ABS Brakes

Haji-Baba · Senior Member

ABS Brakes

rockylizard · Guru

Gday...

While we wait for those who are more technically minded than I, here's some info -

The text below is from this site -

http://cars.about.com/od/thingsyouneedtoknow/fl/All-about-antilock-brakes-ABS.htm

Does ABS work with both disc and drum brakes?

Yes. The antilock system works my modulating the hydraulic (fluid) pressure that applies and releases the brake, rather than the actual brake mechanism itself, and therefore ABS works disc and drum brakes.

Cheers - John

-- Edited by rockylizard on Tuesday 6th of December 2016 10:01:22 PM

Haji-Baba · Senior Member

Thanks John. Good read.

Recently had a situation whereby had a couple of rapid stops on gravel and could feel the front discs doing their job through the ABS. but couldn't feel the rear drums working as expected.

I had the van brakes wound right down and I am pleased I did, if they were working to their maximum I may have seen the van going into a skid and consequently taking the ute off the road.

That is my take on the difference between Electric brakes on the van working to maximum capacity and controlled ABS on the towing vehicle in an emergency stop.

I have had my van brakes lock up on bitumin with the consequential loss of traction on the van wheels causing it to slide sideways.

Someone may have a different opinion, love to hear it.

Have fun Haji-Baba

Aus-Kiwi · Guru

Is there a signal wheel or wires going to axle, brake area to pick up wheel lock up ? Check master cylinder, brake lines under bonnet if there's an ABS module ?

Jaahn · Guru

Hi Haji-Baba smile

My take on your observations about the ABS.

If the van ball weight has increased the read load by a large amount then the rear tires would not lock up at the same decelleration rate, whereas the front wheels would have less weight on them, so would lock up earlier. It is said that to activate the ABS correctly in an accident situation is to stand very hard on the brakes so they all start to lock and the ABS takes over all four wheels and controls them at maximum grip.

In you situation perhaps you were not braking as hard as that, hmm we hope. So perhaps the system was working as it should, controlling the front which was locking and not the rear which had enough grip for the situation. A weight distribution hitch may help here as it evens out the load on axles.

Not sure about the setting on the van brakes but trying it out and adjusting may give you the answers as you seem to have a good idea about it. aww

Jaahn

ants_oz · Veteran Member

Hi there,

Depends on the vehicle - there is no "one size fits all" answer to this question.

Most likely the answer will be yes.

If you would like a more definitive answer (including info on whether its a 3 or 4 channel system), please provide the year, make and model of vehicle.

ants_oz · Veteran Member

Hi there,

Am interested in what observations you made that lead you to believe it was the front discs "doing their job" and that the drums were not.

Pulsation of the ABS unit modulating hydraulic pressure in the system will not readily allow you to identify which wheel (or wheels) are having their braking effort modulated.

Haji-Baba · Senior Member

I believe the stopping power of the ute was excellent, just that I couldn't pick up if the back axle was doing it's job.
It must have been working ok.

Sure, the use of a WDH should keep the axle loadings fairly even and the braking effect on the rear axle would be increased as the vehicle brakes take effect and the van downloading onto the tow ball.

At the same time the vehicle brakes under ABS will not have lost traction therefore maintaining steerage.

However if the van brakes lose traction and lock up the van will invariably skid sideways and we are off the road.

I know it is a curly question but having towed many types of trailers, big and small with over nearly seventy years experience
the modern technology gets in front of me at times.

Thanks for all the advice, shall take it on board.

Have fun Haji-Baba

erad · Guru

ABS brakes work on any wheel which is fitted with the appropriate sensor. The sensors monitor the rate of deceleration and if it senses that the wheel is going to lock up, the ABS computer then reduces the hydraulic pressure to that wheel until it starts to rotate again. It keeps the pressure to the other wheels at the same time. It doesn't matter what type of brake is on what wheel - it works that way. It is like having 4 separate brake pedals on a car, each one waiting for a lockup and acting accordingly when it senses the lockup happening. For this reason, in an emergency stop, with ABS you plant your foot hard on the pedal and let the ABS do the work. With no ABS, you have to do the work yourself and wait (listen) for a lockup and then reduce the pressure on the pedal yourself, and then increase the pressure until you get to the point of lockup again. Repeat this process (as rapidly as possible) until the crisis is over or you hit something.

I have had ABS on my cars for 17 years now, but I have only had the ABS kick in properly twice in that time. I still react the wrong way - as soon as I feel something moving under my foot, I ease off the pedal. WRONG! This is because neither my wife nor I drive in a manner which takes us to crisis braking very often, and we simply are not used to the ABS operating.

Haji-Baba · Senior Member

Very informative erad just as I had expected.

Thanks for that info.

And no I generally don't drive on the limit and very seldom get in a panic stop situation.

One of my main concerns is the relationship between electric van brakes which don't have ABS functions.

On the highway or gravel roads I have my van brakes set to a minimum or thereabouts and drive to that level.

For city driving I set my van brakes up to almost lock up and again drive accordingly.

I do wonder if some of the bad van accidents are partly caused by unequal braking effect of car and van.

Have fun Haji-Baba