TalkingPie

Given that I've never been that happy with the pedal feel from my '99's base, non-ABS brakes, I've set about trying to find ways to improve things. Here I talked about adjusting the brake free play, and fiddling with that yielded some success. However, the longish travel still bugged me, so I read up on this m.net thread by Keith Tanner and decided that getting a Mazdaspeed booster and 15/16" master would make my life better. From my basic calculations based on piston area and boost ratio, I stand to respectively reduce my pedal travel and pedal effort by about 15%.

I managed to buy one on E-bay, and since I've got a couple of months before spring comes and I can start breaking things on my car, I thought I'd ask for you guys' experience. Namely, the things I wonder about are how hard it'll be to get the existing lines to mate with my new master, and exactly how to deal with the fact that the MSM master is for ABS, while my car doesn't have it.

From what I understand, you just have to plug one of the extra exit ports on the master. Where would I get such a plug?

If anyone's done a similar swap, how did you deal with the prop valve? From what I understand, the '04 ABS cars didn't have one at all. I was planning on either doing away with it on my old setup anyway, or possibly slapping in a Wilwood valve if it turns out to be too rear biased.

Thoughts? Opinions? Warnings that I'm about to set up my car to spin off the road backwards in a leaky, DOT4-stinking mess?

Savington

iTrader: (31)

Buy a master that's designed for a car that doesn't have ABS. It's much easier to do this than to try to tee the front line for your car. They are identical except for the additional front brake port on the non-ABS master cylinders.

codrus

Short answer: Do what Savington says.

Long answer: An ABS master has one front output (goes to ABS hydraulic unit), whereas a non-ABS has two (one to each front wheel, one of them by way of the prop valve). If you want to put an ABS master in a non-ABS car, you need to turn one into two, for this you need a tee. FM sells one:

Flyin' Miata : Chassis : Brakes : Metric brake tee

If you want to put a non-ABS master in an ABS car, you need to plug one of the ports. Most of the Mazda masters have one flare nut port and one banjo bolt port, the banjo bolt one is probably easiest to plug. You don't need to do this.

To install the tee, you're going to need to modify both front hard lines so that they meet at two of the ports on the tee. You'll need to bend them, and probably cut and re-flare them. They ought to be long enough to do this, if not then you'd need to fabricate a replacement for one of them to make it longer. You'll also need to fabricate a brand new line to go from the master to the tee. You'll need at least two new flare nuts, the Miata uses common 3/16"/4.75mm tubing (same size) but the threads on the nuts are metric 10mm x 1.0. Most of the stuff they have at your FLAPS is probably SAE threads, and won't work. These guys sell the parts:

http://store.fedhillusa.com/316475mm...dfittings.aspx

They can be bent by hand a bit, or there are tubing bender tools. You need a tubing cutter to cut it, and an SAE brake flaring tool to flare it. Flaring lines is a bit of an art -- expect to to screw up the first half-dozen you do, so you'll want to practice before trying it on the real lines. Flaring is much easier if you have good flaring tools, but they are expensive. Forget the Harbor Freight tool, it sucks. There is a Blue-Point tool that looks similar to the HF one but sucks a lot less. I have one, it works, but it's a bit of a pain. Then there's the hydraulic tools like this one, which are godlike and have prices to match:

Universal Hydraulic Flaring Kit NOT FOR STAINLESS

So you could spend $87 on a non-ABS master from Rockauto that has the ports in the right place, or you can spend $15 on a tee, $2 on lines/nuts, and $200-$600 on tools to install it.

Of course, if you really want to fix the squishy pedal you can go with a 1" master out of a 929, although that will definitely require remaking the lines.

--Ian

TalkingPie

Thanks a lot for the info! It looks like I may have bit off more than I can chew here.

My original plan was to get the booster and a 1" 929 master without ABS. However, Sport boosters are thin on the ground in my parts, and the one seller of one I found wasn't willing to budge on the price, but he was willing to throw in the MSM master for free. So I figured I may as well give that one a try.

I've played with brake lines just enough to have a respect for the difficulty of flaring properly.

Now I need to decide whether to buy another master, which for me means paying more than $87, because of customs and shipping, or trying to make the one I have work.

EErockMiata

99 non sport booster, sport front brakes, 949 willwood 1" master, willwood prop valve. Love the setup, very short pedal travel and great modulation feel. 949 includes the fittings you need to convert the front single output on the willwood master to a dual output to feed both front calipers.

The pedal travel on this car is short enough to make braking difficult for co-drivers on street tires. On r-comps it would be perfect for everyone. Once you get used to it, most people really like it but the first 1-2 sessions can be rough for new comers.

asmasm

iTrader: (1)

Are you also bracing the master?

SchmoozerJoe

iTrader: (2)

Any idea what happens when you mate a 929 Master Cylinder with the thick NB brake booster?

I'm looking to reduce the pedal effort/travel distance.
From the write-up that Keith had over on M.net, it seems like this is the "ticket" to accomplish my goals.

TalkingPie

That would depend on how much you want to decrease your effort by. Going by my simple math, and armed with the high school formula to calculate the surface area of fluid pushed:


I get the following values in square inches for each of the master cylinders:


From there it's just a question of proportions. With each increase in diameter, you get a decrease in pedal travel, and an increase in pedal effort, directly proportional to the increase of the surface area of the cylinder.

Going from a 7/8" to a 15/16" will then decrease your pedal travel, and increase pedal effort, by 14.8%.

Going from a 7/8" to a 1" would do it by 30.6%

According to Keith, the various boosters have the following boost ratios:


Knowing that, you can choose a different booster to compensate for the increased stiffness of putting on a bigger master.

If you go to a 1" master and choose the MSM/Sport-no-ABS booster, you end up with an overall pedal effort nearly identical to stock (about 3% less effort).

If you go to the thicker booster, you'll end up with a pedal effort that's about 36% less than stock.

Feel free to double-check my proportion calculations, but they should be at least in the ballpark. Also note that these calcs assume you're starting out with a "base" car with the 7/8" master and weakest booster. I'm also assuming you're not going to change anything at the calipers.

Personally, I think I'll be happiest with the 1" master and the MSM booster, assuming I can get the brake lines all happy.

I don't know exactly how going to bigger brakes would affect all this. On one hand, bigger brake pistons will make for a softer, easier-to-press pedal, but on the other hand, bigger brakes, like on the Sport cars, have larger discs which will supply more braking torque. This, I guess, would require less force at the caliper cylinders to get the same braking force, but that's just speculation.

scenturion

iTrader: (9)

I dont think it's that simple to estimate what the pedal force will result from mixing and matching boosters and masters. I went down this rabbit hole and it seemed like there was something missing.

Keith found those booster ratio values you quote by taking the ratio of the brake line pressures specified for a given pedal input with and without the booster connected from the service manual.

The manual states that for 44lbf of pedal force, without vacuum to the booster, the line pressure should be 107psi.

With vacuum, that amount of force should give 683 psi for a non-ABS sport (16" wheels) or MSM, and 1038psi for ABS or non-ABS non-sport (15" wheels.)

Ratios:
683/107 = 6.38
1038/107 = 9.70

However, looking at the NB1 manual:
When applying the same 44lbf to the pedal, the line pressure without vacuum should be 163psi and with vacuum it should be 775psi. (775/163=4.75)

Given that the pedal geometry doesnt change from the NB1 to the NB2 (pedal ratio is 4.1 according to various sources), you'd expect the off-vacuum line pressure (lb/in^2) times the master area (in^2) would be the same for both the NB1 and NB2, but it turns out theyre not (98.32 lbs for NB1 vs 73.86lbs for NB2).
So, where does the difference come from?
I suspect the return spring in the master has a non-trivial effect and is providing the difference in these numbers.
Without knowing more about the return spring in the stock master cylinders as well as the 929 1" master, I dont think you can draw any conclusions about the pedal force.

Please let me know if I've made any mistakes but I banged my head against the wall for a while trying to figure it out.

TalkingPie

So I'm trying to find the right 929 1" master, and so far have come up empty. The problem is that every part I've come across, even the ones billed for non-ABS, has only two outlets. Anyone know of any with 3 outlets?

Also, while browsing Centric's catalogue, I discovered that the base '99 master, like I currently have in my car, has 2 inverted flares and one bubble, while the Sport 15/16" one is all inverted. What this means to me, I gather, is that I'm going to need to make at least one new flare. Can someone confirm or deny the accuracy of Centric's specs?

Am I so functionally inept that others have successfully completed this swap, while the logistics of it baffle my feeble brain?

Leafy

iTrader: (1)

Pretty sure centric is wrong on both of them. All the miata masters with 3 outlets I've seen have 2 inverted flare and a banjo bolt.

SchmoozerJoe

iTrader: (2)

Any of you rockstars know where I can source a 929 MC reservoir, besides a junk yard?

My Autozone sourced MC came bare and I've been having a heck of a time finding the reservoir only.

codrus

I haven't personally seen one (I converted my car to ABS, so I wanted the 2-port version) but Rockauto sells masters for 1995 Mazda 929s both with and without ABS. Dorman M390112 is the non-ABS, although it says it's 2-port. I dunno why. http://www.dormanproducts.com/p-2356...der&origin=YMM

In the worst case you can get a T-fitting from FM. Even in the best case a 929 master isn't going to be plug-and-play, so you'll likely be bending and flaring lines anyway.

--Ian

TalkingPie

In researching this today, I came across a post saying that all the 929 masters were 2 port (which confirms what Centric's catalogue shows), but the non-ABS masters had a double banjo fitting at the front port of the master to accommodate the extra brake line. Apparently when you order the ABS version, you get the simpler single-banjo fitting. When you order the non-ABS version, you get no fitting, presumably because you'll reuse the one you already have (or buy it from a source for OEM Mazda parts). I haven't found any mention of people using this double-banjo to adapt to the Miata.

Depending on how involved I want to get with acquiring tools, lines, and skills, once winter is over I may go down the rabbit hole of figuring out exactly how to get this together, like many before me have. Being north of the border, finding and ordering parts and tools is somewhat more expensive and tedious for me. Alternatively, I can still just buy a Sport-no-ABS master, which should be mostly plug-and-play.

It's just odd to me that I see evidence of people swapping in 929 masters for over a decade on numerous models of cars (the RX-7 and Protege guys, as well as the Ford Probulaters, have done it, too), but I can't find a step-by-step spoon-feeding write-up for the Miata.

codrus

I've done it on two cars now (albeit both ABS), and there really isn't much to write up. Unbolt the old one, bolt the new one on. Bend some lines, flare them, screw them down, fill and bleed fluid. Done. It literally took me less than an hour the first time.





--Ian

TalkingPie

To update this for anyone following in the future, I finally went through with upgrading my master and booster. I traded my ABS master with someone else who needed one, and got a factory 15/16" non-ABS one. This was considerably cheaper and less complicated than sourcing a 929 master and acquiring parts, tools, and knowledge to adapt its 2 ports to my non-ABS car's 3.

It took me considerably more than an hour to get the deed done. Aside from my general fumbling, the major stumbling block was that for some reason, once I got everything bolted up, fluid spurted from the banjo nut every time I pressed on the pedal. I don't know if it's because I didn't replace the brass washers with new ones, but shortening the bolt on a grinder allowed me to get things nice and tight. Bending the existing lines to fit the new port locations took some time as well, but the whole thing now looks pretty tidy.

I'm happy with the results. There's less slack in the pedal on initial application, and the pedal is considerably firmer, with slightly less effort required to get my front tires to emit acrid smells.