ABS+EBD on a car with drums at the back

Rouxenator

Rouxenator

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I have been wondering for a while now how they can have ABS and EBD on a car that only has discs in the front and drums in the rear.

The EBD part I can understand, that is just distribution of the braking power, but how do they do ABS on rear drum brakes?
 
ABS is independent of whether the brakes are discs or drums. It prevents the wheels from locking up by continuously applying & releasing the brakes every few milliseconds.
 
OK, dumb question here, but aren't disc brakes hydraulically operated and drum brakes cable operated?
For hydraulics it not a problem to connect the ABS regulator to it, but if the read drum brakes are cable operated how can they have ABS on them?
 
Dont think i've seen a car with rear drums & ABS
 
Lot's of mid range hatches/sedans have discs at the front and drums at the rear. Pretty much all new cars have ABS.
 
True. A lot of the entry level cars like the i10, new Spark, Corsa, Polo and Vivo all have ABS+EBD with discs in front and drums at the back.
 
Rouxenator said:
True. A lot of the entry level cars like the i10, new Spark, Corsa, Polo and Vivo all have ABS+EBD with discs in front and drums at the back.
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Maybe they only have ABS in the front... Wouldn't be a problem in a slippery situation me thinks they are driven and steered at the front so....
 
I just have it in my head that the entry level i10(for example) wont have ABS but one spec level up on the i10 would get you ABS is that not the case?
 
I'll go double check the ABS module/pump on my car to see if it has 2 or 4 outputs. I am pretty sure last time I looked it had 4 outs. Its a Corsa Essentia with drums at the back.
Vegeta said:
I just have it in my head that the entry level i10(for example) wont have ABS but one spec level up on the i10 would get you ABS is that not the case?
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Correct - only the top of the range i10 HS GLS (R125k) has ABS with EBD. Same goes for the Spark, LS (R125k) has ABS with EBD while the base model L (R115k) does not have.
 
Rouxenator said:
OK, dumb question here, but aren't disc brakes hydraulically operated and drum brakes cable operated?
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No, drum brakes on passenger vehicles are hydraulically operated just like disc brakes. There may be some exceptions but I've never heard of or seen any.
The handbrake cable to the drums at the back is separate from the hydraulic system and is only used when using the handbrake.
A 1950's VW Beetle has hydraulically operated drum brakes front and rear.
 
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Thanks Paul. I think I have solved it, it uses ABS all round no matter the type of brakes. This is a photo of the ABS pump & controller on my Corsa Essentia (front disc, read drum) and it clearly has 4 outputs :

20110110517.jpg
 
Yep. The ABS is implemented at the master cylinder (the thing in the picture above :p ), any hydraulic brake can therefore feature ABS. Drum brakes as noted are hydraulic with a secondary set of arms that are attached via cable for the handbrake. Even if you have disc brakes at the rear the handbrake still depresses the caliper mechanically using a cable. So even if you have complete hydraulic failure the brake can be actuated using the handbrake.

Both disc and drum brakes at the rear have bias valves, essentially they decrease the amount of hydraulic pressure applied, the bias is just larger on disc brakes. Hence the reason going from rear drums to discs doesn't make nearly the difference you'd get by upgrading the front calipers and discs.
 
Thanks Gnome. I suppose EBD also happens at the master cylinder then where it distributes the brake force more evenly depending on wheels speed? The reason I initially asked this question was that I saw on some Vauxhall forum they had two types of drum brakes for the Corsa C - one with ABS "lining" and one with out - that's what got me thinking how they can have ABS on drum brakes.
 
Rouxenator said:
Thanks Gnome. I suppose EBD also happens at the master cylinder then where it distributes the brake force more evenly depending on wheels speed?
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What is EBD? Every manufacturer calls these things their own name but essentially there is ABS and stability control in it's various forms (probably EBD).

Rouxenator said:
The reason I initially asked this question was that I saw on some Vauxhall forum they had two types of drum brakes for the Corsa C - one with ABS "lining" and one with out - that's what got me thinking how they can have ABS on drum brakes.
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Hmm, ABS lining? I think they are speaking of the hub which is an integral part of the drum but it has a metal ring. That metal ring has notches, in front of it an inductor is placed (a magnet with wire around it). As the metal ring rotates it creates magnetic flux which generates a current (eg. it is generating electricity :p ). Because the ring has notches the magnetic flux is constantly reversed, therefore it looks like a sine wave if viewed on a oscilloscope. The lower the period of the sine function (meaning the more the sine wave goes from + to -), the higher the speed of the wheel. Therefore the ABS uses that to "know" the speed of the wheel.

All ABS systems use the exact same system, that is a inductor with a metal type ring (the inductor doesn't actually make contact but it is placed very close). That ABS lining is probably the metal ring on the hub.

Without it the car couldn't tell the speed of the wheel and hence no ABS or any stability control for that matter.

Most cars (just about all Opel/BMW engines, all modern VW, etc.) also make use of that same principle to determine crank shaft position in the engine. A little bit different but same principle. Hence if it fails you have a no-start engine or ignition/fuel injection is totally messed up.
 
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