[xBhp Universal Thread]: Rear disc brake on yam FZ16, ...and others

[Lucky Luke]

Hi all,

I start this thread in the Universal Thread section as I think that the subject may be of interest not only to Yamaha FZ16 (FZ-S, Fazer) owners, but to the owners of many other bikes who regret to have a rear drum brake and would like to have a disc fitted on their bike instead.

Having posted some pictures of my Yamaha FZ16-Fazer on he owner's discussion thread, and this bike having been fitted with a rear disc brake, I was requested to give details of this installation.

I must first say that this is no-way a do-it-yourself job (unless one has the machines and the skills) but something that must be done professionally, and with utmost care. Your life, and the life of others, depend on it.

So: how was it done?

1- DISC ASSEMBLY:

The first, and most intriguing thing for most, as it was for me, is: how the heck do you attach a disc to a drum???

The answer lies in a cast aluminium piece, specifically made for that purpose, and that my mechanic simply bought on the market!!! I am in (small) Vietnam, so I guess that such an item will be obtainable in the huge India (no Pandora's "unobtainium" there!). The whole assembly looks as follows (sorry for the quick hand drawings):



The alloy part is threaded on the lathe (counterclockwise, the brake being on the right side!) and also is the steel lining on the inside of the drum (tyre has of course been removed). This is a precision job as the disc will have to be both perfectly centered and in the plane of the wheel. This alloy piece is then simply completely screwed into the drum.
The four mounting hole are then drilled in the already fitted cast piece (there again: precision work!), at the required position for bolting the disc, the cast piece allowing for slight adjustment. In my case, a last surfacing was necessary as a slight wobbling of the disc showed when assembled.
Then the disc (in my case a 220mm. diameter) is simply bolted down, using high quality (Yamaha) bolts and the wheel ready to be fitted back in place, (without tyre first):





2- CALIPER ASSEMBLY:

For this, a KTM caliper support was found of the right dimension (has to correspond to the disc diameter), and of the right shape as I did not want the tyre hugger to be cut-away, as I have seen on some similar installations, but wanted the final result to look like "factory made".

The whole assembly looks like this:




As you can see, the support is bolted together with the suspension arm, then a spacer (that fits loosely into the cast allow piece fitted into the wheel) bears onto the wheel bearing on one side and on the caliper support on the other side, all that held together by the wheel bolt.

To forbid this support to turn, a specially machined steel piece that will slide into the slot in the support is welded to the suspension arm, in a position that will allow the full forward and aft movement for chain tension adjustment while sliding in the caliper support's slot. I did not want this crucial piece to be simply welded to the inner side of the arm but go right through and be welded both sides. Here is the "outer" end of the piece going right through the arm, and which has been grinded to almost flush:




You can see here a small part of the disc and one of it's mounting bolts, the gold color alloy cast piece to which is it bolted, the lower part of the black caliper support right against the suspension arm, and the steel spacer that is right against this support on the right and penetrates the disc mounting piece on the left (and I just notice here that the position of the pad for the chain tension adjustment needs to be rectified ):




This is a view from the left, "through" the wheel, where you can see the forward part of this support, right in front of the disc (= on the left of the picture) and the protrusion of the support that houses the slot into which slides the piece welded to the suspension arm:




Here is a view (well: a "view"... I am not really sure that you can see anything!) from above "showing" the forward part of the caliper support and, barely visible (sorry!!) the piece welded to the suspension arm that slides in the support:




Now, the caliper can be fitted on:






TO BE CONTINUED (master cylinder assembly)

[Noor]

Thread approved

[aargee]

Brilliant!!! Rated 5* for this DIY thread!!!
I'm more eager to read the outcome of this setup + if the responsiveness of the rear disc setup.

[RanjithMN]

Great description there Luke!
What i want to know is-How much more effective is it than the stock drum?and does in reduce locking in panic braking?

[Lucky Luke]

Thanks for the approval (In Mods We Trust! )

3- MASTER CYLINDER ASSEMBLY:

This was more tricky that it seems at first as the right position for it had to be found. Vertical? horizontal? Behind or in front of the ankle protector, with an intermediate push rod or direct?

Finally the simplest, like always, prevailed, and only needed to modify the brake pedal and make one support for the cylinder (or "pump") and a couple of spacers. The whole assembly looks as follows:




The cylinder has been drawn in dotted line for clarity (well: that was the intent....!)

The two protrusions on the aluminium casting of the frame made for bolting the ankle guards looked more than strong enough for bolting-on the cylinder, specially since the position that looked the most appropriate was not going to induce any bending moment on them.

Here is what it did look like in the end:




Also seen from "behind", ie "through" the wheel:




For the fluid reservoir, a small, simple supporting piece was welded to the frame, and the whole thing then looking like that, making the fluid level well visible, and the reservoir protected but easy to open:




ET VOILA!:






4- HOW DOES IT WORK?:

In one word: great!

Call me a poser if you like , but I think it also looks great, and this is what lead me to have this mod done in the first place.

But, very honestly, it also works great.

One thing nobody was sure of was how long the lever (on the brake pedal) that pushes the master cylinder piston had to be, even when comparing to other bikes as the differences seem subtle: too long would mean great effort to get the right pressure in the cylinder, too short excessive pressure with little effort and risk of easily jamming the brake. So, it was kept the original length, just re-welded in a different position (and re-plated), thinking it would be easy to shorten it if the need may be.
It proved just perfect!
Jamming the brake is of course possible: a leg is more than strong enough for that, but this needs unusual effort, and even in "panic" braking I very much doubt that I would block the wheel.

Has road holding been affected by the (undeniable) extra non-suspended weight of this brake compared to the original one? Would need a bike to bike direct comparison! In theory, it should be affected, in practice: I did not feel any bouncing of the wheel. Must say that the rear suspension of this bike is really superb!

What now feels really nice is:
- Immediate response
- very progressive braking power without any movement but only increasing the effort on the pedal
- identical "feel" from both the front brake and the rear: touch, and apply pressure. The equilibrium is instinctual and gives enormous braking power if ones wants to, without (till now! ) having jammed either front or rear brake.
- fantastic even when very hot:just to try, I did many times a "loop" on a not yet open short road section, accelerating to the max speed I could get on this section (about 80kmh), braking full power, U turn, and again and again! Brakes got burning hot: I could not keep my hand less than two centimeters away from the discs, but at no time did they show the slightest loss of power. Had I done this with the original drum brake, unable to cool as well as the disc, it would have simply burnt the pads!

So, there you are: it did cost me some 8 million Vietnam Dong = 400 US Dollars= 16,000 Indian Rupees approximately. Not cheap for sure, but very carefully and professionally done. I would no-way recommend to any body who is not an experienced mechanic, and also has the required equipment (large diameter lathe able to accommodate the wheel, mill, stand-drill and good welding set) to attempt doing such modification an amateur way. This is, as I said at the beginning of this thread, not only your life but the life of others which could be at stake!

This work was performed by HIEN Motos, in Saigon, Vietnam.

If some want more details, you are most welcome

Luc

[kauria]

Nice hand sketches and detailing. I must say that the person who did it is very knowledgeable and master in it. In Kolkata I have never seen such modifications.
Love the work.

KB

[danny king]

This one of the cleanest and most easily understandable DIY info I have ever seen. Good sketches, step by step instructions..
You have made a great effort to make this....

[Lucky Luke]

Originally Posted by danny king

This one of the cleanest and most easily understandable DIY info I have ever seen. Good sketches, step by step instructions..
You have made a great effort to make this....

Thanks Danny, but I really think this should not be a DO It Yourself (DIY) job.

[chinmayachaitanya]

i own a dazzler which has discs both in the front and back........ it has more dis advantages than advantages..........

the most important risk is that the disc locks very quickly and the tyre skids.. so i suggest it is better not to have a rear disc unless you have an efficient abs system

[nagthemissile]

I know that rear disc break is more safer than drum break.What about its maintenance. i heard from local mechs that rear disc break increases maintanince in comparision to drum break like disc plate bending,break fluid hose leakage or damage.Is it a myth or fact?