Can the EVO brake servo be modified?

Nick V

Nick V

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Hi again all!

The other grouse I have about this particular bike is the brakes.

My '09 GSA has ABS II with no power assistance, and I like those brakes a lot.
The '06 GS I've owned for 48 hours has the EVO power-assisted brakes, which - in my opinion - are the bike's worst point.
The power is there if you need it... but what a squeeze you need to give... and they're nearly impossible to modulate smoothly.

I know now what Jeremy Clarkson was moaning about when he drove the McLaren Mercedes SLR... "Push... and nothing happens. Little harder... Still nothing. A little harder... Aaaannnd... My face comes off!"

Since I'm not yet familiar with the inner workings of this particular ABS regulator, I need to tap the brain pool.
To the best of anyone's knowledge, is it possible to modify the ABS regulator to bypass the electric servo, but still retain the anti-lock functionality?

I'm guessing that it should be theoretically possible - the boost function must be provided by an electric pump which works by pressurizing the relevant brake circuit, whilst the ABS functionality is provided by solenoid-operated pressure-release valves.
 
Anyone else?

Please don't tell me I'm the only one who thinks these brakes are the one piranha in the GS's goldfish bowl... :nenau
 
:rob well i think they are the dogs bollocks and they are supremely controlable,
1 finger stoppies theat will do nicely sir :thumby::pullface
 
no complaints from me to........ awsome brake system
 
It wouldn't do for us all to be the same, I wouldn't touch a bike with servo brakes or ABS with a bargepole...........................horses for courses!
 
That's odd... a great deal of positive feedback!
I wonder if there's not something wrong with some aspect of the braking system on this particular bike?

I'll explain: I've owned two '09 GSAs (one of which, I still do) before buying this '06 bike.

The '09s both have second-generation ABS (no servo). On both of them, it's a simple case of the harder you squeeze the lever, the harder you brake.
If you were to plot force applied at the lever vs. actual braking action, these bikes would give a steady, predictable, 45-degree upward plot line.
This is the 'baseline' I'm used to.

The '06 has servo-assisted brakes. With this bike, it's a case of the same initial force at the lever yielding very little response. So you apply a little more, but by now, the brakes feel wooden and there is still not enough response. So you apply even more, and suddenly, the brakes 'grab' harder than you were expecting, forcing you to back off the lever. You don't slow down so much as 'lurch' down.
So the 'plot line' would be quite flat initially, then take a sudden upward jump quite late on the scale.

I'm used to brakes being precision instruments. :nenau I need a craft knife - not a lump hammer! :tears

I had a poke around the brakes last night. The bike originally came from Port Elizabeth before spending time in East London, so it's spent seven years at the coast. However, none of the caliper pistons are siezed, and the brake pads (OE Brembos) all seem in good shape. The amount of metal transfer to the pads *seems* high, though... I suppose I could pull the pads from my '09 to compare them, and see if they've glazed.
 
I was going to suggest you get one of the experience mechanics on here to test ride it but then I saw your location!
Just in case you only need to adapt to them, I think I remember finding mine a little bit on or off in the early days.
 
might be worth swapping the pads,i always fit oe bmw ones, apparantly they are a different compound to the aftermarket brembo fitment.(i have no definitive proof of this though)
braking is always a two finger affair on most servo gs's i have ridden and not as you describe your bike to be.
 
It almost sounds like your servo is starting up after the brakes are applied. I had a minor failure recently when wear on the microswitch on the hand lever meant that the bike failed its startup sequence, so no servo and very wooden brakes. Adjusting the position of the switch (a 2mm allen key) sorted it but it crossed my mind that the position of the switch was critical as, if it breaks too soon the system won't start up (same effect as lever trapped against handguard) and if it breaks too late then the servo fires up after the pads hit the discs, making the brakes very grabby.
 
What a shame we dont have brakes like the old Citroens. A small hydraulic pump charged a pressure tank and the brakes were fed by a simple valve. The result was a very light brake pedal force but when you adapted to it there was a lot of feel in what was going on. A bike with only brakes and maybe suspension height to play with would not need a large pressure tank so space and weight should not be an issue.

There we go - instant solution for shorties like me. Rise and fall suspension so I can reach the floor but also have a high seat and light brakes with lots of lever feel. Lovely. :)
 
Bendy toy said:
What a shame we dont have brakes like the old Citroens. A small hydraulic pump charged a pressure tank and the brakes were fed by a simple valve. The result was a very light brake pedal force but when you adapted to it there was a lot of feel in what was going on. A bike with only brakes and maybe suspension height to play with would not need a large pressure tank so space and weight should not be an issue.

There we go - instant solution for shorties like me. Rise and fall suspension so I can reach the floor but also have a high seat and light brakes with lots of lever feel. Lovely. :)
Click to expand...

Actually the brake valve was a clever device that fed main hydraulic pressure to the front brakes and rear suspension pressure to the rear brakes. That way the rear brakes were always proportional to load and even compensated for weight transfer under braking. Some vehicles had just a main pressure device called an accumulator, others also had a separate brake accumulator. Either way the vehicle could be safely stopped should the pump fail. Pump failures were, in fact, very rare with many of those pumps that were replaced being changed unnecessarily by people who did not understand the system.

John
 
Active suspension is all well and good but Citroen went a long way in that direction with relatively simple hydraulics. They were reliable but could be messed up by people who didnt understand the system.

High pressure hydraulics would also allow brakes to be physically smaller - less unsprung weight and cheaper to make.

What a shame we didnt suggest this to BMW for their new WC bike.
 
Nick V said:
That's odd... a great deal of positive feedback!
I wonder if there's not something wrong with some aspect of the braking system on this particular bike?

I'll explain: I've owned two '09 GSAs (one of which, I still do) before buying this '06 bike.

The '09s both have second-generation ABS (no servo). On both of them, it's a simple case of the harder you squeeze the lever, the harder you brake.
If you were to plot force applied at the lever vs. actual braking action, these bikes would give a steady, predictable, 45-degree upward plot line.
This is the 'baseline' I'm used to.

The '06 has servo-assisted brakes. With this bike, it's a case of the same initial force at the lever yielding very little response. So you apply a little more, but by now, the brakes feel wooden and there is still not enough response. So you apply even more, and suddenly, the brakes 'grab' harder than you were expecting, forcing you to back off the lever. You don't slow down so much as 'lurch' down.
So the 'plot line' would be quite flat initially, then take a sudden upward jump quite late on the scale.

I'm used to brakes being precision instruments. :nenau I need a craft knife - not a lump hammer! :tears

I had a poke around the brakes last night. The bike originally came from Port Elizabeth before spending time in East London, so it's spent seven years at the coast. However, none of the caliper pistons are siezed, and the brake pads (OE Brembos) all seem in good shape. The amount of metal transfer to the pads *seems* high, though... I suppose I could pull the pads from my '09 to compare them, and see if they've glazed.
Click to expand...

Quit worrying. For all the reasons you've posted is why BMW stopped using the servo system. Plus all the cost of the warranty claims..

The Grey One said:
Some vehicles had just a main pressure device called an accumulator, others also had a separate brake accumulator. Either way the vehicle could be safely stopped should the pump fail.
Click to expand...

If the pump failed, or the belt snapped, the amount of stopping power in reserve all depended on the condition of the accumalator sphere ( 20 years worth of citroen owning experience and working on them, plus a bentley, which ran the citroen system for brakes, with two huge brake calipers per front wheel, and rear suspension ;)) . :D
 
Steptoe said:
Quit worrying. For all the reasons you've posted is why BMW stopped using the servo system. Plus all the cost of the warranty claims..



If the pump failed, or the belt snapped, the amount of stopping power in reserve all depended on the condition of the accumalator sphere ( 20 years worth of citroen owning experience and working on them, plus a bentley, which ran the citroen system for brakes, with two huge brake calipers per front wheel, and rear suspension ;)) . :D
Click to expand...

You are right, but if you knew about the system it was very easy to check the accumulator spheres without removing. We also had a test rig for checking the pressure if in any doubt. De pressurise the system and the sphere unscrewed with little effort. Most could be changed in less than 5 mins.

John
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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