Calling GPZ500 owners...

[SilverWings]

Hey guys, looking to pick some brains. I'm mulling over potentially changing the rear brakes on my ER5 from drum to discs, probably mainly using parts from a GPZ since they're already very similar bikes. The drum brake is a pain on my bike and it's out of round, I tried having it skimmed, didn't work and now there's not really enough material to try again. My options are get a new wheel (~£100) or change it to a GPZ wheel and put disc brakes on it (can pick up the parts on ebay for probably around the same price).

What I'd like to know right now is the distance between the ends of the swingarm on the later model GPZs, basically how much space does the wheel, caliper holder, spacers etc take up. I'm trying to gauge how much work it's going to take to fit on my ER5, am I going to have to modify spacers, make new ones etc.

Any responses are much appreciated, obviously this only applies to the models with disc brakes. Could you tell me the year of your bike too?

And if anybody has done this before and has any advice or tips it'll be much appreciated!

[Beehive Bedlam]

My advice is sell the piece of shit ER5 (yes I've ridden one it was awful) and buy a better bike.

[Nobby the Bastard]

It would be cheaper to buy another wheel than convert it to disk. After all, all you'd be doing is making it lock up quicker.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[SilverWings]

Funny, my favourite mechanic says the same thing. Can't understand why :3 Unfortunately for the moment I'm poor and this is reliable, it's not let me down once in 2 years, so I think I'll hold on to it for now

[SilverWings]

It's not that it locks up...it doesn't do much at all. When it gets wet it's at best a 'slow down' lever, and even in the dry it's not very effective. The drum brakes on my own GPZ when I had one were also shite, I just didn't get on with them. Having had bikes with both drum and disc rear brakes I much prefer the feel of discs.

[Nobby the Bastard]

[SilverWings]

[Kickstart]

Hi

It is likely to be a bit of a pain to do. Surprised at the comment on £100 for a rear wheel for one but a quick glance on Ebay shows they are surprisingly expensive (cheapest was £70).

To do the swap you will need to find a mount for the reservoir, modify the footrest hanger to hold the master cylinder, and then swap over the swinging arm. This would be the nasty bit as the GPZ500 has a single shock and the ER5 has twin shocks. You would need to weld some mounts in place on the swinging are (and not sure if there is clearance for the rear brake if the mounts were in the same place).

Personally I would stick with a drum rear brake

All the best

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

[Kal]

Mine is at Katy's at the moment, I'm sure she would be willing to measure it for you.

What did occur to me is how do you intend to attach the calliper?

And while I've made a cup of tea she has actually already replied


I understand what you mean, I prefer discs now I've been riding on them, but even on disc the rear is merely a trailing brake.

After my experience October before last I can cartographically state that the rear on a GPZ is not that effective at stopping the bike on its own.
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Kal...
I Like To Hoon It Hoon It I Like To Hoon It Hoon It I Like To Hoon It Hoon It Ya Like To (HOON IT!).
1984 GB250 Clubman,1983 CB250N Superdream, 1999 GPZ500S

[SilverWings]

Would I need to change the swingarm? Looking at GPZ schematics, the caliper holder sits in place with a small piece of metal on the inside of the swingarm, could I not just get a piece welded on to mine to hold it? Yeah, ER5 wheels are expensive and hard to find, actually been looking for one since my last MOT cos it's gonna be a failure this time round. I messaged a few sellers on Ebay to ask about the condition of the drum and not one got back to me, I'm reluctant to spend that much on something that might not even be any better. Thanks for the input.

[Kal]

Assuming you switch the swinging arm out you then have the issue of a ER5 being a twin shock and a GPZ being monoshock.

Sorry to be a pain n the ass.
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Kal...
I Like To Hoon It Hoon It I Like To Hoon It Hoon It I Like To Hoon It Hoon It Ya Like To (HOON IT!).
1984 GB250 Clubman,1983 CB250N Superdream, 1999 GPZ500S

[SilverWings]

[stinkwheel]

More to the point. The single pot sliding callipers they used on 90's kawasakis are FUCKING shit.

The drum is better and also has the advantage that it can't spit its brake pads out.

Fix your drum.

SOURCE: Me. I've had a GPZ500 with a drum and one with a disc. The drum brake was WAY better.
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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.

[SilverWings]

...not saying I'm necessarily going to put a GPZ caliper on it, I want to know the distance between the swingarm so I can decide whether to use the same wheel, spacers, holder etc, or do I need to make my own. Nothing stopping me finding a better twin piston caliper...

[Kickstart]

Hi

Maybe you could fit the rear plate, and weld in a locating spot for it.

If you fit the rear disk then the caliper will need regular strips and rebuilds.

I can try and measure things up quickly

All the best

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

[redeem ouzzer]

Whoever decided that discs were suitable for a rear brake makes Hitler look like Mother Theresa. Why you would want one out of choice god only knows...
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Be a REAL MAN!

[stinkwheel]

Or you could fix your drum properly. They work well when they are serviceable and require minimal maintainance. Ought to work well enough to lock the rear wheel at will.

Be a lot less time and hassle and work out around the same price.
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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.

[Azoth]

What you're considering would require a fair bit of expertise in rat bike bodgery. How soon do you want or need to ride the bike? The best option is surely to buy another wheel and fit it in under 5 minutes. If the replacement wheel has a tyre attached to it, then that's some additional tyre mileage as an added bonus. Even if it doesn't, a replacement wheel is the fastest and easiest option.
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Safety in numbers

[Kickstart]

Hi

Couple of photos to give you the basic dimensions:-

https://www.alfa-pages.co.uk/TempPicture/DSC_0173.JPG

https://www.alfa-pages.co.uk/TempPicture/DSC_0174.JPG

All the best

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

[Kal]

[Kickstart]

[Kal]

The more parts I am sourcing the longer he is sat on your driveway.

At what point do I need to pay rent?
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Kal...
I Like To Hoon It Hoon It I Like To Hoon It Hoon It I Like To Hoon It Hoon It Ya Like To (HOON IT!).
1984 GB250 Clubman,1983 CB250N Superdream, 1999 GPZ500S

[Kickstart]

[pompousporcup...]

[SilverWings]

Thankyou Katy, very helpful :3