This topic has been addressed before, but in my searching I havn't had much luck sorting my problem.

So hopefully I can get some help here (or Andy might delete the thread for being an overused topic )

Ok I bought an MC21, which has what I believe are ZXR400 USD forks. The brake discs have been changed to VFR400 296mm discs. This seemed all good, but I have encounterd 3 problems, 2 of which I believe can be fixed by fabricating a bracket.

1. The caliper mounts on the ZXR400 forks position the NSR calipers too high on the disc. I.e. only 2/3 of the pad makes contact with the larger-that-standard vfr disc.I assume this problem is common? Will a bracket be able to successfully reposition the caliper?

2. The discs do not sit central between the two pads. I assume this is an offset issue with either the discs or forks? The bracket in my mind should fix this, but I also believe it could be related to problem 3.

3. The front axle that has been used is (in my uneducated eyes) too short for the wheel and forks. The end with the holes (that a thin bar can be passed through to aid with the removal of the axle) sits almost flush with the side of the pinch-clamp area of the fork. The axle also appears to be sporting some home made spacers, which I think could contribute to the wheel not centreing correctly. Could the axle be replaced with a standard ZXR400 model and still work fine? Or should I just have new spacers made?

Has anyone done this conversion and had the same problems? How did you get around them?

Nice to see my reputation preceeds me!

Sounds like a "right proper bodge job" to me.

1. The calipers should NEVER be misaligned. In my opinion, the brakes are the single, most important part of the bike. Riding it like that would be insane. You wouldn't catch me trying to haul up from 130mph with 2/3rds of the pads!
   
   
2. Can't say; not enough info, but the disks should sit centrally in the calipers.
   
   
3. Provided the triples used are the ZXR triples, then I would say the original ZXR axle should be used, and bearings fitted to the wheel to suit its diameter. Custom spacers are almost certainly required too. Depending on both the discs and the wheels used, shims may be required behind the discs, or the wheel turning down to move the discs in more.

Not enough info to make anything other than generalisations.
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Andy.
NSR-WORLD.COM

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Is the bike still in Christchurch mate?

imdying wrote:Is the bike still in Christchurch mate?

Sure is, saw you commented on Kiwibiker too. You in CHCH too? Keen to have a look?

Can always have a look if you're stuck. OAB runs Brembos on his GSXR via adaptor plates, and has never had a problem getting WOFs, but I think he has a friendly tester. They do require certification to be completely legal though.

Andy, do you know if there is any difference between a ZXR400 and ZXR250 front ends (triples and forks)? On closer inspection of the triples they appear to be from a ZXR250, so I'm assuming that the forks are too...

No, sorry I don't. Probably your best bet on here is to hope that Moriwaki-man reads the thread. He's into most things ZXR I believe.

There are a couple others who have posted here that have ZXR forks, but not sure if they are still members.

If there's a ZXR forum, I am sure someone will identify them in seconds, just as smany can identify any NSR forks here in seconds.
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Andy.
NSR-WORLD.COM

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The problem here is a mishmash of parts;

The entire ZXR400 front end (forks, triples, wheel, discs, calipers) would have to work (and potentially work very very well indeed if sprung for the lighter bike, several super fast ZXR400 racers here run stock forks and win).
But once you start mixing you're on the road to making a mess, caliper height, disc offset, wheel spacers and yoke width all need to be considered.
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I had zxr400 forks on mine before i came across rvf400 forks.

Definately sounds like the discs you have on there are still nsr.Measure them.

Using a combo of nsr and zxr400 spacers the wheel shoul fit ok.
You also need to space the calipers as the zxr yokes are slightly wider than the nsr yokes , i had some made up by a local engineering firm that slotted into the fork caliper holes.
Can't remember the exact measurements as i sold the forks.

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it wouldn't be fun if it was easy!

99% sure the discs are VFR. They are definately bigger than std NSR. I'm taking the bike into my engineer this week to try and sort a bracket that will correct the positioning of the calipers to suit NSR wheels with VFR discs.

Re. the tripples, I am wondering if the ZXR250 had a slimmer yoke width. The calipers sit too far in (ie the disc sits very close to the outside edge of the caliper). This makes it a bit harder to deal with because it's not as simple as just spacing it further in. Any ideas here?

In fork related news, had the bike on the track today running in the new engine (low speeds and mild braking don't worry) and had the front wash out on me. I naturally blamed it on the fairly lo quality tyre I had on (and maybe a bit me ), but is there there any chance that the fork set up contribted to the slip? Maybe the rebound of the heavier grade fork made it a bit more difficult for it to handle it?

Ah its coming back to me.
When i first had the zxr forks i was using mc 18 calipers and had the fork bottoms machined as the discs were as yours are in the calipers , but when i switched to mc28 calipers this needed them to use a spacer as they fit the other way round! Sorry i was being dull earlier.

So you need to have a couple of mm taken off the caliper mount (0r the caliper) on the fork to move them out and centralize the disc.

The vfr discs size was right on for zxr forks, but i did try it with the Nsr discs first and they only touched 2/3 of the pad like you're discribing.

Hope my rambling helps.
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it wouldn't be fun if it was easy!

That's interesting, because I could swear that the discs on it are VFR discs. I will pull the wheel off later today and measure up the discs to see. Because there is no point having a bracket made if larger discs are the go.

I have a pic of the discs that might help. I'll also get a pic of the axle and spacers to get some advice. Can you upload pics here?

Put them on a host site like image shack or bike pics and then put a link up for them.
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it wouldn't be fun if it was easy!

Hopefully that works for you guys. These show the calipers/discs/forks

dunkenb wrote:Ah its coming back to me.
When i first had the zxr forks i was using mc 18 calipers and had the fork bottoms machined as the discs were as yours are in the calipers , but when i switched to mc28 calipers this needed them to use a spacer as they fit the other way round! Sorry i was being dull earlier.

So you need to have a couple of mm taken off the caliper mount (0r the caliper) on the fork to move them out and centralize the disc.

The vfr discs size was right on for zxr forks, but i did try it with the Nsr discs first and they only touched 2/3 of the pad like you're discribing.

Hope my rambling helps.

Just had the bike in to an engineer who is going to make up some brackets to reposition the calipers via a bracket. The calipers will end up sitting lower than they are now, but it hopefully should work.

Did a bit more research and it seems that different models of ZXR400 took different sized rotors (300 vs 310mm). It turns out my 296mm VFR discs may be about 14mm to small, whereas yours would have just fit in right. So my options are to make a bracket, get new custom discs machined, or revert back to the original forks. The bracket is probably the cheapest of these options. When I need new discs I guess I can have a custom set made up.

What a nightmare!