chrismore

Here is my setup on my FD autocross racer.

* Chase Bays Dual Piston Manual Brake master with adjustable bias
* I am running the OEM ABS unit which seems to work good enough
* I removed the OEM proportioning valve on the OEM ABS unit since I will be adjusting it via the Chase Bays unit
* I ran the front brake line from the master into the front input of the ABS unit
* Ran the rear brake line into the rear input of the ABS unit

I just installed two brake pressure sensors connects to my ECU so I can check the brake bias.

What I noticed is that regardless of the brake bias setting on the master, I am always 48% front brake bias. That doesn't make any sense.

Is my setup completely wrong?

I am thinking that maybe my issue is that I deleted the OEM prop valve and I am going directly into the ABS unit. It seemed sane with deleting it, but maybe I don't fully know how the OEM ABS pump is plumbed.

Check out the photo here of my setup.

chrismore

(blanking out this message as it was incorrect)

chrismore

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chrismore

This is how I have the Front and Rear plumbed up to my ABS unit, which I now think it opposite. But, that doesn't explain why it seems like the front and rear systems are not interconnected. If I open the bleeder on the front right caliper, I should still have rear brake pressure. I don't. The rear goes down at the same rate as the front.

Maybe what I am trying to do is not possible even if I do swap the lines.

chrismore

The reason I connected the master cylinder lines on those sides is because I thought the FR FL & R on top of the ABS OUT lines would be on the same side as the input.

See here on top:

chrismore

More info: Apparently the markings on the inputs for the ABS are:

P = Primary
S = secondary

I assume Primary = Front and Secondary = Rear.

If that is true, I have it opposite. I have the front plugged into Secondary. I only just found the S & P markings as I really went off of the sides on top of the valve, which appears to be wrong.

I will confirm and report back.

chrismore

(blanking out message as it is not relevant anymore)

chrismore

Update: I have confirmed that I do not have the ABS connected in the opposite direction. I capped off the front AN lines and I had a helper press on the brake pedal and confirmed that the rear brakes had pressure, but not the front. I confirmed the opposite. Also during these two tests, the brake pressure sensors were reading only on the side that wasn't capped off. Thus, the ABS unit is not feeding back into the other sensor and the front and rear are two discrete systems. Phew.

ABS inputs:

S = Front brakes
P = Rear brakes

I thought maybe I had the ABS hooked up opposite, but it all checks out fine.

So... that leaves only one potential issue. The Chase Bays dual master. Maybe there is a problem with the master and/or the bias valve. The valve all the way in or all the way out reads the exact same bias: 48% front, 52% rear. The dual piston is supposed to be separate so I wonder if there is a bypass issue and all of the pressure is flowing together across the front and rear balancing the differential leading to the same bias regardless of the ****.

I am emailing Chase Bays

billyboy

I thought the whole point of that set-up (and common with similar systems), the adjustment of the rear bias was entirely via their adjustable proportioning valve and the front brakes plumbed directly off the master. With the ABS still there, it would seem to be working at cross purposes with their system I would have thought......do they actually recommend connection to the pump?

TeamRX8

iTrader: (2)

first, I would also never recommend flex hoses between the MC and ABS module for braking, especially for autox. That’s guaranteed to kill feel and response. Even though they’re new; hard, yet easy to plumb, cunifer lines are preferred.

edit: this was before I realized it’s suppose to be a manual non-ABS system. Flex hoses may be ok for manual brakes. My comment above applies to a pulsing ABS system.

second, go back to your opening post, it’s the dual-piston manual brakes setup. The key word being “manual”. Which I believe also eliminates the brake booster canister? This kit is designed to eliminate the ABS module with the bias valve on the rear brake circuit for that purpose. In other words, you’re giving up ABS with this system.

Which if I’m reading it correctly, the lines have to be purchased separately. It seems to me that you maybe either have the wrong brake lines, or if it’s designed to go through the abs module then that needs to be unplugged or have the fuse pulled maybe? Honestly, it’s not clear looking at it on the website. They have videos though

here is the generic install vid that applies to the FD even though the vehicle is a Miata


and here a specific vid, except for the RHD FD; there’s not an ABS module in the vid above or in this system, it ties directly to the lines going to the calipers.



I’d suggest you give them a call to determine what you may have vs. what you may need.
.

chrismore

Very good questions and it is very possible that what I am trying to do is just not possible with this setup.

>first, I would also never recommend flex hoses between the MC and ABS module for braking, especially for autox. That’s guaranteed to kill feel and response. Even though they’re new; hard, yet easy to plumb, cunifer lines are preferred.

Yes, I would convert to hard lines only when I have my final setup. I don't want to do it until I know this is the path.

>second, go back to your opening post, it’s the dual-piston manual brakes setup. The key word being “manual”. Which I believe also eliminates the brake booster canister? This kit is designed to eliminate the ABS module with the bias valve on the rear brake circuit for that purpose. In other words, you’re giving up ABS with this system.

Yes, their dual piston manual brakes setup does eliminate the ABS, but it isn't required. You order the ABS delete kit separately. I did not. I just got shorter lines and instead of running them to the calipers, I ran them to the ABS pump. I asked them about this and they didn't say it wouldn't work, but they have never tried it.

They said the reason they normally delete the ABS is:

1) More simple system
2) Lighter
3) Most people want to delete the ABS

From talking to other autocross FDs at the national level, they kept their ABS unit or at least added a different ABS unit. I can't find anyone who has done my exact setup. It should be possible to do manual brakes and ABS. I mean, race cars that have manual brakes and ABS are a thing. Maybe it is our OEM ABS is just possible.

>Which if I’m reading it correctly, the lines have to be purchased separately. It seems to me that you maybe either have the wrong brake lines, or if it’s designed to go through the abs module then that needs to be unplugged or have the fuse pulled maybe? Honestly, it’s not clear looking at it on the website. They have videos though

Correct. You order the flexible hoses separately. I sent them back once I confirmed my ABS was working. I can feel it clicking away under my feet when I threshold brake. So, I know the system is working, but the bias seems to be the problem. Especially now that I added data, it confirmed what my butt was feeling.

>if it’s designed to go through the abs module then that needs to be unplugged or have the fuse pulled maybe? Honestly, it’s not clear looking at it on the website. They have videos though

The chase bays manual brakes are meant to plug right into the calipers. I told them what I was trying to do, but they didn't say "that will never work" it was more "we haven't tried that". I will see what they say about my latest email where I now have data.

TeamRX8

iTrader: (2)

-incorrect info/deleted-

chrismore

Maybe they didn't think it through. Initially I was going to ABS delete, but I got the ABS working, so I returned their longer lines. They didn't confirm it was going to work, but just that it wasn't tested by them.

Assuming that the front end rear are independent circuits in ABS pump and that I have the OEM proportioning valve deleted, do you know physically how the ABS pump is overriding my bias setting when I'm sitting in the car not driving? The car isn't even moving, so the pump isn't doing anything at all.

I'm not saying you are wrong, but I'm trying to understand how the pump could be doing this.

Why doesn't this happen with the OEM proportioning valve that has a fixed bias and is plumbed into ABS pump just like I'm doing with the Chase Bays master? How would a dumb ABS pump even know what is upstream of the hydraulic inputs?

billyboy

Cup cars did with M4/5 ABS 4 channel - probably worthwhile keeping an eye out for a frequently destroyed one of those, rather than try and make a silk purse out of a sow's ear, 30 year old system and poor mans dual master set-up.

As I see it, short of winding it in and entirely cutting off fluid to the rear circuit, that proportioning valve will have very limited value before the pump.

It's a crime against nature, as one wag would put it - and really a waste, I'm sure Chase Bay just went flex line for end user simplicity. A very fast, non crazy aero circuit FD here, ran braid to and from the ABS just for keeping appearance consistent with the rest of the engine bay and it seemed to work pretty ok. Short of being in the top percentile, most drivers would probably be hard pressed to tell the difference between that and hardline.

jkstill

iTrader: (11)

Andy Mckee's XP RX-7 has manual brakes plus ABS. ABS has been relocated to behind the driver's seat last time I saw it.

My autocross FD has the same Chase Bays dual MC setup. My FD does not have ABS however.

I have found in my experience that FD ABS. sticky tires do not mix well. It is 3 channel ABS, and more than once sent me off course when the rear end got a little lively and the ABS went into ice mode.

No ABS, no Brake Booster - it absolutely works for me.

If a reliable 4 channel ABS were to be installed, that would also be nice. Some folks have used tge RX8 ABS for that reason.

chrismore

Let me ask Andy because I ran this by him when I went down this path.

chrismore

Agree that I would probably better off with no ABS than an old 3-channel ABS. I am about to go that path, but let me talk to Andy as he helped me during this build.

As for sticky tires, I have 315 fronts and 335 rear Hoosiers.

chrismore

Ok, folks.... here are the answers.

1) Yes, you can have manual brakes AND ABS

2) Yes, you can run a prop valve before the bias, but having it completely open is probably best for max rear bias

3) Yes, the OEM FD ABS is sufficient enough for sticky tires

4) Yes, the OEM FD ABS is sufficient to win nationals at autocrossing

How do I know this?

I just asked Andy McKee. He has been running this setup for 10 years now and has won plenty of national titles in his FD. He has two brake lines that go directly from this manual master brakes into the OEM ABS pump exactly how I have it. He even has a prop valve connected to the rear lines BEFORE the ABS pump, just as I do. He also runs full racing slicks as I do and it has not been a problem.

Given that my bias **** is doing nothing at the moment and my pressure sensors are before the ABS, it is still possible I am having some issue with the chase bays master. I am going to try just capping off the lines before going into the ABS and test. That would eliminate everything except the Chase Bays unit. If the pressure still does not change, I could have a master cylinder or bias valve issue.

chrismore

I have narrowed down the problem and I believe it is either:

a) the Chase Bays master
b) The bias **** connected to the master

I eliminated the ABS unit all together and capped off the lines after the sensors, but before the ABS. This would simulate if the master was connected directly to the calipers and bypassing the ABS. I then turned on the ECU and measured the brake bias with the prop **** all in or all out. There should be a difference if it was working. No difference, 49% front brake bias regardless if the **** is in or out. Something is wrong with the master or bias valve. I even swapped the sensors and still no difference.

See photo below of how I capped off the lines. I basically just created a closed system where the only variables are related to the Chase Bays unit.

TeamRX8

iTrader: (2)

my most sincere apology then, and I edit-deleted what was still possible

I never knew what Andy had on his, haven’t seen him in over 10 years at least. but more like 15. If he said so, then it must be. I wish you would have mentioned it sooner, but accept that I must be in the wrong.
.

chrismore

Honestly, I didn't know until I asked him a few hours ago. When you first responded, that was before I talked to Andy again. As soon as I talked to him to confirm his setup, I posted back here again.

I just emailed Chase Bays that I think it is their master cylinder as I completely isolated it from everything else and the problem still exists.

Thank you!

chrismore

While we just learned here that Andy is using a very similar setup, we could probably deduce that my setup should work by analyzing the system.

This is the logic I used when I first built this system using manual brakes and the OEM ABS system.

Facts:

1. Let's think about the hydraulic brake light as an electronic communication cable. The only "data" that the line is communicating is how much pressure is being applied to the fluid. Regardless if the master cylinder is boosted by engine vacuum or not (manual), the information that is being communicated via the brake line is the same. It is just pressure.
2. The ABS unit has no idea what is upstream of the hydraulic lines. Boosted, manual, or an airline connected, the only "information" being sent down the line pressure.
3. The OEM ABS unit had a proportioning valve attached to the outside of the ABS between the master cylinder and the ABS unit and was reducing the pressure to the rear brakes

With these facts, I then decided the following setup should technically work.

• Switching from a manual boosted master to a manual master with a different pedal connection to increase the leverage
• Removing the OEM proportioning valve and replacing it with one with a **** should give me more flexibility than a fixed ratio
• Installing the proportioning valve between the ABS and the master is the same setup as OEM
• Installing brake pressure sensors just before the ABS pump to measure the pressure ratio between front and rear to aid with chassis setup

There are three reasons why I switched to manual master and retaining the ABS is:

1. I am left foot braker now and more pedal effort helps with retaining the brain
2. With a manual master cylinder, I don't have to worry about the high boost levels and on/off throttle situations impacting pedal feel
3. ABS will help when I am racing in the rain, which will surely happen at nationals

j9fd3s

iTrader: (3)

this one might not be relevant, but ive rebuilt a couple of FC ABS pumps, and its a really simple device. i don't see why it wouldn't work.

each circuit of the ABS pump is the same. there is a passage with a solenoid on it, and that solenoid opens a chamber with a spring in it. basically when you pressurize the passage by stepping on the brake pedal, it just goes right to the caliper. when the ABS turns on, it cycles the solenoid which then lowers the pressure. if this sounds kind of like a fuel rail and injector, you're conceptually in the ballpark. the spring in the chamber (and there is a motor), lets the system add fluid back in, otherwise when the ABS ran the pedal would just go to the floor.

and that is it. the Rx7 used a 3 channel system, so its got 3 passages, 3 solenoids, etc. there is a solenoid for each front wheel, and then one for the rear. a 4 channel would give each rear wheel a channel.
the controller basically is just counting teeth on the wheel speed sensors, and then when the brake switch is on, it'll be active.

so in summary, the hardware is super simple, its basic and almost crude. if there is any magic its the control box, but most of the time its just counting teeth and looking for a wheel that is different

TeamRX8

iTrader: (2)

curiosity killed the nosey cat; any update?
.

TwinCharged RX7

iTrader: (14)

This might not be exactly the same, but I believe it's the same in concept. I've been doing a lot of research on the MK60 system. For several actual racers (including some really nice C5 vette race cars by privateers), they use the a proportioning valve if a race car. Less relevant on a street car. They use it because for things like trail braking, dialing in the bias is helpful, because the ABS is not engaging. But when standing on the brakes hard in a braking zone, the ABS does its own pressure adjustment to obtain the fastest possible deceleration and essentially makes it seem like the proportioning valve doesn't exist.