Front brake M/C options?

[GoRacers]

Hi all.

I searched a while, but didn't find the exact info I am looking for.

I'm on my 4th front M/C on this 78 xs11. The first two OEM units leaked at the reservoir. Then I went with an aftermarket unit, but it didn't move enough fluid for both front calipers. Now, I have one off of a Kawi KZ900, with 5/8" bore. The bike stops fine for commuting, but I haven't tried a real "emergency" stop yet. I have to use almost the whole lever's travel to get a quick stop.

Stainless steel brake lines all around; I'll try and bleed the fronts AGAIN to make sure that isn't my issue.

The brakes have been "de-linked;" the front two calipers are run off of the front m/c, and the rear m/c is connected only to the rear brake.

What other master cylinder options have people tried when using both front calipers?

[jwhughes3]

I have the 16mm MC from Mikes with SS lines. Works great.


BTW the 78 was never a linked setup. If it was linked when you got it someone put an 81 midnight MC on it.

John

[BA80]

The first two OEM units leaked at the reservoir.

I had that problem with my front MC when I went through it. I put some ThreeBond on the flat surfaces between the reservoir and the body and haven't had a leak since.

[jetmechmarty]

If you want to get serious about the brakes, call Michael Morse. Find him at www.650central.com or www.vintagebrake.com

[CatatonicBug]

I had that problem with my front MC when I went through it. I put some ThreeBond on the flat surfaces between the reservoir and the body and haven't had a leak since.

The 850 I put back on the road had a leaky reservoir. All I had to do was get a new O-ring for it. Took some elbow grease to get the reservoir back in, but it stopped the leak.

[crazy steve]

I had that problem with my front MC when I went through it. I put some ThreeBond on the flat surfaces between the reservoir and the body and haven't had a leak since.

+1 on that.... Cheap insurance anytime you rebuild one.

[GoRacers]

I have the 16mm MC from Mikes with SS lines. Works great.


BTW the 78 was never a linked setup. If it was linked when you got it someone put an 81 midnight MC on it.

John

Good to know. I'm not too educated on differences between years yet, I just read a thread about a linked setup and assumed they were all that way.

I have a 5/8" (pretty much equal to 16mm) MC with stainless lines. Guess I need to bleed them again.

[fredintoon]

Hi all.
I'm on my 4th front M/C on this 78 xs11. The first two OEM units leaked at the reservoir. Then I went with an aftermarket unit, but it didn't move enough fluid for both front calipers. Now, I have one off of a Kawi KZ900, with 5/8" bore. The bike stops fine for commuting, but I haven't tried a real "emergency" stop yet. I have to use almost the whole lever's travel to get a quick stop.

Hi Ryan,
FWIW, the stock front m/c bore on my XS11 Special is 11/16".
Using a 5/8" or a 16mm m/c reduces the piston area by ~15%.
Reducing the m/c piston area gives a better feel and a more powerful brake but you pay for it with a longer lever travel.
Stainless lines and a good bleed job should see you with good brakes.

[crazy steve]

One thing should be noted when installing stainless braided lines; how many lines did you use? Many use just two lines, one for each caliper from the master rather than using three lines as per OEM to eliminate the line splitter. Yamaha used that splitter for a reason (as do almost all OEM manufucturers); all flexible brake lines have a certain amount of 'give' in them, so by minimizing total line length you get a better 'feel'. 'Simplifying' by running only two lines adds about 25% more line, reducing the effectiveness by the same. Add in a smaller master bore with increased lever travel and you can end up with marginal brakes, even with stainless lines.

[TopCatGr58]

Hey Steve,

With Vinyl lines I would agree with you in the loss of pressure due to line expansion. But with SS lines, they don't expand...or at least not very much vs. the OEM vinyl ones. And once the dual full length lines are bled, they are full of fluid, so no extra fluid is required to be driven, the MC pushes the same amount of fluid required by each caliper whether it goes from 1 line into 2, or down 2 full length lines. It's the same volume of fluid that is required to displace the caliper pistons to actuate the brakes the same distance, so with SS lines there shouldn't be any loss of pressure or volume whether 3 lines or 2 lines are used. I understand what you're saying about more line area to stretch, but I really can't believe that they stretch 25% vs. SOLID metal lines.

When I replaced my OEM 81MC 12 years ago I got a smaller single caliper designed MC, not knowing the difference. I had to pump the lever a bit with the vinyl lines. Once I put on SS lines ,albeit they were the 1 into 2 design because I didn't realize I could have used just 2 full length ones, the brake lever became much firmer.

Then when I did my modern dual piston caliper mod, the total piston area for them was about 15% more, but surprisingly they seem to take less lever travel and feel even firmer. I think it's because the pads/pistons don't retract back as far as the OEM style so less total lever travel/volume is required to reapply them.

So....GoRacers, if you have SS lines on there, you should have a decently firm lever with minimal travel, especially with the standard calipers. Have you rebuilt the front calipers? If the square O-ring has formed corrosion behind it in the caliper housing, it will excessively squeeze the pistons making it harder to actuate them, and they will not slide easily, the overtight O-ring will roll and the piston will usually keep retracting back into the caliper instead of sliding towards the rotor and staying closer to it, so it keeps taking more and more brake fluid to move the piston farther to actuate the brakes.

T.C.

[crazy steve]

Hey Steve,

With Vinyl lines I would agree with you in the loss of pressure due to line expansion. But with SS lines, they don't expand...or at least not very much vs. the OEM vinyl ones. And once the dual full length lines are bled, they are full of fluid, so no extra fluid is required to be driven, the MC pushes the same amount of fluid required by each caliper whether it goes from 1 line into 2, or down 2 full length lines. It's the same volume of fluid that is required to displace the caliper pistons to actuate the brakes the same distance, so with SS lines there shouldn't be any loss of pressure or volume whether 3 lines or 2 lines are used. I understand what you're saying about more line area to stretch, but I really can't believe that they stretch 25% vs. SOLID metal lines..

TC, braided stainless lines do expand; not nearly as much as OEM, but there's still more than enough to notice if you have a basis for comparison. And not all stainless lines are created equal, some have less or more expansion than others. The 25% number I put up refers to the extra line length (roughly) that you would have if running two full lines in the front rather than one from the master to the splitter, then one each to the calipers. If you go from (as an example) 3' of line with X amount of line expansion loss, adding another foot of line has to increase loss.

The reason I know this is I've seen it. When I was building CheepoChopper, I originally hooked up the front brake with braided stainless lines all the way from the master to the caliper, with a coupling at the bottom of the fork stem. Brake worked fine, nice solid lever but I didn't care for how it looked. What to do...

Well, looking at a stock HD front line, I realized that Harley used hard steel brake line everyplace they could. Stock, the line is steel from the master to the bottom of the fork stem with a short, 3" rubber piece in the middle so you can adjust the handlebars. Using that as an idea, I fabbed a hard line (no rubber because I had the bars where I wanted them) to replace the upper line. Once installed, this reduced lever travel by about 30%. Very little travel, and rock-hard. I was frankly surprised at the amount of difference, but it's very real.

This is also why Yamaha used a steel 'front-to-back' brake line on the LH/XJ linked brakes; all rubber would have given a really spongy brake feel. And I suspect that replacing that long hard line with braided (even if you did all the lines) might leave you with little or no improvement over the OEM system, as while you improved over the rubber lines, you would lose at the former hard line.

I'm not saying this is the problem in this specific case, but it's something to look at. I'll admit it makes me cringe sometimes when I see posts altering the brakes on these bikes without the owners/riders taking all factors into consideration...

[GoRacers]

So....GoRacers, if you have SS lines on there, you should have a decently firm lever with minimal travel, especially with the standard calipers. Have you rebuilt the front calipers? If the square O-ring has formed corrosion behind it in the caliper housing, it will excessively squeeze the pistons making it harder to actuate them, and they will not slide easily, the overtight O-ring will roll and the piston will usually keep retracting back into the caliper instead of sliding towards the rotor and staying closer to it, so it keeps taking more and more brake fluid to move the piston farther to actuate the brakes.

T.C.

I haven't done much with the front brakes other than swapping master cylinders. Previous owner did the ss lines. I do believe they are working fine, just not enough pressure.

I'm thinking more and more that they just need a better bleeding. Doing that later today.

[crazy steve]

You can always reinstall one of the OEM units after resealing the reservior...

[GoRacers]

Bled them both again and cleaned up the reservoir and gasket surfaces before reinstalling the reservoir lid (fluid was seeping out a tiny bit).

Haven't ridden it yet, but the lever is much, much firmer. Can't get it even halfway to the hand grip anymore. Looks like that did the trick.

[Spivester]

Making sense

My '80 standard has the OEM MC but has stainless lines following the stock pattern. I thought something was wrong as I have almost no lever travel and it is VERY stiff when squeezed. That said, the old brakes are not overwhelmingly strong. If the hard lever is a normal response to going to SS lines, I won't replace it as I was planning on doing, but rather do new brake pads and drill the rotors as I had intended as my second step. What do you experts think?