91 FJ1200 front brake question

[andyb]

Arnie, that's the difference in leverage.

If you consider the area of the piston in the master compared to that of the calipers, you get a ratio.  What that ratio is, I don't know (and it really doesn't matter here).  Functionally you may consider the calipers to be a fixed area, unless you're changing to a caliper with a different piston area (total, say, 6pots or a different 4pot or really big singles or...).

A 5/8" master has a larger bore than a 14mm.  Quick math says 5/8" = 0.625" = 15.875mm.  Total area is then 197mm^2.  A 14mm master has 153mm^2.  So, a 14mm master has (153/197) 77% less fluid moved per given distance traveled by the piston, so the stroke is longer by 28%.  This means that the usable travel at the lever is longer, giving a bigger sweet spot and less pressure required.

If you replace a poorly functioning component with one that's different, yet in better condition, the system will work better.  So it's a question of what you want to end up with vs what you're starting with, and the condition that you're starting out in.

[andyb]

The monobloc calipers have an advantage in that they are more rigid, so more clamping force is transmitted into squeezing the pads onto the disc, rather than pushing the caliper apart.


(also, hey woot, 500 posts)

[Arnie]

AndyB

That's exactly what I was trying to explain without all the numbers.  We're in agreement.

Leon,

The FJ MC will work on the blue spot calipers and have less lever travel than the newer 14mm MCs *BUT* you may find them grabby and too sensitive with blue spots.

You could also have caliper seals that are stuck on the piston and retracting them too far.  This might be causing the "excess" lever travel you're complaining about.  Certainly worth checking.

Cheers,
Arnie

[andyb]

Arnie:  Yes, just was clarifying the WHY of it.

As a side note, ask a nurse.  When you flush a PICC or other CVC device, most institutions require that you use a 10mL syringe.  The rationale is that the bore on a 10 is much larger than a 3 or other smaller one, reducing your leverage, and preventing you from blowing the line to hell (you make less pressure with a given amount of pressure at your thumb).  There's your trivia for the day.


Also, it's on my todo list to my FJ, going to a 14mm master on the clutch, to provide a lighter and more precise clutch, to make drag launches easier to modulate power on.

[the fan]

Clarify the lever movement for me. Is there a large amount of movement before the screw hits the plunger? is the movement after the screw hits the plunger? I am betting its the latter. if not you may have a bent or damaged lever.

I adjusted a few stock set-ups and could usually get good feel and power. My YZF had the same calipers and a similar master and felt really good. In any case the later model FJ all should have better brakes stock than your GS. I have worked on several examples of both.

The problem could lie with the lines or the fluid. I recently worked on an older bike, and in the process of bleeding the brakes inadvertently mixed 2 different brands of fluid. For whatever reason the Dot 3 synthetic and Dot 4 wouldn't mix and I could never get good pressure. Flushing the system and re bleeding solved the mystery problem in his case.

I have also found several systems hard to properly bleed and often the problem is a trapped air bubble. The easiest method to remove the bubbles is to park the bike in such a way that the lever end of the master cylinder is the highest point in the system and zip tying the lever over night. This will usually allow any trapped air to escape. In most cases the air is trapped at the top banjo fitting.

in extreme cases I will install a banjo with a bleeder similar to the one pictured below:


One time in 100 bleeding brakes can be an absolute nightmare, but keep at it until it all works. The worst set I ever did involved removing the system from the bike and fabricating a bracket that ensured no possible air pockets in the system. That was the easy part. Getting it back on the bike with out messing it up was the challenge.

[RichBaker]

My feeling is that the problem lies with the master cylinder.
If I were to replace that, is the stock FJ m/c compatible with the blue dot caliper upgrade?

There is a screw that you can adjust on the lever to take up some of the slack you're complaining about.
IIRC it's a 5mm screw with a locknut and this is actually what contacts the MC piston assembly.

You can change the master cylinder completely and it will be "compatible" (maybe usable is better) with new brakes should you decide to change.  Be aware that the FJ MC is a 5/8" (15.875mm) bore vs 14mm for most of the newer MC units.  This means that the 14mm bore MC's will have greater lever travel (which you want to minimize) to move the same amount of fluid.  They will require less squeeze though.

BTW  I have ridden ONE FJ that had brakes which had similar 'bite' and power to the gold/blue spot brakes.  They did have SS lines and the owner was obsessed with making them as good as the newer brake units.  They did require more squeeze than newer brakes.

Cheers,
Arnie

I am aware of this adjustment screw and it is set as deep as it can go.
The thought of trying a longer screw comes to mind.

The FJ m/c would be a better choice if I were to use blue dot calipers? (ie., less lever travel)

Thanks, Leon

You want to adjust that screw so it is NOT touching the piston.... if you adjust it too far, it will cover the hole that lets fluid back into the master and it WILL lock the brakes eventually.

Most of us that have replaced our frt calipers and MC with modern blue/gold spot parts get them off ebay. My '99 R1 complete system cost me $50 + S&H.... a pair of factory OEM pads for an FJ cost more. 

I will NOT run EBC pads up front, ever since my LBS talked me into trying a set of the kevlar pads. They SUCKED! I could pull as hard as I felt safe on the lever and no slowing down.... until I suddenly had a locked-up front wheel, thankfully I didn't crash. My best results have always been with OEM replacement pads.

[Arnie]

Also, it's on my todo list to my FJ, going to a 14mm master on the clutch, to provide a lighter and more precise clutch, to make drag launches easier to modulate power on.

AndyB,

Be cautious with this.  Going to a 14mm clutch mc may not get the slave to fully release the clutch.  This results in difficulty in changing to neutral.   Every part of the system has to be exactly right to keep the clutch from dragging at least a bit.  DAMHIKIJDOK

Arnie
 

[1tinindian]

With a little modification to the brake lever, I was able to decrease  the lever pull to a more acceptable amount and after test riding it several time, I'm much happier with the feel and will go with this for the time being.

You all have a great amount of knowledge on this topic and I learn alot with every post.

Thanks, Leon

[cyclenutk75]

I have the identical issue with my 89.  A friend had the identical problem with his 84.  I know because we were both complaining about the front brakes, so we swaped bikes.  New pads, changing fluid, thorough bleeding did not help. He bought a used set of SS braided brake lines on ebay.  Totally fixed the problem.  Obviously my stock brake lines are "bulging" under pressure. You can feel it if you pinch the line with your fingers while pulling hard on the brake. I'm going to invest in braided brake lines.

[SILVERGOAT]

My 89 had seen better days. I found a master cylinder, calipers, pads AND steel brake lines assembled from an 05 FZ1 w/ 4800 miles on eBay for $80.00. The only modification I made was to cut a small notch in the front of the right handlebar to clear the brake lamp switch to rotate the assembly downward for the proper angle. Much better.

[Question Mark]

 I had a '90. Arnie said it best. R6/R1 calipers----flea bay I found a set for $76. Then ss brake lines. Even just the calipers was amazingly better.My '90 behaved the same way yours does.Cheap,quick, and direct fit fix....like having a new bike

[1tinindian]

I'm on the hunt for R1/R6 calipers now.
Still wonder if it will be OK to use the FJ master, but not too worried if I would have to replace it with a newer style.

Thanks for all the great input.

Anyone here currently running blue dots with the stock FJ  master?
Feedback on how it works?

Thanks,
Leon

[SlowOldGuy]

Anyone here currently running blue dots with the stock FJ  master?
Feedback on how it works?

I am.  I'm not a big brake user and I like it just fine.

It requires a bit more squeeze effort, but I personally don't like "one-finger" brakes as I'm sure they would put me on my head in a panic situation where I'd probably grab a big handful and lockup the fornt end.  But that's just me.

DavidR

[Harvy]

Anyone here currently running blue dots with the stock FJ  master?
Feedback on how it works?

I am too Leon, - OEM master with 2003 gold dots.
Very happy with performance. I'm mainly a 1 finger on the lever at all times rider, 2 if pushing it harder. I find 1 finger control perfectly adequate for my everyday controlability. I also have braided lines, sintered pads and Kagizumi rotors.

Harvy

[1tinindian]

Excellent guys, that helps my understanding a little better.

Now, If I were to also get the proper M/C to go with the blue/gold dot caliper, what M/C would I need to look for if I wanted to avoid the "specimen cup" reservoir? Model and year would greatly help my search for the correct pieces.
Is there anything that would be a direct mount to my stock bars?

Thanks again!

Leon