twin calipers more lever travel than single?

[DimitriT]

I just finished upgrading the single rotor front brake on the 750T to a twin. The results were a nice improvement overall. Braking is much more effective and I can now confidently pull as hard as I want without worrying that the brake will fade on me (the way the single used to do). That along with the Dunlop tires make the bike quite a bit safer (which was my intent).

As part of the conversion I rebuilt both calipers and the master. Braided hoses were also part of the conversion.

Now I did notice one difference which was unexpected and negative:

the initial bit of travel on the lever feels unresponsive and springy

I'm talking the first 30-40% of travel

once I get past this, the brakes engage nicely and there's no problem

I've carefully bled the system several times and have done everything I can think of to
eliminate any air bubbles.

But I'm not sure its air trapped in the system.. the brakes work. in fact they work very
well.

It's just that the point at which they engage is much further that what I was getting with
the single caliper.

Is this normal? Anything I can look for?

I'm using the original pads (which are like 20+ years old and most worn). Could that affect it?

 

[Nessism]

Dual disc master cylinders are larger diameter than singles. What you describe is normal. If it's too spongy for your liking, get a different master.

 

[tkent02]

I just finished upgrading the single rotor front brake on the 750T to a twin. The results were a nice improvement overall. Braking is much more effective and I can now confidently pull as hard as I want without worrying that the brake will fade on me (the way the single used to do). That along with the Dunlop tires make the bike quite a bit safer (which was my intent).

As part of the conversion I rebuilt both calipers and the master. Braided hoses were also part of the conversion.

Now I did notice one difference which was unexpected and negative:

the initial bit of travel on the lever feels unresponsive and springy

I'm talking the first 30-40% of travel

once I get past this, the brakes engage nicely and there's no problem

I've carefully bled the system several times and have done everything I can think of to
eliminate any air bubbles.

But I'm not sure its air trapped in the system.. the brakes work. in fact they work very
well.

It's just that the point at which they engage is much further that what I was getting with
the single caliper.

Is this normal? Anything I can look for?

I'm using the original pads (which are like 20+ years old and most worn). Could that affect it?

Normal, you have twice as many pads to move into the position where they touch the rotors, so it takes more fluid movement.

Master cylinders designed for twin rotors have a larger piston diameter and so more fluid movement, you get them coming on quicker but you get less pressure at the pad too, if you can live with the increased lever travel you get more powerful braking with the single rotor MC.

Go with new pads for more braking with less finger pressure, some brands have more than others. I just put some Vesrahs on my GS1000, they seem fairly grippy.

Break the pads in properly.

Also braided steel brake lines will tighten up your lever a little bit, or a lot depending on how bad your old hoses are.

Suzuki recommends changing the original hoses every year, bet that hasn't been done in a while.

 

[Matchless]

The single front caliper master cylinder has a 1/2" bore, it is stamped on the bottom. The the twins use a 5/8" bore, also stamped on the bottom. You now want to move twice the amount of brake fluid and the travel will double up on the 1/2".

 

[Road_Clam]

Normal, you have twice as many pads to move into the position where they touch the rotors, so it takes more fluid movement.

Master cylinders designed for twin rotors have a larger piston diameter and so more fluid movement, you get them coming on quicker but you get less pressure at the pad too, if you can live with the increased lever travel you get more powerful braking with the single rotor MC.

Go with new pads for more braking with less finger pressure, some brands have more than others. I just put some Vesrahs on my GS1000, they seem fairly grippy.

Break the pads in properly.

Also braided steel brake lines will tighten up your lever a little bit, or a lot depending on how bad your old hoses are.

Suzuki recommends changing the original hoses every year, bet that hasn't been done in a while.

This is exactly my thoughts as well. I remember reading a very interesting tech article reguarding brake fluid volume vs. MC piston diamnter, vs. braking force.

I am thinking you would benifit from finding an "E" model dual disc master cylinder......

 

[DimitriT]

Well, it sounds like this is normal..

I am using the master from the donor bike (a 650G) which had the twin calipers.
I also have braided hoses.

I'm guessing that the extra hoses and calipers absorb some of the hydraulic pressure
before the pads apply enough force to engage. Probably the small amount of
expansion/compression in the hoses and the caliper and master seals gets multiplied
for the twin rotor setup.

But once the expansion/compression reaches some limit the brakes engage very nicely.

If there was an air bubble, the brakes would never fully engage. I'd pull the handle and
the bike would continue to roll. That's not happening so I'm excluding that possibility.

 

[Road_Clam]

I had a REAL challenging time ridding my anti-dive system completely of air. I got a tip from my long time Suzuki tech buddy Jay to bleed as normal first, then remove the caliper, hold it in your hand, crack the bleeder screw and gently roll the caliper in a circular motion at all angles to allow stubborn trapped air to exit the bleed screw. When you see a slight "slosh" exit the bleeder rather than consistant drips, you know you expelled an air bubble..... works like a charm !!!

 

[tkent02]

If there was an air bubble, the brakes would never fully engage. I'd pull the handle and
the bike would continue to roll. That's not happening so I'm excluding that possibility.

Not true, a small amount of air can only compress so far, after is is squeezed down to nothing the brakes will feel fine.
Would explain your lever moving too far and then working normally.

If you have the dual piston MC and steel lines the lever should not move very far at all

Try taking all the parts off the bike without disconnecting the lines, turn them over and all around, tap them lightly with something to move air bubbles around, bleed bleed bleed.

Do the calipers, the MC and especially the joint where all three lines come together.