Glazedham42

iTrader: (4)

Alright, I've been doing my homework on this subject so I'm hoping that we can uncover some new ground here. However, I will need some technical help from you more experienced members. I am switching my 1985 GS to a full GSL-SE suspension. I also understand that I will need to change the brake proportioning valve when I change to the GSL-SE brakes, otherwise I will probably see premature lockup of the rear brakes if I continue to use the GS proportioning valve.

So here is what we know so far about the 1984-1985 cars:
-The S and GS used the same proportioning valve as they both had drum brakes (Part No: FA07-43-900)
-The GSL and GSL-SE used the same proportioning valve as they both had disc brakes (Part No: FA66-43-900)

So I managed to locate a FA66 proportioning valve off of a 1984 GSL and bought it. However, on closer inspection it is in very poor condition. It has a lot of rust and corrosion inside and looks like it has been at the bottom of the ocean for 20 years. I figured I could take it apart and rebuild it, and get it functional, but it took me an hour of soaking in Kroil just to get the thing apart. Even if I get it reassembled, I'm not sure that it will move freely. It has a lot of rust and scale buildup. So my idea is to take the important guts from the GSL valve and put them into the GS casting, assuming that will work correctly.

I'm trying to determine what parts are actually different/important between these two things and the only thing I see that is different is the spring. You can see the guts in the picture below.

The green anodized piston is from the GSL valve and the pink anodized piston is from the GS valve. I measured both of them with a dial caliper, and I don't see any differences. They black rubber spring perch is missing from the green piston because it is still stuck in the GSL valve casting. I can't get it to come out of there. It should also have one that matches the pink valve though. The springs are also the same length, but the windings go opposite directions as you can see in the picture. My thought is that the spring is the critical component inside these things, and I'm guessing that they have a different stiffness (spring constant).

So my overall thought is this: If I take the spring from the GSL proportioning valve, and install it inside the GS valve and leave everything else the same will it work like a GSL valve? I don't fully understand how these things work. So I'm hoping that someone with a little better knowledge of these in general, or an in-depth knowledge of the Rx-7 proportioning valves will know.

Also, for anyone that is wondering about how to identify these things, I found out that Mazda does stamp the part numbers on the outside of them. If you see FA66 that means it's a GSL/GSL-SE valve. If you see FA07 then you know it's a S/GS valve.

Anyone have any input or thoughts?

Siraniko

iTrader: (13)

thats not really a proportioning valve as the proportioning valve for rear brakes is located in the the master cylinder. If I'm wrong, dont be shy lol

Kinda off topic but for GS to GSL/GSL-SE rear disc brake conversion, many have recommended to remove the valve (ball) on a Non-GSL/GSL-SE master cylinder to prevent the rear disc from locking up. However, I've tried both (removal and non-removal of the valve off non-GSL master cylinder) but I didnt notice a slight difference. Again, these are my experience with SA/FB (based and GS version)/RX-2/RX-3 to rear disc brake conversion.

Glazedham42

iTrader: (4)

Ball?

Siraniko

iTrader: (13)

yup, its on the m/c. you need to drill the outlet (rear brake line) to remove the valve.

Jeff20B

iTrader: (13)

Never seen that before. Are they really those colors when they come out?

The blue car is an S model and the previous owner swapped in a disc brake rearend. I think someone changed the master at some point to a disc brake unit, but left the proportioning valve alone. It causes the pedal to go low and the rear calipers tend to be a little draggy, but not enough that you feel it while driving. You can hear the rears squeal a little in reverse. Maybe caused by some residual pressure that drums require?

I think I still have a spare master and prop set from an 84 GSL. I'd like to swap the prop valves and/or just the little colored piston things. But I don't know much about brakes.

Kentetsu

I didn't mess with any of that crap when I put the GSL rear in my GS. Never even a trace of an issue, and you know my car gets a thorough workout.



.

Glazedham42

iTrader: (4)

Cool, I know if anyone would have the rear lock up under hard braking it would definitely be your car! Love watching your YouTube videos. Watching the twin keeps me motivated to finish Gus.

So you left the proportioning valve/distribution block thing from the GS. Did you even bother switching over to a GSL/GSL-SE brake master cylinder? Or are you still using the stock GS master cylinder too? I'm thinking I need to at least change to the GSL-SE master cylinder at a minimum? Don't the GSL-SE rear brakes displace more fluid or something? For some reason I thought the GSL-SE had a beefier master cylinder to accommodate the bigger brakes in the back....

Glazedham42

iTrader: (4)

Yeah, they are really that cool anodized color when you take them out. I was quite surprised to say the least. I'm so used to every single piece of this car having that same old yellow zinc chromate finish on it that to see something anodized like this really caught me off guard.

82transam

iTrader: (18)

For what it's worth, when I switched to a GSL rear I just left the booster and prop valve from my S in there and it worked fine ( I only switched the master cylinder). Years later when I put the T2 brakes (which are much bigger than the SE's) all around I left everything else alone and it works great. The fronts lock up before the rears and it is very predictable.

If I were you I'd just leave the prop valve that's in there, in there

j9fd3s

iTrader: (3)

there is a valve in the master, but i cannot remember what its called! its not the proportioning valve though.

drum brakes generally have a little check valve in the master, so they don't release too fast, but discs don't need it, so when you swap to discs you need to pop it out. peepers got an after market master, and the valve just came out with a small screwdriver.

the proportioning valve is trickier. Mazda USUALLY has the graph in the FSM, but they didn't for the SA/FB. obviously they are different, but how much? you might have better luck in the racing section the racers will make these adjustable. we have one kicking around that has had the big bolt drilled turned into a jamb nut, so the preload is adjustable. you aren't going to notice any difference unless you do some testing, and that means finding a place to do panic stops and measure the differences

Jeff20B

iTrader: (13)

Glazedham42, I just realized you have an 84-85. They had a different pedal and master setup that leads to a firmer pedal and it reacts sooner when you push it. My GSL-SE is this way. My bro's was this way. If you compare with my 81 or Percent's 83, they've got more pedal travel before the brakes react. So now I'm not sure what year my master cylinder came from. It could be from the doner GSL where the disc brake rear came from, or could still be the stock drum brake master, although when I got the car, the bottom line fitting was loose and dripping fluid over a long time which damaged the paint on the frame rail.

Glazedham42

iTrader: (4)

Thanks for all the great input everyone. Sounds like the best bet is to put the GS prop valve back together and continue using it as normal, and switch out the master cylinder to a GSL-SE unit?

GB7

iTrader: (1)

The valve in the master cylinder is a residual pressure valve. only found in drum brake master cylinder, you can remove it from the master and then you have a disc brake master.

DreamInRotary

iTrader: (49)

I have been studying this myself, thank you for posting Ham!

It would make sense that the spring constant between the two springs in the valves would be different, allowing a different displacement of fluid over a range of pressures to ensure that the front brakes engage before the rears.

I'm swapping to an 84 GSL rear end in my 84 GS and I'm planning on swapping both proportional valve and master cylinder. But Kentetsu has some reeaallly convincing YouTube videos, as already stated, that make me consider otherwise.

What's the saying? "If it ain't broke don't fix it?"

Jeff20B

iTrader: (13)

Well you guys have 84-85 cars. So perhaps what kentetsu is saying is just fine, on 84-85 cars. But on the 83 and earlier, perhaps there are some differences. Not enough to make me go out and mess with the 81 because it ain't broke, so I'm not gonna "fix" it.

notveryhappyjack

iTrader: (4)

On my previous car 85 GS I did the same GSL rear end swap into a GS chassis, never touched anything other then the handbrake cables, just hooked it up and went, brakes were totally fine for my spirited street driving shens

gerald m

The residual pressure valve is intended for shoe brakes and keeps a tiny bit of pressure in the rear brake system so that when the brakes are applied the rear brakes actually( start )to work first keeping front wheel skid to a minimum . If the valve was not used on shoe applications the rear brakes would lag terribly causing even more front wheel lock up and less rear brake activation , Mainly due to the two different amounts of fluid need for the front compared to the rear activation , Also the disc type of braking system require less pressure to preform braking compared to the old style brake shoe system . The disc brake system only returns the pads until they are just touching the disc where as the shoe system is returned with springs as far as the brake adjuster allows , The valve also cannot work proper if the rear shoe brake system is not adjusted up to their proper position . The only thing that might happen with the disc set up in the rear of a original shoe set up is you may find the rear brakes are a tiny bit more aggressive . than the old style shoe setup was . Old school track guys always use to set their rear brakes right to the top so they would work first to help prevent front brake fade, .. I hope this makes some kind of sense Gerald m.

ray green

iTrader: (14)

On a trivial note (because I don't have a clue how any of this stuff works but I'm going to have to figure it out pretty soon to do my own GS/GSL swap) I'm guessing those brake valves (whatever they do) are different colors for safety reasons.

Because they are part of the brake system and may in fact substitute but not work correctly if switched, causing a serious braking issue, the color code is there to help assure shops don't accidentally install the wrong one (not that a color blind mechanic would notice).

Incidentally, if you were successful in transplanting the guts of the green GSL valve into the red GS valve you would frustrate this safety system and possibly cause problems for an unaware owner down the road, should you either sell the car or get so old your memory starts to fade.

Thanks for posting this up Jamie, I'll be taking notes. And I'll be looking to you Gene for some expert local advice.

gerald m

A proportional by pass is a totally different piece and is usually situated close to the master cyl. and controls the amount of fluid allowed to go to either front or rear brakes some models also have a electrical switch that activates a light on the dash telling the operator that there is a low pressure situation in either front or rear or both systems . the pictures are of a proportional by pass system and come in all shapes and sizes , some have a double system. The purpose of this valve is to control brake fluid to front and rear brakes and prevent rear brake lock up and control weight transfer braking on panic braking situations. The colors I don't think mean anything and is used to prevent corrosion on the aluminum part you will find many different colors and some different colors on the same type of application . you can think what you want but that is what these things do .. The residual valve by the way is usually situated in the master cylinder , after removing the brake lines the residual valve can be removed with a pick , with a kit there is sometimes a screw supplied to inset and tighten into the end of the valve then the valve can be removed with the screw most master cylinder kits come with the residual valve most people throw them away especially the screw because most don't know what it is for.. Gerald m.

wickdgt

iTrader: (1)

Bringing this back old thread. I did the Tii conversion brakes on my 1985 RX7. It had the GS disc brake at the rear. Now I did a 9" rear end conversion and use the GSL-SE rotors and Calipers. Up front I have the Turbo ii 4 piston calipers. I have good brakes up front but the rears I can see the rotor still looks like new and when I move the car on reverse I can hear the pad dragging. When on jack stands and I push the brake pedal the rears work fine, but when on the road I don't feel them working at all. Do I need to put on a GSL-SE master cylinder, any mods on the 85 master cylinder I need to do, or just install an aftermarket proportioning valve. Thanks for any info:

Edgar

gerald m

Brake proportioning valves .. I all honesty there are only a handful of people on this site that understand exactly how brake proportioning works nor do many understand that that there is more than one thing related to brake proportioning and not just the valve but size of master cylinder ,, size of pistons and volume they hold ,, amount of braking surface on rotors and pads , when you change one thing more can be effected how brake pressure is distributed to the front and rear now take away the understanding that replacing, modifying, or just plain fiddling with your proportioning valve can do more harm than good. While it is not quite black magic, there are plenty of opportunities to throw the system into disarray without even knowing it. Hope this wright up will help people to understand how the darn things work PROPERLY . Sorry the graphs would not load .. Gerald m.

Consequently, we offer this quick look into these devices and their mechanical siblings. A small amount of knowledge can yield surprising benefits, not the least of which is avoiding nasty surprises.
Rear Brake Pressure Control

In general, there are three ways to deal with rear brake pressure: leave it alone, make it proportional to the front brake pressure, or control it in a way that combines these two strategies.
Strategy 1: Leave it Alone

If no device were used to modify the rear brake pressure, then as shown in Figure A, the front brake pressure and rear brake pressure would always be equal. Naturally, this is the easiest way to deal with the issue, but in order to prevent rear bias under all conditions, the rear brake itself would need to be absolutely tiny.



As you can imagine, this is not a realistic solution and is not found in the real world.

Strategy 2: True Proportioning

True proportioning, as shown in Figure B, would result in rear brake pressures being linearly proportional to front brake pressures under all conditions. Ironic as it may seem, “proportioning valves” do not provide this kind of control, as they are not the purely proportional devices their name would imply.

This type of pressure regulation is certainly possible to achieve, but it typically requires tandem master cylinders and an adjustable reaction linkage, the same setup found on nearly every purpose-built racing car today.


On vehicles so equipped, the proportioning ratio is achieved through a combination of master cylinder piston diameter selection and the adjustment of a mechanical reaction linkage that connects the two master cylinders. Also known as a bias bar, the linkage geometry determines the front-to-rear force distribution coming from the brake pedal assembly. The significant benefit to this set-up is that a bias bar can be designed in such a way that the driver can adjust the front-to-rear proportioning ratio while at speed.

In the example shown below, an adjustment of the bias bar of 0.010 inches results in an increase in front master input cylinder force from 125lb to 133lb. At the same time, the rear master cylinder input force drops from 125lb to 117lb.

Real-time driver control over bias makes adjustments for changing track conditions or fuel load practically effortless. The complexity of this design makes it highly impractical for street use, but on track it simply can not be beat for ease of adjustment.

Combining Strategies – The Misnamed Proportioning Valve

Conventional proportioning valves should really be referred to as “braking force regulators” or “brake pressure regulating valves.” While their name might imply true proportional control, in reality they provide a combination of the control found in Figures A and B.

Up to certain pressures, these valves allow equal pressure to both the front and rear brakes (à la Figure A). However, once a preset pressure point is reached (600 psi in the example), the rear brake pressure continues to build, but at a slower rate (or slope) than the front brake pressure. Figure C displays this for us quite clearly.


Looking at the diagrams, one can see that it is possible to design both a Type B system and a Type C system that ultimately give the same brake balance at the point of maximum deceleration. (Note that Figures B and C both generate 950 psi of rear brake-line pressure when the front brake-line pressure is at 2000 psi.)

However, one can also see that Type C systems—those that use proportioning valves—can bring us closer to optimum balance at lower deceleration levels. This benefit is relatively meaningless in a racing application, as the vehicle is always operating at maximum decelerations, but it is of great advantage on the street.

In so many words, the proportioning valve allows us to drive around town under optimized brake-balance conditions (good for front brake-pad life) but also keeps everything in check when we need maximum braking (good for stability).

Due to their compact size and relatively low cost, these devices can be found on nearly every vehicle which requires rear brake pressure reduction to achieve optimum brake bias. Typical passenger cars and production-based race cars fall neatly into this category.

Height-Sensing Proportioning Valves

Some vehicle’s proportioning valves go one step farther, as the kneepoint on the graph can vary with the amount of weight on the rear axle. Effectively, as the rear axle weight increases, a linkage between the axle and the body is compressed. This linkage acts on a cam inside the proportioning valve which increases the preload on the proportioning valve spring. The end result is that more rear braking (bias) is allowed as weight is added to the rear axle, helping to take advantage of the increased traction now available at the rear tires. Figure D illustrates this relationship quite clearly.

So, Can One Adjust The Proportioning Valve?

Believe it or not, in nearly all cases the OEM valves are well matched to the original brake system and should not be tampered with, as there are no parts inside that are able to be modified by ambitious owners. Unfortunately, some are externally adjustable, so the temptation to tinker is right there in front of us!

One point to ponder is that because they are a mechanical device, proportioning valves must be designed as a best compromise for use under all conditions. High speed, low speed, fully loaded, and empty vehicle scenarios must all be evaluated and figured into the proportioning valve design.

Of course if you have modified your vehicle in a way that impacts front-to-rear bias you might be standing out in left field! As a refresher from our bias article, we will bring forward again the lists of modifications which can influence front-to-rear bias.

Factors that will increase front bias

Increased front rotor diameter
Increased front brake pad coefficient of friction
Increased front caliper piston diameter(s)
Decreased rear rotor diameter
Decreased rear brake pad coefficient of friction
Decreased rear caliper piston diameter(s)
Lower center of gravity (i.e. lowered vehicle)
More weight on rear axle (i.e. loaded)
Less weight on front axle
Less sticky tires (lower deceleration limit)

Factors that will increase rear bias

Increased rear rotor diameter
Increased rear brake pad coefficient of friction
Increased rear caliper piston diameter(s)
Decreased front rotor diameter
Decreased front brake pad coefficient of friction
Decreased front caliper piston diameter(s)
Higher center of gravity (i.e. raised vehicle)
Less weight on rear axle (i.e. unloaded)
More weight on front axle
More sticky tires (higher deceleration limit)

Proportioning Modifications

We could start this section by clearly stating that you should not modify your proportioning valve. But, what fun would that be? In all seriousness, making changes to the proportioning valve to effect brake bias should be left to those with the proper tools and measurement devices, but if you have tweaked your vehicle beyond recognition, this may be your only solution to restore a sense of proper bias to your braking system.

We’ll start here with three of the most basic rules regarding proportioning valve installation and selection.

1. If you have the deeply-rooted need to install your own adjustable proportioning valve, be advised that they should NEVER be installed if the factory unit is still in place. Proportioning valves in series with one another can do nasty, unpredictable things!

2. If you have the deeply-rooted need to install your own adjustable proportioning valve, be advised that they should NEVER be installed in-line to the front brakes. The effect would be to make your vehicle rear-biased before you could say “terminal oversteer.” Front brake line pressure should always be left alone – only the rear pressures should be considered for proportioning.

3. In all cases, the basic brake system balance needs to be close to optimized to start with. This is the only way that a proportioning valve can be effectively utilized. You should never assume that simply adding a proportioning valve will address all rear-bias conditions, as even the best proportioning valves must be well-matched to the target vehicle.

Proportioning Valve Selection

Selecting the correct adjustable proportioning valve for your vehicle entails not only selecting the proper point at which slope limiting begins (the kneepoint), but also selecting the proper rate at which rear brake line pressure builds after that point (the slope). Nearly every adjustable proportioning valve on the market today has an adjustable knee point (the point at which the rear brake line pressure begins to be controlled), but a fixed slope (the rate at which it builds beyond the knee point). While one parameter is adjustable, both are critical to system performance. Note that in Figure E the two curves have the same knee point, but the slopes vary greatly.


So how does one select the right kneepoint and slope? Without the test and measurement resources of a major automotive manufacturer, it’s next to impossible to say. Of course, you could trial-and-error your way into a solution that you believe to be appropriate, but without testing under all conditions of loading, speed, and road conditions there might be one operating condition just waiting to bite you.

In short, if you find yourself thinking, “I wonder how I would pick the right proportioning valve for my car?” you probably shouldn’t be changing it yourself.

Electronic Proportioning: No Tampering Allowed

As a small sidebar to the mechanical proportioning valve discussed here, there is a movement afoot to replace the proportioning valve function with the hardware performing the ABS function. While this is not yet the norm, most high-end performance cars already have this feature as standard equipment and one can predict with reasonable certainty that the trend will continue.

Based on information gathered from the four ABS wheel speed sensors, the Dynamic Rear Proportioning (DRP) or Electronic Brake force Distribution (EBD) algorithms calculate the front-to-rear slip ratio of the four tires. Then, given preset thresholds and parameters, the ABS hardware can intervene and modify the brake pressure going to the rear wheels automatically.

Because DRP and EBD are based on actual wheel slip and not on brake line pressure, this type of rear proportioning is more flexible and adaptable to modifications one might make to their vehicle. It is also less expensive, as the OEM can now remove the mechanical proportioning valve from the vehicle and replace its function with other hardware already on board.

Naturally, the OEM does not want owners fiddling with their front-to-rear proportioning, and as a result there is no way for the enthusiast to reprogram DRP or EBD to suit their desires. Of course, if the vehicle’s original front-to-rear bias is in tact in the first place, there is no need to reprogram anyway.

Plan Wisely

In summary, there is more to the proportioning valve than meets the eye. You should make every attempt to carefully plan and select your brake modifications so that you are able to retain and reap the benefits of the stock proportioning valve. In other words, pay attention to (and don’t stray too far from) the factory bias in the first place and you will be ahead of the game.

If for other reasons you are forced to scrap the stock unit and replace it with an aftermarket unit, be advised that selection and adjustment are not for the uninitiated. While there is more than one way to achieve optimum balance at the point of maximum deceleration, without the right amount of know-how you might be making compromises under partial braking conditions that were not present with the factory hardware.

Again, remember that simply adding or replacing a proportioning valve may not be enough to remedy basket-case bias scenarios. Proper planning and up-front design should ensure that the base vehicle bias is appropriate from the start, enabling the proportioning valve to be used properly as a fine-tuning device.



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wickdgt

iTrader: (1)

Good info Gerald and I see what is saying don't mess with the proportioning valave, or replace it. but still I did not get the answer, do I need to get a GSL-SE master cylinder due to it is for disc brakes.

Maybe I didn't explain my self well. The RX7 I have has stock front brake calipers, but at the rear it had drums, but I change the rear end for a GS disc brake and it braked fine. When I did the Tubo ii conversion up front and installed a 9" rear end with the GSL-SE rotors and calipers is when I notice that my rear rotors still look like they came out of the box. Will the GSL-SE master cylinder do the job? Thanks for the info you have provided.


Edgar

gerald m

Well IMO you need what ever components that are matched to you braking equipment , you cant expect the original master cyl. to produce the same pressures and volumes as the new components might need , That is where they are talking about 2 masters instead of one but that is just to much screwing around .
The residual valve in the master cylinder for sure won't be right (( it is responsible for keeping just a fraction of pressure in the front or rear system according to what you have for brakes so the master doesn't need to pump more oil than it can ,, shoe or pads ,,

The residual valve usually comes in a rebuild kit and is located in the outlets of the master cyl. (( Right where the oil comes out )) there is usually a self tapping screw in the kit you screw it into the outlet and pull the residual valve out .. sometimes when people complain about brakes being soft on the first pump and then good and solid after the second pump = most often this is air in the system sometimes however the residual valve is leaking back that little bit of oil that it is suppose to hold in line and require and extra bit of oil to complete the stroke . In your case the back brakes section of the master could be by passing the R valve and when the brakes are stroked the master only supplies enough to partially make the rear brakes work proper ..

I would be changing the master to accommodate the braking system you have now , trying to match each section of the master to what ever you have for equipment ,,,, If you have disc brakes on the rear then the master should be for the same size pistons in the calipers as a larger piston area will require a little more fluid than a smaller piston did or vise versa same as the front brakes same thing applies .. so to have things work as intended you need a master that will feed both front and rear brakes to what ever they are originally intended for ..Just because you cant turn the rear wheel with brakes applied really don't cut much ice because it would take almost no pressure to do that .. you might want to set up a pair of gauges to read front and rear pressures when brakes are applied . that will tell you quite a bit on how much oil is being supplied to both front and rear .. BTW I'm not a professional Just a old dude that has spent a lot of ]time trying to go fast and then even the harder part of trying to stop .. Me thinks with lazy rear brakes your front brakes tend to fade on high speed braking .

If all else fails there is the manual residual valve that can be set manually to what ever you want for pressure , BE CAREFUL RESIDUAL VALVES WHEN SCREWED WITH CAN BE FINICKY TO SAY THE LEAST and should never have two in the same line . I hope I haven't confused you wickegt. Happy to try to help Gerald m.

gerald m

Guess I kinda left out the proportioning valve which as someone else explained is also important . The different colors seems to me I read on this forum somewhere are designated for different applications in the factory ,, Instead of reading numbers or whatever they can tell at a glance which color is for what type of valve , don't know who supplied Mazda with brake components I thinking more than one company as most are all the plain color as someone pointed out ,,

So the color does mean something so don't be putting a blue one where a red one came from (( I think you will find that there is a tiny bit difference in lengths etc. for a different amount of liquid ??? .. IMO brake parts in general are relatively inexpensive and should be replaced with new when ever possible , most times a rebuilt master will not last long and should be replaced with new , Some people will say they want to rebuild and save the landfill , well do your self a favor and buy new then take all your old iron down to the scrap metal buyer once a year and get a couple bucks back as well as keeping the iron out of our landfills . POOR BRAKES KILL PEOPLE keep them in good shape . More than enough said .

j9fd3s

iTrader: (3)

T2 front calipers and GSL-SE rear calipers are a factory combination, Mazda uses the same rear caliper size from the GSL-SE to the FD.


Sumitomo is the default brake supplier, as they actually own the bank that owns Mazda.