Replacing my first master cylinder, anything I need to know?

I've always paid to have this done before, but that just isn't a reality anymore for financial and trust reasons. So I'm going to do it myself.

93 miata, no ABS

Everyone suggests bench bleeding before install to prevent air build up, but I want to drain and replace all the fluid in the system when I do this, so I'm thinking I'm going to skip bench bleeding.

Is there a "best way"to get all the old fluid out of the system? Open all 4 bleeders and let it sit? Bleed each wheel individually until nothing comes out?

Should I run acetone or isopropyl through to get all the dot3 out since I want to refill with dot 4? I don't think this is necessary, but the thread about cleaning brake lines got me thinking about it.

One more question, I've seen some people on the spec miata forum mention an o ring between the MC and booster, that appears in some years parts diagrams but not on the 93. Is there an o ring or gasket that goes between or not? My centric master didn't come with any, and before I'm stuck with a vehicle on stands, I'd like to know to pick one up if it's needed.

1.) Bench bleed the master per instructions.

2.) Install newly bled master.

3.) Bleed each wheel per normal: passenger's rear -> driver's rear -> passenger's front -> driver's front.

It much easier to bleed with fluid in the lines than without.

If the miata is anything like the other Japanese cars I've owned it will suck to bend your body around to get to the bolts and nuts holding it to the firewall. Prepare for a chiropractor visit.

In reply to Pete Gossett:

Will it pose an issue bench bleeding and filling with dot 4 while there is dot 3 in the system? I've heard lots of bad things about mixing fluids which was why I was thinning of doing it dry.

One more thing I just thought of, as I plan on eventually upgrading to 1.8 brakes, should I send back this matter and get one for a 1.8? I don't know if there's a difference in the master cylinder or not.

With a new MC, you pretty much must do this to get all the air out of the MC. Doing it on a bench means you can move the MC to all sorts of positions you can't do on the car to be sure you get all the air out.

After the MC is bench bled, install it and fill the reservoir with clean fluid.

Open the RR bleed screw and push the piston all the way in, as if you were doing a pad replacement. This pushes almost all the old fluid out through the bleeder and minimizes the mixing of old and new fluid.

Then just let it gravity bleed until you see clean fluid coming out the bleeder.

Close that one and repeat the process at each of the other 3 corners.

DOT3 and DOT4 are 100% OK to mix.

AngryCorvair wrote: With a new MC, you pretty much *must* do this to get all the air out of the MC. Doing it on a bench means you can move the MC to all sorts of positions you can't do on the car to be sure you get all the air out. After the MC is bench bled, install it and fill the reservoir with clean fluid. Open the RR bleed screw and push the piston all the way in, as if you were doing a pad replacement. This pushes almost all the old fluid out through the bleeder and minimizes the mixing of old and new fluid. Then just let it gravity bleed until you see clean fluid coming out the bleeder. Close that one and repeat the process at each of the other 3 corners.

That makes it sound so easy. Will this work on an ABS car?

There are no differences in calipers between 1.6 and 1.8 miatas, just the caliper brackets, rotors, and pads were needed when I swapped my old 90 Miata to 1.8 brakes.

Here are some tips, choose your new fluid carefully for maximum wet boiling point (some DOT4 fluids have higher boiling points than some DOT5.1 fluids, so consider both) and consider installing speed bleeders since you'll need to bleed the whole system anyway.

I was thinking of dot 5 not mixing with 3 i guess, I know some of them don't mix. Of course, I make a thread asking about mixing fluids s and what's the first bottle I see in the store? Dot 3 and 4 blended.

Ok, then I guess I just need to find a big bowl or spare bucket to bench bleed in.

DOT 5 is a separate beast as you were thinking. 3 / 4 / 5.1 are all compatible though.

Most MC will come with thread-in plastic fittings and some vinyl tubing, so you can loop both circuits back to the resevoir for bench bleeding. Check the box before you leave the FLAPS to make sure you have two fittings and hoses.

A bench vice is almost a must for this. If you don't have a bench, you can do it on the car by slightly pulling the hardlines away to leave room for the bench bleeders. Bolt tje MC to the booster, loop the bench bleeder back to the resevoir and slowly press the pedal through it's range of motion until you stop seeing air bubbles in the vinyl tubing. If you go that route, I'd recommend putting a piece of 2x4 or 4x4 on the floorboard for a pedal stop. It's possible to overextend the MC on some cars and damage the seals if you go all the way to the floor.

Now you're going to bleed the hell out of the system, so make sure you have a quart of fluid. I own a Mity-vac, Motive power bleeder, one-man bleeders, etc. Ultimately, it has been my experience that the two-man brake bleeding procedure is still the best. Even if you do it a fancy way, the final bleed with 2-people yields great results.

Edit:

My first MC replacement (1990 Dodge Daytona) was done by a nice old fella in the ghetto near Krogers where I worked at the time. I couldn't afford the tools yet. He did it on his lunch break for $20 and a box of fried chicken from Kroger Deli, but let me 'help.' So about a day's pay.

Thinking about the whole bench bleeding thing, can using a pressure bleeder allow for skipping that step? You'd have to blow the air all the way through the system, but for a thorough flush or a system with lots of new parts, that's not necessarily a big deal.

Simple, use a pressure bleeder to bleed the system before changing the master.

This way there is fresh fluid in place at the calipers.

Change the master, remove some of the fluid in the reservoir after the install using a turkey baster.

Then hook the pressure bleeder to each caliper and push the fluid back up into the master.

Need to build a pressure bleeder?

Instructions here: DIY Pressure Bleeder

No bench bleed needed.

Or you can bench bleed and then bleed the brakes using the pressure bleeder. Whichever is easier for you.

Here's another link to a DIY pressure builder:

DIY Pressure Bleeder #2

And a YouChube bideo:

https://www.youtube.com/embed/Mdcn1USVQ-w

Never, never, never, never, never, never, under any possible combination of situations, not even once, think that there is no need for you to bench bleed a master cylinder. I even go to great lengths to never let a line bleed out if I'm changing a caliper or hose, and I own a professional style brake bleeder and I've been a journeyman since 1986. It is just so much easier.

You may get away with it nine times out of ten, but that tenth time will have you using combinations of swear words that would make a Dutchman blush.

So- Never, never, never, never, never ever, not even once, install a master cylinder without bench bleeding it.

Just in case you missed it, never, never, never pass on doing a bench bleed.

Ever.

Not even once.

The last master I did, took 20 minutes to bench bleed. I finally ended up tapping it with a hammer to get the air out of it so it would bleed. If it had been in the car, I would have ended up pulling it, bench bleeding it and reinstalling it. That would have sucked.

Don't do it.

Ever.

In reply to Toyman01:

I would suggest that if there is a GRM person local to you that has done it before and look over your shoulder I would strongly recommend it. I don't know what the Pizza payment rate is for a master cylinder replacement but I think one large Pie should cover it. This is not a hard or difficult job but there are things that can go wrong and with it being the master control of the brakes for the whole car having an experienced eye on things is a good thing. It will also more than likely save you a bunch of time as well. If you were closer I would say bring the car and a pie by and we can get it done in an hour. Maybe two depending on how much pizza eating we do.

As stated its not a bad job. Ive had the master cylinder on and off my wagon about 4 times now. Bench bleeding is annoying but its such a huge help. Take the time to do it and you will thank yourself.

I replaced the MC in my turbo van a few years ago. It's not overly complicated but as stated, a bench bleed is highly recommended.

I just did the RN Truck a few weeks ago. Again. Damn thing only lasted like 200K miles or something. Fortunately it had a lifetime warranty. It came with all the pieces to bench bleed. Hoses, fittings, etc. Just grab it in the vice, put the hoses and fittings on, push the end in with a big screwdriver until no more bubbles come out. If you want to do the optional bench bleeding that is. I hear some people recommend it.

In reply to RevRico:

One other tip - when you bench bleed it and/or during installation, yes fluid you just worked so hard getting the air out of will leak out of the MC. It's generally not a big deal as long as you keep the reservoirs topped off, so don't worry too much about it.

Then I shall start with a bench bleed. And probably buy another quart of fluid.

I'm taking the hood off to do it. 4 bolts to prevent multiple head bashings sounds like a fair trade off.

Unfortunately, this is all that was in the box. But as I'm not in a huge hurry, next event being May 14th, I'll take it shopping with me and get some vinyl tubing that fits so I can bleed it that way in my bench vise.

These pressure bleeders look interesting, I may have to experiment. At the very least, I won't have trouble finding someone to push the pedal all day. And depending on when I do it, I do like Dean's idea, I know someone experienced who might be able to watch over my shoulder, that helps sometimes.

Most parts stores will carry a universal bench bleeding kit (comes with a ton of different plastic fittings, hoses, and clips to clip the hoses to the rim of the reservoir) for cheap.

Also, don't get any brake fluid on the paint, not a bad idea to put some towels down.

No tube is no real problem, other than creating a bit of a mess. One hand for the screwdriver to push the piston, other hand with two fingers to act as check valves. Mount in vise, then short strokes to force the fluid past your fingertips, and not let air back in. Keep making short strokes until you see no more bubbles coming up the ports into the reservoir.

Then carry the dripping mess over to the car, and do up the lines close to finger tight before you worry about the mount and pushrod clevis. When the slightly loose connections are dripping, snug up and you are likely done, unless you have a line running into the top of the cylinder. A garden hose following installation is a nice finishing touch.