The dreaded "Spooge" hole

[trbig]

I have been having a lot of problems with my rear brake on my XJ. I cleaned the master cylinder and spooge hole repeatedly, I removed the caliper piston and sanded any small pits to make sure they were smooth, removed the O-ring and cleaned it and the groove it sits in.. and it would still hang up on me.

I then changed out with a totally different brake system from my parts bike. the M/C appears to be from an XS. I cleaned the M/C, spooge hole, caliper, piston, O-ring, and groove. I bled everything with new fluid.. and the brakes still would hang up on it.

I thought that replacing the rubber line with stainless would help it, so I bought one, re-cleaned everything AGAIN, installed it, and the M/C wouldn't pump any fluid.. it would leak out past the plunger on the bottom. Grrrr!!! So... back to the original M/C which I cleaned AGAIN, installed, and my rear brakes still hang. &*)@!!! The only thing I know left to do is to buy a kit and use a new O-ring in the caliper.

The other thing I'm wondering about, is that I read on here a while back about someone drilling their spooge hole a little bigger, and wondered if it worked. What I WOULD like to know, are facts about if this would work or not and why. Also.. any other opinions as to what to do. What I WOULDN'T like to hear, are opinions of how I shoudln't do this because someone made it that size for a reason.. with no FACTS as to why one shouldn't be opened up a bit.

Thanks.

Tod

[prometheus578]

"TRBIG wants a bigger hole."

What I WOULDN'T like to hear, are opinions of how I shouldn't do this because someone made it that size for a reason.. with no FACTS as to why one shouldn't be opened up a bit

Guess that I'll just have to keep my mouth shut, now, won't I?
But, I won't.

What you lovingly refer to as a "spooge hole"....

Wow, now there's a term of endearment that's not used enough. You married guys might want to try that one out.
"Hey Honey-bun, can you come in the kitchen and open this jar of pickles for me?"
"Sure... be right there, my little Spooge Hole".

Sorry... must be the new medication....
anyway....

What you lovingly refer to as a "spooge hole"... the engineers who designed the thing referred to as a relief port.
I will try to explain it's function in simple terms... (for reasons I know all too well.)

That front cup on the master cylinder piston called the "primary seal" is what makes the whole system work. Now, your master cylinder has two holes, the relief port and the supply port. When not being used, that primary seal is positioned between the two ports.
Now, when you squeeze the brake lever, that piston starts moving forward... the primary seal pushing brake fluid in front of it.
A certain amount of this brake fluid under pressure heads down to the brake caliper and starts that moving a little... and the rest of that brake fluid under pressure escapes back into the brake fluid reservoir through the relief port(Spooge hole)
(A simple test will let you know if the spooge hole is clear. Open up the reservoir, place your face over it and squeeze the brake lever. If you get hit in the eye by a high pressure stream of brake fluid, then it's clear.)
Now then, to continue....
Once that primary seal gets past the relief port, then all the compression on the fluid, applied by the brake lever, is then transferred to the brake caliper.
So, actually, that relief port (spooge hole) is also a metering port of sorts.
As you squeeze the brake lever.. some of the force escapes, while the caliper starts moving toward the rotor... and then once the primary seal is past the relief port, full pressure is applied to the caliper.
So... lets see what happens if some boob decides to make that relief port hole larger.
We now have a larger hole.
We squeeze the brake lever.
There is no gradual movement of the brake caliper piston as all the fluid under pressure moves back into the reservoir.
Once that primary seal gets past the now larger relief port, all fluid pressure gets sent immediately to the caliper and it slams forward and the brakes lock up.
So... you've lost your ability to feather the brakes... to apply a slow and gradual pressure that you can feel in your finger tips.
Your brakes now have only two modes.. fully off... and fully on! Have fun!

This "spooge hole" of yours also plays a part in releasing brake pressure... as once you release the brake lever, the master piston(under spring pressure) moves back... the primary seal uncovers the relief port and the fluid under pressure flows back in to the reservoir, and the brake caliper piston retracts the brake pad from the rotor, etc.

Now then... since you've probably already been squirted in the face doing the spooge hole cleanliness test.. we can assume that the hole is clear.

Two things cause the brake caliper piston to retract. (OK maybe three.. but I'll have to think hard.)
Slight imperfections on the surface of the brake rotor and slight warpage of the rotor itself. A "high spot" on the spinning rotor will push the piston back in a little bit giving clearance between the rotor and the brake pad.
But, the number one thing that causes the piston to retract is that little square edged O-ring in the caliper.
Ya see... in order for brakes to work, and then not work, the brake pad only needs to move forward a very small distance to make contact with the rotor, and then retract that same small distance.
This is why that O-ring around the caliper piston is square sided, and not a normal round O-ring like we're used to seeing everywhere else.
When one applies the brake... the piston moves outward... And the square o-ring that seals the piston flexes/twists as the piston moves.
Once the pressure is released from the system, that square O-ring tries to regain it's original shape, and in doing so, retracts the piston with it.

Anyway... I'm tired of writing.
What your problem is... I don't know.
(What the problem is with your bike's brakes, I don't know either)

I'm not there to see what everything looks like.
What I would do is to recheck the whole rear caliper bracket assembly to make sure it's all assembled correctly and not binding.
You've also got some strange XJ thing. Don't they have a linked system to the front brakes? I'd check the metering/proportioning valve system.
If you open the bleed screw on the caliper and fluid squirts out and the brakes release, then you have a pressure issue somewhere.
If you've released the pressure as above and the brakes are still stuck, it's a caliper/piston issue.

[trbig]

A stock XJ M/C does have a proportion valve, but I removed the line that goes to the front, so only the rear tire is affected by the rear brake pedal. The 2nd M/C I had used had no proportion valve on it and possibly came from an XS, but not sure.

If you open the bleed screw on the caliper and fluid squirts out and the brakes release, then you have a pressure issue somewhere.

Did they teach you that at the Motorcycle Mechanics Institute.. or did you figure that one out all by your lonesome?


Yes, whenever the brakes start to hang, I can loosen the bleeder and a bit of fluid squirts out. Two different styles of M/C, two different calipers, three different lines, new pads... all the same problem. As stated, I will order a new O-ring for the caliper, but not sure what to do if that doesn't work.

Anyone have a set of drum brakes that will fit on here?? (Just kidding.. I like my curve-spoked,sissy, swirly, flowery lookin' wheels. Seriously.)


Tod

[prometheus578]

"Why, I've never been so insulted...!"

Did they teach you that at the Motorcycle Mechanics Institute.. or did you figure that one out all by your lonesome?

Oh.. gettin a little snippy, huh?
Fine... I guess I'll just go and bother someone else.
At least my brakes work!

[DiverRay]

PROM, Insulted??

Oh.. gettin a little snippy, huh?
Fine... I guess I'll just go and bother someone else.
At least my brakes work!

Tod,
I think what Prom was trying to say is you will need to CLEAN the brake system, again. May I suggest you have Bohn do the cleaning? I know he is good at that!
I WOULD take everything apart, clean all metal with brakeclean, and all the rubber parts with plenty of new brake fluid. Then put it all back together. Don't forget to check the rubber on the mount bolt, and put some high temp grease on the slider bolt for the caliper mount.

[Ivan]

Two things that struck me Tod, they have bit me in the past.

From what you describe, everything is clean and clear. So, my past experiences might help.

One time in band camp, I had a brake line that the interior lining came loose on and acted like a check valve to the fluid. The caliper on that car would lock the right front wheel solid, and take days to release, unless the bleeder valve was opened.

Another time at boy scout camp, I rebuilt a master cylinder with one of the lip seals in backward. They should both open toward the hose. In this case, the plunger would move forward and the seal would not let any more fluid into the pressure zone of the MC. It would squirt fluid all over the hood of the truck when the pedal was released.

I know you tried a different line, so the first one probably isn't it. You also come across as being smarter than the average bear so I suspect the second isn't it either. For this reason I didn't even suggest that your push rod length might not be set right. Things like that only happen to silverbacks.

Maybe my rambling will help you think of other problems not so readily apparent.

[trbig]

PROM, Insulted??

I think the insulted one figured it out for me in PM. Surprised he hasn't gotten back on here to gloat..

He guessed the pushrod adjustment.. as the loveable silverback also hit on. (No really.. he is. With a full body wax.. he looks pretty presentable)

Anyway... when I had the 2nd M/C on, it would build up pressure going down the road.. obviously operating the M/C piston on bumps. I realized this, but thought that it SHOULD have bled the pressure off afterwards. Not knowing the innards, as the magnificent and humble Prometheus does, he explained in very simple terms so I could understand that the rod probably has the piston pushed in slightly and blocking the return port. I'll be away all week and won't be able to try out the theory until next weekend. So until then....


Tod

[Ivan]

I had the same thing happen to me when I first had my XS. I adjusted the pushrod to long, and the brake dragged ever so slightly. After a few miles the friction heated up the caliper enough that the fluid expanded and locked it up completely. Felt like a loss of power, to the point it just wouldn't go. Was riding two up with my wife at the time and she commented on the car behind us smelling like something was burning. Luckily we were close to a pawn shop and we ran in and bought a couple of their el cheapo wrenches from a large bucket to get us going. FWIW, those wrenches are still in the tool box on the XS.

[thewiz]

Hope you got it ...

I had a similar problem on an F once. Cleaned, re-cleaned to no avail. The sharp-eyed Planedick noticed that the rotor wasn't fully centered up in the caliper which, he theorized, caused the piston to have to travel too far in order to make the pad contact the disc. Once the pad did contact the rotor, the piston at that point was overextended and wouldn't return correctly or actually at all. Like Ivan's experience, the increased friction sooner than later locked up the caliper.

At Dick's suggestion, I centered up the rotor with a 3/4 washer by shimming the caliper mount on the axle to center the rotor thus reducing the piston travel. Took a couple of trys to get the right thickness washer in there but once I did ... Boom .. no more lock up. Good luck !!

[fredintoon]

Did they teach you that at the Motorcycle Mechanics Institute.. or did you figure that one out all by your lonesome?

>
Hi Tod,
neither of those, it was the emergency doctor at the eye hospital who told him:-
"You've been peering down spooge holes again, haven't you?"
(and this from a man who squirted acetone into his eye when checking if his paint gun was clean.)

[XS Jeff]

I also carry a 8mm wrench for this exact reason.