GPR Camp: Replica Racers

Long long ago in a... oh wait. Okay this is another thread from the past that I'm including for historical purposes. It's simply here to illustrate some evolution of thought on how I came to believe what I currently believe about brakes on these bikes. Lots of photos, and some outdated information, but should be a good read for someone interested in these sorts of things.

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4/8/2011

Some time ago now I did some research and implemented an upgrade on the front master on my Black bike. I post this to the A-forum and it seems that I should make a similar post here - I'm going to lift a bunch of my text from the other post so the context may read a little strange. I got a lot of my information on this upgrade from the Croco Racing site.

This is the stock master found on my bike:


The GPRs comes with braided lines, as do the Derbi Motards. Both front and rear brakes, and since I've upgraded my moped with a front system from a Derbi SM even it has braided lines. I'm also running the Freodo pads—which make a huge difference over the other pads I've tried like the EBCs.

The Crock site is really worth a read on this topic (and others). Those boys in France have put in some serious effort. From their site I gather the master to pick up is the Brembo PR16. I was unable to find one of those yesterday, however I heard today that they are the stock master on 2007 Yamaha R1s. I imagine that plenty of sailors have placed these bikes in the yards, and some bountiful booty is to be had by the clever two stroke rider. The Crock boys suggest upgrading the caliper if you go this route.

For the stock caliper they suggest something in the way of a 13mm - and the RS125 master is a 12.7mm which is right in the ball park. By the way I did look and the GPR125s use the same master as the GPR50s (at least in the 2004/5 editions), so these upgrades apply there as well - yet the 125 does have an improved caliper and could jump to the brembo master straight away.

SD - I'll give you an update once I make the switch. It's been rather cold here lately and I don't have the proper jets to set my bike up for the conditions—it is currently unhappy and unridable. Your being in Antarctica you might afford me some cold weather tips. I would like to do a brake test with the stock and then switch over to the RS125 master and do a test to have metrics, however I'll probably just make the switch.

That said yes if you go to a much larger bore on the master you turn your system into a on/off switch with zero modulation. A 19mm would do that for sure. The Crock site states that the 16 is still within modulation territory—though pushing it.

You are also right about the travel—it allows the lever to be adjusted closer to the bar and thus needs less effort by the rider. This is something for which I am looking.

As to calipers—I need to do some research. I need to measure the centers on the mount to be able to find out what caliper might fit on the GPR. I believe they are at 100mm just from looking at them. If that is the case there are many options, one of which would be the caliper on the RS125—though I doubt as many of these have been swapped as the masters because these are rather nice calipers.

Here is what a Brembo 16 looks like:



I fitted the Aprilia RS125 lever on the GPR. It went pretty well over all though I probably have a bit more effort to put into it to make it right.

Here's a photo of it on the bike:



The stock brake light switch swapped over just fine. The unit I bought didn't come with a reservoir so I picked up one of the aluminum ones made for the motocrossers. I have to fabricate a mount for it so right now it's just floating there.

Everything went pretty smoothly with the swap, the line and line guide needed to be adjusted a bit, it is very easy to set it such that it collides with the clocks. The brake light switch wires are just barely long enough, anymore length needed and they wouldn't work. I left pretty much everything else stock including the banjo bolt, line, etc.

The biggest disappointment with this lever is that there are zero adjustments—you have to love it the way it is.

The lever itself is quite comfortable—I liked it right away. Braking power is good. It did take some time for the lever to settle—letting it sit over night seemed to fix that issue.

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12/20/2011

For quite sometime now I've been posting up on 125cc about brake upgrades for the 05+ GPRs. There is the caliper for the GPR 125 although they are hard to find and everyone says they are crap. I've done a lot of searching around and I found many different calipers that for some reason or another have all been deemed unworthy.

Stage6 the re-brander of many fine parts has a four piston caliper that looked like it could work so I order one. There are some pretty big issues which I outlined on 125cc thus:

toratora wrote:The caliper came today—well it came yesterday when the UPS man knock with the boom of a door mouse, and yes that is to say so quietly I couldn't hear him from the next room. : | So for today I left the friggen door open!

From the photos you can see that they sent me the old style caliper. The unit had also been previously open and scuffed up a bit. No where on the box, or the caliper does it say where it was manufactured. Like any event one can expect both good and bad and there's plenty of both with this unit. Lets start with the good.

Good
- Mounting bolt spacing is the same
- Offset to the disc is the same
- the pad is slightly wider
- the quality appears to be quite good

Bad
- M8 bolts for mounting (the stock bolts are M10)
- there is need of a spacer to the mounts
- the pad as about a 1/4 inch

I took the caliper out to the local machine shop to see what they thought about it, and the possibility to make a spacer that was an M10 bolt into the forks and an M8 place in which to mount the caliper. It looks like it can be done so with some proper measuring this story may continue.

Here are the photos:

!	Message from: toratora
	Please note this is no longer a suggested solution!

Found a nice R6 master on teh ebay for the GPR.

!	Message from: toratora
	Please note this mod is no longer suggested!

Whilst waiting for the heat cycles to cool on the new top end I figured it was time to implement the R6 master on the GPR.

First I did some clearance checking, and it looked like it was going to work well.









The brake switch for the R6 Brembo has different connectors that the Derbi. I opened them up to fit over the new tabs and then soldered them into place. It is hard to solder in the dark when you can't see what you are doing! Still it came out okay.











The only issue is that the adjuster screw taps the faring just a little bit (I don't think you'd even notice it unless you were looking) at full turn to the lock–this could probably be dealt with by moving the lever around. For me it't not really an issue, and putting an ASV lever on there should ameliorate the situation completely.

It was dark when I got it all done so I'll have to get some finished photos in the light. Bleeding with this setup is easy because there is a bleed screw on the top. : P

The action is direct, although there is still some good modulation. The disc had collected some oxidation while sitting around and while I scoured them they still loaded up the pads so I'll need to clean them out for a proper test.

Having compared the Stage6 caliper with the stock 50 caliper I felt that it just wasn't enough caliper to do the job. I suppose I could have installed it and given it a go however I decided to try another direction.

On the GPR 125's they come equipped with a four piston caliper. My buddies that have this caliper don't really sing any praises for it however it looks to be significantly more robust than the Stage6 caliper, although Stage6 is nicely finished. I've been on the lookout for one of these for a while. I'd find them in Germany but they wouldn't ship to the States.

Then I found out that the Giliara SC125 is a rebranded Derbi GPR 125 and I found a caliper for sale. It was reasonably priced, however GB loves to charge bank for their Royal Mail so it was quite a few £ to have it cross the Atlantic.

I took a bunch of photos of it because whilst on the look out I had trouble finding photos of this caliper. This one will require a fair amount of cleanup before it makes it on to my GPR. I'm hoping that it will be a nice match with the R6 Master.

Had some cycles to engage in brake action on the GPR. I'm really happy with how it's coming along. : )

Previously I had a chance to do some clean up work and the caliper looks quite nice after serious scrubbing action. It turns out that the caliper had a recent rebuild and came with Ferodo pads. I'm a big fan of the Ferodo pads and was happy to see this caliper came with a set. Sadly the caliper had sat out for some time and the pistons were a little corroded. Turns out this is a common problem with this caliper. I employed the MC to push out the pistons so that I could clean them. Thankfully there were no leaks and I was able to get all for pistons to move smoothly without sticking. : )

I also employed the 125 brake line because the fixture at the caliper had a slightly different angle.









Once on the bike it is as if I have a CUP bike. : P







One good thing I did was ask for the hardware to be included with the caliper. The 125 four piston caliper uses slightly shorter mounting bolts than the 50 two piston caliper. The ones from the 50 will bottom out before securing the 125 caliper.

!	Message from: toratora
	Please note while not totally depreciated this is not the currency suggested mod. The Brembo RCS14 works much better.

When we last tuned into this channel I had just fitted the R6 Brembo master on to the GPR. Today I installed the Brembo 16/18 master.

Here you can see that it is going to take slightly less space than the R6 master.



The following photos are of it fitted. I currently have the cowl removed to repair the head lamp mounts. This made for an easy master swap out.

The actual installation of the master went quite well, and bleeding the system was a snap since it has a bleeder on the actual master (the R6 master did as well--the stock Derbi master doesn't nor did the Aprilia RS125 master which I had employed prior to the R6 master).

I picked this master up used from Speed Corky who had bought it from SuperNes. The reservoir didn't have the rubber bladder in it so it leaks. I'm going to look into finding a replacement tomorrow. The mount for the reservoir had been tightened too much and striped out in the mount. I'm going to have to see if I can remove it and deform the aluminum a bit and refit it because for now it is a bit too loose. The last issue is that there is no place to mount a brake switch. To over come this issue I'll probably install a pressure switch at the banjo bolt like Derbi employs on the rear brake master.

On to the bit you've probably been waiting for with baited breath--how does it feel and work? With all of the various caliper/master combinations I've had on the GPR this is without a doubt the best feel and power combination. I've only done a quick up and down the street test with it. Tomorrow I'll actually take it out for a proper test, however it would appear this is the hot ticket for upgraded GPR brakeness action.

It was time to place the front cowl on the bike. I found that with the mirrors it was too heavy to support the cowl with just the center support so I had to add the mid fairing. Once that was in place I could check the clearance of the new master. Additionally there's a photo of the rear master with the pressure switch—I'll need to add something like this to the front now.

Last night on the FNR I gave the brake system a pretty good work out and I am ever so pleased with the performance I'm getting. There is a lot more feel with this setup than with the R6 master. It is also easier to pull. The R6 master when pulled hard may have had slightly more stopping force. I'll do some more testing of it tomorrow. Now to find one of those sexy floating front discs...has anyone sourced possible alternatives to the stock unit?

From the photos you should be able to see that there's plenty of space--more so that I had with the R6 Brembo, and probably about the same as the stock unit. With the exception of when the head lamp was loose I really haven't had any clearance issues with any of the calipers. The R6 adjustment knob would some time touch the head lamp, but only just barely and that was no cause for concern.

The current setup consists of a 125 AJP 4 piston front caliper, Brembo 16x18 master, Ferodo pads front and rear, stock discs, and Procircuit reservoirs front and rear. Pretty Tasty Action.

Cool Topic, I'm looking to upgrade myself, just not sure which direction. I was looking at new prices for brakes from the big bikes and well the prices have killed that idea!

I think purchasing the master and calipers from the GPR125 would be the easy solution and would fit the bike and look the part, so this idea is on the table for sure.

The other option is the go with the Stage 6 route, purchasing the master and caliper. I gather the caliper will need the bolt holes to be bored out and recesses re cut to work for the M10 bolts.

No rush for now, so will keep options open!

I take braking rather seriously. At the very least I upgrade the pads to Ferodos. After that I see if an upgraded caliper/master system can be employed. The older GPRs (first gen) had a better system than the 2005 bikes as far as stopping power. The 2005 bikes came with a sexy system that just lacked ability. They were larger discs, radial caliper, and radial master. Even still I wasn't happy with the performance.

The first upgrade I employed was a master from a 2009 Aprilia RS125. This was an improved setup, but after I employed on R6 master on the Mito I was no longer satisfied with the way the GPR was stopping. I bought the Stage6 caliper because outside of Chinese websites it was the only aftermarket radial caliper I found that had the same mounting spacing as the GPR. It does have the same spacing however it employs a smaller bolt and there isn't enough material on the caliper to bore out to the bolt size employed on the Derbi fork. One possible solution is to fit the forks with a helicoil for the smaller bolt and then supply a higher strength bolt to compensate for the smaller size. I decided this method held too much risk for this critical system.

At that point I went hunting for the AJP four piston caliper from the 125 and finally secured one. With the success I found with the R6 master on the Mito I employed that same master with the 125 caliper. This system stopped well however there was little modulation and the lever had to be pulled hard. I called it the three finger brake--because you really needed to use three fingers to get proper braking done. I was unhappy with this system.

At that point I replaced the R6 master with the Brembo 16x18. This is by far the best system I've found for this bike. I now have much improved braking, it is modulatable, and can be done comfortably with two fingers.

From the 125ccSB website I conversated with Banzai and DangerousDave about the stock 125 system. They were unimpressed with the performance of the stock set up on the 125 GPR—so I cannot recommend that system. One of the issues found on the 125 is that the caliper freezes up. So it is important to keep an eye on it. I've been looking for a rebuild kit for it and believe there is one—just have to find an AJP supplier that will order it (or find the part number and then Benji will do so). The one I bought was in pretty bad shape so I had to clean it out. I put a lot of effort in to the clean up work including removal of the pistons. Important on these APJ calipers--the pistons are teflon coated so avoid abrasive materials on the pistons. That said it seems that it is the stock 125 master that is the weak link.

I am still a little surprised that the Brembo and the R6 (which is a Brembo too) are so different. They are both 16's, and I'm told by Banzai that the stock 125 master is a 16 as well. Even still there is a huge different in feel making the Brembo worth the money spent. Yes I did over all spend a lot of money figuring out what was a good system—that's just how experimenting goes. Lucky for my readers they can profit from my effort.

My findings from all of this experimenting:
Caliper—AJP 4 piston from the 125 GPR
Master—Brembo 16x18 forged master
Pads—Ferodo
Line—braided line from the 125 GPR
Fluid—I went with some decent dot 4 (Bel-Ray)

Another thing I noticed is that on this Cup bike they are running the 125 system (in an other photo it is clear to see them running the 125 AJP master). Interestingly they have fitted the forks with a means to adjust them. I'd sure like to find more information on these forks.

Looks like the forks have at least adjustable preload, but otherwise Malossi sell race forks for the bike with preload, compression and rebound adjustment. Think Benji could source those for a reasonable price? They are about 900 Euros in er.... Europe!!

So back to brake, think what you are saying is go for the 125 calipers and a brembo master? Metrakit used to makea floating disk also.