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Discussion Starter #1
I know it's probably elsewhere on the forum, but can someone tell me if the rear brake handle is a combo brake which includes some braking force in the front, too? On an 06 400.

Thanks.
 

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Yes, the rear brake also operates the front. Supposedly the brake ratio is 70% rear and 30% front. The front caliper unit is actually two separate calipers, one above the other.
 

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If you follow the brake hose from the left lever down you will see that it leads to a proportioning valve bolted to the steering head. From that valve a hose goes to the front caliper and a steel line goes to the back of the bike to connect to the hose for the back caliper.
 

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Discussion Starter #4
I wonder why a combined braking system is used - is it supposed to be safer? And is it something you need to keep in mind when braking? I know the front brake typically supplies most of the stopping force, but I wouldn't want to over-apply it if it's also applied by using the rear. Hopefully it's nothing you have to think about while riding.
 

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It's kind of a safety thing in that it does provide some front wheel braking for those folks that are afraid to use their front brake. For those that use their brakes properly it provides no advantage that I can see.

The proportioning valve combined with the smaller piston it activates on the front wheel act together to keep you from applying a lot of force to the front wheel. That means you still have to use the right lever if you want to get proper braking out of the front wheel.

For all intents during normal riding you don't have to worry about it much. The reduced braking applied to the front wheel does not cause much by the way of issues. Your not anywhere near the limits of the front tire so your right hand brake is still in control of the braking limit threshold.

Only way I can see it would get you in trouble is if you are braking with just the right lever and are near the limit of the front tire then suddenly jam on the left lever.
 

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I call it as an early attempt at ABS Braking. :cool:
 

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Maybe you call it that but it does nothing about preventing wheel lockup like an ABS unit would.
 

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Absolutely Correct! I have locked up my brakes a few times. :neutral:
 

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I do not thing the 'proportioning valve' is indeed a proportioning valve at all.

The proportionality is introduced in the front caliper itself by having working pistons of differing sizes (effective areas) so when hydraulic pressure arrives from the 'rear brake master cylinder' it is connected to the smaller piston(s) in the front caliper. Conversely hydraulic pressure from the front master cylinder is connected to the larger piston(s) in the front caliper.

See this picture - linky

Well that's how it was on my olde svelte.
 

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You might be right about that Norman. One place in the manual calls it a proportioning valve and another calls it a delay valve. Neither explains how it works so that is anyone's guess. All they tell you about it is how to remove and reinstall it.

Somewhere I saw that the valve sends 30% to the front wheel and 70% to the rear wheel but I don't remember where I saw it. I don't think it is anywhere in the manual. It might have just been something someone wrote in a post.
 

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Piston diameter and pressure would not equate to the same thing. If there is 100psi in the line it would be pushing the piston at that pressure no matter the piston size. A larger piston does give more even pressure distribution on the pad however. I think they used smaller pistons on the secondary front caliper for cost and weight/size savings.
 

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Speedandstyle - would you care to read your last post as I cannot understand what you are saying.
 

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Speedandstyle - would you care to read your last post as I cannot understand what you are saying.
You stated that the smaller piston equals lower pressure on the secondary caliper.
I say that the piston size has nothing to do with the pressure.

The pressure would be generated at the master cylinder. The pressure is reduced at the "proportioning valve"{Suzuki does call it a valve in the parts diagrams}. The valve gives most of the pressure to the rear caliper but some to the front{70/30 split}.

The smaller piston size is simply to save on cost, weight and size.
 

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You stated that the smaller piston equals lower pressure on the secondary caliper.
I say that the piston size has nothing to do with the pressure.

The pressure would be generated at the master cylinder. The pressure is reduced at the "proportioning valve"{Suzuki does call it a valve in the parts diagrams}. The valve gives most of the pressure to the rear caliper but some to the front{70/30 split}.

Snipped
Well I never actually said that - what I actually said was
The proportionality is introduced in the front caliper itself by having working pistons of differing sizes (effective areas) so when hydraulic pressure arrives from the 'rear brake master cylinder' it is connected to the smaller piston(s) in the front caliper. Conversely hydraulic pressure from the front master cylinder is connected to the larger piston(s) in the front caliper.
Snipped
So bearing in mind there are physical laws in play here, the key one being:

Force=Pressure x Area

The force we are interested in is that applied by the piston and with aid of the caliper to both pads effectively applying a 'clamping force' to the disc.

The force is generated by the piston and as shown by the formulae is the product of two factors - The hydraulic pressure and the area subjected to that pressure in this case the effective area of the piston.

So all things being equal for any given hydraulic pressure, the force developed is proportional to the effective working area of the pistons.

Moving on the valve shown in the drawing. This is,I believe, a delay valve.

A delay valve cuts the hydraulic pressure to assure that only when strong braking is applied, pressure is also created at the front wheel.

In other words if you only lightly apply the rear brake then insufficient pressure will be generated to 'lift' the delay valve and allow hydraulic pressure to be passed downstream and no braking will be applied at the front wheel (This would commonly be the situation when manoeurving - like say in a car park when 'unexpected braking' on a turned front wheel would be disastrous.

Otherwise when applying the brakes with sufficient intent the delay valve will lift, hydraulic pressure would build downstream and a smaller clamping force will be generated (via the small pistons) than would be the case operating the front brake lever to develop the same hydraulic pressure.

It really is very simple and has absolutely nothing to do with cost and weight.
 

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The smaller piston may exert less force than the larger one{with equal hydraulic pressure} but not as much as you might think. The reason being is the pad size, which is exactly the same size for both. The force for actually stopping the wheel is there between the pads and the rotor

However your idea of a delay valve may be correct. I did a quick test and if you spin the rear wheel the brake lever immediately affects it. But with the front you have to pull the lever in a fair amount further before it does.

So again you may be correct. The rear brake lever works the rear brake unless you pull it a lot then it also activates the front. This would make some sense and would help with those who overuse the rear{or use rear only} from preventing a rear lock up and slide. But in this scenario the secondary caliper would have almost as much force as the primary and not the 70/30 ratio assumed. Of coarse it is possible that the "valve" has both delay and proportioning abilities!
 

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I would think that if they were trying to reduce cost and weight they would have just gone with a non linked braking system.
 

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I would think that if they were trying to reduce cost and weight they would have just gone with a non linked braking system.
Manufacturers are always looking at ways to reduce costs, regardless of what it is. They have engineers that rework other engineers designs with that in mind, sometimes with disastrous results.
 

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Manufacturers are always looking at ways to reduce costs, regardless of what it is. They have engineers that rework other engineers designs with that in mind, sometimes with disastrous results.
A true enough statement but I fail to see how it applies to what I said.

If reducing cost were the issue then they would have just installed a simple split system and bypassed all the cost of the valve and extra hose the linked system required.
 

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The smaller piston may exert less force than the larger one{with equal hydraulic pressure} but not as much as you might think. The reason being is the pad size, which is exactly the same size for both. The force for actually stopping the wheel is there between the pads and the rotor

However your idea of a delay valve may be correct. I did a quick test and if you spin the rear wheel the brake lever immediately affects it. But with the front you have to pull the lever in a fair amount further before it does.

So again you may be correct. The rear brake lever works the rear brake unless you pull it a lot then it also activates the front. This would make some sense and would help with those who overuse the rear{or use rear only} from preventing a rear lock up and slide. But in this scenario the secondary caliper would have almost as much force as the primary and not the 70/30 ratio assumed. Of coarse it is possible that the "valve" has both delay and proportioning abilities!
With all due respect - do you have a science and/or an engineering background?

This is all about physics and I have given you the formulae, the point you raise about the pads themselves is irrelevant because as you indicate they are the same size so in those terms they are a 'constant'.

Try the formulaes out with real figures the differences in force will surprise you.

I am done with this.
 

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OK I will admit that I am wrong on this. After doing a little more research I found that pad size does NOT affect the clamping force of a brake. It does affect heat distribution and reduce wear but larger pads do not give better braking ability. I was wrong on that!

I went ahead and did the math or rough guess from measuring the piston sizes in the photo and the larger primary caliper has slightly over twice as much force as the smaller secondary caliper. So it is much more than I thought.
 
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