Quote from: SAFE-T on October 20, 2011, 09:14:24 AM
Taught motorcycle courses with the Canada Safety Council for almost 15 yrs.

It was my constant experience that the harder you use the front brake to stop faster, the less you should use the rear brake. Most people are used to driving cars, where you push with your entire leg to apply the brakes. I observed students doing this on their bikes as well during braking exercises. The student would actually lift their heel off the peg and push down HARD with their leg, with the result being they would lock up the rear brake.

This is absolutely, 100% correct. The harder you apply the front brake, the softer you need to apply the rear. The old 70%/30% braking figure only applies to very routine stops on modern bikes. For more aggressive braking, the number is closer to 90/10, and on the track, we brake so hard that most of us don't use the rear at all.

A big mistake a lot of riders make is that in an emergency situation, they apply the front and rear brake harder than they normally would, when in fact what you want to do in that situation is apply the front harder, and the rear more gently. In doing so, you prevent the rear from locking up, while still benefiting from muscle memory and the bonus it provides to stability and stoppie resistance.

Of course, lots of factors affect how much you apply the rear brake. In the rain, it's absolutely necessary to use the rear to get maximum braking power out of the bike. The rear brake also serves as a good lockup indicator in those conditions.

Cruisers, and long heavy sport touring bikes tend to benefit from more application of the rear brake than sport bikes. Sport bikes benefit more than motards.

With a passenger, again, you need to apply the rear-brake more aggressively than you would solo. When I used to commute 2-up in the rain, I'd apply front and back about 50/50.

Quote from: NorwayGT1 on October 20, 2011, 09:48:36 PM
I found out that if your tires are cold your chances of locking up your tires are a whole lot better! It didnt do it again because that wormed the tire up and i kept on riding for a while and that in it self made the tire nice a worm!

As you say NorwayGT1 your describing a tyre issue not a brake issue. 

As I start pushing the boundaries of what my K9 can do I too have noticed that under harsh braking the stock suspension is not up to the task.  The soft (comfy) suspension allows the bike to become unstable when you combine both types of braking.  I have experienced excessive shudder in the front and I am pretty sure that I have unloaded the rear wheel to the point where it has been allowed to momentarily lock up when combining aggressive braking and engine braking.

FWIW I like the brakes on the GS, I find they give good feed back and are predictable without fail.

Quote from: uninhibited on October 20, 2011, 10:50:27 PMAs you say NorwayGT1 your describing a tyre issue not a brake issue.

A tire issue that has a huge impact on brake performance. Poor suspension performance can also have a devastating impact on brake performance.

yeah my rear tire is due for replacement it has plenty of side grip but the top is getting worn down quit a bit. and fyi i never said i didnt like the break on the gs... they did their job lol, my tire just was not worm so it locked up. but  hey you live and learn

Quote from: uninhibited on October 20, 2011, 10:50:27 PM

As I start pushing the boundaries of what my K9 can do I too have noticed that under harsh braking the stock suspension is not up to the task.

Excuse me for interrupting here but. . .
What is this K9 you speak of?
Are you referring to a 2009 GS500F?
Thanks,
-Ej-

Model is GS500FK9 meaning a 2009. The letter indicate the year with some letters skipped. Seems starting in 2000 they used K? which is a number indicating the year. Much of that can be found in the front of a Haynes manual, Suzuki service manual or just looking up various years in the parts catalogs.

Examples: 1992 = N
1994 = R  (O and Q skipped)
1997-2000 = W, X, Y, Z
2007+ = K7, K8, K9, etc.
Not sure what 2010 or after is.

Quote from: adidasguy on October 21, 2011, 04:24:28 PM

Examples: 1992 = N
1994 = R  (O and Q skipped)
1997-2000 = W, X, Y, Z
2007+ = K7, K8, K9, etc.

Ohh, Got it! 

Quote from: adidasguy on October 20, 2011, 10:15:59 PM
How old are your tires? Was air pressure OK?

Old tires get hard and don't grab the road. I locked up Trey the first month I had him: rear tire had good tread but was old and hard. New tire: never happened again.

Moral: tread noes not equate to good tires.

The rear brake locks period. I can't think of a single bike that you can mash your rear brake and not lock it. Slow and steady on the rear, firm and deliberate on the front. The problem is the GS is the only bike I can accidentally lock the rear on. I have to make a deliberate effort (because the feed back tells me to back off) to lock up the rear on a better quality bike.

Quote from: Dr.McNinja on October 21, 2011, 05:57:31 PM

The rear brake locks period.
I can't think of a single bike that you can mash your rear brake and not lock it.
Slow and steady on the rear, firm and deliberate on the front.

The problem is the GS is the only bike I can accidentally lock the rear on.
I have to make a deliberate effort (because the feed back tells me to back off) to lock up the rear on a better quality bike.

Yes! I believe your onto something.

DISCLAIMER:
My particular 07 GS500F is obviously defective. MSF braking practice drills wont repair it.
However, with the help of this thread (that's you guys) I'm gonna' figure this out. 

UPDATE. . .
Adidasguy sent me a bunch of very interesting links for used GS500 parts.
I didn't realize that there were so many parts available for low prices.
The Pinwall Cycle link was also a nice surprise!
I have to start tearing into the bike for a closer look but my plan is to methodically replace. . .
1.) Rotor
2.) Master cylinder
3.) Caliper
4.) Pads

I have my reasons for doing the rotor first.
Since the bike was new I was never real happy about the run-out on the rear rotor, (that's another story).
If I mic it off the bike and it's not true, I obviously have a bigger mystery to deal with.

I'll be back with some photos of what I found.
Regards,
-Ej-

I'd first replace the calipers and pads with one of the really good ones from Pinwall for $14.95. That's easiest to do - no need to remove the wheel. Only 2 bolts on the bracket, 1 bolt on the torque arm and the brake line.

I believe the master cylinder is OK unless it is leaking.

With the rear caliper off and fluid out, you can manually pump the brake lever and see if you feel any sticking. It should move real easy. Possible something bad in the pedal or linkage to the MC.

It's been 2 years since I had my hands into this bike other than routine maintenance.
I guess I'm getting the winter itch for a tear-down a little early this year.

In about ten days or so I should have a selection of GS brake parts in my hands and I'll start the "experiment". I'll take lots of pictures too.
This thread will most likely go stale by then so I will be sure to PM you and a few of the others that have also complained about the rear brake issue when I post my results & photos in this thread.

Thank you adidasguy and the rest of the crew here that have posted. It's all been helpful stuff.
Thanks!
-Ej-

Quote from: Electrojake on October 21, 2011, 06:33:02 PM
Since the bike was new I was never real happy about the run-out on the rear rotor, (that's another story).

That would be a BIG piece of information to leave out...   

BTW, I checked the Fiche and it does look like Suzuki updated the rear brake part for certain late model bikes. Not sure what's changed, but it is a newer part.

In between work and rain I took the GS to a practice spot and did several panic stops from 35 MPH down to zero, on the rear brake only.
Actually it was not all that bad, ( I should stop whining so much). 
It just requires a lot of concentration to find the thin line between max braking and a locked rear wheel. My other bikes are indeed more forgiving.

I did a quick check of the run-out with a dial indicator and the rear disk is not true.
I'll post a short video of the test soon as time permits.
And thanks for the continued comments. I'm no master mechanic so all your input helps!
-Ej-

Quote from: Electrojake on October 27, 2011, 02:06:24 PM
Actually it was not all that bad, ( I should stop whining so much).
I did a quick check of the run-out with a dial indicator and the rear disk is not true.

That would explain a lot. Congrats on taking time to to some braking exercises.

Is it the wheel or just the rotor that is not true? Or something on the back of the rotor so it doesn't sit true? Ever a rear crash or drop with this rotor?

Since you admitted you're a whiner  , don't get that cheap Chinese crap. Get yourself a good rotor - spend the money or get a quality OEM used one. 
http://www.ebay.com/itm/00-Suzuki-GS500-500-REAR-BRAKE-DISC-ROTOR-/130575534071?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item1e66e887f7

http://www.ebay.com/itm/2005-SUZUKI-GS500F-REAR-BRAKE-ROTOR-6-02mm-/330602255127?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item4cf96e1317

http://www.ebay.com/itm/2002-SUZUKI-GS-500-REAR-ROTOR-316-/110671485954?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item19c488dc02

http://www.ebay.com/itm/09-SUZUKI-GS-500-F-REAR-BRAKE-ROTOR-GS500F-GS500-/250800923345?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item3a64e662d1

I look at the photos for wear, go for low mileage, newer vintages and no rust. Price: many bike breakers have a fixed price and do not base price on quality so do not let price be your main indicator of quality. I've bought the rotors from a bike with 240 miles for under $50.

I did a quick check of the rear last night on the GS500F. . .
Click the link to see my cheesy rotor video- http://youtu.be/SM0snKJE8KU

I have to pull the rear wheel off the bike and remove the rotor before I buy anything.
However, if I find the rotor to be out, it will be interesting to see if the wheel is true, or perhaps a defective wheel at the factory pulled the rotor into a warp.

I have been looking at after-market rear rotors such as the two different EBC units pictured below...

...and...

Cost: About $130 for the stock Suzuki rotor and about $150 for a snazzy after-market rotor.
Thanks again,
-Ej-