I just upgraded my Master Cylinder...here's what I found

[Numbchux]

Credit where credit is due. Caboobaroo found some of this years ago. I took it a step further, 

 

 

Looks like the pattern for all XTs, EA82s, and EJs (certainly into the early 2000s) is this: Without hillholder cars had 4-ports on the master, the hillholder also functions as a splitter, so cars equipped with one only have 3 ports on the master. Similarly the ABS pump also functions as a splitter for both channels, as such, those masters have 2 ports.

 

Looks like XT6s had 15/16" bore masters, EA82s had 7/8" (I didn't look into this too closely, as it doesn't apply to me at all, there may be more to it), non-ABS EJs had 1", ABS EJ cars and all SVXs had 1 1/16"

 

You may notice in my list above, there's a crossover. Non-ABS (AFAIK, FWD only) SVXs had a 1 1/16" bore master with 4 ports. FYI, the official Subaru electronic catalog doesn't show FWD SVXs as being an option for '92-'93, but it does for a '94-'97, and many aftermarket catalogs followed suit.

 

 

Having an auto trans, my '89 XT6 does not have a hill holder, and therefore has a 4-port 15/16" master.

 

I suspect over the 5ish years of basically serving as nothing more than a parts car, I got air in the master, and it needed bench bleeding. I decided if I was going to the trouble, it was going to get an upgrade while I was at it.

 

As far as I can find, only Cardone makes a remanufactured masters for a FWD SVX. Part # 11-3849. It's either that or used (OE rebuild kits are discontinued...). Luckily those Cardone units are not terribly expensive.

 

 

As I mentioned, my old system was not working as intended, but still, after the swap, this is the most positive feeling EA82/XT brake pedal I've ever owned....despite the fact that this car has significantly more caliper volume than a stock EA82 (T-leg front 2-pot calipers, 200SX rears which have larger pistons than stock Subaru). I used the XT6 reservoir in the SVX master, the tab for the lock down screw didn't line up quite right, but it's still a tight fit in the grommets, so I'm not worried.

 

It would also be super easy to use a T fitting or 2 to adapt a 2 port EJ master to a 3- or 4-port EA82/XT chassis.

[TomRhere]

Thanks for the info.

 

The M/C is the only brake related part I haven't changed on my '88 Wagon, and I believe it needs a new one. Brakes work good, but I think they should be better than they are.

[maozebong]

ah, kudos to you and caboobaroo for doing the legwork on this... its always helpful if youre on the road and have to go to a random parts house for parts. its hard enough to get stuff for ea82 wagons in part houses these days, knowing that one off an early legacy or svx will not only bolt up, but improve the braking is a gem of some knowledge. 

[Uberoo]

For better braking feel the legacy brake booster will bolt on,but the EA MC needs to be modified slightly to fit. The MC bolt pattern is slightly different between the two, so the EA MC needs to have its mounting holes ovaled out.

[Numbchux]

but the EA MC needs to be modified slightly to fit. The MC bolt pattern is slightly different between the two, so the EA MC needs to have its mounting holes ovaled out.

SVX master bolted right up to my XT6 booster. 4-cyl XT and EA82 share a part number for Masters, so I doubt EA82s are different. Maybe EA81s or earlier, though.

[Caboobaroo]

I picked up the non ABS FWD SVX master cylinder as my hill holder is leaking and I was planning on deleting it. The one I picked up is a Centric part and came with the resevoir. Not having a garage for all my stuff, I have yet to dig it out and swap it over.

[Numbchux]

Oh yea, I see that now. 13047019. Only says '94-'95. Looks like it's a brand-new unit, with reservoir, but is $100 more than the cardone reman one without the res.

[Turbone]

I bought a mc for a 92 Leg SS around 3yrs ago. The part isnt even in the Rockauto system any more.

I cant recall if it was ABS or not, but being 92 it may not have been.

I dont recall if I plugged a port or what.

CRS and being old etc

[D3F0]

I am using the AWD 1997 Subaru SVX ABS master cylinder on my RX. Going to T the ends to the front and use the the hill holder to split the rear. Also i am going to route in a hydraulic E brake for the rear. Will make a little thread eventually on it.  Using a Wilwood compact mater cylinder for the E brake. =)

[turbosubarubrat]

I'm eventually going to put a legacy brake booster and master cylinder in my ea81 hatch along with a proportioning valve. I was looking at my parts car shell test fitting the non abs brake booster it looks like if i hit the strut tower a few times it will clear

Edited January 20, 2016 by turbosubarubrat

[D3F0]

Good info so i Just swapped a 1997 Subaru SVX master cylinder into mine. 

Those are the parts I used. 

Stock Line and hill holder all suck

Got my old flare tool out

Then made all kinds of flares haha

Also I am adding a hydraulic e brake  

Ebay special with Willwood master cylinder upgrade.

Got all the lines hooked up 

Kind of hard to see but this is how I did it

 

In the pic above the line with white tape goes to the hill holder. That controls the front right and back left wheels. I changed it to control the rears.

Red marked line goes to front left(driver side) and the other blue marked line to the back rear. 

In the above pic the line goes from the back port of the master cylinder into the E brake then back into the hilholder which has been re plumed to run just the rears. 

This swap sucked and was no fun I will update once I actually drive this car next month when it is actually done. Still doing rust repair.

 

 

 

[Numbchux]

I feel the need to say, at this point. Subaru puts the LF and RR on one circuit, and RF and LR on another so that if you have a hydraulic failure on one circuit, you still have balanced braking force on the other.

 

With that said, I have replumbed several cars the way you describe (it's the only way to do a hydraulic handbrake), and it works just fine. Just know that if you have a failure, you will only have front or rear brakes.

[D3F0]

Yes I am aware that is why I am redoing 90% of my lines in nickel copper. Then I am even building shields for them out of metal to protect them from the abuse this car is going to take. 

Edited January 22, 2016 by D3F0

[SubieBrat]

Just curious, could I get a legacy MC on an ea81 without changing the booster?

[D3F0]

Yes I believe so they all bolt on to the booster with 2 bolts. You could also swap the booster and  the master cylinder over that is what I would do so you get better pedal feel. 

[Numbchux]

Just curious, could I get a legacy MC on an ea81 without changing the booster?

 

I assume that Uberoo was referring to an EA81 car with this post, but in typical fashion, it's pretty unclear what he's working on and how it needed to be modified.

 

For better braking feel the legacy brake booster will bolt on,but the EA MC needs to be modified slightly to fit. The MC bolt pattern is slightly different between the two, so the EA MC needs to have its mounting holes ovaled out.

 

But it sounds to me like the EA82/EJ 2-bolt pattern between the master cylinder and the booster is slightly different from the EA81, and so the EJ master would need to be modified slightly, but does still work.

[robm]

I am not sure why you regard a larger diameter master cylinder as an "upgrade"? 

 

The new MC will not provide the same amount of force at the wheel cylinders as the original.  People have commented above that the pedal seems "firmer".

 

Can you still lock all 4 wheels on dry pavement with this set-up?  Can your elderly mother still lock all 4 wheels? 

 

 

[Caboobaroo]

The master cylinder is strictly an upgrade for cars with calipers that are larger then stock. Going from a single piston caliper and drum brakes to twin piston front calipers and single piston rear calipers, you need the larger master cylinder to push the proper amount of fluid. If you dont, you have a very low pedal before the brakes engage. This can also take out the seal in the original master cylinder as its now pushing the seal past the wear points it has created over time.

 

My XT6 has a stock 15/16" master cylinder bore but my pedal is a bit lower now with 2005 WRX brakes front and rear compared to the stock calipers. I bought the SVX master cylinder in preperation for STI Brembos calipers when I get around to it.

[Numbchux]

I am not sure why you regard a larger diameter master cylinder as an "upgrade"? 

 

The new MC will not provide the same amount of force at the wheel cylinders as the original.  People have commented above that the pedal seems "firmer".

 

Can you still lock all 4 wheels on dry pavement with this set-up?  Can your elderly mother still lock all 4 wheels? 

 

The primary reason to do this upgrade, is to regain some of the leverage lost by upgrading calipers. But ultimately it takes a pretty significant change to make it genuinely dangerous. And it's almost impossible to describe it.

 

Food for thought, it's extremely common practice on stage rally cars to completely remove the brake booster (as the constant modulation of both brakes and throttle simultaneously that is common in rally technique will use up the vacuum in the booster, and give very inconsistent brake force), and it's still more than possible to make an emergency stop for most people (no, your elderly mother probably can't, but she won't be able to get in over the roll cage, either).

 

 

 

Some math for you. A stock XT6 has about 5992 square mm of total Caliper piston area (54mm front pistons, and 30mm rear, 2 of each), and 452 square mm of Master Cylinder area. Which means, assuming the same volume of fluid passed through the system, the piston travel ratio is about 13:1 (13mm of travel at the Master, moves the caliper pistons 1mm. Note, this does not take into account the mechanical advantage of the pedal).

 

My XT6 has dual-piston, ver. 1 WRX front calipers, and Nissan 200SX rears, leaving me with a total area of 8076 square mm (4 front pistons at 43mm, and 2 rears at 38). Before I swapped the Master Cylinder, left me with a ratio of over 17:1, not to mention the air in the system. 

 

And the 1 1/16 Master is 572 square mm, that makes a ratio of 14:1. Which actually means I still have less leverage than a stock car.

 

If you were to do this Master Cylinder upgrade, with stock XT6 calipers (5992/572), you'd have a ratio of closer to 10.5:1.

 

 

of course, none of this takes into account the fact that I also went from 260mm rotors to 276mm, or that dual piston calipers apply the force more efficiently to the pad than single, etc. etc.

 

 

Ultimately, the change in the amount of force required on the pedal is very reasonable, but the change in how far your foot has to move to do the same job is considerable. This reduces your reaction time to apply the brakes, which is where the advantage comes in.

Edited March 23, 2016 by Numbchux

[D3F0]

I really love the math up there! I ran into this exact question on an engineering test lately. Its all about the numbers! 

Pressure = Force/ Area =)

[robm]

It is good to know you guys have thought about this, and are not just going out with a "bigger is better" attitude. With larger brake cylinders, the larger MC is an improvement.  I am not quite sure I agree with your numbers?  For instance, 1-1/16" = 27 mm dia. which has an area of pi*27*27/4 = 572 mm2.  Also, that is a dual piston - which makes a difference.  And dual diagonal, vs. setting them up as front/rear makes a difference too.  I can see why proportioning valves get useful.  I am not sure what you have done with your numbers, but as long as you remembered to square the diameter to get an area the proportions should be correct and everything should come out in the wash.

 

I haven't been lucky enough to drive a car without power brakes since my last 510 bit the dust/rust.  An advantage to servo-less brakes is faster response, even if a bit more force is needed.  ABS not required if you can tap the brake pedal at 3 times per second, and the brakes actually come on and off.    Worked great in the snow, and I bet it works on the rally circuit too.  But I find modern brakes seem to be set up to need the additional force from the servo, so they get pretty hard to use without.  In other words, the MC is too large for comfortable braking without it.  The Datsun had a 3/4" MC.  I can't find any specs on brake caliper and cylinder area, and I just gave away all my 510 books to someone who could use them.  (Never fails, you never need something till you get rid of it!)  It would be interesting to compare the 2 systems.

Edited March 23, 2016 by robm

[Numbchux]

DOH. Brain fart. I did the formula for Circumference (Pi*D)....not Area

 

It doesn't completely throw the comparison off, since I did it all the same way, but I redid it correctly and edited my post.

[robm]

Those numbers line up better with my calculations.

 

But doesn't the dual piston/dual diagonal brake circuit also come into play, reducing the mechanical advantage?  The MC is dual piston, and each piston drives one front and one rear brake.   So stock advantage is about 6.73:1, and the modified MC will provide about 8.23:1?  Or is there something else going on here?  And actually, the larger number is more mechanical advantage,  not less.  The pedal travels further, but takes less force to provide the same clamping force the wheel.  But then the rest of the geometry comes in, like rotor diameter etc.

 

Also, I had a look at MC's on Rockauto, just to see what was going on.  Why are these MC's 3 port?  What does the 3rd port do?  Now I am interested, I might as well learn all I can about these things. 

 

Thanks for the education.

[Numbchux]

Nope, not dual piston like a brake caliper, both EA82 and EJs have dual-channel Master Cylinder which has a piston between the front and back half of the cylinder that allows some brake force to be sent to one channel, even if a brake line blows on the other channel. The only change is the bore diameter.

 

 

 

The simplest brake systems (No Hill holder, no ABS) have 4 ports on the master cylinder, one for each wheel. The hill holder acts as a splitter for one of those circuits, so 3 port master, one channel has one line going to the hill holder, and then 2 to the 2 wheels on that channel. The ABS pump acts as a splitter for both channels, 2 port master, 2 lines to the ABS pump, and 4 lines from there.

 

These Masters could be mixed and matched with a splitters/plugs from your local auto parts store. It seems counter-intuitive to have a bottleneck like that, but that's how the stock system works on those cars....

Edited March 24, 2016 by Numbchux

[D3F0]

Those numbers line up better with my calculations.

 

But doesn't the dual piston/dual diagonal brake circuit also come into play, reducing the mechanical advantage?  The MC is dual piston, and each piston drives one front and one rear brake.   So stock advantage is about 6.73:1, and the modified MC will provide about 8.23:1?  Or is there something else going on here?  And actually, the larger number is more mechanical advantage,  not less.  The pedal travels further, but takes less force to provide the same clamping force the wheel.  But then the rest of the geometry comes in, like rotor diameter etc.

 

Also, I had a look at MC's on Rockauto, just to see what was going on.  Why are these MC's 3 port?  What does the 3rd port do?  Now I am interested, I might as well learn all I can about these things. 

 

Thanks for the education.

 

When you say as the pedal travels further but takes less force to provide the same clamping force to the wheel, are you talking about the actual force to press the brake pedal? If so you are wrong it will take more force with a stock brake system to push the pedal to bring a car to a stop. I believe it will travel less overall but take more force. A lot of people have that backwards. +1 with the  hill holder or abs pumps being Ts in the brake system, 1 line will go into them and two will go out.