FZR1000 Braking inconsistently

tahitianrider

tahitianrider

Been Around the Block
Hey!
So I just got myself a nice vintage sportbike: a 1988 FZR 1000 Genesis.
The bike is running, but I already have a long to do list for the restoration of this sweet bike.
One thing that is weird to me is the rear brake: when applying a constant light pressure on the rear brake, it brake inconsistently, it will brake harder, then smoother, then harder, etc. following the same pace, it kinda feels like when you try to lock the rear wheel with an ABS bike.

The disc is not bent, I've put the bike on a stand and spin the wheel to check if it was bent (by eye)
I did plan on bleeding the brake with new DOT4 etc. during the restoration but I just though this was strange...

Any ideas?

Thanks :)
 
It certainly sounds like a rotor that's out of round or has a high spot on one side.
 
It does sound like a rotor but a thorough clean and flush (and new pads) for the entire rear brake system should also be done to be sure. While you are at it, get a stainless line to replace the old oem hose. You can also check the thickness of your rotor against the spec to see if it's too worn as well. If so, replacements aren't very expensive.

https://www.ebay.com/itm/Rear-Brake-Disc-Rotor-For-Yamaha-XP-500-T-Max-01-11-FZR-1000-EX-XJR-1200-RD-350/264359497202?fits=Year%3A1988%7CModel%3AFZR1000%7CMake%3AYamaha&hash=item3d8d0dcdf2:g:dIIAAOSwO5JdARQf
 
This may sound dumb, but as you check the brake components, go over the entire wheel and make sure everything is nice and tight as well. All fasteners, axle adjusters, etc...
 
Sounds like a warped disc, but I had this symptom with a Chinese replacement disc when pad material built up on it, cleaned the disc with brake cleaner, disc felt fine until the pad material built up again.

I've never had this problem with 80s Yamahs OEM discs though.

Sent from my SM-T560 using Tapatalk
 
Thanks for the help! Yeah it definitely sounds like a bad rotor, but it seemed fine by eye, it also seems to be a stock rotor and no a cheap replacement one.

Anyway, replacement rotors are cheap enough so I bought a new one to see if the problem was indeed the rotor, it is Chinese wave rotor but I can just change it again if the quality isn't good enough, at least I'd know if the current rotor is the problem that way.

I will also change the whole wheel anyway, this is the stock wheel and it looks terrible, all the stock paint is coming off, and I got a nice set of replacement wheels with the bike so I'll install those ones along with new tires.

I though about installing a stainless steel braided brake line when bleeding the rear brake, but I noticed that the rear wheel already locks and slide super easily on the road, I had to brake, not even that hard a few time and I sent the rear wheel sliding. So my though was: why would I need even better brake performance when the rear wheel already lock and slide so quickly?
 
tahitianrider said:
....
I though about installing a stainless steel braided brake line when bleeding the rear brake, but I noticed that the rear wheel already locks and slide super easily on the road, I had to brake, not even that hard a few time and I sent the rear wheel sliding. So my though was: why would I need even better brake performance when the rear wheel already lock and slide so quickly?
Click to expand...

If the rear brake line is the original, I'd still replace it. The old ones dry out, crack, and flex/expand over time. You'll get a better braking feel from a stainless line, they don't expand under pressure like oem rubber hoses do.
 
canyoncarver said:
If the rear brake line is the original, I'd still replace it. The old ones dry out, crack, and flex/expand over time. You'll get a better braking feel from a stainless line, they don't expand under pressure like oem rubber hoses do.
Click to expand...

Yeah a stainless steel brake line is definitely a good improvement for sure, and I have to admit that a nice red braided line would look nice with the new red fairings :)
To be honest I didn't feel any difference when I switched to stainless lines on my '84 FJ600 but at least I now know I can rely on the brake and that the lines won't age and crack.
 
If the rear wheel is locked, it basically is no longer providing much braking force. The rear wheel should only lock if you stomp on the brake pedal and that's not a good way to ride. Brakes should be squeezed and not grabbed. At the front, squeeze to get the front end settled and then progressively apply more pressure.

If the brakes garb, the wheel locks and that causes all sorts of issues. My son had that on a TZ350. front brake grabbed and teh whel locked and in a nano second he hit the ground at close to 140. Not something to be encouraged.

Your rear wheel could be locking up because of that high spot. When the wheels and lines and rotor are replaced, try the rear brake again and if it still locks up, look for a different diameter master cylinder
 
Yeah the rear was locking up even though I was gently squeezing it, out of all the bikes I've rode, this never happen on any other bike, even with enduro tires on road. When commuting and riding gently (I commute every day on bike), I use more the rear brake to slow down very slowly, to a red light for example (not when I really need to brake of course...)

Damn that sounds bad, hope he was OK. But yeah I guess that high spot is causing the wheel to lock, I'll try again when everything will be replaced, the rear tire is pretty worn out too.
 
Thanks. He's fine. No lasting damage to him and the bike was able to be repaired - aluminum tank took some panel beating though :-(

When you have the parts replaced -- including that tire, so how it runs and stops.
 
teazer said:
Thanks. He's fine. No lasting damage to him and the bike was able to be repaired - aluminum tank took some panel beating though :-(

When you have the parts replaced -- including that tire, so how it runs and stops.
Click to expand...

As long as the people are fine, bikes can be fixed ;)

Yeah I'll test everything once the bike is back together, right now I started to tear it to pieces for restoration. I'll put the braided line on the rear brake, I'll also install a nissin master cylinder and braided line I got with the bike as spares up front.

The tire doesn't look that old, I need to check but I'd say less than 5 y/o, it is pretty worn out though.
 
A fresh set of rubber probably wouldn't hurt. No point in taking unnecessary risks with old rubber that's past its use by date. The costs of teh consequences are usually much higher than the savings in using old rubber. ;-)
 
Yes indeed, the brand new bridgestone BT 016 are already sitting on my balcony waiting to be mounted on the spare wheels :)
 
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