[ElekVins]

I've been struggling for a while now with an issue I didn't manage to fix.
My juice rear drum is blocking after some miles (when it's getting hot I assume).
When the bike is in the garage it's working perfectly, same if I go around the block. Then if I go on longer ride it starts to block. Once it's blocking, if I release the purge it goes back to normal imediately.
I had this problem for a while now, so I changed the master cylinder, the wheel cylinder, even the brake lines, and of course I purged it many times and cleaned the circuit inside.
The only thing that aren't new now are the shoes and the springs inside which both looks in good condition to me.

Did this happened to someone here before?
Any suggestion or idea?

 

[JasonMcElroy]

It's happened to me.

You running a home-made brake linkage or control by chance? Make some pedal stop feature?

If the piston in the MC is returning fully, this can block the port that allows the release of pressure into the main chamber (or at least I think that's what it's for). Not returning all the way can be from a pedal stop (or pedal hitting something before returning all the way) or a worn out spring in the MC or a crapped up piston in the MC.

I'd rebuild the MC. Cheap insurance and you can see what's going on. Try to find a real (oem) rebuild kit. I've found the third-party ones to have weak springs and messed up piston sizes that do not allow free travel.

Jason

 

[ElekVins]

Thank you Jason for your reply.
It's a stock configuration on 67 FL.
Because of that problem, I rebuilt my old MC with a kit... the problem remained so I bought a whole brand new MC, and still the problem remains...
So that is 3 different configurations on the MC with still the same problem at the wheel...

Vins

 

[buckman50]

Any chance you bought an MC or MC rebuild kit that was for disc brakes?

If my memory serves me correctly, there is some kind of "screen" that is either added (or removed...cant remember which) to the disc brake-purposed MC.

Jason...you recall this as being a concern for juice drum applications?

 

[old.wrench]

You may want to make sure that the "residual pressure check valve" (fancy name for a washer, usually a rubber coated one) is correctly installed in the rear master cylinder if your running a hydraulic drum brake. It will help balance the pressure between the master and the wheel cylinder.

Regards,
Geo.

 

[JasonMcElroy]

Here is a diagram (generic, not exactly a motorcycle one, but the parts are the same) of an MC showing the residual pressure valve. It looks just like a sewing thimble. It should be installed to the that FLAT end is against the flat rubber seal washer at the bottom of the MC bore.

If it's clogged up, it could result in retained pressure in the line keeping the shoes dragging and building up heat.

Another thought. . . if you just cleaned the system and mixed brake fluid types, you could have a clot in the line.

And another. . . did you take a apart the wheel cylinder to ensure the pistons are returning freely?

Jason

p.s. - The residual pressure valve is used for DRUM BRAKES ONLY

 

[old.wrench]

Good, Jason. A picture is worth a thousand words^^^^^^. Like Jason mentions, the check valve is only used for hydraulic drum brakes. If you are running a disc brake, you can use the same master, but OMIT the residual pressure check valve. This is a pretty general statement and doesn't take into consideration stuff like bore diameter etc.

 

[ElekVins]

If I remember correctly the MC I ordered was for 65 to 84 or something like this, there was a sheet of paper with the exploded view of it sayin' it was set up for a drum, with the washer, and that I should remove the washer if i wanted to run it on a disk...
so I didn't open it...

 

[ElekVins]

This is the sheet of paper I'm talking about, so as I was mounting it for a drum I didn't touch it...

 

[buckman50]

Better double-check that and compare the new MC (and its contained parts) against the rebuild kit in the "old" MC.

I chased my tail on this with a disk brake setup once....figuring that what I bought was correct. Suffuce it to say...it wasnt.

 

[buckman50]

BTW...the washer in front of the residual check valve was left IN my "for disk brakes" MC. Again...check it to be certain.

*Note the Dot 5 as well...as Jason pointed out above.

 

[ElekVins]

Ok, then I guess I have to disassemble that fuckin' thing again...
I'll let you know what's inside when it's done
In the meantime if someone else had the same problem with a different diagnostic than the MC, I'm open to other inputs

 

[old.wrench]

Elekvin, as you mentioned about other things to consider - if your master is mounted in the usual position up front, this will probably not be a concern, but if its mounted towards the rear like on a FX and it is close to your exhaust and gets hot, that can cause a problem like what your experiencing.

 

[Larry T]

How is your brake rod adjusted? It needs a little play in it. If it doesn't let the mc piston come completely back, the piston will block a bleed hole in the mc and act exactly like your bike.
Larry T

 

[buckman50]

Another thought...

Whats your bleeding/purging procedure?

Are you sure when you bleed/purge the system you arent allowing air in???

 

[ElekVins]

Elekvin, as you mentioned about other things to consider - if your master is mounted in the usual position up front, this will probably not be a concern, but if its mounted towards the rear like on a FX and it is close to your exhaust and gets hot, that can cause a problem like what your experiencing.

It's in the stock FL position, up front, thanks for the info anyway

 

[ElekVins]

How is your brake rod adjusted? It needs a little play in it. If it doesn't let the mc piston come completely back, the piston will block a bleed hole in the mc and act exactly like your bike.
Larry T

Thanks for the Input Larry, I'm not sure there is a play in my brake rod, I'll check that first before disassemble again

Vins

 

[ElekVins]

Another thought...

Whats your bleeding/purging procedure?

Are you sure when you bleed/purge the system you arent allowing air in???

I'm doin' it the regular way, don't think I allow air in it while proceding

but talking about air, one thing I noticed is that, if I don't ride for a week or two, first time I'll brake, I'll have to pump the fluid 2 or 3 times to get pressure... Isn't it weird ?

Vins

 

[JasonMcElroy]

air, one thing I noticed is that, if I don't ride for a week or two, first time I'll brake, I'll have to pump the fluid 2 or 3 times to get pressure... Isn't it weird ?

I think that's normal on drums. All mine do it and they're bled fine. As long as you don't have to do it while riding. You can reduce this effect by using the eccentric shoe adjusters to keep the shoes very close the drum. That way they won't recede so far and won't take as much pedal to come back up after sitting for a few days.

I believe it's the return spring pressure on the shoes pushing the fluid slowly past the residual pressure valve.

Jason

 

[ElekVins]

How is your brake rod adjusted? It needs a little play in it. If it doesn't let the mc piston come completely back, the piston will block a bleed hole in the mc and act exactly like your bike.
Larry T

That was my problem, you nailed it !

Thanks for the input, problem solved , it now brakes like a charm

Vins