Getting rid of the rear brake hub

There seems to be more and more members appearing that are racing the ZXR400 so i've created a special section just for you to show off results, discuss meets etc etc.

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robel
Posts: 4
Joined: Sun May 11, 2014 11:06 am
My Bike: ZXR400 L's & H. TZR250
Location: Maidenhead, Berks. UK

Getting rid of the rear brake hub

Post by robel » Thu Apr 14, 2016 8:02 pm

The Modification to fit a swinging arm brake calliper only requires two pieces of metal. It is also necessary to turn up a spacer. The length of the spacer is equal to the length of the standard spacer plus the length of the spacer that is fitted into the hub that you are replacing. The ends of the spacer should be the same diameter as the end of the free spacer and the end of the hub spacer. Being of an economic persuasion (i.e. a cheap skate) I used what I had in my scrap box.
The right angle bracket needs to be just as long as the flat topped part at the back of the swinging arm, the section that is parallel to the axle adjustment. In the pics you will see a couple of vertical ‘slots’ in this bracket. These are not necessary, they just happened to be in my piece metal when I found it! You will have to drill and tap the rear of the swinging arm to fix the rear of the bracket. The front of the bracket can have nut on the underside of the bolt where it goes through the swinging arm.
The vertical plate to which the calliper is fixed was also some scrap. You can see in the pics that the calliper is bolted to this plate using two bolts of suitable size for the calliper chosen. This was fine for Brands Hatch as it was set with the correct rear sprocket for this track. What I need to do is make the calliper fixing holes into slots so that I can readjust the calliper position when I change sprockets. (I am not actually sure that this plate is long enough to allow full adjustment of the sprocket range. I might have to change it for a longer piece).
Again, I had available the calliper that I used but any 125cc front calliper will provide excellent braking (the scrutineers were happy, but my daughter rarely uses the back brake anyway). A couple of washers and a nut bought the centre of the callipers in line with the brake disc.
The only remaining problem was that the disc was too ‘fat’ to go in the slot. I took the calliper into its two halves checked where fluid transfer hole between the two halves was and filed the slot wider – there was plenty of ‘meat’ spare to do this. Took great care to clear the swarf out and re-assembled it. Put it all together and the last action was to remove the torsion arm.
Excellent rear brake and a considerable saving in weight. If you need more photos or information please pm me.
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Dominik
Posts: 106
Joined: Tue Oct 07, 2014 11:05 am
My Bike: Zxr 400 L3
Location: Trier - Germany

Re: Getting rid of the rear brake hub

Post by Dominik » Fri Apr 15, 2016 6:23 am

Don't you think it looks a bit... ugly? A smaller rear disc saves even more weight and you can easily adjust the caliper to the right position necessary therefore. However how much weight did you save?
Zxr 400 SL - 130kg

robel
Posts: 4
Joined: Sun May 11, 2014 11:06 am
My Bike: ZXR400 L's & H. TZR250
Location: Maidenhead, Berks. UK

Re: Getting rid of the rear brake hub

Post by robel » Fri Apr 15, 2016 10:49 am

Don't know what to say about the ugly bit - I understand atheistically it won't please everybody and I do subscribe to the view that if something looks good it probably is good BUT I think racers have a more pragmatic attitude - function supercedes looks.

An equally important point of the whole exercise was that when my daughter was on her own in the garages and needed to change sprockets between races she had to juggle the wheel, the spacer, the hub and the axle and so I decided to cut down the number of components. I also put back the dust seal in the wheel which then holds in place the new long spacer.

I don't know in absolute terms the weight saving but if I hold two aluminium brackets and the small caliper in one hand and the hub with brake assembly together with the torsion bar in the other there is a huge difference. Also better race engineers than I have said that although the hub together with the torsion bar can rotate about the axle it still limits the ideal action of the suspension.

shaggy69
Posts: 63
Joined: Sat Jun 18, 2011 8:10 pm
My Bike: ZXR 400 Racebike

Re: Getting rid of the rear brake hub

Post by shaggy69 » Thu Apr 28, 2016 4:50 pm

The last comment about limiting the action of the suspension is the whole point of the 'torsion' bar. If u use the back brake, even slightly, it helps to reduce squatting of the rear over crests and reduced rate at which back lifts under heavy front braking. It does this by forming almost a fixed triangle where the swingarm is one side, the torsion bar the other and the line from caliper/torsion bar bolt to spindle the third. A triangle is an exceptionally difficult shape to distort.
To prove this, bounce on the back suspension of your ZXR (with torsion bar), it will rise and fall easily. Now try the same with back brake pressed hard. It is more difficult to compress rear suspension. Now compress it with brake off and hold down, before releasing hold back brake on....it'll rise slower if at all but will spring back quicker if u release brake.
It's all down to triangulation of the main pivot points, using the back brake effectively locks out the two rear pivots, not totally , but enough to make a difference if you know when and how.

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zimm
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Joined: Tue Oct 10, 2006 12:32 am
My Bike: ZXR400-M4
Location: Herefordshire

Re: Getting rid of the rear brake hub

Post by zimm » Thu Apr 28, 2016 8:31 pm

shaggy69 wrote:The last comment about limiting the action of the suspension is the whole point of the 'torsion' bar. If u use the back brake, even slightly, it helps to reduce squatting of the rear over crests and reduced rate at which back lifts under heavy front braking. It does this by forming almost a fixed triangle where the swingarm is one side, the torsion bar the other and the line from caliper/torsion bar bolt to spindle the third. A triangle is an exceptionally difficult shape to distort.
To prove this, bounce on the back suspension of your ZXR (with torsion bar), it will rise and fall easily. Now try the same with back brake pressed hard. It is more difficult to compress rear suspension. Now compress it with brake off and hold down, before releasing hold back brake on....it'll rise slower if at all but will spring back quicker if u release brake.
It's all down to triangulation of the main pivot points, using the back brake effectively locks out the two rear pivots, not totally , but enough to make a difference if you know when and how.
what he said !

horses for courses though.. lots of more modern bikes just have the caliper attached to the swingarm.. lots of people never use the back brake..

I use a lot of back brake and like the way the zxr's linked system works
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shaggy69
Posts: 63
Joined: Sat Jun 18, 2011 8:10 pm
My Bike: ZXR 400 Racebike

Re: Getting rid of the rear brake hub

Post by shaggy69 » Fri Apr 29, 2016 7:03 am

I use it in wet to stop front diving so much and to keep bike level on the track...use it at Isle of Man to stop back squatting over fast crests :)

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