Adjusting the ABS unit

[scooterollie]

I know there is some controversy over the ABS dampener unit found on many of our Chinese scoots. Some remove it, some prefer to leave it on and others don't really care one way or another. The ABS unit may cause the front brake to feel slightly softer than the rear disc, if your scoot is so equipped. You can adjust the dampening effect to firm up the feel of the front brake. In doing so, you are probably reducing the effectiveness (if there is any) of the ABS unit.

Look at the bottom of the ABS unit. You will see a hex nut cap. Mine is 16mm, probably the same for all. Carefully unscrew the cap (counter-clockwise). With the cap removed, look up inside the ABS unit and you will see that there is a recessed 6 mm allen set screw. Turning this screw will adjust the tension of the dampener. I turned mine in (clockwise as you look up onto the screw) 1/4 turn. I would suggest 1/8 - 1/4 turn max at first, then take a ride to check the feel. Right now, 1/4 turn seems to be about right for my scoot.

The supposed purpose of the ABS unit is to "absorb" or "bleed off" some of the spike in hydraulic pressure created when you apply the front brake suddenly and with great force, reducing the chance of locking up the front wheel. Often, in a panic brake, we will do a quick, forceful jab on the brake, then let up some. The wheel could lock up, causing loss of control before we let up. If the "ABS" unit absorbs some of that spike in hydraulic pressure, it could help to some degree. Of course, it is not true ABS as we have come to know it today. Since this device first appeared on the market quite a number of years ago, it has been surrounded by considerable controversy. I believe it was first invented by a guy in Texas. If it is marketed as a true ABS system, then folks could be mislead. You should understand what it is as well as what it is not. Tests in the past on automotive applications have shown the device to afford a slight reduction in lockup under just the right conditions. If you stand on the brakes and do not let up, don't expect it to modulate the wheel as a true ABS system does.

[somecallmetim]

Take that silly thing off and throw it away, or make a shift knob for your lawn tractor out of it. Safety comes from developing riding skills, not from relying on dubious gadgets that prevent you from doing so. If you are in the habit of applying the front brake "suddenly and with great force" you are an accident looking for a place to happen, "ABS" or not.

[scooterollie]

somecallmetim;
I won't disagree with you about safe riding skills. That is not the purpose of my post. I am not pushing the device, only trying to explain the concept behind it and how its action may be modified. While it is admirable to hope all will achieve safe riding expertise, we know that is not going to be the case for everyone. Look around you and you see folks who will always over-react in a panic situation or not ever achieve the level of skill achieved by others, no matter what, in the operation of any kind of machinery. Take the information for what it is and do what you wish with your scoot.

[woodlark]

Scooterollie,

You may be interested to hear that my Baron/Wussi 250 has ABS dampers on both wheels. I don't think I have heard that any of the other scooters do. So far I have not had to "lock" the brakes (and hope I never do). Braking feel has been fine in normal operation.

[scooterollie]

woodlark;
I thought I had seen a scoot somewhere with units on both brakes but couldn't remember which scoot brand. Some prefer the feel w/o them and I can appreciate that. They definitely won't do any harm and under the right circumstance might help someone. It won't prevent lockup, just reduce the chance. Under certain circumstances, true ABS may actually increase stopping distance slightly but I wouldn't want to give it up because of the increase in directional stability true ABS provides when braking on slippery surfaces.

[somecallmetim]

I can't help being just a bit suspicious of the functionality of any device, as opposed to being a sales gimmick, which isn't found on any other vehicle, 2-wheeled or otherwise, except cheap scooters from China. It can't be because it's expensive to make, or because no-one else is capable of the technology. These things were advertised in motorcycle magazines 35 years ago, then quickly disappeared from the market (after a couple of lawsuits maybe?). I can't agree that they can't do any harm; they can either increase your stopping distance or do nothing at all, depending on how you adjust them.

[scooterollie]

I don't believe it was as long as 35 years ago. They were first marketed for cars, trucks, etc. Don't know when they moved to two wheeled vehicles. For more than 20 years I belonged to a GMC motor home club - the unique FWD motor home made from 1973 - 1978. These vehicles were prone to lockup of the 4 rear wheels during some braking conditions. Installation of two of these units in the split braking system dramatically reduced the problem. I disagree that they will increase stopping distance. They only absorb the initial "surge" or spike of pressure on hard application, they do not reduce the hydraulic pressure in the system. As far as doing nothing at all, only if you would adjust them so as to not allow any dampening. What would be the point in doing that? In the end, it's your choice. Do what you wish on your scoot. I am not saying they are the best device in the world, only that there is some technical merit to them and that there is a lot of misinformation about them.

[woodlark]

I had a buddy back in PA who had one of those GMC motor homes. I've always thought they were one of the nicest motor homes available because the weren't quite as big and bulky as some of the others (of course they weren't as roomy either).

[scooterollie]

woodlark;
Great cruising machine. Very low center of gravity, aerodynamic, 455 Olds front wheel drive w/final drive gearing same as the Toronado, good gas mileage, 6 wheel independent suspension - torsion bars in front & air bags in rear. Compact but well equipped - 20 years ahead of their time.

[somecallmetim]

The GMC motorhome had front and rear brakes operated by the same brake pedal. If the rear brakes were prone to locking up, that's a pressure distribution problem, calling for a pressure proportioning valve or smaller rear wheel cylinders or a master cylinder with different sized bores; something to reduce the pressure to the rear brakes relative to the front. If the "ABS" thing fixed the problem, then that's what it was doing: reducing the pressure to the rear brakes. On a scooter, there's a separate system for each wheel, so proportioning is not an issue. I don't buy the whole "spikes" argument, but assuming that "spikes" are a problem, and putting something compressible in the hydraulic system to damp them out is desireable, you could just introduce a small amount of air into the system and accomplish the same thing; a low, mushy brake lever. None of this answers the question of why no other vehicles, that I know of, except cheap Chinese scooters, come with these devices? Don't Piaggio, Suzuki, Harley-Davidson, Chrysler or Daewoo know about something that's so cheap, safe, and effective and has been around for at least 25 years? I guess I'm just a cynic; I never believed in the 200 mpg carburetor either.

[scooterollie]

The GMC motor home HAS a proportioning valve and a dual DIAGONALLY split system - each serving three wheels. The trailing rear wheel tends to lock up under hard braking because of the dynamics of the suspension setup and forward weight shift. This is normal on this coach and happens with a perfectly functioning proportioning valve. It is time to put this discussion to rest!