Front Disc Brake Modification

Working up how to set up the brake on the right side to get the Brembo caliper in the right orientation.

I mocked up the front end to see where I am at with the fender bracket and I wanted to see how the fork brace fit. Hopefully this won't start another "Is a fork brace required" thread. My opinion at this point is that with the stronger brakes and floating disk a fork brace may be needed. I will need to go through the exercise of figuring out whether it can be adjusted correctly to insure that the forks slide smoothly. I'm not really able to do that until it is all mounted on the bike. I'm doing what I can inside because it's -20 F in the garage right now and I am laid up from back surgery.

Here is my right side brake mock up for the MKIII. I see that I have a big problem with the fender brace and now am wishing I wouldn't have bought a brand new stainless fender (pricey to say the least), because there are other options.

http://www.flickr.com/photos/22794316@N03/11820522173/

It is coming together though

dennisgb said:

Ron L said:

You realize these calipers are designed to fit behind the fork leg? They have a larger piston (34 mm) and a smaller piston (30 mm). It probably will work fine reversed, but it's not the way it was designed. Brembo has been making top quality brakes for a long time, so I would assume they have a good reason for this design.

Click to expand...

Ron,

I knew the pistons were different, but didn't know that they were designed to be placed in a certain orientation.

Dennis

Click to expand...

Dennis,
For what it's worth I've also put the same type caliper on the rear, albeit with a standard disc, so this means the piston orientation is correct on the rear brake.
Even with the pistons in the wrong orientation at the front (something I only found out here) the brakes are far superior to a standard set up. The rear caliper bracket was much more of a challenge to make !

sam

Well I must thank you for the above info, I never knew all that.
I will have to swap over the fork leg and brake now, but at least my rear one is ok.
sam

I did always wonder why drums never worked going backwards !

Well Sam it looks like we got the scoop now. Very helpful information from everyone on the proper mounting of these brakes. Saved me a bunch of headaches going down the wrong track and then having to go back again.

In regards to the rear brake I am planning to do the mods that Ron L did to his Commando.

http://www.flickr.com/photos/22794316@N03/11821323135/

This is all Ducati components including the mounting bracket, disc and Brembo caliper. A mounting hub has to be fabricated but it's not too much different than the ones I made up front. I haven't started on this yet but have all the parts.

Al-otment said:

Firstly, it wasn't John Hudson and the bikes didn't pull to the right, according to the 'Commando Service Notes'.
It was Mr T.R Stevens who wrote the majority of the 'Commando Service Notes' and in particular the story regarding the bikes pulling to the left with the caliper mounted behind the right hand fork leg. To be honest it sounds like a "bloke down the pub said" type of story. If it was the case, then I think without first knowing the accuracy of the frames etc one could not conclude it was purely due to the orientation of the caliper. I'm wary of 'word of mouth' stories, facts get easily misconstrued - as in the above quote for example.

Click to expand...

I tend to agree. If it was such a big problem how come there isn't more information about it? Also, when does this problem occur? When applying the brakes? If so why would it move to the left? Is there some secret to leading or trailing brakes? Why don't other bikes with single right hand brakes have this problem? It all seems so vague and unexplainable.

If this is real, it leans my thinking toward fork twist, which is why I think a fork brace makes sense, particularly with upgraded brakes. But then we can discuss why the racer's never put them on their bikes and how hard it is to get the forks adjusted properly and any number of other reasons why this is a bad idea...but then I need to prove that to myself because the reasons for having one seem sound to me...regardless of speed or riding preferences and a myriad of other issues.

dennisgb said:

I tend to agree. If it was such a big problem how come there isn't more information about it? Also, when does this problem occur? When applying the brakes? If so why would it move to the left? Is there some secret to leading or trailing brakes? Why don't other bikes with single right hand brakes have this problem? It all seems so vague and unexplainable.

If this is real, it leans my thinking toward fork twist, which is why I think a fork brace makes sense, particularly with upgraded brakes. But then we can discuss why the racer's never put them on their bikes and how hard it is to get the forks adjusted properly and any number of other reasons why this is a bad idea...but then I need to prove that to myself because the reasons for having one seem sound to me...regardless of speed or riding preferences and a myriad of other issues.

Click to expand...

Fork twist definitely exists, but I think it's greater when going through a corner at speed due to the centrifugal force generated by the front wheel, rather than under braking. I don't notice the forks binding or locking-up under braking, just the normal telescopic problem of increased bump transmission as the spring compresses due to the weight transference. I've got a Lockheed 2 piston caliper with Mick Hemmings 'Norvil' 10.5" disc, mounted L/H side in front of the fork leg, 19" alloy rim. Peter Williams was keen to get the wheel assembly as light as possible (e.g tubeless tyres) to reduce centrifugal force. Twin discs, especially large dia., are going to increase CF therefore increasing fork twist.

Braces do make sense, especially with the relatively small dia. Norton stanchions and small dia. front wheel spindle - but in use I don't notice any significant problems, so one is not high on my list of priorities at the moment.

I have spent a lot on these forks and hoping to get the best performance. I have billet yokes (triple trees), new springs, stanchions, Landsdowne dampers, sleeves and turcite bushings from JS Motorsport. I hoping that I will have smooth function and a good base to find the proper adjustment of the fork brace.

In playing with this today, I see some issues that will take a bit to sort out. It's a little difficult to get things correct with the forks off the bike, but it does point out the issues. It's part of the reason I wanted to mock the whole thing up to see how hard it will be to get the fork brace adjusted.

It looks to me like the stanchion and slider function needs to be tested without the springs to insure that the bushing fit is right (smooth function). This seemed good on the bench when I assembled them the first time but I need to put the JS bushings and sleeves in (I rebuilt them with stock parts originally). Once the stanchion, damper and slider assemblies are verified and assembled with the springs the best idea I can come up with is to assemble them to the lower yoke on a flat plate in order to get the yokes square to the sliders and lock the clamp nuts to hold the forks square. The axel will likely need to be up on a precision V block. I may play with the "squeeze" of the sliders (inward towards each other), to try and get a feel of the tolerance or center point of function. Essentially see if I can force them not to work and find what feels best. Then take some measurements to see where I am once the fork brace is installed to compare to the measurements without the brace.

The reason I think there is a need to go through a measurement process is because when I assembled the fork brace and fender, I see a serious problem with position. First there is clearance in the holes of the brace and the fender brackets. This allows for adjustment, but could easily pull things out of square if not assembled properly. The other issue is width of the brace. This needs to be accurate to not put forces on the stanchions and sliders. I believe this can be adjusted or shimmed but I first need to determine if the brace width is close. In trying to assemble this it was very difficult to tell what was happening. It's difficult enough to get all the parts in there and lined up to the studs. I couldn't tell anything during this process...so I think I need to know where things need to be...

I am seeing the issues with getting this right. There likely is more to it than I see right now. :shock:

I finished the caliper mounting bracket in 6061 Aluminum.

http://www.flickr.com/photos/22794316@N03/11847736895/

http://www.flickr.com/photos/22794316@N03/11848149494/

Need to get some proper bolts. May still add some lightening holes.

Whoose fork brace are you using? Are they available?

JD

JD,

I have tried to figure out who makes this hoop fork brace and if you do a search you'll find a bunch of different companies who made them...but then if you search them individually nothing comes up. I got it on Ebay for $100 US used. Keep your eyes open they show up from time to time.

I went this direction after reading about problems with adjusting the other types of braces (Hyde). My thinking is/was that this brace would be a little more forgiving and if it needs adjusting it would be easier. It's rigid as heck though so I may be wrong about that. Positioning is important to get smooth slider movement. We'll see.

Dennis

Straight line braking ain't gonna twist Roadholder but dangerous leaned trail braking sure could and the snap backs are murder. I've had good luck going down world wide list of Brit Iron vendors on searches like this as waiting and hoping to show up by luck may take too long. The bolt on inside of sliders like mudgaurd brace and flair tube braces are easier to fit than the stanchion slide thru type that have driven even the best brace makers like RGM out of dealing with the about universal complaints. I had to buy new stanchions to have a chance to get my RGM to work with weeks of diddling- filing-sanding-forcing cycles till just springs friction restriction felt.

When I did new caliper mount I built wheel/rotor to fit right then clamped caliper on where I wanted it, so no question centered-aligned perfect then filled in the gap with metal w/o reassuming nothing but would allow accurate stable measures/fitting of bolt on adaptor.

hobot said:

The bolt on inside of sliders like mudgaurd brace and flair tube braces are easier to fit than the stanchion slide thru type that have driven even the best brace makers like RGM out of dealing with the about universal complaints. I had to buy new stanchions to have a chance to get my RGM to work with weeks of diddling- filing-sanding-forcing cycles till just springs friction restriction felt.

Click to expand...

I understand the issues with getting the brace adjusted. When I put the forks together to look at things and see how they fit it was a nightmare to get the brace in place. Once I do measurements it should make more sense, but I still see it as a challenge to get it installed without putting pressure on the sliders that could cause them to stick or wear improperly...the jury is still out but I hope it works.

hobot said:

When I did new caliper mount I built wheel/rotor to fit right then clamped caliper on where I wanted it, so no question centered-aligned perfect then filled in the gap with metal w/o reassuming nothing but would allow accurate stable measures/fitting of bolt on adaptor.

Click to expand...

I found a detailed drawing of the Brembo on line that actually shows the center line of the pads on the disk radius with dimensions to the bolt positions. The CAD drawing that I made allowed me to make a bracket that is accurate in terms of position. When I look at the pads with the caliper mounted to the bracket, the arc of the pads match the disc exactly and the pads are about an 1/8" or so below the top of the disc. In the other plane, the bracket holds the caliper dead center on the disc with the spacer in place when mounted to the bracket. I feel pretty good about the results.

I feel pretty good about the results.

Click to expand...

Yeah man Dennis that's a feel good report for the rest of us too. Hope you got tire and nerves enough to get safe whoa's with more than adequate power.

hobot said:

I feel pretty good about the results.

Click to expand...

Yeah man Dennis that's a feel good report for the rest of us too. Hope you got tire and nerves enough to get safe whoa's with more than adequate power.

Click to expand...

Ha! Yes tires are on the list for sure...safe whoa's with more than adequate power...not so sure what that means. The one concern is will I have too much brake. The MC is sized right and I have adjustable brake lever so thinking I should be able to get it all into a comfort zone...which was my intention going into this. Would hate to see that I have so much brake grip it bends the down tubes the first time I have a panic stop :shock:

I decided to go down the route of having my original mastercylinder sleeved by RGM. the disc has gone off to be bead blasted and then Zinc plated. Caliper rebuild kit on the way.

This will keep external originality and should result in reasonable brakes that will be OK in Normal use, but not for multiple alpine pass descents!

Any hints on rebuilding the caliper

Caliper rebuild is pretty easy...do a thread search there is plenty of info.

+1 on this modification.I believe he recommends the step to be 1 mm.You will notice the difference immediately.
Mike

dennisgb said:

hobot said:

The bolt on inside of sliders like mudgaurd brace and flair tube braces are easier to fit than the stanchion slide thru type that have driven even the best brace makers like RGM out of dealing with the about universal complaints. I had to buy new stanchions to have a chance to get my RGM to work with weeks of diddling- filing-sanding-forcing cycles till just springs friction restriction felt.

Click to expand...

I understand the issues with getting the brace adjusted. When I put the forks together to look at things and see how they fit it was a nightmare to get the brace in place. Once I do measurements it should make more sense, but I still see it as a challenge to get it installed without putting pressure on the sliders that could cause them to stick or wear improperly...the jury is still out but I hope it works.

hobot said:

When I did new caliper mount I built wheel/rotor to fit right then clamped caliper on where I wanted it, so no question centered-aligned perfect then filled in the gap with metal w/o reassuming nothing but would allow accurate stable measures/fitting of bolt on adaptor.

Click to expand...

I found a detailed drawing of the Brembo on line that actually shows the center line of the pads on the disk radius with dimensions to the bolt positions. The CAD drawing that I made allowed me to make a bracket that is accurate in terms of position. When I look at the pads with the caliper mounted to the bracket, the arc of the pads match the disc exactly and the pads are about an 1/8" or so below the top of the disc. In the other plane, the bracket holds the caliper dead center on the disc with the spacer in place when mounted to the bracket. I feel pretty good about the results.

Click to expand...

I spent today swapping the forks round to get the caliper pistons in the right orientation, havent been able to ride it yet to see if it feels any different, but job done anyweay, have to do my other bike now.
Thanks to Ludwig for his piston information.
sam

dennisgb said:

JD,

I have tried to figure out who makes this hoop fork brace and if you do a search you'll find a bunch of different companies who made them...but then if you search them individually nothing comes up. I got it on Ebay for $100 US used. Keep your eyes open they show up from time to time.

I went this direction after reading about problems with adjusting the other types of braces (Hyde). My thinking is/was that this brace would be a little more forgiving and if it needs adjusting it would be easier. It's rigid as heck though so I may be wrong about that. Positioning is important to get smooth slider movement. We'll see.

Dennis

Click to expand...

This was advice I got when I was having fork strict ion problems with my BMW.

After years of messing with forks, this is what I do to keep forks working properly through the assembly process. Rather than trying to fix a problem later, I try to correct problems before they become a problem. This works for me.

When I'm putting together a set of forks, I never put the springs or oil in until the last moment. I'll assemble the forks into the yokes with out the brace or axle in place. Put the top nuts on without the springs (don't tiighten). Slide the axle in, leave the wheel off. Put the nut on the axle but don't try to tighten it as there's nothing to tighten to. Grab the axle in the middle and slide the forks up and down, how do they feel? If there is any stiffness, address it now. Try rotating the fork legs (one at a time) to see if there is any better movement in a different spot.

Now that the forks have been slid up and down a few times, tighten the axle pinch bolt. Slide the forks up and down, any change?

Tighten the top nuts, slide the forks up and down, any change?

Tighten the yoke pinch nuts, slide the forks up and down, any change?

Set the fork brace on and thread on the nuts but DON'T tighten them. Slide the forks up and down, any change?

Tighten one side of the fork brace, slide the forks up and down, any change?

Look at the other side of the fork brace, any space between the fork brace and the lower leg? If there is any space or if the brace fits crooked at all, the moment the brace is tightened, the forks WILL bind. The fork brace must be "tuned" to fit both lower legs perfectly. No shims, no nothing,... it must be tuned to fit perfectly.

Each time anything on the forks is assembled or tightened, the forks must be tested. If there is any tightening or stiffness, you have to go back that step and figure out what went wrong and fix it. The forks MUST move freely BEFORE oil or the springs are added.

chasbmw said:

dennisgb said:

JD,

I have tried to figure out who makes this hoop fork brace and if you do a search you'll find a bunch of different companies who made them...but then if you search them individually nothing comes up. I got it on Ebay for $100 US used. Keep your eyes open they show up from time to time.

I went this direction after reading about problems with adjusting the other types of braces (Hyde). My thinking is/was that this brace would be a little more forgiving and if it needs adjusting it would be easier. It's rigid as heck though so I may be wrong about that. Positioning is important to get smooth slider movement. We'll see.

Dennis

Click to expand...

This was advice I got when I was having fork strict ion problems with my BMW.



After years of messing with forks, this is what I do to keep forks working properly through the assembly process. Rather than trying to fix a problem later, I try to correct problems before they become a problem. This works for me.

When I'm putting together a set of forks, I never put the springs or oil in until the last moment. I'll assemble the forks into the yokes with out the brace or axle in place. Put the top nuts on without the springs (don't tiighten). Slide the axle in, leave the wheel off. Put the nut on the axle but don't try to tighten it as there's nothing to tighten to. Grab the axle in the middle and slide the forks up and down, how do they feel? If there is any stiffness, address it now. Try rotating the fork legs (one at a time) to see if there is any better movement in a different spot.

Now that the forks have been slid up and down a few times, tighten the axle pinch bolt. Slide the forks up and down, any change?

Tighten the top nuts, slide the forks up and down, any change?

Tighten the yoke pinch nuts, slide the forks up and down, any change?

Set the fork brace on and thread on the nuts but DON'T tighten them. Slide the forks up and down, any change?

Tighten one side of the fork brace, slide the forks up and down, any change?

Look at the other side of the fork brace, any space between the fork brace and the lower leg? If there is any space or if the brace fits crooked at all, the moment the brace is tightened, the forks WILL bind. The fork brace must be "tuned" to fit both lower legs perfectly. No shims, no nothing,... it must be tuned to fit perfectly.

Each time anything on the forks is assembled or tightened, the forks must be tested. If there is any tightening or stiffness, you have to go back that step and figure out what went wrong and fix it. The forks MUST move freely BEFORE oil or the springs are added.

Click to expand...

I like your logic Charles. That is a very sensible approach.