Master-cylinder 750 SECA

Its the old problem XJ750 SECA Master Cylinder headache. You know, the one buried behind the headlight and a mess of wires with the hidden reservoir.?

Here is the background: rebuilt MC a few months ago with parts from XJ4ever. Reinstalled with new stainless braided lines and bled fine. Good pressure, worked fine; except my calipers were not releasing, so I decided to pull them off too and rebuild.

Now after reinstalling the calipers, I can't get the system bled! I've tried all the recommended tactics; vibratory sander, letting it sit for a day with the lever tied close and a bleed screw open. Taken apart everything at the junction up to MC, tried vacuum bleeding but couldn't pull fluid through. The MC will create pressure, but doesn't seem to pull any fluid from the reservoir. Pulled MC off again to inspect. Disassembled MC; everything looks fine, All passages are clear, inside bore is clean and smooth, rubber gaskets appear fine. it should be good, right? Only been 2-1/2 months since I rebuilt and hasn't been used. The piston pushes in, but seems to take forever to spring back. What is going on? It's like one of the rubber parts are too tight?

 

Ok, I got the master cylinder piston to return now. It springs right back. I still cannot the MC to take fluid from the reservoir. ??

Tried the vacuum again, and it just collapses the plastic tubing, even after the bleeder is opened; nothing comes through, not even air except what leaks around the bleeder and the attachment.

 

Is it possible that internal spring is in backwards or the lip on the piston has curled back when installed?
Did you hone the mc bore before installing new parts?
Is cable too tight or stiff not letting piston return all the way?
Or the little vent hole in mc blocked?
Bleeder screw has crap in it ( drill bit by hand is best)
You have probably checked all of the above and it's making you NUTS!

 

Pull the bleeder fitting off of the caliper. Clean the gunk out of it, or replace it with a new one.

Brake fluid won't flow (much) if the lines are full of air, and you can't get the air out if the bleeder is clogged.

 

The thing is, it worked prior and I didn't touch it since until the brake calipers rebuild. It does return now.
I didn't hone the bore, but did polish it with some Emory cloth and it was clean and smooth, almost shiny, no pitting. Checked spring orientation.
I can feel pressure on the outlet port when the piston compresses. Confirmed vent hole is clear; saw brake cleaner spray through it (yes, the teeny tiny one too).
The bleeder valve is same result on all four bleeder points (both sides, calipers and anti dive.) So I think it unlikely that all four bleeder valves are full of gunk, besides, I cleaned those too when I had the calipers apart.

YES, it is driving me absolutely NUTS, since I know it was working before I disassembled the calipers! The only thing I did to the MC is the lines emptied as they hung there unattached to anything.
I even disconnected the brake line on one side of the junction; no fluid, but I can feel air pressure when I hold my finger over it and squeeze the lever, yet the reservoir remains full.

@k-moe , respectfully, I followed your procedure(s) exactly and many times over with slight variations, even the sander. Left bleeders open with lever tied for 2 consecutive nights and also during day while at work twice. Been fighting with this for the last 4 evenings now. At one point, I did have fluid going through the system, but could never get firm pressure to squeeze the calipers. I have now taken the MC off and reinstalled at least 4 times this evening.

 

Some questions that might help me clarify my thinking:

Did you tear down, thoroughly clean, and rebuild the calipers?

Did you thoroughly flush the distribution block that is on the forks?

I will tell you that if the bleeder wasn't clogged the vacuum line to your vacuum bleeder pump would not collapse. There are a few nooks and crannies in the claiper that are difficult to get spotless. Perhaps a bit of crud loosened up and blocked the bleeder.


I recommend walking away from the problem for a day or two. Fresh eyes, and a fresh brain, often exposes solutions that were hidden before.

 

Yes, with new seals too.
At this point, the entire brake system has been gone through. There isn't a trace of old fluid or gunk left.

If you mean flush it with brake cleaner at the time of new line install, yes. I can't even get fluid to flow through the bent metal tube between the junction and the MC; i disconnect the tube prior to the distibution block and nothing is there. It is like the MC isnt taking any fluid in.

Probably a good idea. This is the last thing I needed to do before taking it out on the street, my first ride, so I am a little anxious to get it done. Also taking advantage of time while my wife is away out of town.

I really appreciate the help, at this point, I am just stumped.

 

I'd suggest when you're ready to come back, take a look at the system in sequence. Bench test the MC. If that works, connect the next component and test, and so on. This should narrow down where the problem is.

 

Dont know if this is helpful or not, but I think it confirms the bleeder passages are ok.
I connected a tubing sourced to brake fluid into the anti-dive bleeder then attached a vacuum to the caliper on same side and opened both bleeders. I was able to draw fluid between the two and vice-versa.
Then I connected the vacuum to the left anti-dive and was able to draw fluid all the way through; that is right anti-dive, through right caliper, up the line to the distributive junction, down the left line, through left caliper, and out left anti-dive. Did the same thing with both calipers as well; so we know fluid is flowing through from the junction on down. Next I will remove the bent metal tube between junction and MC; suspect it is OK, but will confirm. Will also inspect the inlet into the junction. After that is the MC itself, which I have already taken apart and inspected multiple times. Still not able to pull fluid with vacuum from MC to any of the four bleeder screws.

Enough for tonight. Need to sleep on it. Besides, I'm out of brake fluid.

 

Could that metal tube be kinked/collapsed?

 

Nope. Pulled it, blew air through it, sprayed brake cleaner through it. Open passage.

 

Yea out of brake fluid kind of does you in for tonight... NO bad dreams about not being able to stop

 

Allright. At this point I think that your work shows there is a problem with the master cylinder (or you have made the mistake of feeding you mogwai after midnight). . The trouble is that I can't ever say that I've had a pronblem with one after a rebuild, so I'm having to work from the same point that you are; inexperience. While you're on a break from solving this, I'll do some pondering. I wonder if maybe one of the piston seals is not seated correctly, or had a bit of schmoo on it that is now blocking the outlet.

 

OOO OOOO Mr. Kotter!!! OOO...

I know it's a royal PITA to check on this MC, but maybe the problem is a plugged return port. When bleeding do you have the fill cap closed? That combination could prevent fluid from being able to be moved.

 

when your bleeder line collapses, crack open the line going into the wheel cylinder. this will prove the bleeder is open.
i find that without teflon tape the bleeders leak past the threads enough not to let the line collapse.
do these MC's need primed?

 

Got some more brake fluid.
Unattached the steel tube from the MC. Attached a tubing to that submerged into brake fluid.
Used a vacuum at the caliper and anti-dive bleeders and got a steady stream of fluid flow through; no bubbles.
Did the same on the left side, got a steady stream of fluid through, but mixed with steady stream of bubbles. Hmm.?

Could it be I don't have everything sealed up on the left side somewhere? Possibly in the brake cylinder itself? I thought of this before, but didn't see any fluid at any of the connections. Maybe when the MC piston is returning, it is pulling air backwards in through the leak instead of from the reservoir?

@k-moe I tried both with the filler cap in place and off. First off, thinking it would allow air to replace the fluid in the reservoir as it is depleted.

 

Disassembled MC, AGAIN!
Just to verify, this is the orientation and order of the MC parts. Correct?



Close up of the rubber gaskets. Look to be in good shape. They were new when I rebuilt MC about 10 weeks ago, and has been sitting idle since. Orientation of the skirt shaped seal on the plunger is correct?


Interior of MC bore, shining light in through the return port to the reservoir. You can see the pin-point of ligh also, so those passages are clear.


Could it be that the brake cylinders are inserted too far, blocking off proper flow from the brake line? Even the slightest gap should allow fluid through, I mean, look at the bleeder screws, those openings are small.

I also know the passage from my reservoir is clear; it empties out onto my garage floor every time I separate it from the MC to remove it. Gawd, I must have lost at least a quart of that stuff by now!

 

So, now I'm wondering if it might have something to do with the diaphragm in the reservoir and not allowing atmospheric pressure to replace fluid that may be pumped out.?
When I cleaned out the reservoir, the gasket was very stretched out. It has a permament impression of the fluid level float in it from it being pulled? or pushed down for a very long time. Does anyone know what the diaphragm is supposed to look like?

Unfortunately location on this machine is a beast to deal with, it is difficult (if not nearly impossible) to test operation with the reservoir cover off without removing handle bars first, or removing reservoir to take cover off, then install on MC (not easy), then remove again to replace cover and reinstall again again after testing. But then again, leaving the filler cap off while bleeding should serve the same purpose.?

I was about to consider replacing the seals on the MC again, but the $90 for a rebuild kit is too much for a "lets see if this works." approach. I think by this point, I would be able to replace seals with MC in situ. It would be a great mystery if it needed replaced already, but this whole situation is a mystery.

I attached a clear tubing to the end of the metal tube and had a syringe at the end of the tubing held upright. When I activate the MC, a little geyser of fluid fillied up into the syringe barrel. Also disconnected lines from calipers and am able to pump fluid through, so I am fairly confident ?? that the seals are OK.

 

The diaphram on the reservoir helps seals the outside air from getting to the brake fluid. The cover has a vent hole in it (I can't remember where) that allows the diaphram to move as the brake fluid level in the master cylinder drops. If you're not getting fluid to move with the fill cap off, then the diaphram is not the problem since the system is open at that point.

Pull her off of the bike (PITA I know), and see what she does when set up on the bench without the reservoir cover in placce.

 

Just a question when I did brakes on my Seca I bleed the left anti-dive, then left caliper , then go to the right anti-dive , right caliper , I use a one man bleeder. To make this all easier I pull the headlight bucket bolts pull headlight out of bracket , remove MC cover use a long funnel and add brake fluid as required. It took a few times to pull fluid thru , but finally got a firm feel . Is your cable to MC adjusted properly ?

 

I have played with the brake cable adjustment allowing just a tiny bit of play before engaging the lever to push the piston.
I successfully bled them prior when I rebuilt the MC before rebuilding the calipers; had good pressure, not too difficult. The brakes wouldn't release though and locked the wheel. Being that the bike sat for so long, not knowing the condition of the calipers, I decided to rebuild those as well when I took the wheel off for new tires, inspection of bearings, and rebuilding of forks.
I started bleeding Right AD, then Right Caliper then over to left, as the right side is closer (slightly) to the MC. TBH, I have so many attempts this go around, I have rotated back and forth between them all in different orders. Seems that once the AD get bled, the calipers are easy to follow, but I go back to the AD for a second round, then calipers again and repeating. Just not seeing any movement in calipers at all due to lack of pressure.

Headlight is already off and out of the way as it is mounted in the fairing, which is currently off of the bike. The MC isn't so difficult to remove now; lots of practice in the last few days (week)! I can get it out in about 2-3 minutes LOL. The most difficult part I have, besides getting pressure, is getting the reservoir attached and seated to the MC after installing, but I'm sure this is just technique and getting the proper combination of angles and twist. To fill, I have about a 12 inch tubing attached to a syringe. Before, I was using a plastic bottle with a fliptop spout into a bendy straw from a water bottle.

It just seems that the MC is not pulling fluid in from the reservoir to replace fluid that is bled. I wonder if one of the MC seals is allowing leakage back; or from the suck back on the return, the vacuum created is pulling air in from maybe one of the rebuilt calipers? but yet, I don't see any leakage from that point, or any other even though the calipers are full. I even tried reverse bleeding by pushing fluid in through the caliper and/or AD using a syringe and tubing attached to bleeder screw.

This may be notable; the return at at times is VERY slow, and others, it springs right back. It was even like this out of the bike and depressing the piston with a screwdriver while testing MC by itself.

I am contemplating tearing down the calipers again to see if I see something. Not giving up, something will fall into place one of these times.

 

Where did you get the master cylinder rebuild kit from?
What brand is it?

 

XJ4Ever, along with new SS lines

 

Well, it could be a problem with the seals, but we've sold lots of these kits and have never heard of an issue before. The seals would have to be installed backwards or have a full tear thru them to not be able to push fluid; even 30-year old original m/c's can still pump fluid (albeit weakly).

So, let's go down the line, taking it from the top:

1) Reservoir, alone, not attached to the m/c: does fluid flow out of it (it should!) ?

2) Reservoir, attached to m/c, without the piston installed, does fluid flow out of the m/c (it should!) ?

3) Reservoir, attached to m/c, with the piston installed, but NO SEALS ON THE PISTON, does fluid flow out of the m/c (it should!) ?

4) Reservoir, attached to m/c, with piston installed AND SEALS INSTALLED, does fluid flow out of the m/c (it should not!) ?

5) Reservoir, attached to m/c, with piston and seals installed, and piston actuated ("pumped"), does fluid flow out of the m/c (it should!) ?

6) Same as above, but now attach the metal output line to the m/c, and piston actuated ("pumped"), does fluid flow out of the metal line (it should!) ?

7) Same as above, but now hook up metal output line to the distribution block, actuate the m/c, does fluid flow out of the distro block outputs (it should!) ?

8) Same as above, but now attach the brake lines to the distro block otuputs, actuate the m/c, does fluid flow out of the ends of the brake lines (it should!) ?


You may have done most or all of the above, but it would be best (if you have skipped some of the steps above) if all steps were done in that order (or, in complete reverse order would be okay, too). We have to isolate where the problem exists.....then we can work on figuring out why.

 

Well, it seems as something is going on with the seal. With the MC off and with the reservoir attached, I could not get it pump any fluid. To the above questions:

1. Yes!
2. Yes
3. Yes
4. No
5. NO!

Strangely though, with piston inserted, but without the seal, it sprayed fluid out the port.
So it seems it has something to do with the piston seal. What happened between the original rebuild and now..????

Inspected the seal and I don't see anything obvious wrong with it; no tears, nicks, or other imperfections that I can see. See my prior post for installation orientation.

Inspected the bore again as well and it looks clean and smooth, no pitting, scratches, gouges, or other defects.

Played around with reinstalling seals and everything and was intermittently able to get fluid to flow, but most times not. The seal seems to be tight, because as I mentioned before, the return is slow to non-existent with the seal installed. Even when I remove the circlip, I usually still have to extract the piston.

 

I am led to believe that the lack of or weak return is what may be causing my issue. It is on the return that more fluid is pulled from the reservoir, correct?
Maybe weak spring? Even though I feel it is already quite smooth, I think I will try to polish the MC bore this weekend in an attempt to reduce friction of the seals against the MC bore walls and facilitate the return.
I WILL get this figured out.

 

Upon return brake fluid is allowed to come back into the master cylinder from the brake lines and calipers.

Let's have you do a crazy thing. Even though the pison seal is the right way around, go ahead and reverse it. What happens?

 

Ha ha! Tried it last eve. I thought it crazy too, but what the heck? No improvement. The piston was darn near stuck in there; couldn't pull it out. Used a bolt of very similar diameter to the opening in the back of piston concave where the lever rod inserts, and had to thread it into the softer aluminum to have something to pull/ pry the piston out.

 

I've let this set for a while and have been working with Len from XJ4Ever behind the scenes.

Did some more work tonight and even substituted MC seals again. Bench tested with a spray of brake fluid all over garage floor. Reassembled MC and was still having similar problems; i.e. No pressure built up, but movement of fluid back and forth in clear tubing attached to open bleeder valves, weak or no return. Just didn't make sense.? No air in lines. Worked with it for a couple hours.

I began to isolate each component one by one again. When I disconnected the right anti-dive unit line, and just ran a line to the caliper on the right side using the banjo-bolt from the a-d unit-- I got pressure!! Firm brake lever. Both brake calipers activated, and they release. So it is the right a-d unit causing the problem. Must have done something when I had it off when I rebuilt the forks?

Anybody want to suggest what to do with the anti-dive unit that could have caused all of this nonsense? I suppose I have to remove my fork again.?

 

Remove the anti-dive unit for inspection. The brake fluid side is seperate from the fork oil side (though the fork oil will drain out when you remove the anti-dive unit from the fork).
When you had the forks off did you open up the anti-dive units for cleaning?

 

you might have automatic brakes when the forks compress, won't that be fun

 

Wow, what a nightmare this appears to be. I admire your persistence and patience getting to the bottom of this.

Len carries the parts to rebuild the anti-dive assembly. If you do so I recommend grease on the hydraulic side to remove the piston as they are typically corroded and stubborn to remove. Any kind of metal tool poked in there can easily damage the bore and is not recommended.

You can also just remove the hydraulic portion of the anti-dive and not worry about losing fork oil if you choose to just clean/rebuild the hydraulic portion.

If you did not clean / rebuild as k-moe asked I would be suspicious of the bleeder valve not seating well and allowing air into the system. I think normally the pistons corrode so much they do not leak. A leaky anti-dive unit will weep brake fluid out at the junction of the hydraulic portion to the fork oil proportioning assembly.

 

The system did act as though there was an air leak. Is it possible for brake fluid to leak and mingle with the fork oil? I never saw any leaking fluid anywhere around the anti-dive units, or elsewhere in my attempts to bleed. Away from the bike for a few days. Will at least take the hydraulic portion of the anti-dive off and tear down/clean/inspect when I can get back to her.
May have to change out all bleeder screws as a preventive measure.

I'm sure my inexperience has caused me more trouble and duration than necessary.

@k-moe, no, not really.

@Polock, automatic brakes synced with the forks do not sound fun at all!

 

yes

 

The anti-dive works via a pair of pistons (there's more to it, but this part is all that matters for this problem). The little one on the brake side has an o-ring that seals it. The larger piston on the fork side has an o-ring and a rubber/plastic cap that seals the brake side of things from the fork side of things. If all three of those fail, brake fluid can be forced into the fork.

 

I removed the brake side of the anti-dive unit. The fork side seems OK as far as I can tell. The piston on top moves up and down freely with the internal spring.

On the brake side, as suspected, the external part under the plastic cap was full of crap; grime, sand, dirt...
Unfortunately, the little circlip is rusted in place; in fact, the ears (the little rings) on the circlip both corroded and broke off. Currently working on removing the circlip to get to the internals. Seems frozen in place. Got it soaking in penetrating fluid and tapping on the circlip with a flat bladed screwdriver to try to break it free so that I can pry it out.

Should the larger plunger piece being held in place by the circlip, move to take pressure off of the circlip? It doesn't seem to budge. May be easier just to find another anti-dive unit.

 

The circlip just holds the washer, which then captivates the plunger assembly so there should be no pressure on the circlip. If you don't go with replacing the entire assembly then a grease gun is the best method to remove the plunger to avoid scarring the bore with metal tools.

Here is a link to some great pictures:

http://xjbikes.com/forums/threads/anti-dive-fork-explosion.41895/

 

So, I suspect the leaking air in my brake system may be around that O-ring? Or the bleeder valve? Good news, I didn't see any brake fluid or fork fluid in or around the anti-dive unit. In order to remove the little plunger to replace the O-Ring do I need to remove the circlip and washer?

I may leave the anti-dive portion disconnected for a bit, just so I can take her out around the block now that I have some front brake action. This will be my first ride on this bike, and my first ride at all since I took the MSF course over a year ago.

 

The circip must come out in order to remove the washer and piston.
Based on what you are seeing, I find it odd that there is no sign of a leak. I'd expect to see brake fluid all over the inside of the housing if there were. I'd also expect that the piston would not be stuck.


This thread may be helpful.
Anti-Dive Fork Explosion

 

Thinking I may just try to find a replacement anti-dive unit; at least the hydraulic portion. The circlip is fused in the groove. Can't get the little piston plunger to move in either direction. Used grease gun to try to push out, used C-Clamp to try to push in. Frozen. For all that effort, might as well just try to pick up another.

 

That's probably the best bet. If you can't find one at an affordable price, take yours to a machine shop. They can either TIG weld tabs onto the circlip, or use an EDM tool to remove it.
The main thing that tends to happen with the anti-dive is people not changing the brake fluid on schedule. That leads to the fluid gunkingup, and the o-rings and piston getting crusty. A good soak in fresh brake fluid usually frees them up.

 

Continuation of the anti-dive.
I have gotten the circlip and the retaining shim washer from the anti-dive unit (the upper, brake piston assembly section). I cannot get the plunger piston shaft removed. As I understand, it is the shim washer that retains the piston shaft.? I have tried using a grease gun, similar to the procedure used to expel brake cylinder pistons, and nothing. Once the unit is full of grease, unable to pump anymore in and I feel hard pressure on the grease gun lever. I have also tried pushing it in using a C-Clamp on the piston itself. It will not go either direction.

Next possibility? Though about cutting a slot in the end of the piston to get a flat bladed screwdriver to twist it and possibly break free. I do not understand what could be keeping it in place as there is only a small O-ring retaining it within the piston cylinder. I have gently tried using a needle-nose vice grips, but do not want to mar or damage the small piston, so quickly abandoned that. Besides, if grease gun pressure isn't moving it, doubt I would be able to extract using pulling with a vice grip.

Looking at the diagram, it doesn't appear that the small air bleed screw, looks like a small allen head set screw, on the side could be holding it in place. What is the purpose of this screw anyway? Incidentally, found out it is swappable (is that even a word?) with the bleeder screw. Just in case, maybe I will swap positions with those two and try the grease gun again later when I get home this eve.?

 

Crud on the o-ring is what's retaining it. Give it a soak in penetrating oil, then retun to using a set of pliers with padding on the jaws to spin the piston in the bore as you gently pull outward.

Crusty brake fluid residue is probably the #1 cause for the anti-dive system to stop working.

 

I got the plunger out of the brake side of the anti dive by using an air assisted grease gun and xj4ever's piston popper.
( $20.00 +- from harbor freight ) aim the bore of the A.D. unit into a plastic bucket cause the plunger shoots out like a bullet
when it finally releases.