Larger master cylinder:
Note: My car is non-ABS so not all of this may be applicable to ABS equiped models.
Background: About 2 or so years ago(along with the brake bias adjuster post) I ran into this page regarding a master cylinder upgrade from 15/16" to 1" from a 93 929.
. Really interesting stuff and really good information to read. Then the topic surfaced on Probetalk ( http://forums.probetalk.com/showthre...aster+cylinder
) and I was again in the thick of things again. In fact I found out all sorts of things regarding the 2nd gen Probe/MX6 MC and the 3rd gen RX7 and the 93 929. The MC bores for the 2nd gen MX6 and the 3rd gen RX7 are the same(15/16") the archetecture of the MCs were similar and the rod stroke ratio was the same(4-1?)..Basically it would work for the 2nd genners also.
I think thats as far as it went as it didnt seem that anyone had the desire?/money?/balls? to try it. All that work for the 2nd gen and I couldnt even benefit.......or could I?
There are 2 different archetectures for the 2nd gen MCs. One that is the same as the 3rd gen RX7 and one that is....you guessed it: based on the 1st gen MC. The 1st gen master cylinder bore? 7/8". Time to go to work.
One on the right is off a 94 PGT manual(dont remember if it was ABS or not). Has 2 fittings for the brake lines, a larger interface for the brake booster is an "outie" and has a very short brake booster plunger.
One on the left is from a 96 626 automatic
non-abs. Looks very much like the 1st gen master cylinder with a few changes. It has 3
fittings for brake lines and the 2 fittings for the brakes that we need to use are on the same side instead of opposite sides like the stock master cylinder. Bingo! We have a winner.
EDIT: From Chunchoy14.
btw, the master cylinder you had for the 96 626 that had the 3 holes, the odd hole is not for the clutch line(the clutch master cylinder feeds off the reservior on the brake master). Automatic and Manual brake master cylinders(not reservoir) are the same. ABS modelled master cylinders have 2 holes, non-abs 3 holes. Reservoirs with a nipple on it is for manual cars. No nipple=automatic. You have a automatic reservior w/ a non-abs mc. Just a small clarification.
First we have to do something about that extra bottom fitting or else things are going to get messy pretty quickly. Hmm..How about a bolt cut down to fit? Sounds good to me. Metric DAMMIT, metric. Remember that.
Ok thats looking mighty good. I should note that I changed things slightly to include a new copper crush washer to get a tight leak proof seal.
Now we need to fabricate new brake lines for the other driver side outlet. You could get some stock and roll your own....but why do that when there is a more simple solution? As it turns out the hard lines on the 1st gen proportioning valve exit from the same side. Why not source a second drivers side(front) hard line from another 1stgen non-ABS car since it will exit the proportioning valve and enter the new master cylinder on the same side? Yeah...thats what I was thinking too.
How convenient that Mazda saw fit to have pre-made lines for this upgrade already. ABS guys. You may not be this lucky. If you try this you will probably have to fab your own lines.
Here are some side by side shots of the 2nd gen and 1st gen master cylinders.
Incidentally. I got both of the 2nd gen master cylinders from the junkyard and promptly rebuilt the 626 MC. They could have been perfectly fine for all I knew, but who knows? Again....NO SHORTCUTS.
Disassembly of the stock master cylinder is pretty simple, if not messy. Again..Use good quality wrenches(flare) on the brake fittings.
That would be the stock hard lines and then the refitted lines for the new master cylinder. The 2nd line only has to be slightly bent to fit correctly, massaged really. The action isnt enough to crimp or weaken the line at all as it was pretty much in the correct position already.
The last thing to be done is to install the new larger(15/16") master cylinder. But before doing that its best to bench bleed the master cylinder as it is very dry at this point. Bench bleeding the MC ensures that there is no trapped air in the MC. There are horror tales of people who have not and have suffered with spongy brakes for years(the calipers bleed without bubbles but there is still air trapped in the MC). Keep bleeding the MC until there is NO bubbles remaining its going to take time(I think I did 5 bleedings of the MC before I was satisfied).
(gratuitous shot of the goodridge clutch line)
After all of this is done the whole system needed to be bled CORRECTLY and THOROUGHLY
(can you imagine, the calipers, brake lines and proportioning valve were all without fluid? ack!).
Get a pressure bleeder if you are doing anything of this magnatude(or build your own RAMI?). It helps a lot. If not, hijack another person to help you. That way one person is checking the flow of fluid and checking for bubbles while the other is working the brake pedal. AGAIN Dont **** this up. Get it right even if it takes a while. No cheating.
I worked by my self bleeding the system(speedbleeders rock) and had a gallon of the cheapest brake fluid to run through the lines. I normally use ATE super Blue as my regular fluid, but the cheap stuff was welcome because...it was cheap(duh) and its clear color was better to check for bubbles than the ATE super Blue(which is ,surprise surprise, blue in color). Overall I did 3 full brake flushes(with one more to go with the ATE super Blue) and went through a half gallon of brake fluid.
Did it work?
You bet it did!
I had to adjust the brake booster plunger depth to get the correct clearance to the master cylinder(manual sez 0mm of play with no preload), but it is EXACTLY as advertised.
A firm...No I mean FIRM
pedal. There is about a 1/2-3/4"? of movement of the brake pedal and then thats it, no more movement. The feel of the brakes is outstanding. The folks who have done this for other cars speak in terms of "better resolution" when they refer to the feel of the brakes. This is the same term I would have to use. There seems to be much more feedback into what is happening with the brakes. Its now pressure, not pedal travel, that determines what % of braking power you have. Nice.
Why did I do this? Partially to see if I could(someone pointed out that no one else has done this for the 1st gen....ever. It made me pause to think about that).
As I autocross more and more I am looking for tools to help me be a better driver. Having the ability to feel the brakes better is a great tool I thought I could use. Left foot braking is also another thing that I would like to use and with the increased feel of the brake pedal I feel more confident of putting my left foot down. Previously my left foot felt "uncalibrated" in trying to use the stock brakes and its longer pedal travel, now things feel a bit more natural.
It worked, and I KNEW it could
Ok before I go on to the next bit of madness. Beding in brakes. Read the instructions that come with your aftermarket pads. If not for that, there are very good techincal articles on the net (check Stoptechs site for thier tecnical papers, good reading)
I did 5 runs, on a very unused road(this is a must) of 40-15mph moderate braking and then 60-15mph hard braking, sat for a while to cool the brakes(parking brake off) and then repeated with 10 60-15mph hard braking runs. Youll be smelling the pads at this point(I had smoke billowing out of the rims). Let cool for the day(parking brakes off). Check them the next day. Drive.
OK...If you are still with me this far....The last bit of madness, the piece de resistance.