Suzuki GS500 Front Brake Upgrade.


Suzuki GS500 front brake upgrade?

George Benes asks:

Hi, I own a 1993 Suzuki GS500E and was looking at changing the front brakes from a single disk (on the right side) to a dual disk, like many sport bikes, for better stopping power. The lower fork on the left side does not have a mount on it, so can I buy a new right-side tube and stanchion, flip it around and bolt it on in place of the left fork, which doesn't have a brake caliper mount? Also how and what can I use to connect both calipers? Is this a better way to go than upgrading the current caliper and disk setup?

...and MO answers:

You probably can't flip a right side fork leg around and put it on the left; on almost all newer bikes the axle mounts differently on one fork leg (Harley Davidson has such a kit for the 883 Sportster line - editor). Usually the axle screws into one leg and the other leg clamps around the axle. Before you go out and spend a lot of money, I'd start first by making sure that the stock brakes are up to spec and that you have fresh Dot 4 or 5 brake fluid.Making the brake lines wouldn't be a problem; you can make custom lines yourself. Just head on down to the local auto-racing shop that sells Earl's brake line kits and follow the instructions.

What you haven't said is what problem you are trying to solve - do your brakes fade? Are they just not strong enough? Does the lever come back too close to the bars?

Before you go out and spend a lot of money, I'd start first by making sure that the stock brakes are up to spec and that you have fresh Dot 4 or 5 brake fluid, depending on what the manufacturer specifies, preferably a high-temperature variety such as Motul. Rebuild the master cylinder and caliper if they need it. Then make sure the rotor is straight. And definitely make sure the brake system is bled really well - This last item is probably the most frequent cause of poor brake performance. Some systems bleed easily, some are nearly impossible to get completely bled.

Here's a tip: Whenever bleeding a brake system, unbolt the master cylinder/brake lever from the bars and hold the "L" junction (where the banjo bolt connects the brake line and master cylinder) in such a way the air can float all the way up through the joint and into the master cylinder. Then, squeeze the brake lever while lightly tapping the banjo bolt with a wrench. This will eradicate the few air bubbles that tend to get caught here since most of these junctions are at an angle (like "^" instead of "<") due to slanted clip-on bars.

If your brakes still fade, try experimenting with pad compounds. I don't know off hand what will work on GS500s, ask the people you race against. I'm still using the old asbestos Ferodo pads which are unavailable now, I have some Kevlar Braking pads to try on the RZ when the Ferodos wear out. Watch out for brake rotor temperatures with some modern Kevlar pads.

Then, if you're still unsatisfied or the brakes aren't strong enough, you should consider going to a better caliper and perhaps a better quality and/or larger rotor. I'd go with a single rotor system, it will be lighter (and that's crucial unsprung weight too) and simpler. A GS500 isn't really fast enough to need a full dual-disk setup, not to mention that a single disk is also cheaper, and easier to maintain.

If you improve your brakes, or even if you don't, make sure to put stiffer fork springs in the fork and change the oil.

If you want to do it yourself, you should be able to find a used GSXR caliper to fit. You may have to make an adapter plate, or you might get lucky and have it bolt right on. Make sure that the pads sweep the disk fully or it'll be nearly useless. The disk also has to be centered in the caliper, sometimes you can get a caliper that looks like it fits but the disk is offset to one side or the other - take care to avoid this, because an offset rotor introduces twisting forces that the front end wasn't designed to take, and you could end up with "brake steer." Also, as the pads wear our, you run the risk of one side's piston traveling out too far and cocking in their bores, which can make the brakes drag, or worse.

Make sure that the replacement caliper's piston area isn't too much different than stock if you keep the stock master cylinder. If the area's greater, then you will get more leverage (less pressure needed on the lever) but more travel. If it's less, you get less leverage but less travel. Going too far either way is bad; if you have too much travel you run the risk of the lever coming back to the bar if the brakes fade in a race. If you don't have enough leverage then you may get hand cramps during a race. Note, however, that steel braided brake lines will give you less effective travel on at the bars since the brake lines won't be expanding in diameter, so you could use a slightly larger bore caliper while retaining the same (and often less - some brake lines flex a lot) overall travel.

If you improve your brakes, or even if you don't, make sure to put stiffer fork springs in the fork and change the oil. The GS500 is notorious for having too-soft fork springs. Heavier oil may be also called for, it depends on your preferences and the track surfaces where you race. You'll get less front-end dive with stiffer springs so you will feel more secure under hard braking, and have some fork travel left to absorb bumps.

If you're dead-set on getting dual disks, look into replacing the whole front end with a GSXR unit, either from a 600 or a 750. They will probably bolt on. A 1991 or later upside-down fork is overkill for a GS500 - and it's expensive. Hell, they're overkill on my 65hp RZ. I'd suggest conventional forks from a 1989 or 1990. These forks are large-diameter and have dual disks. They'll be cheaper too.

--Eric Murray

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