too much rear brake? GPz750

Earlier today I messed up a bit, a nice sunny day and I overtook in a bad place. My bad I know, the last time I smashed up a GPz I was 19...over 25 years ago.

I realised the mistake as soon as I'd pulled out but decided to open it wide and get out of a potentially dangerous situation. A car then appeared in the distance, there would have been room for all three of us and I'm pretty certain I could have carried on accelerating and made then overtake, Instead I jammed on the brakes hard and scrubbed a load of speed of, from about 70 to 40mph...the rear locked up and screeched and the bike fishtailed a bit before i let off. I pulled back in behind the car I was overtaking with lots of spare road, and waved apologetically at the oncoming car :blush: (which I don't think had needed to brake)

So bad riding on my part, and also poor use of the rear brake. :pinch: Just a heads up, these are dangerous toys even if you have been riding for a while and a lapse of concentration can be lethal.

I know some of the earlier kz had the rear disc brake reduced to avoid this lock up, and that sintered metal pads are generally not recommended on rears for this reason. Has anyone here
used a different bore rear mater cylinder to make the rear a bit more progressive?

Glad you kept it upright.

On my bike, the KZ1000P, which is 800lbs and change with rider, it's pretty easy to lock up the rear brake. I do two things to deal with this:

1) After I bleed/flush the rear brake, I let a little bit of air back in the bleeder valve to soften them up.
2) (this is KZP specific) I adjust the rear brake pedal so that it hits the front engine guard before reaching the full extent of its travel.

I then road test with hard braking from 20-30MPH to 0 to ensure that I can't easily lock the rear wheel.

The front brakes I keep hard and fully bled, as they're easier to control.

You could also try using softer pad material (kevlar?) and/or intentionally contaminating your rear brake pad/rotor with oil.

I have the same issue with my 79 KZ750 twin. 650Ed suggested cutting some grooves in the pads with a hack saw to reduce the effectiveness of the rear brake. It seems like a simple fix. I haven't gotten to it yet, so I can't report on the outcome.
Bill

I think for now maybe bleed it again, just not so well this time. Longer term I think maybe a smaller rear master cylinder piston.

cutting some grooves in the pads with a hack saw to reduce the effectiveness of the rear brake

Unfortunately it wouldn't work, unless you actually removed part of the outer edge of the pads. Small changes in area of pads doesn't affect braking,. Whilst the pad area is less. the pad pressure (force divided by area) increases proportionately.

Removal from the outer edge of the pads or fitting a smaller diameter disc would reduce braking force, by bringing the centre of pressure closer to the axle hence - reducing braking tourque.

For the compressive force from the brake piston, braking force comes from pad friction - which is a function of pad pressure. Lower pad pressure over bigger pad area = higher pad pressure over smaller pad area.

I can lock up my rear drum in a heart beat. Sometimes it's good, sometimes not. I wouldn't fudge around with it, I'd just get use to it.
In the wreck I left a J mark in the road when I put it sideways and bailed. The bike went under the truck and out the other side. I don't remember what happened to me, just no time for the front and step off.
Steve
I still have the brake stay with blood on it. I'm glad I don't remember. :dry:

I never use the rear brake unless in a emergency brake situation (and then only alittle to help the front brake) or for stops at lights or hills etc.. It really is quite useless for anything else, well except wheelies but ive sold my triple.

Was a heart beat away from buying a ZZR600 Kawasaki a couple times but I have a bad habit of clamping on the front brakes with all my might in a total panic stop and don't want to end up over the handlebars........ I drilled my rears years ago to try and stop the sqeaking (did'nt help) ..... need to practice a little cause I tend to stay away from them for this reason.

I can lock my front wheel before it tries to throw me.
Steve