drain repeat then rise with hot water, shake dry, then fill with about 3 oz of Isopropil alcohol shake, drain, repeat then blow dry with compressed air , then blow warm air through it with a hair dryer then reinstall , the res will look like new and should be thoroughly clean inside" - MrMerlin
So with those good counsels, I proceeded. I am glad I did. First, there was a lot of gray crud that came out, clogging the drains like Herman K described. But as it got cleaner and cleaner (multiple iterations of Stan's "shake with gusto" technique) I started to more clearly see a UFO in the reservoir. Here is a pic of the cleaned reservoir and what I finally removed to its left:
As can be seen, the "UFO" is part of a seal from, without a doubt, a brake fluid container. As Captain Slow found, there is a baffle in the filler neck, right past where you can see, that should prevent something like this from entering the reservoir (which is why neither Jon nor I could get a tube in to drain it). This baffle has a very small opening, which should give one enough time to retrieve whatever one has dropped into the filler neck, as long as it is noticed! In this case it probably swirled around out of sight until it finally found it's way into the tank (maybe helped by my pressurized bleeder). By the way, it took almost 2 hours of pumping cleaning fluid through the tank with my parts washer nozzle, changing the angle around to move the seal part first over to the baffle opening, and then finally through it. That reservoir is plenty clean now!
I thought I would post this thread with a more specific title to make the information a little easier to find, and illustrate an important maintenance item.
BTW, you can see the brake fluid check switch with its rubber top removed on the top of the tank. I'm posting a separate thread on that interesting little thing.
as an add on to this info ,
I would also suggest that if your installing a new MC that you use some Dow Corning 111 on the rubber grommets where they seal against the MC housing,
this will reduce the chance that the MC will rust.
Rust will occur when the car gets wet,
water will run down the reservoir and work its way into the grommets.
If your using the old grommets than it could be a potential leak point as the grommet bore could be badly corroded and thus once disturbed it could spell the end of the MC,
NOTE if your fitting new seals they will not fit into a rough area,
you wont know its going to leak till after you have filled the reservoir.
Good notes here Stan, and thanks. Since I installed a new MC from Roger I didn't have to worry about old grommets, although I did use a thin coat of brake fluid rather than the Dow Corning 111 (that needs to get added to the shop) on the reservoir barbs.. One thing I found I was very grateful for your comments on was how necessary it is to seat the reservoir barbs fully home into those grommets. Not easy! But the hold-down bracket for the reservoir just won't fit if you don't do it right. Tomorrow I'll fill the reservoir, test for leaks, and hopefully be done with this!
Just for giggles, has anyone ever tried the process for whitening yellowed plastics? Apparently the vintage computer hobbyists use a mix of peroxide, oxi-clean, and xanthan gum to make their Amigas and Commodore 64s white again.
Martin the DC111 used on the grommets is for long term protection,
I would get some before you fill the tank,
once water runs down the tank then it will wick into the grommet,
if the DC 111 is there the water will not be able to pass.
Rob I never heard this before ,
but the reservoir will look like new if you follow the posted directions
Why does it not surprise me that a 928 hobbyist has casual knowledge of how vintage computer hobbyists make their Commodore 64s white again? Not making fun...it's a good thing
A couple things about swapping the BMC:
1. I used a MityVac to suck the fluid out through the bleeder on the S4's original MC. It got 95% of the fluid out. That's how I got around not being able to shove a small hose into the filler neck. Best part, with vacuum applied to the hose connected to the bleeder there are no drips when pulling the hose off. Not a drop of fluid.
2. I used DC111 on the grommets and on the O-ring between the BMC and the booster. I do like the DC111 stuff. It's meant for SCUBA gear and it's very obvious it's purpose is to be a tenacious O-ring lubricant that seals it from saltwater. It kinda looks like Vaseline, but the consistency is different.
3. I let gravity (buoyancy) bleed the MC for at least 4 days. I repeated Stan's MC bleeding process daily until only fluid purged...and then did it all again to be sure. Brakes are firm and function more positively...hard to describe, but they feel much better. I think the seals were leaking in the old BMC.
07-27-2015, 09:27 AM
Cleaning Brake Master Cylinder Reservoir
