Master Cylinder rebuild

[scoot]

I tore down my Lockheed Master Cylinder, stripped it, parkerized it, and put a rebuild kit in it. When I inserted the aluminum plunger with the O-ring, it was tight but didn’t seem excessive. The problem I’m having is the spring doesn’t have enough force to return the plunger after each pump. The only way I can get it to return is inserting the air compressor nozzle into the brake line port. Everything is well saturated in DOT 3. On the one pump you get, it squirts fluid out the brake line port. Is this a common problem with the rebuild kits? Not sure if I need a smaller O-ring, stronger spring, or hone the master cylinder?

[Chris Haynes]

Definitely hone the cylinder. The Parkerizing has made it a rough surface.

[scoot]

Thanks Chris,
I Didn't realize parkerizing made that big of a difference.
I will give it a try tonight. I'm just concerned I’ll take out too much material and it will start leaking.

[Robert Luland]

Why were you parkerizing it? All master cilnders were painted silver as far as I know. Bob L

[flat-happy]

you really should change over to dot 5 fluid after flushing out all of the dot 3. if you get the dot 3 on anything it will remove any paint you get it on. if the 3 and 5 mix it will dissolve anything rubber like o-rings cups hoses etc. the dot 5 is more slippery too

[scoot]

This is the second rebuild kit going into this master cylinder. The first time I assembled and installed it on the bike, I ran DOT 5. It leaked horribly. I was told by several people that all rebuild kits are to be used with DOT 3 because DOT 5 will not swell the seals and cause it to leak.

[vph-d]

Back in the mid 70s when DOT 5 first came out, 5 compliant m/c parts were marked with a yellow and white ring. The -58 m/c rebuild kits were DOT 5 compliant, and also contained the residual pressure valve since the kit was used for drum and disc brakes. I think the master cylinders were always painted silver.
VPH-D

[scoot]

The two different rebuild kits I used, NOS and antique cycle supply, had no colored markings. The guy at Antique Cycle specifically said they were for use with DOT 3. I would prefer to use DOT 5 so I guess I can give it another shot after the hone.
The master cylinder is suppose to be silver on a 64FLH? I parkerized it almost 8 months ago, I need to dig up where I found that info.

[bmh]

Been running DOT5 in mine since the mid 80's. The biggest problem is getting them cleaned out, if there is any DOT3 residue left it will turn everything to jello in short order , and trust me there is not always room for jello Flush them clean with lots of alchohol. The only leaks I ever encountered were when someone honed out thier bore. Unlike a wheel cylinder, you can't work the hone completely through and the bore seems to taper rather easily because your working the thraot more than the bottom of the bore.

[Robert Luland]

Scoot, lets me lend my experience here. Let’s start with the brake fluid. I’ve been running dot 5 in all my motor cycles without incident for 26 years. In fact I drained my 86 Ford 350 services van and put in dot-5 a year after I bought it and I know the person that still running it without problems and will probably never will. Let’s look at the Harley master cylinder. As far as I know it’s the only manufacture that had a cast iron master cylinder. This beats aluminum hands down. Until! Dot 3 hydraulic fluid is Lockheed’s choice. It’s hydroscopic. It loves water. It soaks it up. When you mix the two of them together it makes acid. I don’t know why but water in hydraulic fluid seems to go to the bottom unlike oil. Just look at a set of bad lower fork parts. There will be pitting everywhere. The master cylinder seal only moves ¾” in the front of the cylinder. Every bad cylinder I’ve seen has pitting on the bottom ½” from the front. You have to hone this till it’s gone or the bore has exceeded the seals capacity to do its job. Just look in there with a flash light. The only way you’re going to get in there is with a dingle berry hone. I guess you could get it with one of them three legged sprung contraptions. Now I got a question. Earlier someone mentioned a residual pressure valve. I was rebuilding one of these a couple of weeks ago. In the rebuild kit was a rubber coated washer with a hole in the middle. I’ve never seen this before. Is this the residual pressure valve? Do you just discard it if it’s a drum brake? PS: Run dot 5 handsdown. Bob L

[vph-d]

IIRC, the valve was for disc brakes only. The kit was to fit '58 thru part of '79, so the valve was included for those with disc brakes.
VPH-D

[bmh]

IIRC, the valve was for disc brakes only. The kit was to fit '58 thru part of '79, so the valve was included for those with disc brakes.
VPH-D

That is absolutely incorrect! the residual pressure valve is MANDATORY for drum brake applications. Please see the note on page 2-40B of the 1970-1977 FL/FX factory service manual, as well as the diagram on page 2-41A, items 12 valve & 13 valve seat. Both are labeled 1972 and earlier. The seat is the rubber washer that Bob referred to, the valve is a thing that looks kinda like a cut off thimble. The master cylinder must be correct for the application. Using a master cylinder with the valve in a disc application will cause the brake to drag, most likely turning the rotor blue and destroying it and possibly causing unexpected rear wheel lock up usually at the worst possible time. Use of a cylinder without the valve in drum brake applications will cause erratic brake action at best and will most likely cause a real lack of brakes when you need them most. I also see in my manual which was revised 9-76 a note that states use DOT 5 fluid only and to change it every 5000 miles or once a year. I change mine every other year in all my bikes, cheap insurance that my brakes will be tip-top when I really need them.

[scoot]

In what order is the master cylinder assembled with the rubber washer? My manual doesnt show or talk about this piece at all.

[Robert Luland]

In what order is the master cylinder assembled with the rubber washer? My manual doesnt show or talk about this piece at all.

Scoot you took the words out of my mouth. I to want to know the ansewer to this riddle. I looked in all my books and non of them show that washer. Bob L

[knuckleheadtim]

I looked high and low for a picture with the washer in it, no joy. The washer goes in first and the spring assembly pushes it against the bottom of the bore. It serves two purposes; it keeps a slight residual pressure in the brake system so gravity doesn't cause the fluid to drain back into the master drawing air past the wheel cylinder cups, and it does the same when you release the brake pedal quickly.

This residual pressure is less than it takes to overcome the spring pressure on drum brakes, so the brakes won't drag. On a disk brake system it could defintely cause the caliper to drag.

Harleys did have a unique "return spring" in the calipers, but iI don't believe the washer is ever used on a disk brake system.

Just as important as checking the washer is making certain the tiny compensating port in the master cylinder is uncovered when the brake is released. The allows fluid to pass back and forth between the reservoir and the front of the piston so there is no pressure or vacuum built up from expansion and contraction. Because the hole is so tiny, it can easily get plugged with dirt, rust, or glass beads. If the pushrod has no free play, it can also cause the piston cup to slightly cover the compensation port. You can check it from the filler with a small wire.

The result of a blocked compensation port is high pressure buildup in the system which can burn the shoes and destroy rotor or drums, not to mention the safety factor of losing the brakes.

One note about Dot 5 fluid; it does NOT absorb moisture like Dot 3, so the moisture can settle on the bottom and do damage. It's best in a sealed system with a diaphragm in the cap to the moisture out. Dot 3 fluid should be flushed yearly to purge the moisture absorbed by the fluid which can lower the boiling point and cause fade.