GPZ500 Rear wheel/chain/brake

[stephen_o]

Hi all, can you help me with a problem so I can sort it before it becomes something bigger please.

Had new chain (tight links) and new boot on rear brake, these were needed for mot. On picking bike up all is fine, and rear wheel spins freely however the back brake was poor. Ive done 200 miles on the bike over 5 days and noticed tonight the rear is begining to bind or drag again. I cant see or hear any clunking in the chain and the back brake has become more effective which leads me to think maybe the brake is binding or dragging...How do I sort it before I have a bigger issue...Its been really nice to ride the bike with everything right for a week almost and want to keep it that way.

Thanks

Stephen
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current scoot 2009 Yamaha YBR250 + Current Pootle 2013 Nissan Leaf

[Kickstart]

Hi

With a GPZ500 (with a drum brake) the pivots for the operating cam for the brakes can seize up. I would suggest taking the wheel off, taking off the drum brake plate, take off the brake shoes and push out the operating pin (you will need to remove brake arm), clean it up and lube it then reassemble

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[stephen_o]

Thanks for the quick reply, my apologies but because I had just answered in another post from someone about my old clapped out CG I was thinking that the GPZ had drum brakes (will never forget the horrendous power charge through the stop box on mod 1 in pouring rain fuming with myself that I had blown it because I couldn't stop the bike quick on dual drums in the wet for the examiner to say.."yes youve passed because your entitled to extra leeway for an old bike") so typed drum instead of disc. The GPZ has disc brakes front and back.
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current scoot 2009 Yamaha YBR250 + Current Pootle 2013 Nissan Leaf

[Kickstart]

Hi

Ah, thought you mentioned drum, and the early ones have a drum rear brake.

If it has a disk rear brake then it is a single piston sliding caliper. they are a doddle to strip down and rebuild.

Check the wheel bearings while you are at it. Especially the sprocket carrier bearing, and also check that the spacer is in place between the sprocket carrier bearing and the wheel itself.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Rogerborg]

My 500 had a rear disc brake in the sense that there was a disc at the rear with a brake on it.

It is easy enough to clean out, you just need to pump the piston out and polish it, fish the seal out (I use a £1 shop dental pick filed blunt), and clean out thoroughly behind it (same tool), re-assemble and bleed (reverse bleed with a syringe by preference).

Then you'll have a disc at the rear with a brake on it that doesn't bind.
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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[stinkwheel]

'94 was the changeover year between disc and drum.

The rear discs are famously rubbish but shouldn't be binding.

In my experience, binding was normally caused by corrosion around one of the sliding pins.

One of the pins is fully enclosed inside the calliper casting, this one is usually fine. The other runs in an open hole right through the casting with a rubber boot over it, corrosion used to build up between the alloy of the calliper and the rubber boot. The pin itself was usually clean.

So a case of pull the calliper off the pins (this should be do-able by hand, if it isn't, this is definately the problem), try to get the rubber boot out without tearing it. Tear it. Order a new one, scrape/wiggle/polish the alloy corrosion out of the hole in the calliper while you're waiting for the new boot to arrive (may as well clean up the piston like Roger described too).

Grease both sides of the boot this time, reassemble.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

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