My single disc, '88 FXR has a PN 45019-85 front master cylinder with 5/8" bore, and 12 mm banjo bolt.

I picked up a 45013-82A mc with 3/4" bore, 10 mm banjo bolt at a flea market. The catalog states this fits '82-'85 Big Twins with dual discs. Will this mc work on my bike?

Thanks

 

doubt it. sounds like two different cylinders. id send it back and get the right one. besides with 10mm bolt i would think the hose would have some play in it.

 

It might work if you changed out the hose. The dual disc MC has a bigger bore, which means it pushes more fluid for the same amount of lever travel. This would give you a "firmer" lever than your original one. I think you'll have to pull the lever harder to get the same amount of clamping force at the disk too, but I'd have to think about that. This may or may not be a problem for you. In other words, it might be noticeable, it might make no difference to you.

 

You'll have a brake but not as great as orig Go to another swap meet and get the right one

 

Learned this from working on old military and antique stuff that you have to "improvise" on sometimes...

A smaller master cylinder bore will require less physical effort to get the same amount of pressure to the wheel cylinder (caliper). Conversely, a larger wheel cylinder (caliper) bore will apply more pressure to the brake shoes (pads)

Think about it... imagine a 100lb girl standing on your hand with a broad-heeled work boot - yes, it would be very uncomfortable. Now imagine the same girl wearing a spike-heeled boot and standing on your hand... it would likely punch a hole thru it! It's the concentration of force that makes the difference.

But bear in mind, the travel length and consequent amount of fluid required to move the shoes must be taken into consideration. Some, if not most drum brakes have the adjustment on the heel of the shoe and the return springs compress the wheel cylinders a fair amount of travel. With disc brakes it's easy - the travel of the caliper is microscopic compared to a drum/shoe arrangement, thereby requiring much less fluid to actuate braking.

No matter what, make certain all the plumbing is leak-free, and that you bleed every bit of air out of the system... and that's generally MUCH easier said than done!

 

Buy a 12 dollar rebuild kit and just rebuild your master cylinder. Doesn't take 15 minutes and all will work right . Now if you want better brakes add a jay brake 6 piston caliper and new rotor from JERIH for 350 tolal and have 2 finger brakes that are better than the new stuff hd is selling. I did it to mine

 

My current master cyl works fine, but I saw this chromed unit, for a great price, and just wanted to add some 'bling'. Unfortunately it was mis-labeled - the box had the wrong part number.

With further research I have found a 'banjo adapter bolt with 10mm threads using a 12mm line'. So, maybe somebody else has done this swap? I'll give it a try, see how the brake works and if no good, I'll have a slightly used, chrome master cylinder for sale.

Thanks for all your comments.

 

You are missing the point ,that 3/4 master cylinder with out 2 dic brake set up does not work. It will get you killed. It takes a much greater amount of pressure to squeese the grip to make the same kind of force at the caliper. You can always talk to some one at one of the aftermanket brake companies and tell them you have the 3/4 bore in there brand and see what they say.

 

Hmm, been running a 1972-1981 3/4" bore master cylinder on a 1987 FLST single disc for about 4 years or so. It works fine; yes, the effort required is more than the stock 5/8" bore, but not enough more to worry about.

 

pococj,


" been running a 1972-1981 3/4" bore master cylinder on a 1987 FLST single disc for about 4 years or so. It works fine; yes, the effort required is more than the stock 5/8" bore, but not enough more to worry about."


Well, that's good news. I assume your original master cyclinder had the 5/8" bore with 12mm banjo? Did you replace the brake line/banjo fitting, or use an adaptor bolt? There is this piece available

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Banjo adapter bolt, 10mm threads using 12mm line. Use on our part No. 90-344 handlebar master cylinder. Comes with two aluminum gaskets. Chrome plated. U.SA MADE.
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