RotaryRocket88

iTrader: (7)

Looking good; it's turned into a very clean setup. I like the braided lines, and all of your shiny nuts and bolts make me want to raid a junkyard for fresh replacements.

clokker

iTrader: (2)

As many trips to the yard as I've made lately (nearly every day for two weeks), I finally made a "shopping list" for hardware.

One day it's been 6mm nuts and bolts, the next, 8mm, and so on.
Under door panels is a rich source for perfect condition 6mm stuff, rear seat mounting spots are good for 8mm and I always keep an open eye for weird spacers, brackets and doo-dads.
Don't forget rubber body plugs (look in the trunk) and electrical harness mounting clips.
There's lots of weird and wonderful stuff to be found once you train your eye to look for it.

Limit your search to Japanese cars.
Although European cars are also metric, they use a different convention for the thread/head relationship.
On our cars the most common wrench sizes will be 8,10, 12, 14 and 17mm.
On a European car, for the same bolt sizes (and yes, the threads will interchange) the wrench sizes will be 9, 11, 13, 15mm, etc.

Nothing worse than working with a bunch of fasteners (say, on the UIM) and having to stop and find a 13mm socket when all the others are 12mm.
Drives pro mechanics crazy.

This disparity also holds true for American hardware stores.
The 8mm bolts/nuts at Ace Hardware will have a 13mm head instead of the Japanese spec 12mm. One Ace around here has a special selection of "small head" metric fasteners which are Japanese conformant but they have the gall to charge more for them.

Screw that, shop the junkyard instead.

Black91n/a

I've read that you can use the complete 929 MC and booster in place of the NA unit, applicable years are between 92-95. I'll be picking one up this weekend and hopefully I like it, otherwise I might have to get one of those 1" MC's to fit the stock NA booster if I want a stiffer pedal. Good work on figuring that all out and telling us all about it.

clokker

iTrader: (2)

That's what I originally wanted to do but couldn't find any 929's to pirate.
Lots of 626's- which don't work for us- but not a single 929.

Since I never saw the car, I don't know how easy that swap might be.
If you're lucky enough to find one, make sure you grab it's proportioning valve as well (if it's not mounted like ours), just to give you another option when you install.
Also, pay attention to the location of the vacuum nipple on the booster...if it's not where the stock one is you'll have to figure out how to make it work.
There are a huge variety of formed hoses on different cars that might work out and you should grab one if necessary.
Our hose has the check valve inside it but most cars do not...the standard external check valve will work just fine.

Finally, make sure you are doing this with the correct outcome in mind.
Swapping the MC has no effect on braking distance- that's what the calipers and rotors will do.
All the MC changes is the pedal feel/travel.
This change in "feel" might translate into better braking practice but it would take larger rotors and calipers to significantly affect braking distance.

If you do try the 929 setup, please post pics- I'd love to see it.

Black91n/a

It's best to keep the stock proportioning valve unless you really know what you're doing, since the other valve might be set up for vastly different brakes and it could make your brakes go way out of balance, vastly increasing stopping distances.

clokker

iTrader: (2)

I don't claim to really know what I'm doing and in general, would agree.
In fact, that's something I considered when I first spied the Q45 MC.

I did a bit of research to assuage my concerns.

First, I disassembled a proportion bypass valve (Mazda's terminology) just to see what it looked like.
Basically, just a spring-loaded restrictor...actually pretty crude.
Then I looked at the FSM, which makes no distinction between the single and four-piston caliper systems when speccing the proportioning valve...I believe Mazda uses the same valve for both.

This lead me to conclude that the basic function of the valve is simply to prevent the rear brakes from locking before the fronts and our stock valve (along with the Toyota unit I also took apart) was not especially precise in how this was done.

In theory, the integrated Infinity valve appears to function identically to the Mazda unit although the Infinity part cannot be taken apart, so I'm only speculating. Duplicating the function would explain why the Infinity outlet ports are reversed from normal practice...the front circuit is the rear port, the rear comes out the front (OK, that just sounds weird...).

Anyway, the point of all this is to say that I think that the braking systems would have to be way different- say rear drum instead of disk- before the proportioning valve would make too much difference.
On a street car I doubt you'd ever notice and if the car is tracked, I'd hope you have a better and more precise valve to work with- if not twin cylinders with a bias bar.

None of this is meant to discount your advice, Black91n/a, and I did state previously that the 1" Subie cylinder with the stock valve was my main recommendation- but if someone wanted to get a bit further into the experiment, a different valve might be interesting ( and more easily adaptable) to try.

As an aside...
Yesterday I had the opportunity to make a "panic stop" under controlled (albeit wet) conditions and the brakes worked perfectly.
Not a scientific test but comforting nonetheless.

clokker

iTrader: (2)

Thought this was over, eh?
Nope.

Earlier in the thread I casually wondered about the relationship between booster and master cylinder.
Does a larger MC require- or benefit from- a larger booster unit?

I've done some reading and the answer seems to be "Yes".

The cars that originally came with the 4-piston calipers have a different booster- physically smaller but twin diaphragm.
Of course, finding a suitable booster to try on our cars is not as simple as finding the master cylinder but a phenomenal twist of luck put such a unit right in my hands.

Wandering the junkyard last Saturday- getting ready to leave, actually- I glanced at a car in passing and stopped short.
I could see a Honda sticker under the hood and what grabbed my eye was the booster assembly.
Most- if not all- of the Hondas I've looked at have the master cylinder mounting bolts clocked at an angle instead of horizontally like ours. I've pretty much ignored Hondas as a source for cylinders/booster for this very reason.

This one though was horizontal and because the engine was already gone, I could get a good look at it.
T'was obviously a dual diaphragm booster (they have multiple steps on the sides) and looked to be the same size as my single diaphragm unit (approx. 9.5").
The master cylinder was also MIA and when I looked inside the cabin, someone had already undone all the hardware...back in the engine bay, I simply lifted the booster out.

I walked it over to the (only) RX7 in the yard (whose booster I'd already procured a few weeks ago) and it popped right in.
A perfect fit.
Stud length was identical to the stock Mazda piece (2"), diameter was the same...the only difference was the Honda part was about 1" deeper.
Looked like it'd work.

I bought it.

BEYOND HERE BE DRAGONS...

At home, a side by side comparison showed that the Honda booster had two significant but overcomeable differences.

First, the shaft that the clevis fits on was 8mm instead of 10mm like the Mazda's.
The Honda clevis was too short and too narrow to fit my aluminum brake lever, so that would have to be changed somehow.

Second, unlike any other booster I'd looked at, the Honda did not have an adjustable pushrod for the MC and it was clearly too short for any of my master cylinders.

The clevis was a simple fix.
I took the stock Mazda clevis and threaded a 8mm helicoil into the 10mm threads.
Worked like a champ and the clevis now threaded onto the Honda shaft.

The pushpin was a bit harder and required turning an adaptor to slip over the pushrod and extend it the necessary amount.

All told, both mods took under an hour and the booster was ready to install.

Because of the braided steel lines I'd already put in place, the front brakes were able to remain connected as I removed the master cylinder and old booster.
The rear brake is a hard line and had to be undone.
No biggie, I took this opportunity to install the new speedbleeders on the rear calipers and was soon all done.

Now for the $64,000 question...did it make a difference?

Oh yes, it certainly did.

In fact, of all the changes I've made so far- including the initial swap from the 7/8" to 1 1/16" MC- this was the single most dramatic difference in feel.

I don't know how to describe it really but it feels like I've doubled the rotor and caliper sizes...this thing feels like it has BRAKES!.

Need more seat time with them to get a better idea, but I'm pretty stoked.

If anyone is interested, the Honda booster came off a 1997 Integra GS-R.
It's the only one like it in the yard so I don't know if any other years or models use it.

If you can deal with the (relatively) minor mods needed to adapt it, this would make a perfect match to your upgraded master cylinder.

'87Rex7

iTrader: (1)

I too would like to see.

Realred96

Great find. i wonder what the feel would be like with just the booster upgrade and stock MC?

Here in Houston a Integra GS-R would never even make to to the junk yard. The ricers would be all over it.

I wonder if a standard Integra or Civic booster would work?

HotRodMex

iTrader: (3)

Just wondering, why don't you think a 626 booster/MC will work?

clokker

iTrader: (2)

My guess is that you would be overboosted but I am no expert, so feel free to try it.
I am not aware of the science behind matching the two units but have to figure that the OEM engineers are and they put smaller boosters with smaller cylinders.
From what I can tell after a bit of online research, the Integra came with a 1" cylinder to match this booster, so I'm in the right ballpark.

Remember...none of what I've done affects the actual braking, this is all done to alter the "feel".
To physically change the brake performance you'd have to go to the wheelwell and change caliper piston size, rotor diameter, pad characteristics and tires.

IIRC, the studs on the booster aren't long enough to clear our firewall.
Either that or the bolt pattern is wrong.

I've looked at so many cars that they blend together but I do remember ruling out the 626 as a donor.

Black91n/a

That's not entirely true. I've done quite a lot of looking into alternate brake bias valves and I've found that there's a HUGE variety of biases out there. Everything from weight distribution, wheel base, disk diameter, piston diameter, number of pistons, tire size and especially ABS affect it. Case and point is the Miata, much remained the same from 1990-2005, but it had about 5 different valves as the brakes got bigger and the ABS was added and got more sophisticated. For "normal" driving you probably won't notice, but for panic stops you might end up going backwards into the bushes if you get it wrong and will almost certainly end up with longer stopping distances as the bias will probably be worse.

Moral of the story is that the bias valve needs to be matched to the brakes at the wheels and the car, NOT the master cylinder. Unless you really know what you're doing keep the stock valve.

clokker

iTrader: (2)

In theory, I suppose I would have to agree.
In practice however, I can absolutely guarantee that my stopping distances have not gotten worse, nor does the rear end want to lock up.

Unfortunately, I have no way to quantify my "foot dyno" impressions with hard data, so I'll accede to your more theoretical advice.

Just out of curiosity, have you seen the pressure graphs for the five different examples of the Miata or are you just going by part numbers?
A simple change in the config of the part- say, a relocated mounting tab- would result in a new part number even if the actual performance was identical.

A sterling- and closer to home- example would be the S4 and S5 NA BAC valves...two different part numbers but the same part, difference being the connector shape and nipple orientation.

Had I been more prescient, I would have tried to come up with some sort of "before/after" data to semi-validate the at-this-point unprovable statement that I have gone forwards, not backwards, with these mods.
When I started the process however, I had no idea that I'd get as deeply into it as I did- certainly not to the extent of deleting the prop valve.

It's possible that in a few weeks I could arrange a comparison between my car and a T2 (it's in the finishing stages right now) but since we have different tires and brake pads, it would be a very questionable dataset.
At this point, reverting back to the stock setup to make a more valid comparison would be arduous at best and, given that I'm not trying to sell this project to anyone, pointless from my perspective.

I do appreciate your caution Black, and believe me, would not have posted the project if I felt it was reckless or dangerous.

I suspect that most folks will stop at the larger MC swap that retains the stock lines and valve, so your concerns would be allayed.
I on the other hand, am happy with the setup I ended up with and feel perfectly comfortable with the brake performance it provides.

Black91n/a

http://www.flyinmiata.com/tech/stock_bpv.php

Info on the different valves is in the link above, notice how different they are (although their way of calculating "bias" is wrong).

My dad's 1992 Miata has brakes off of a 1994 and he swapped from the stock 1992 valve to the 1994-1997 non-ABS vavle and noticed that the front lockup he'd been having on track got much better. I know the FC has too much rear bias on track, so I think the 1994-1997 non-ABS valve might be better, but I'm planning on using an adjustable valve.

Note also that different pad friction coefficients will change the bias, since the brakes will need different amounts of pressure to apply the same amount of torque to the wheels.

Any valve will be imperfect, since it's only a 2 slope curve, but they can be better or worse and it's almost certain that a non-stock valve will be worse.

I got my 929 booster and MC, I'll report back once they're in and I'll get some pictures. It certainly looks like it'll work, but don't hold your breath on the report, it may be a while before I get to it, I've got a lot of other stuff to do too.

clokker

iTrader: (2)

Isn't there a hint of "Do as I say, not as I do" here?

If "it's almost certain that a non-stock valve will be worse", how do you justify swapping out valves and ending up with an adjustable one?

As you note, simply swapping the brake pads will affect bias and who among us is still using OEM pads?
Furthermore, like many here, I've also changed wheel diameter and width, both of which will also change brake performance.

As always, when modifying any system, especially one as crucial as the brakes, the onus will fall one each builder to monitor the resulting performance and proceed accordingly.
To make a blanket statement that any change from stock will be worse seems a trifle too broad though.

Good luck with the 929 swap, like to hear about the results.

Black91n/a

I'd put myself into the category of "unless you know what you're doing". For me, at the track, the stock valve gives too much rear bias, so I'm planning to use the adjustable one to get the bias back to where it's closer to ideal.

clokker

iTrader: (2)

Fair enough.

What does too much rear bias feel like?
Obviously, totally locking the rears and still not stopping would be an extreme example but the valves you've tried are only subtly different, so what's tipping you off that it's still not right?

Black91n/a

Locking rear brakes is what tipped me off. This is bad as it's unstable and can lead to a spin, but it also means that you can't brake quite as hard as you could with perfect balance. It's a common issue amongst racers.

I haven't actually used any other valve, I figure I'll just go straight to an in-cockpit adjustable setup so I can make it just right. I looked up the specs for a lot of valves and some are WAY different, I can tell you that much right now.

Black91n/a

One thing to add about the 929 MC, be sure to get the banjo fitting that goes on the front port of the MC. It may be very difficult to source the correct parts needed to make the proper connection without it.

clokker

iTrader: (2)

What kind of banjo is it, a double, perchance?
Mitsubishi Monteros use a sweet double banjo if you need one.

Jeez, I know way too much about obscure brake hardware now.

wrankin

A couple comments here -

One item that was not mentioned that affects brake bias is the weight and location (height) of the center of mass of the car. That will affect the weight transfer from the rear to the front and thus the brake bias.

Size and type of tire will also impact this. In fact our actual braking distance is pretty much governed by the tires, rather than the size and type of brake system (but the bias does come into play here). If you can can lock up your tires, then your callipers and rotors are not your limiting factor in stopping.

In racing you are attempting to use every single ounce of traction you have without locking up the tires. This is called Threshold Braking. Once a tire locks up you lose traction on that tire. If the rears lock up first, the back end loses grip and will try and pass the front end going into the turn, which is a Very Bad Thing.

What does it feel like? Like the back end is completely loose. Not fun.

You want to adjust the bias so that the fronts lock up just a hair before the rears. That way the front will lose grip first and the chance of a spin is reduced.

So many things affect what the correct rear bias should be set to. The grip of the tires under braking, the weight of the car, wheelbase, the weather (you need more rear bias in the rain since you don't brake as hard). It's no surprise that Mazda tweaked the bias setting for the Miata as they introduced and developed the models.

-b

Black91n/a

Just a single banjo that has a 10mm female flare on the other end, so that you can hook your brake line to it. There's a picture here: http://robrobinette.com/mastercylinder929.htm

The FC swap will be similiar, but will require the use of a tee to get the two front lines to hook up to the single front port on the 929 MC (at least for a non-ABS FC and an ABS 929 MC).

clokker

iTrader: (2)

Update:
Brakes have been working fine.
Even had to make a semi"panic" stop the other day when the moron in front of me tailended the car in front of him...my car stopped with no drama or weird handling...road was wet, too.

However...it's been in the back of my mind to try the big 1 1/16" MC again now that I have the larger, double diaphragm booster.
That MC had the best, most positive "pedal feel" but needed a lot of effort with my original booster, something I thought should be a non-issue now.

Black91n/a would be happy as well since I'd have to reinstall the stock Mazda proportioning valve.

Since I had completely redone all my hardlines to fit the last install (oh, optimism!), this "reconversion" wasn't as simple as it should have been and I had to cobble it together figuring that I'd tart it up if I decided to keep it.

For those not keeping up, the "new" system has the 9 1/2" Integra double-diaphragm booster, the stock RX7 proportioning valve, a Subaru 1 1/16" master cylinder and freshly rebuilt calipers with braided steel lines and Hawk HPS pads on all four corners.

Based on my past results I was expecting a short throw, firm pedal that didn't require undue force to operate.

That's not what I got.
Car stops fine but the pedal travel is longer than I remember from the first time I had this MC in and effort is not as linear as I expected.

I'm thinking that I may have miscalculated the booster pushrod to MC piston distance and there is slop in there that shouldn't be.
This Integra booster does not have an adjustable pushrod and I'm having to make spacers that slip over it and extend it's length to mate to the recessed piston on the MC.
I thought I was careful in my calculations but it feels like the pedal travels a ways before braking actually starts, which is exactly what I'd expect if the pushrod is too short.

This pushrod length is a pretty finicky adjustment- 10 or 20 thousandths can make a lot of difference (brakes will drag when the rod is too long) and even though I've done it before, I think I screwed it up this time.
Fortunately I used braided lines for the connections to the master cylinder, so it can be slipped off the booster studs without undoing anything (I am really getting tired of bleeding brakes!).
This means I can slip on a new rod spacer without much trouble and see what happens.
That's the plan for today.

Frankly, after all the time I've put into this project (it;s now been over a month), I look back longingly at the twin MC/bias bar set up I fabbed up for my 240Z.
No booster, no proportioning valve, much simpler plumbing.

Knowing me, no matter the outcome of today's labor, I'll probably explore that option next.

*sigh*

1SWEET7

iTrader: (1)

Thanks for being the guinea pig for this stuff. Tons of great info.

clokker

iTrader: (2)

You're welcome, although I must admit, "taking one for the team" was not the original plan.

I pulled the MC (again!) and recalculated the pushrod extender length...turns out I was spot on the first time.
Since I was unhappy with the results and it's so easy to swap, I decided to make a new, longer one anyway. I figured that the worst that could happen was the brakes dragging for a little bit.
My driveway has some angle to it and I decided that if she'd "free roll" in neutral I'd risk a longer ride.

The original measurements lead to a pushrod that was .625" with a .400 recess to slip over the Honda rod...so I was extending by .225" to mate with the MC piston.
I made a new piece (with the same recess) that was .685 long and figured I could whittle it down if need be.

Doesn't seem to be necessary.
Even with this "preload" on the piston, the brakes don't drag...I must admit I'm somewhat at a loss for an explanation.
Pedal travel is back to what I expected and the whole "feel" is quite good.

I took her out for a short (20 mile) drive to get some heat into the system and everything stayed kosher- no drag, no loss of pedal, etc. Didn't have occasion to make a really hard stop but normal type braking is the best it's been so far.

So, I guess I'd call it a success.

Now to start calculating for the twin MC setup...