Instead of installing the pressure transducer after the master cylinder like they say, how about installing it after the anti-lock brake unit to give the trailer brakes some sort of anti-lock function? It's probably not as simple as that, but I would like to know what I'm missing. Also, are there any other makes of brake controllers that look at brake line pressure?

 

Not real knowledgable about brakesmart. But don't think that is a good idea as the ABS uses sensors on the wheel to control that wheels braking. The trailer wheel would be at the whim of the tow vehical.
Just MHO.

Davey

 

I would GUESS that the Brakesmart also does NOT update as fast as the ABS (10 times a second or whatever it is) and the effect would be lost on the controller.

 

I theory, that would be great, but in reality it won't work well because the brakes aren't matched. The trailer wheels may or may not be locked up, but it doesn't matter because the ABS on the truck wouldn't know either way, so it would not be affective in that direction. Looking at the flip side, if the truck's rear wheels were locked up, and you had a heavy load, the trailer wheels my not be locked up, but when the line pressure goes down for the rear wheels of the truck it would also go down for the trailer bakes, and if they aren't locked up, you just decrease their effectiveness, which is probably a bad thing since whatever is happening, you wanted to stop badly enough to lock the rear wheels of the truck.

If you could figure out a way to put sensors on the trailer wheels, and have an automatic, stepped, rise in resistance in the trailer wiring, controlled by the computer that reads the sensors, that would provide ABS for the trailer brakes. Seems logical, but is probably cost prohibitive.

Chris

 

Stamey, I beg to differ. The rear wheels of the truck do not have ABS sensors yet they are pulsed along with the front wheels whenever the front wheel sensors detect slippage. The trailer brakes would mimick the rear truck brakes in my scenario. But I think Sidewinder is right, the Brakesmart is probably not able to sense and react to the rapid and frequent pressure spikes of ABS in action. And the electric trailer brakes might just hum or chatter even if you are able to switch them on and off 10 or more times each second! Still, I'm going to call Brakesmart about this at some point and post their response.

 

You know you have it bad when you feel the urge to B.O.M.B your brake controller

Fred I am proud of you

 

I have to politely differ with Fredbert...

The rear wheel ABS is not activated in unison with the front wheels and they do have a sensor. According to the manual, it is a three channel system, and the sensor for the rear wheels is a hall effect sensor mounted on the rear end...

Anyway, even if the brake controller did react to the anti-lock pulses, I don't think the trailer would. With electric brakes, the magnets get attracted to the rotating armature, which pulls the lever the magnet is mounted on. That cams the primary shoe into the drum, which then pushes the secondary shoe into the drum.

I'm no expert, but I would think that a trailer system must react considerably more slowly than hydraulic disks that the anti-lock's pulses were designed for. I would think that the arms and magnets in the trailer brakes would just chatter, even if the controller could feed it a pulsed anti-lock signal.

In any event, it would appear that lots of engineers spent lots of time designing, testing, and refining the Brakesmart. I'd bet that if it could be made to perform better by moving the pressure sensor, the Brakesmart people would have done so themselves.

Good to be thinking outside the box, though...

 

Umm, look on top of the differential, right in the center. You will see the ABS sensor. This has been on most trucks since the late 80's. If the truck has 4 wheel ABS there will be separate sensors on each of the front wheels, with tone rings. The single sensor on the rear is all that's needed since if one wheel stops the ring gear will be stopped also.

I agree regarding the reaction time of the BrakeSmart sensor, especially considering the way electric trailer brakes work, on the drag theory.

Chris

 

Oops, I stand corrected! Except for some 1500s, Rams do have 4 wheel, 3 channel ABS systems. At least we were able to answer my "dumb Brakesmart question". But I'm still going to call them just to hear what they have to say.

PS: How can the ring gear (and pinion and drive shaft) not rotate at all when one wheel is still turning? I think its rotational speed suddenly drops to half when one wheel locks up, and that is what the sensor is looking for.

 

That one messed with me for a little while, when I read about how a certain locker setup works, but it when you think about it, only 1 of the 3, drive shaft, or either wheel, can stop. I'm not getting on thin ice because I can't get my head around the mechanics at this moment. If the one wheel locks up, I believe the other wheel must double in speed to keep turning, given the driveshaft turning at a constant speed. Given this is a highly unlikely occurrence in a situation where one wheel is turning and the other locks up, the driveshaft will slow down/stop, which means the ring grear is stopped.
The example I saw was with a side gear that got locked in this locker, and I was trying to work out how, by positively locking only one side gear, still having regular spider gears in the carrier, you could cause both wheels to have to turn. I saw an animation and studied it. I understand now, but may not be able to explain it to anyone else.

If anyone can explain this better/correctly, please chime in.

Another thought is, since these are not steering wheels, subject to so much lateral force, it doesn't matter if only one rear wheel locks up. They are measuring for when both lock up, which could cause a rear end to come around. I don't know how much merit this carries either, but it's all I could think of.


Chris

 

Stamey,

I've pondered the antilock on the diff too, and like you, looked at all the scenarios. How can you measure in the middle and predict each wheel?

Here's my take on it. If the truck is in 2WD and one wheel (say the right one) has less traction, and it begins to lock up, meaning it's rate of slowing is greater than can be justified by the truck's normal stopping, what happens to the other wheel and how does the ring gear sensor see the problem. Hmmm. I think that if one wheel begins to skid while braking, it has less traction than the other one that is not skidding. And therefore, it cannot accelerate the higher traction wheel through the differential. So the ring gear slows (remember, we're in 2wd). And the sensor notices a reductuon in speed. If both wheels begin to skid the ring gear slows and, again, the sensor notices a reduction in speed. The wheel with the greater traction cannot skid first and cause the wheel with less traction to accelerate and maintain an even ring gear speed. But the skidding wheel only has half the effect on speed as if both wheels skid at the same time. So the system must be set up to activate with the lower value as a recognized skid.

What do you think? does that make sense?

When I first saw the setup I thought it was not a good idea, but it seems to work and it is simple.

In 4WD it seems like the higher traction rear wheel could skid and accelerate the lower traction rear wheel to make up the difference. If the front had more traction and kept the rear driveshaft turning the truck could slide and fool the antilock. Or all wheels could skid and the antilock would notice the rears locking and kick in to stop them from skidding and get the fronts rolling too. Hmmm. Is that right?

Wetspirit

 

As I said, I'm no authority in this area, but I'm thinking that the rear wheels, as they are not used for steering, are not that sensitive. I doubt the sensor is complicated enough to notice and calculate the rate of deceleration to determine if one wheel is locked or not. I'm betting the ABS doesn't kick in on the rear axle until the ring gear stops, which means both wheels are locked. The fronts have separate sensors because they are not directly connected to each other unless in 4WD.
I wonder if the new Fords, with the integrated brake controller, factor in any ABS in the trailer brake operation. I doubt it, for reasons already discussed above, but I still wonder if it was thought about when they designed it.

Chris

 

I've had one side of the rear locked up, and the ABS was none the wiser...

Left side was on snow/ice, right side was on pavement. no big deal, but it did happen.

The other 99% of the time though, both rears lock up simultaneously.

Even Toyota went to a 3-channel system in the Supra TT in '96 when they were trying to cut costs, and that thing has a need for some serious brakes too, just for a different reason than our trucks..

4-channel is better, but unless you're trail-braking into a corner carrying big speed, 3-channel will get the job done most of the time..

 

I had heard the Ford unit is a glorified Prodigy.

 

Bobbyofthejordans...how is the Jordan working for you?