can't lock front brakes

[p_s]

'85 GS550ES

I went to a parking lot yesterday for the first time ever to just practice braking. At 30 mph and lower I can't seem to lock the front. I have stainless brake lines, new seals and fluid. The lever is very stiff and I was grabbing as hard as I could. I'm not sure what the pads are--the PO put them in. Green backing with gray pads. I have a fairly soft front tire--an Avon Roadrider.

Do I need a MC with a smaller bore or is that just how old bikes are? A friend has a stock '88 Ninja that has never seen a wrench and he says he can lock the front with two fingers.

[rphillips]

The only times I've locked the front, I dumped the bike. I hope I never lock the front again. Sorry, that didn't answer your question.

[GQROD]

Perhaps a manual pump vac bleeder.

rphillips i know how you feel i dumped a trainer bike at 30mph locking up the front brakes! personally i'd rather not have them lock up.

It seems with the anti dive it is difficult to porperly bleed the brakes. I manually bled mine the old school way not with a ez vac brake bleeder, and i cannot lock my front brakes. Though i would not want to.

On my porsche i went with a LARGER bore MC to get more pressure i went from a 17mm to 19mm and stainless lines and this made the brake pedal firmer than stock. Big improvement over stock.

I don't know what the solution is for these bikes with anti dive other than to remove the anti dive from the forks.

[Zooks]

Does it pull the bike up from a decent speed? Does it feel responsive enough that you will be able to stop when a car pulls out of a driveway onto the road without looking?
If you answered yes & yes - don't worry about it.

Old bikes tend to have 'spongey' brakes. As long as you feel safe with it. If not, you might think about a later model brake upgrade.

[p_s]

The brakes aren't spongy whatsoever. Much stiffer than my neighbor's 2008 SV650 with rubber lines. I can't get the lever anywhere near the grip. I also don't have the brake linked anti-dive on my bike (that was changed in '84 or '85). I just think there must be some braking force left if I can't lock it up.

P.S. I used a vacuum brake bleeder today to do the car. What a PITA! It was less of an environmental disaster than when I change the other fluids on the car, but only because there is less of it to begin with. Still had to call the wife out to pump the brakes. Next time I might find a spare MC cap and plumb it to compressed air and pressure bleed the brakes.

[Mark M]

On my porsche i went with a LARGER bore MC to get more pressure i went from a 17mm to 19mm and stainless lines and this made the brake pedal firmer than stock. Big improvement over stock.

I hate to tell you this, but a larger bore generates less pressure for any given amount of pedal or lever force, not more. It will firm up the feel because it takes more force to generate any given level of stopping force.

Mark

[Big T]

You shouldn't be locking up the brake at 20 or 30, it's a loss of control.

The question you need to ask is, did my tire moan?

Well, did it?

That's the sound of nearly at brake lock up.

If it doesn't moan (this is more apparent at speed) then you need to try:

1. Softer brake pads
2. More modern calipers (as in the Kawasaki twinpot mod - see Performance)

The master cylinder cannot create a higher coefficient of friction between the rotor and the pad, and that is what you need to stop faster.

Modern bikes, like your buddies, stop faster because they have 4 piston brakes, better brake material, bigger and better rotors, and stickier tires. Plus better balance of the Center of mass and all that physics stuff.

It is 30 year old technology, after all.

[GQROD]

I hate to tell you this, but a larger bore generates less pressure for any given amount of pedal or lever force, not more. It will firm up the feel because it takes more force to generate any given level of stopping force.

Mark

Thanks for the correction.

Just expressing the experience i have had with a required modification on a popular car that worked for me, as such perhaps a bigger mc is available to give the same level of increased braking performance for the GS that i experienced with my porsche. Although pedal effort is higher( increased pedal pressure i should have said is needed ), it provides less pedal travel and eliminates the spongy feeling of the original lines.

I pasted this following article ( using car braking systems as example but some principles may apply to bikes) which goes into detail explaining the pros and cons of bigger bore mc's. Ultimately it's a matter of what you are looking to achieve from your ride, that determines what size mc is best to use.

"Technical Corner

With regard to braking it’s always helpful to refresh the basic rules of brake systems. If you fit larger discs you will increase the braking mechanical advantage. This will reduce pedal effort. If you find this results in brakes that are too sensitive for track use you can increase pedal effort by changing the master cylinder or removing the brake servo. A larger master cylinder bore size will increase pedal effort but reduce pedal travel. Master cylinders are usually available in inch sizes, pedal effort in lbs per sq inch and piston sizes in mm (great!).

Some formulas will demonstrate what you might end up with:

If you increase disc size from 284mm to 300mm you would end up with a 5% decrease in the pedal force required to get the same braking force. Therefore a 100lb force required before would become 95lb

New pedal force = Pedal force x (Old brake disc radius/New brake disc radius)

The rolling radius of the tyre has the opposite effect - increase the diameter of the tyre/wheel combination and you increase the pedal force required.

New pedal force = Pedal force x (Old tyre radius/New tyre radius)

In this case if you went from a 14” Wheel with 195/60 up to a 16” wheel with 205/55 you would increase the pedal effort required by 10%.

When looking at master cylinders the formula is as follows:

New pedal force = Pedal force x (new master cylinder bore diameter²/ old master cylinder bore diameter)²

Because of the square in the above formula the effect of a change is more pronounced. E.g a move from a 1” master cylinder to a 1.25” master cylinder will change the pedal force required from 100lbs to 156lbs.

Next thing to remember is bigger pistons in the calipers mean more force and, therefore, less pedal effort. Bigger pistons in the calipers mean more pedal movement. For comparing one brake to another on the same car, you can simply multiply the total caliper piston area times the effective radius. If you have a sliding calliper although it has piston(s) on one side the area should be doubled. A single piston sliding calliper with the same piston size as a twin fixed calliper will have the same clamping force.

When planning your braking modifications it is a good idea to consider these factors. Naturally bigger brakes often require bigger wheels so the two cancel each other out to a degree."

[GQROD]

The brakes aren't spongy whatsoever. Much stiffer than my neighbor's 2008 SV650 with rubber lines. I can't get the lever anywhere near the grip. I also don't have the brake linked anti-dive on my bike (that was changed in '84 or '85). I just think there must be some braking force left if I can't lock it up.

P.S. I used a vacuum brake bleeder today to do the car. What a PITA! It was less of an environmental disaster than when I change the other fluids on the car, but only because there is less of it to begin with. Still had to call the wife out to pump the brakes. Next time I might find a spare MC cap and plumb it to compressed air and pressure bleed the brakes.

Thanks for clarifying that i was under the impression all the E and ES's 83-86 had the anti-dive.

[fast pom]

You say you have new break pads how new ? have you given them time to bed in

[p_s]

You say you have new break pads how new ? have you given them time to bed in

Er, actually not that new. 4.5 years old & about 10k miles, but there's still 2 or 3 mm of pad before the wear indicators. I have a pair of spare rotors so I might get sintered pads next time and see what happens.

I'm not really looking to lock the front, but I'm not getting the howl either. I was really trying to get it to lockup at low speeds (like 20) so I could learn how to modulate it and learn how to get the tire to howl but not lock-up. On the rear brake this is no problem. I understand it has to do with the ratio of the bores and the number of pots and so on. I might look into putting on a different MC if that'd give me more braking power but otherwise I'll probably just leave it alone.

I've never been in a situation where I simply needed more braking power, but I've only been riding for 2.5 years.

[silverhorse47]

The combination of hard lever and no lock is a puzzle. If the throw of the plunger in the mc is too short, or the diameter of the bore is too small for the system, that would account for the pistons not having enough travel to drive the pads into the disk.
But if that were the case I do not think you would have a 'stiff' lever.
I would look for some mechanical problem...filthy dirty cylinders, seriously scored pistons, deranged levers, worn rubber bits...things that would actually impede motion between the lever and the pad.

In the interests of diagnoses, could you put something like bits of paper or cardboard between the pad and the disk and see if the pad actually can come tight against the disk when the lever is compressed? This would determine whether the problem was too much travel or poor hydraulic performance.
S.

[p_s]

In the interests of diagnoses, could you put something like bits of paper or cardboard between the pad and the disk and see if the pad actually can come tight against the disk when the lever is compressed? This would determine whether the problem was too much travel or poor hydraulic performance.

I pulled the covers and you could see the shims flexing slightly when I pull the lever. The tire spins freely when I release the lever. The seals & pistons in the calipers are 6 months/8k miles old, the MC seal & piston is 4.5 years/11k miles old. The bike still stops very quickly if you really grab the lever. I was just wondering what was normal, and it seems like noone here with a stock braking system can lock the front, so I guess I am satisfied that nothing is wrong. I was a little surprised that my friend's Ninja, which is just 3 years younger, brakes like modern sportbikes--2 finger lock up.

[silverhorse47]

I must be out of my element. You lost me at 'shims'
S.

[p_s]

I must be out of my element. You lost me at 'shims'
S.

#13. It moves.