Hi,

I am replacing my old brake servo on the 1998 NB I have. It did little to nothing. My wife asked my if it could be like her Peugeot (new car, look at the brake pedal and your head hits the wind screen if it wasn't for the safety belt), so I decided to search the www for an upgrade. I found that there are thicker servos that amplify more than the one I have, so I picked one up from ebay second hand from a source I bought from before. Tonight, I tackled the unpleasant task of removing the old one, but it came of easier than I expected. But now that I have them on the bench, I find there is a difference and I seem to miss a part.

Here they are, the old one:


And this is the new one:


First of all, when I blow into the old one, via the vacuum connection, it is almost air tight. It probably should be all air tight, hence it is not functioning well. But when I blow on the new one, no resistance. I miss the closing thingy / sealing thingy in the hole the master cylinder will fit into. Is that part available somewhere? I don't know what it's called, so googling for it is difficult. And it does not seem retrievable from the old one, but if there is a trick please let me know.

Secondly, as the old booster is thin and the new one is thick, the brass looking parts that go into the master cylinder is of different length for each one. But I cannot get them undone, to exchange them. How is that done?

All input is welcome. BTW, I know I should probably renew some brake lines but that is no problem, I have the tools and the experience.

Cheers,

Hugo

 

As I have little else to do tonight, I googled for brake servos and master cylinders. I found something.
- My old servo has a seal in the throat. My master cylinder has a short straight aluminium neck to fit into the throat.
- My new serco has no seal and a deeper throat. And I find many master MX5 NB master cilinders on ebay that have a longer thing sticking out of the neck, and the neck has a rubber ring on it. Like this one:


Would forking out the cash for the matching master cylinder be the easy fix?

Cheers,

Hugo

 

When I was researching my master cylinder swap, my reading suggested that the master cylinders from the bigger and small servos don't interchange easily. Given the relative affordability of masters, especially second hand, I just bought a matched set. No problems since install 5 years ago. As a bonus, if you put in a bigger 15/16" master cylinder you get a more direct-feeling pedal, which was actually the primary reason for my making the swap in the first place.

 

I examined the brake servos of my '91 NA, '03 NBFL Sport and '01 1.6 NBFL (fatter double diaphragm). ⅞" masters from early NAs will only match their respective servos.

Brake tech info at Miata Net

I'd simply buy a 15/16" NB master cylinder, mount it to the fatter booster, and Bob's your uncle.

 

Damit bin ich einverstanden! That link is also sehr nuetzvoll.

In order to save considerable hassle, be sure to get a master that matches your car with regards to having ABS.

 

Thanks for all the info. I just bought the matching cylinder on ebat Germany, should arrive somewhere next week.

Cheers,

Hugo

 

Hmmm, OK, I bought the 15/16" master, or so I thought. Today I received the part and it isn't. It has one part reading 1-2, and the other (closest to the servo) reading 7/8. And it has two exits while my old one had three; one directly to the left front wheel, one through the balancer to the right front wheel and the last one thought the balancer to the rear.

Now I do want to make this work, soon, as I need the car back on the road. It is our second car, but it is amazing how often my wife needs the family car as soon as the MX5 worked on. Anyway, I have two exits and three directions to feed. Here's the current state:




My guess is the rear section (closest to the servo) is thinner, hence more pressure (same force less area), so should feed the front brakes. So to the left front, and via the balancer to the right front. I can make a T-piece into the line coming from the master cylinder to the left front. Then I can hook the remaining exit, on the larger fron section, to the rear via the balancer. Does that make sense?

Cheers,

Hugo

 

Did the swap last Winter; I ended up using a "T" fitting to generate the additional line port. Just have to find the correct flare end T. See photos.

 

Sorry, now that I see the photo I attached, I see I hadn't yet made up the last line. You can see how I made the extra port 'tho. Not sure where a completed project photo is.

 

Here you go.

 

I wouldn't let the t fitting dangle around freely. I'd be too worried about premature failure due to fatigue.

I mounted mine like this:

 

AFAIK the brake master doesn't make for any proportioning. This is done in the brake prop valve. Until the knee point both front and rear brake lines see the same pressure. IOW, it shouldn't matter what port you connect to which port at the prop valve, as long as from the prop valve on it goes to the right end. For what it's worth, the port near the booster is the rear brake port; the one(s) towards the front bumper are those for the front brakes.

 

Thanks again. I just bought a new flange-tool (old one is MIA), copper line and nuts, and a T-piece. I'll fix it, thanks for all the input.

Thanks, Tomrev, for the pic with the booster stopper in the brace bar. Good idea, I'll fab something like that too.

Cheers,

Hugo

 

I don't want to discourage someone who's willing to get their hands dirty, but if the master is the wrong size and the wrong ABS type, I'd consider trying to find a source for the right one. The 15/16" takes up a good bit of that slack travel at the beginning of the pedal stroke. On my car I felt it was well worth a few dollars/euros, and then you don't have to go sourcing T-pieces.

Either way, good luck!

 

In my case, it is the 15/16th MC that paired with the bigger NB vacuum can. Problem was that it has one less output port, hence the need for the "T".

 

@TalkingPie; thanks, you're probably right. This just gets the car back on the road. Now I know exactly what to source and I have the time to carefully do so. I might have overspent 20 bucks in the process, but that's OK. It's not only our second car, but also a hobby.

Hugo