79 front Master Cylinder

[Mickster]

Ever since you guys helped me sort out all those carb issues to get the bike running about as good as it's gonna get until a top end rebuild happens, it's been a lot of fun riding around on these country roads and into town for groceries and such.

So now, the front master cylinder on the 79 XS is dripping fluid out of the area where the brake lever contacts the cylinder. I think this is causing the pads to not release off the disc completely, wherefore it drags and squeels.

I ordered a master cylinder rebuild kit on Amazon which comes from LongHorn Moto and is supposed to be an OEM replacement parts kit

https://www.amazon.com/gp/product/B001KO4WKY/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1

Any input on that?

Next, after I clean and rebuild the unit it needs to get painted. Right now it's just corroded raw aluminum that is super icky cause all the previous coating has been eroded off.

Is there a paint available at an auto parts store, WalMart, Lowes, that will somewhat resist the aggressive nature of brake fluid? Even if I have to brush it on?

 

[gggGary]

Stores sell brake caliper paint, scrupulous prep, and curing will really help durability, some low temp oven, or at least sunny window time? You will often find parts with recent paint hanging on wires above my wood stove in the winter. In the great white north MC "rebuilds" are often possible reusing the original parts. May not be that lucky in Texas heat. As has been endlessly mentioned; an MC with a smaller bore and a stainless steel brake line does wonders for brake effort and feel.

 

[ThatXS650Guy]

As has been endlessly mentioned; an MC with a smaller bore and a stainless steel brake line does wonders for brake effort and feel.

This! If you are running the original 14mm MC with the stock single disk do yourself a favor and upgrade to a smaller MC instead of rebuilding the stock original. You will thank us later.

 

[Mickster]

ThatXS650Guy, That's all well and good. It's too late cause I already ordered the above kit. All I'm trying to do is fix a leaking MC with whatever the stock bore is, 13-14 mm or whatever it is cause I don't know what came from Japan. I'm hoping that what I ordered will work. It's a 1979 XS650 with the stock single disc.

Meanwhile, any recommendations on the paint?

 

[5twins]

Your leaky MC isn't causing the caliper to drag and stick. That's a whole 'nother issue. The caliper needs to come apart and be thoroughly cleaned out. To get one of these front brake set-ups working OK, you can't go just part way or "half in". You have to clean out the entire system, replace the ancient rubber brake line too.

 

[fredintoon]

ThatXS650Guy, That's all well and good. It's too late cause I already ordered the above kit. All I'm trying to do is fix a leaking MC with whatever the stock bore is, 13-14 mm or whatever it is cause I don't know what came from Japan. I'm hoping that what I ordered will work. It's a 1979 XS650 with the stock single disc.
Meanwhile, any recommendations on the paint?

Hi Mickster,
2-part paints have better resistance to brake fluid's paint-stripping powers, the hard part is finding a small enough quantity unless it's scrounged off a bigger paint job.
If you are adamantly opposed to buying a smaller m/c, you could add the second (leftside) disk & caliper that the stocker was sized to operate.
And fer fuxsake swap out those 32-years past the "use by" date fabric brake hoses before they burst, eh?

 

[Mickster]

Well fellas, as usual, you have the right answers.

Since I'll have the front brake system down I'll replace the old brake hose and rebuild the caliper.

 

[ThatXS650Guy]

ThatXS650Guy, That's all well and good. It's too late cause I already ordered the above kit. All I'm trying to do is fix a leaking MC with whatever the stock bore is, 13-14 mm or whatever it is cause I don't know what came from Japan. I'm hoping that what I ordered will work. It's a 1979 XS650 with the stock single disc.

Meanwhile, any recommendations on the paint?

Just trying to save you from wasting time and money. The stock one will work when rebuilt but 1), it is suboptimal with a single disc 2), it is ugly as sin, 3) it was designed to work with the rototiller bars which almost everyone but JetMechanicMarty tosses.
As for the paint, caliper paint works well but won't stand up to brake fluid. If you are rebuilding and replacing you might as well switch to DOT5. It takes more work to get a firm lever but it doesn't eat paint.

 

[Mickster]

Just so I understand this. If I rebuild the MC, replace the lines and rebuild the caliper, clean everything, I can refill with DOT 5 and there won't be any problems, even though the original stuff was all engineered to work with DOT3?

 

[5twins]

Yes, but the system must be totally clean with no left over traces of the old DOT 3. The two types don't mix. I put DOT 5 in one bike many years ago, I'll never do it again. The only benefit really is it won't eat paint. It didn't work any better than the DOT 3 and it is more expensive.

 

[ThatXS650Guy]

The only benefit really is it won't eat paint. It didn't work any better than the DOT 3 and it is more expensive.

At the risk of disagreeing with 5Twins... Totally worth it.

 

[Mickster]

I took apart the MC and after seeing the icky mess in there I have decided to completely rebuild the front brake system. I already have the MC rebuild kit coming, today I'll order the 41" stainless brake line and front brake caliper rebuild kit from Mikes. This will eliminate the two lines and junction block set up I currently have.

My Clymer manual says that the "Bridge Bolts" on the caliper must be replaced each time they are removed. Why is that? And do they really have to be replaced. And if they do, where do I get them?

Can I re-use the copper sealing washers from the old brake lines? I don't see any on Mikes website.

 

[fredintoon]

I took apart the MC and after seeing the icky mess in there I have decided to completely rebuild the front brake system. I already have the MC rebuild kit coming, today I'll order the 41" stainless brake line and front brake caliper rebuild kit from Mikes. This will eliminate the two lines and junction block set up I currently have.
My Clymer manual says that the "Bridge Bolts" on the caliper must be replaced each time they are removed. Why is that? And do they really have to be replaced. And if they do, where do I get them?
Can I re-use the copper sealing washers from the old brake lines? I don't see any on Mikes website.

Hi Mickster,
while I'd use a smaller area piston M/C the stocker works kinda OK and a single stainless brake line is an upgrade as well as a simplification.
Yeah, mine sez that too. I have no Idea why neither so I've never bothered. Just in case there IS a reason, try a Yamaha dealer.
Sure you can. Heat to dull red with a Bernz Torch to anneal them.
Quench or air cool don't matter with copper but quenching pops the oxide off them to look nice.

 

[5twins]

If you have slightly lower than stock bars, the 41" line will probably be too long. A 90cm line (35.4") works well. You can get one off eBay for less than $10 .....

https://www.ebay.com/itm/45-120mm-M...var=640991001941&_trksid=p2060353.m2749.l2649

I think the bridge bolts referred to in that manual are for the older style caliper. It can be split in half and those bolts are what hold the 2 halves together.

 

[member28833]

Just trying to save you from wasting time and money. The stock one will work when rebuilt but 1), it is suboptimal with a single disc 2), it is ugly as sin, 3) it was designed to work with the rototiller bars which almost everyone but JetMechanicMarty tosses.

You just might be lucky enough to add the lft. side brake components off a XS 750,850,1100 standard and have a double disc set up if you search locally for used XS parts. Salvage yards do wonders.
I agree that the "special" MC sits at an odd angle on other handlebar choices.
Correction.. some other handlebars.
Just another option
-R

 

[5twins]

The Special MC actually sits quite nicely on Euro bars because of the way they droop down slightly on the ends .....

 

[member28833]

The Special MC actually sits quite nicely on Euro bars because of the way they droop down slightly on the ends .....

Oh, ah ha, I see . Good pic.
I tried to mount a "special" MC on cafe bars and it was a no go.

 

[member28833]

The Special MC actually sits quite nicely on Euro bars because of the way they droop down slightly on the ends .....

Now Im wondering if my own 78E stock master cylinder is a poor fit on those BikeMaster Euro bars ? My own master cylinder is rebuilt and great .
Hmm?

 

[5twins]

I ran my stock Standard MC on Euro bars for years. It did sit at a bit of an angle but that never caused any problems .....

 

[member28833]

Interesting.. all these choices.
Thanks 5twins