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-   -   Retrofitting CBS (combined braking system)? (https://www.team-bhp.com/forum/motorbikes/174988-retrofitting-cbs-combined-braking-system.html)

Retrofitting the Combined Braking System to a Honda Scooter

Now that 2-wheeler companies are required to fit either CBS or ABS to new scooters sold, I was wondering if anyone has retrofitted the CBS on their scooter. I have been asking around, but the mechanics seem reluctant.

Mine is an Aviator with a disc brake (so hydraulics involved) so may be this is more complicated. But I have seen the same reluctance even when I've asked about the CBS retrofit to my (wife's) Activa. My own thought is that this should be simple enough.

Any inputs?

Only one point from me - AFAIK, your Aviator came factory-fitted with CBS. So you don't have to retrofit it.

As for your wife's Activa, instead of asking around in FNGs, I think the best idea will be to visit the Honda A.S.S. and look for a parts catalogue. I believe it is a not so complicated cable-operated mechanism, and you may be able to get it fixed at Honda A.S.S. itself.

Thanks, but the A S S has been uncooperative (I asked them first), also my Aviator did not come with the CBS (old 102 cc model).

But I will call them again and ask, who knows they may be less arrogant now.

Oh is it, I wasn't aware of this. Sorry.

Good luck with finding the parts. If the A.S.S. does not help, I think the best idea would be to find another Activa for reference, and make a list of the parts that you need.

For the Aviator, my humble suggestion would be to leave it as it is. Being a hydraulic-cum-mechanical CBS, it is probably going to be an expensive and complicated affair. And brakes being safety critical, are better left alone in the after-market.

So true, and thanks for bringing it up - I almost forgot this very important point in my enthusiasm. [Just got the disc brake fluid and the piston changed at the FNG and was flabbergasted at the casual attitude of the mechanic - plenty of water on the covers of the reservoir after a casual wipe - a 'No' to every attempt to cajole him to flush the system completely]. I do apply the front brake anyway (thanks to the driving license procedures at Arizona) in combination with the rear one. I will get my brakes serviced again from my (other) competent mechanic soon.

I will not change the system on my Aviator, but will try what you suggested on the Activa.

I doubt if the ASS can retrofit anything. Generally most ASS refrain from retrofitting anything. I have 2010 cbz Xtreme single disc version, the bite is quite pathetic and the headlight throw is useless.

I approached the ASS and asked them to fit disc brake and master cylinder from Karizma to the front wheel and fit a new rear disc break from Hunk or the newer version of CBZ to the rear. They flatly refused saying it cannot be done.

On the other hand a mechanic from FNG said it can be done easily provided I can get him all the spares. Most ASS will wash your vehicle and return it after stealing some fuel.:deadhorse

IMO, retrofitting CBS on a motorcycle or scooter that did not originally have it ranges from difficult to almost impossible.

The easiest way would be to have a vehicle that did not have CBS but it is now available on the latest production model.
The brake parts on the new model may fit onto the old model with little problem (or they may not fit at all if the supporting parts are not designed for them).

If the new model is not equipped with CBS and replacement parts are not available the problem becomes more involved.

First, the only moderately easy design to modify must have hydraulic brakes on both the front and rear wheel.
Only with a hydraulic brake system can the pressure from the master cylinder be directed equally to both wheels at the same time.

This, a hydraulic system will do automatically as long as suitable high pressure hoses are connected to the master cylinder and both wheels brake pistons.
(Fluid pressure in a closed hydraulic system will be at the same pressure everywhere provided modulators or regulators are not between the master cylinder and the brakes).

For this hydraulic system to work properly as a braking system, the sizes of the front and rear brake pistons must be sized correctly.
The size of the front brake should apply approximately 80-85 percent of the braking force with the rear brake applying approximately 15 to 20 percent.

If existing parts are taken from several different motorcycles the likely combination of brake parts being correct is very unlikely.

What if the front end has a disk brake and the rear end has a mechanical drum brake?

A real problem exists with this setup. The two brakes receive their energy in two totally different ways.

The disk brake relies on hydraulic pressure. The drum brake relies on a force that is applied to a steel cable or rod.

The only solution that comes to mind is to design a hydraulic piston connected to the master cylinder that will provide force to the rear brakes steel cable or rod.
To the best of my knowledge, such a thing does not exist unless someone wants to try to cobble up something. (This hydraulic piston must be sized to provide exactly the right amount of force).

Cobbled up somethings do not have the engineering expertise needed for a design that involves a life/death situation.

My first recommendation for anyone seriously wanting a CBS system is to find a motorcycle or scooter that already has it and buy the machine.
Only then will you know that the proper engineering went into the design.

My second recommendation is to learn how to use both brakes on your existing machine properly.

Properly in this case means use the front brake to develop 80-90 percent of your braking and the rear brake to provide the remaining 10-20 percent.

Actually, IMO, this is the best solution.

A CBS system has no way of knowing what the riding conditions are so it must be designed to meet the average conditions. This is fine as long as the actual conditions are average, like a smooth, dry, slightly dusty road.

As soon as the riding conditions are not average, like a wet, muddy, sandy or potholed road, only the rider knows this and by using his/her knowledge they will adjust the amount of front and rear brake force needed at that moment to safely stop the machine.

(Under wet, muddy conditions the best braking combination may be 20-30 percent front and 70-80 percent rear to prevent locking up the front wheel.
The CBS system won't know this at the time.)

Thanks ArizonaJim.

I am assuming that the CBS for the Honda Activa that comes with a drum-drum config is a very simple one. I have tested this version and it is near impossible to lock up the wheels (I could be wrong here). I do use the front brakes (Luckily, I got my DL in Arizona :D, where the DMV makes sure you have learnt to use the front and rear brakes to stop before they grant you your DL).

The diagram on the left shows how the CBS is achieved in this scooter; the more complicated ones used on high end bikes use the system on the right.

I'll have to investigate the differences between the old model Activa (without CBS) and the near identical new Activa with CBS. The Aviator has a front disc and rear drum, so is more complicated (most likely, they use a mechanical force divider here too to operate the hydraulics - I doubt they would use a more expensive system in a price sensitive market)

But in anycase, I've thought about what you and Viju have said, and given the total lack of safety conciousness among mechanics here, I've come to the conclusion that messing around with a critical system is not a good idea.

mvadg
Thank you for the nice picture of several different CBS systems.

As you noted, they use hydraulic pressure to provide the braking force.
Hydraulic brakes of course has been used for over 60 years on drum brakes quite successfully.
I hope I didn't give the impression that CBS can only be used with disk brakes when I mentioned motorcycles that had a drum brake on the rear.
That is why I said "What if the front end has a disk brake and the rear end has a mechanical drum brake?". I intended convey the idea that trying to combine a mechanical and hydraulic brake system on the same machine is wrought with problems.

Your decision to refrain from messing with existing brake systems is an excellent one.
Ride safe. :)