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PART 2: Removal and replacement
Keep in mind that this vehicle is a 1991 Integra and does not have ABS. Your car may be slightly different. Maybe easier, maybe harder. Consult a proper workshop manual, or know what you're doing before you begin. ABS systems especially can require special bleeding techniques in order to do a proper job. The jobber I bought my rebuilt MC from asked me if I had ABS, so I assume the ABS master cylinders may be different in some way.
It's an easy job, but you must be clean, clean, clean about it. Brakes are the only thing keeping you from crashing into people and things. The last thing you want in the system is dirt, and there's lots of that under your hood.
Since the dealer does not sell rebuilt MCs or rebuild kits to the public, and since a new one was $350, I bought an aftermarket rebuilt from UAP for $74. You need to reuse your plastic reservoir and a rubber seal at the rear of the housing.
Anyway, on with the show...
First things first. They tell you to disconnect the battery. That's probably in case you drop something into the alternator or otherwise short out important, expensive stuff. So do it. Just make sure you've got your radio's anti theft code handy first...
Here's the installation before I started. Pretty filthy. Two things I notice right off the bat: 1) Access is terrible, with cables everywhere, and 2) the alternator is right underneath. Any cleaning solvents and dirt chunks are going to fall right in. Also, my car has a clutch cable, so I have no clutch Master Cylinder to confuse with the brake one. If you find two reservoirs under there, make sure you're attacking the one with the big black cake-pan behind it! also, not all Master Cylinders have an integral reservoir. Some have their reservoirs remotely mounted, and connected to the MC with a short hose.
I use zip-ties to tie the various cables out of the way, unbolt any unboltable stuff, and remove any easily removable hoses, such as the booster vacuum hose. Then I stuff clean towels on top of the alternator to protect it. Access is still poor, and you'll need every inch you can get.
Now I need to make sure the hydraulics are very clean, with no dirt anywhere around the screw threads. I just used a liberal spray of brake cleaner and a bit of work with an old toothbrush.
This flare wrench is worth its weight in clean brake fluid. If there's any corrosion (you know there will be...), a regular 10mm open-end wrench stands an excellent chance of rounding the flare nuts. All you need to do is crack the nuts loose, which is easier to do with the MC still bolted to the booster. Do NOT remove them at this time.
Now, here's where I made a mistake, never having done this before. I actually removed the hydraulic connections BEFORE unbolting the MC from the booster. Bad idea in my case for two reasons:
1) All the mucking around you'll do will increase the chance of introducing dirt into the lines, and
2) I was not able to withdraw the front line from the housing because of the shock tower.
So I did them back up loosely again and unbolted the MC from the booster. Two nuts, and you'll really need your assortment of extensions to find the right length to be able to swing the ratchet. Notice the yellow paint? That's what the factory puts on all bolts/nuts to indicate that those bolts/nuts have been properly torqued.
Watch those nuts! Don't drop them!
View here is from directly overhead, just in front of the booster. You can see my 12mm socket to the left of the MC.
Well, it's free and I can undo the hydraulics for real now. Then I check the line ends to make sure there's no dirt. We're clean.
Watch your paint! The open hydraulics on the MC will start to drip as soon as you remove the fittings. The fluid in the lines didn't drip out, so no danger of air in the lines that way.
Let's take look at the booster. The silver thing is the famous adjustable pushrod that the pedal linkage pushes on to operate the brakes. This is the thing that's misadjusted if your brakes lock on as you drive.
Oh, looks like I missed something. That's the rear MC seal. It got stuck in the booster. You need to use this with the rebuilt MC I bought. This little piece only comes with the $350 kit at the dealer. There was no fluid in the booster at all.
Pour the fluid out and peek down the reservoir. How clean is it after 14 years on the car? Pretty good. Must be those regular, annual fluid changes! This particular reservoir is held on with a screw clamp, so it's easy to remove. There's no O-ring or gasket.
The thing that looks like a bent bar is actually a solid wall that separates the front and rear chambers of the reservoir.
Inside the front chamber (closest to my hand in the left pic) you can see the two tiny holes for the first circuit. The second circuit uses the rear chamber and ports that run horizontally to the rear of the housing.
Old MC on top, new one on the bottom. The new one is identical in every respect to the original.
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Now that we have the MC on the bench, it's time to clean everything up, swap the reservoir and rear seal to the new Master Cylinder, and prepare for bench bleeding. You need to bench-bleed, otherwise all that air in the new MC will end up in your lines. It's a lot easier to remove it at the MC than at the wheels. Have a look at that, then return here for re-installation.
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It sounds kind of weasely to say that "installation is the reverse of removal", but in this case it's literally true. After bench-bleeding, just feed the hydraulic lines into their holes while guiding the new MC back onto the studs on the booster.
Tighten the hydraulic connections to maybe 7 ft-lbs. They only have to be tight enough not to leak, which doesn't take much. If you overtighten them, you could damage them.
Here's my new one, in place:
Update, one week later: Remember how I advised you to make sure you can get at the reservoir clamp bolt? Well, I should have also advised you to check for leaks at the bottom of the reservoir! Mine was seeping slightly, just enough to make the side of the MC body wet over a period of days. I had to snug the clamp down a bit more. Seems to have done the trick.
One other thing I noticed is that since the new MC was full of fluid and was dripping slightly, this helped to evacuate any stray air from the hydraulic joins as I reconnected them, so the pedal was firm immediately when I tried it.
PART 6: Checking the pedal freeplay
After the usual checks all around to make sure everything was tight and leak-free, and all hoses put back where they should have been, I checked the freeplay at the pedal. And promptly ran into a problem. Pedal freeplay is best felt with your fingers, with a very light push. There ought to be a tiny bit of fairly easy movement before you feel the pedal hit hard against something. What's happening at the hard spot is that the pushrod has contacted the rear of the MC plunger.
There must be some clearance between the pushrod and the MC plunger, otherwise your brakes may lock on as you drive. If there is too much clearance, the pedal will feel soft and will have excessive travel. I ended up with the latter. The manual specifies 1 to 5mm clearance. I had 10mm. I did not think to check the clearance before I started, so I don't know what it originally was. The pedal definitely felt looser than before though, in spite of a very thorough bleeding session.
It's time to adjust the booster pushrod.