I was wondering why if your going to put ABS on car or truck why the back only?????

 

I would assume because it costs more to have 4 wheel ABS as opposed to only 2 wheel. As far as I know my truck has 4 wheel ABS.

-Brian

 

Precisely. Dollars and cents. Granted, the smart thing is to use 4 wheel ABS, but rear wheel abs only requires one simple module, one sensor on the diff, and one simple exciter ring in the diff. 4 wheel requires additional processing, two additional speed sensors on the front end, and a much more complicated module to modulate the 3 ABS channels independently/jointly as necessary.

-Joe

 

In addition to all the things already mentioned, pickups are notorious for rear tire traction issues due to tha lack of rear weight distibution. So it stands to reason that since the rears are most likely to skid during hard braking that they would be the best candidates for ABS. This way you dont swap ends as easily.

And yes, individual sensors on each wheel would be best but I guess the differential only is still better than none at all.

 

thanks guys for your answers

 

Some vehicles use 4-channel ABS and do brake each wheel independently, but like you said, with rear braking action being so highly traction-limited, and the fact that they only have ONE brake line feeding both rear wheels, it's simpler to use just a single channel back there. To have true 4-wheel ABS, you would need an additional channel to control, and additional brake line running to the rear, a second rear brake hose on the axle... a royal pain in the butt on a solid rear axle. 4-wheel independent suspensions and many sports cars can do it much easier.

-Joe

 

I'm sure this doesn't really answer the question. I had two of the 97-03 pickups with the RWAL system (rear wheel antilock). They were by far the worst brakes I have ever had. All sorts of weird stuff happening with the pedal even when the conditions didn't warrant ABS activation. Even my old 83 F150 had better brakes. Now the 4 wheel system is another story. It still amazes me how well it works in the snow.

 

I think everyone is right about the rwal and trucks. Especally without a load the rear end would lock up much more easily on a truck then on a car. the earliest rwal's used a valve attached to an arm to the body. It would sense the axle tourque and release pressure to the rear brakes. Later they used a sensor in the diff. that read the gears and when they stopped it would release the rears.( seems that this system is most prone to problems mostly with the sensor or the elec. connection) I concur that 4wheel ABS is very good and have had it keep me out of trouble several times.