Dual Piston Front Brakes = Change in Bias on an ABS Car?

[2JZ_MA70]

The abs and non-abs systems do have external proportioning valve. It is siting on the left strut tower in the front. Its normaly painted blue. Wilwood has a adjustable proportioning valve you may want to try that... That would limit the pressure in the front brakes...
But the fact is that you need rear brakes to match the fronts to take the full advantage of the kit...

JDUB what you are describing is abs operation but it only controls wheel lockup not brake bias. Even if his ABS was workign it would kick on on every stop.

I can feel the love on this forum... they guy has a problem and is looking for a solution and you guys are jumping on him.

 

[2JZ_MA70]

No I dont think you are geting the whole picture cause this ABS solenoids don't do anything untill the ABS system sees wheel lockup. The presure simply passes trough the ABS solenoid. That is in case the system fails you still have brakes... The MK3 has a very simple abs system and it doesnt control brake pressure (its simply diverts and relieves pressure from the caliper).
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=BR&P=48
here is the system diagram...
The system is no different than Car with no ABS with the addition of hydraulic unit and computer to control it few sensors totell the computer what is going on. That is it. The system only works in WHEEL LOCKUP situation the rest of the time is a NON-ABS system and that is why they have a proportioning valves on the ABS cars... The ABS is simply an add on to prevent wheel lock and alow you to steer.

Ok now to the real problem... he has too much stopping power in the front causing wheels to lockup under moderate pressure. Hydraulic pressure is part of the equasion on how much stopping power you have so if you balance the presure you balance the front to rear braking. Now like I sad this is not the corect fix but it would certanly help...

 

[adampecush]

I think the point here is that the difference in brake size with the stock proportioning valve prevents proper bias in situations where ABS is NOT active. This will potentially lead to the front brakes supplying too much braking force and the rears not enough. The consequence of this is that ABS will be triggered prematurely as the front wheels will begin to slip at a lower pedal pressure than a properly biased system. Consider the following (i'm using extremely arbitrary numbers for the purpose of this post)

Assume a 60/40 f/r bias pre-upgrade. Thanks to the brake upgrade, lets say 400 psi now causes a front lock and 600 psi causes a rear lock. At the threshold of locking the fronts (400 psi), you are only sending 267 psi to the rear, which is less than half of what they require for their lock threshold. Clearly, with the stock bias, you will be under-utilizing the rear brakes up to the point of lock-up which can potentially throw off the balance of the car under demanding conditions. Sure, once the ABS kicks in, everything will change, but up to that point, the brake balance is less than ideal.

I personally don't want to be having to trigger abs with each stop to get proper bias out of my braking system. Ideally, I'd like the brakes to perform so the front and rear pads will wear at a similar rate. With an out-of-bias system, this isn't going to happen unless I brake so hard I'm triggering ABS at each stop.

 

[adampecush]

Adam - We are talking about max braking events, per the orginal post. If you are triggering ABS on every stop with the upgraded front brakes, something is very wrong. ABS triggers at wheel lock (a max braking event)...by defination, it is impossible to be "premature".

What about a non-full pressure brake application?

Given a certain pedal pressure, a properly proportioned system should distribute the braking load evenly based on how much braking force can be applied before lock. A poorly proportioned system (at the same pressure) will supply too much pressure to the front and not enough to the rear, resulting in locking of the front but not the rear. At the lockup threshold of the front, you are nowhere near the lockup threshold of the rear, resulting in a lower overall braking force.

Ideally you would want all wheels to lock at the same time...I consider the tendency for the front to lock while the rears are still under the threshold "premature".

 

[Poodles]

Few points that I'm sure some people should know...

-The proportioning valve is there to LOWER rear brake bias as a rear lockup is deadly.
-The ABS master cylinder is different from the non-ABS master more than likely to allow the system to divert pressure to the front or back when needed.

Also, a simple fix for this is putting harsh pads on the back...

 

[2JZ_MA70]

The botom line is the car with or without ABS intervention is not setup coreclty. I would get it as close as posible without ABS and then let the ABS do its job... there are many ways to get it fixed. Anything from calipers with smaller pistons to different fiction coefficient pads to adjustable proportioning valves to rear brakes. I would not go into the rear brakes unless they are overheating. But pads is easy enough to try...

As far as pressures in the ABS system yes the diverted pressure is pumped out by the pump in the hydraulic unit and that increases teh overal pressure but I would say that in MK3 SUPRA THE ABS IS ONLY TO PREVENT WHEEL LOCKUP DURING BRAKING AND HELP MAINTAIN CONTROL not to adjust brake bias....

Acctualy I would tell you that wheel lockup in DRY WARM-HOT condition would give you the shortest stoping distance VS ABS considering the same car, same tire, same condition, same braking system and same pressure. But that would leave you with flat spots on the tire and no steering response... Hense the "maintain steering control"...

 

[Poodles]

No

If you lock the tires you INCREASE braking distance. Just like if you spin your tires and it's hard to get them to get traction once it's lost.

Also, keep in mind that ALL OEM braking systems are meant to lock the fronts FIRST. A rear lockup situation is DEADLY as the ass comes out and there isn't a damn thing you can do about it.

You truely don't have a clue.

 

[Enraged]

Ok, so what's your point?

So far you've asked about removing ABS (installing a proportioning valve) and now, threshold braking (i.e. optimum braking without ABS). The whole point of this thread is there is an ABS system available, but needs to be repaired vs installing said proportioning valve.

Defeating the ABS is a definite downgrade. Can you do it, yes. Can you practice threshold braking, yes, but there is no way it will be as good as ABS.
Can you justify removing the ABS just so you don't have to fix it...no way.

The whole point of this forum is to ask questions, which is what I did. Nowhere was I arguing whether or not ABS was better or worse.

 

[rayall01]

The whole point of this forum is to ask questions, which is what I did. Nowhere was I arguing whether or not ABS was better or worse.

But your were trying to get out of fixing your ABS, and that's just a real bad thing to do on any car. I've read this thread, and it seems people are saying what they're saying in order to convince you to mend your evil ways.

 

[2JZ_MA70]

Ok dude. You dont know me, you dont know what i do... there is no point of saying im incompetent... I MAKE MY LIVING ON CAR FAR MORE COMPLICATED THAN THE SUPRA AND I DO GOOD AT IT. I have plenty car related schooling and experience.

You are WRONG!!! because ABS SYSTEMS (IN MK3 SUPRAS) DONT ADJUST BRAKE PRESURE BIAS. Very simple if they did all 3 chanels will go in ABS operation not just the individual front or the rear. Those systems were not implemented at that time. If you want to talk about new ABS and theory of operation I can get you some technical manuals from what I deal with.

As far as stoping distance in wheel lock vs wheel rotating... DO some reserch and and then talk.... because obviously YOU sir have NOO CLUE!!!!

Im done this is pointless...

Zazzin do what you want but the botom line is research the info yourself because there is a LOT of BS floating around.

I have no ABS in my car and Im runing stagered tires (height and width) i have no Issues stoping and have never locked up the brakes yet...

 

[Enraged]

But your were trying to get out of fixing your ABS, and that's just a real bad thing to do on any car. I've read this thread, and it seems people are saying what they're saying in order to convince you to mend your evil ways.

I think you have confused me with the OP.

 

[Enraged]

Yes it is...it looked like you were going somewhere with your comments. Otherwise, why would you ask questions concerning a non-ABS car...unless the OP is going to remove it (a bad move).
Keeping a thread like this on track is hard enough...but, no harm, no foul.

I think you were reading into my posts a bit much. Sometimes a question is just a question.

 

[Zazzn]

Jdub, you need to calm down, you need to step back. The anger and tone of your responses do not help anyone. I appreciate your feedback but there is no need to make anyone feel stupid, dumb for lack of knowledge on a particular subject.

I appreciate all the info that has been shared here. Adam, 2jz_ma70 and enraged thanks for seeing my side of view.

While I understand everything that JDub is saying, I don't think he understands my problem clearly. Yes the ABS would fix my solution but not the way I would like. It would entail me to mash the breaks to the ground to achieve 4 wheels to lock up however; the ABS would trigger fixing the issue.

But this is not my goal, I would love to hit the max break threshold on all for corners without triggering ABS, which is impossible now. Quite frankly the car worked very well without ABS on the stock system and now it is actually quite scary and unpredictable because of how quickly the front breaks grab.

I don’t know if you have these brakes Jdub, but if you don’t then how can you argue my estimations on how the breaks feel. When I say 95/5% 6 these numbers are partly out of my ass since they are form the seat of my ass estimations. I have them on my car and I know how the car felt previous to the breaks.

-Doward I’m not saying there is anything wrong with the breaks, I’m just simply saying I need a solution for this which does not include working around the issue using ABS. The BBK is doing everything as advertised, and I knew this would probably be a problem that I would have to solve. I will eventually fix the abs, but as I said I don’t like the ABS on the mk3 because if you hit a bump in the road while trying to break lightly, it triggers the ABS as the wheel locks for a split second, while all my gen 2 abs systems do not do this. (mk4 supra and aristo)

I'm trying to achieve max break threshold on all 4 corners but I cannot achieve this ANYLONGER because I have too much stopping power in the front. If depress the pedal 1/3 of the way down I am at max threshold on the front and it’s borderline locking up however, the rears are barely doing anything. The ONLY way I can achieve max threshold would be to lock the fronts triggering the ABS and then keep pressing harder on the brake pedal so that the rears get more pressure. That is unless I don't understand the ABS JDUB. In which case does the ABS divert more pressure to the rears when the fronts lock?

 

[Poodles]

Indirectly they will (through the master), and if they detect lockup (keep in mind it's a 3 channel system, both back wheels are on one throught he sensor in the tranny), they will activate the ABS there.

Also keep in mind that big brakes on a non-ABS car with good tires would actually need MORE front bias as the car dives and unloads the rear wheels.

Rear lockup is EXTREMELY dangerous. My old truck had an auto bias control in the back (had a lever attacked to the frame and the actuator was on the axle) so that as the rear got unloaded it would use less and less pressure. Somehow the arm got bent, so under emergency braking the back tires locked and I went sideways on a very busy road, and no, I didn't swerve at all!

It's very easy to check the codes for ABS, start here and go to the next page: http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=BR&P=51

You could even wire in a switch to the dasht o turn it on/off if you wanted to...

 

[Turbo Drifter]

I have been able to get my breaks working great with out ABS. I removed it all about 3 years ago and the pedal feel is greatly improved. I also have AP racing breaks in the front and stock breaks in the back with Hawk HP+ Pads. I get very linear break feel and if I lock up both front and rear do at about the same time with a slight bias to the front.

I'm very happy with the way the car works and look forward to getting on the road course.

Good Luck Eric!

 

[Zazzn]

:wave: :wave: :wave: :wave: :wave:

Answer the question then, do you have this kit on your car?
Do you know how the kit responds?
Since when does a point of view become FACT?
Would I not have a better impression of upgrade since I've installed and used the BBK?
Do you have numbers on how much the breaking bias has changed since adding the BBK?
It sounds like you are harping but I don't even know if you have the facts considering you say "60-70% I would believe"

Stop being an asshat :3d_frown: I'm not here to attack or belittle you. You seem hell bent on doing it to me or anyone that argues with you. As the moderator of the forum set a good example for everyone else.

Indirectly they will (through the master), and if they detect lockup (keep in mind it's a 3 channel system, both back wheels are on one throught he sensor in the tranny), they will activate the ABS there.

Also keep in mind that big brakes on a non-ABS car with good tires would actually need MORE front bias as the car dives and unloads the rear wheels.

Rear lockup is EXTREMELY dangerous. My old truck had an auto bias control in the back (had a lever attacked to the frame and the actuator was on the axle) so that as the rear got unloaded it would use less and less pressure. Somehow the arm got bent, so under emergency braking the back tires locked and I went sideways on a very busy road, and no, I didn't swerve at all!

It's very easy to check the codes for ABS, start here and go to the next page: http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=BR&P=51

You could even wire in a switch to the dasht o turn it on/off if you wanted to...

Understood poodles, I'm not trying to say I want a 40/60 setup I want back the 60/40 setup that I had stock so that if I press the breaks 30% I still get 30% front and 10% back instead of 30% front and 0% back. I've felt rear lock up on my parents old 89 caravan, the rear end would start to fishtail... What a POS that van was haha.

 

[Poodles]

The stock valve may be adjustable, if I had a spare I'd check...

 

[jdub]

Answer the question then, do you have this kit on your car?
Do you know how the kit responds?
Since when does a point of view become FACT?
Would I not have a better impression of upgrade since I've installed and used the BBK?
Do you have numbers on how much the breaking bias has changed since adding the BBK?
It sounds like you are harping but I don't even know if you have the facts considering you say "60-70% I would believe"

Stop being an asshat :3d_frown: I'm not here to attack or belittle you like you seem hell bent on doing to me or anyone that argues with you. As the moderator of the forum set a good example for everyone else.

Zazzn - I do not have to have this kit to understand how ABS works or to know what you are doing. I don't pull numbers out (like 95%) because it would be out of my ass...just like you did.
I told you do what you want...I'm done trying to help you or assist this endevor in any way. Have at it...figure it out for yourself.

BTW - Maybe you should take a look on the mirror as to who is calling the kettle black here. You can call your gang off Zazzn.

 

[IJ.]

<Non ABS Car with a balanced FULL set of AP 4 piston calipers on Mk4TT DBA Rotors and if I had the room for the parts and the wheel speed sensors I'd have ABS in a flash.

Been driving performance cars for 30+ years an am an ok peddler but I do get it wrong from time to time and in those situations ABS would be a huge help.

Personally I don't get the BBK on the front only as a Mk3 chassis set up correctly will put a huge load on the rears (I've had mine Blue and smoking after a hard run through my test course)

 

[T701jz]

lol...someone prolly got a detention after school with that comments.

Zazzn: any thing that you change on a calibrated system will need re-calibrating; solenoid, valve, line...etc.

That's the fun of upgrading...you get to do your own R&D.

Like JDUB said-Just remove the ABS ...you will not be able to achieve threshold breaking with it installed. You are still going to have problems with the rear if you do not upgrade to a similar system as the front.