Topic: Spongey front brake 500

[Kevnz]

Hi Guys,
I'm hoping the collective mind can help me out here. Firstly, what you all know; like most of our bikes the brakes on a 500 consist of: master cylinder, flexible top hose, 3 way union with brake switch, flexible lower hose, rigid hose into caliper.
Mine has kitted master cyl, new top hose, o\hauled caliper with new seal, piston and pads. I cannot get a firm lever. I usually do a bleed from the master cyl, as in just pump until the bubbles stop coming, tie the lever to the bars for a day or so and bingo, all good. Has worked several times in the past, not so this time. If I plug the lower end of the bottom hose, the lever is rock solid, so the problem is in the caliper, but even bleeding using the nipple doesn't let any air out. The piston is moving, but the lever will pull right back to the bar and doesn't pump up, or only very little. What am I missing? Used exactly the same procedure on my other 500 and it worked perfectly overnight.
Thanks for any input.

[dave500]

did the new kit have the correct length piston?

[bryanj]

Did you clean the corners of the seal groove?
Did you free up and clean the pivot pin?
Have you got the fender brace in correct place?

Have seen all these affect the feel and pull

[Kevnz]

did the new kit have the correct length piston?

Same kit I used on the other bike and had no issue with that one.

[Kevnz]

Did you clean the corners of the seal groove?
Did you free up and clean the pivot pin?
Have you got the fender brace in correct place?

Have seen all these affect the feel and pull

Yes, bead blasted and painted. Cleaned groove, brace all bolted up. This is not related to brake "feel" as such, it isn't working. With lever tied to bars, can turn the wheel by hand. Had the whole setup on the workbench because I was sick of spraying brake fluid all over my newly painted components. No improvement. Piston moves, just won't clamp. The caliper seal looked uniform; can't put it in back to front can you? ( ie does it have a leading edge?)

[bryanj]

Nope it doesnt but the point i made was the seal groove needs to be scraped out with a pointed pick, especially in the corners. Nothing else i have seen removes the corrosion, even a dremel with wire brush just polishes the crud.

The fender braceneeds to be on the wheel side of the caliper bracket not between bracket and slider.

The way the caliper works is the seal groove is slightly shaped causing the seal to take the shape of a diamond slightly, when you apply the brake the seal distorts and it is only this distortion that retracts the piston hence everything has to be supper clean.

What you describe tells me there is air in the caliper you could try pumping the piston out with caliper unbolted and pushing back in with g clamp a couple of times.
Also have you adjusted the bolt and spring to give the 6 thou clearance on back pad to disc, if everything is freethis can make a big difference

[newday777]

Did you bleed the master cylinder first using the banjo bolt as a bleed point before bleeding at the caliper? That is the best way to start a system bleed is the master cylinder has been rebuilt or gone dry and is essential to get the air out of the master cylinder.
Use old rags under and around the banjo bolt to catch the drips and spray.
Cover the tank and all other painted parts with an old towel and a thin layer of plastic sheeting from spray and drips.
Keep a spray bottle of clean water handy to spray and wipe off any fluid on painted parts.

[Kevnz]

Yes, took particular care cleaning the groove, and yes, started the bleeding process at the M\c. As mentioned, with lower hose blocked, lever is rock hard, so no air between the m\c and the caliper. Dave may have a point, though; just because I ordered X doesn't mean I got X and I don't recall comparing pistons. If the piston is the same diameter, but seals different distance apart, would displace less fluid? Would that cause the problem, or would next pump take up the slack? Piston moves and retracts ok. With the setup on the bench and pumped up, the piston was fully clamping the disc (substitute) tightly, but the lever was still spongey. I would think that even if the fluid displacement volume is wrong, it would still eventually go hard if there was no air in it.

[newday777]

Yes, took particular care cleaning the groove, and yes, started the bleeding process at the M\c. As mentioned, with lower hose blocked, lever is rock hard, so no air between the m\c and the caliper. Dave may have a point, though; just because I ordered X doesn't mean I got X and I don't recall comparing pistons. If the piston is the same diameter, but seals different distance apart, would displace less fluid? Would that cause the problem, or would next pump take up the slack? Piston moves and retracts ok. With the setup on the bench and pumped up, the piston was fully clamping the disc (substitute) tightly, but the lever was still spongey. I would think that even if the fluid displacement volume is wrong, it would still eventually go hard if there was no air in it.

What exactly did you buy to rebuild the master and caliper?(Aftermarket kit? brand? Part numbers?)

How much is this 'spongy' you have?(lever travel) And what sort of 'hard' are you expecting?

Did you put on new stainless steel brake hoses to replace the rubber lines?

[Kevnz]

EFFDA377305P
EFFDA-377-305P M\C kit from DSS. Ditto aftermarket caliper piston and seal. On my other bike(s) the lever has maybe 20mm travel before the lever goes hard. This one pulls right to the bar and won't lock the wheel. You most assuredly could not ride the bike like this, at least not twice The top hose is new and I initially kitted it with a stainless braided hose in search of a harder feel, but reverted to standard so I could plug the lower hose for testing as I didn't have anything to plug the braided hose. Braided hose back on, but no improvement. Thinking about it, the amount of fluid displacement by the m\c is irrelevant when the hose is blocked, but it does prove the m\c works and doesn't leak. But could it matter if the caliper piston displaces more than that amount when it retracts? Would you be able to pump it up under those circumstances? Might need to start swapping out components, at least narrow it to either m\c or caliper.

[Deltarider]

Did you free up and clean the pivot pin?

Although this has been discussed before, here's my view once more. I don't see why you would take things apart, unless you have diagnosed there's a problem. This is easily done by checking for play and a smooth movement. I do not know mechanics that take the pivot out without an indication. Ofcourse I've checked in the manuals. Clearly it's not a maintenance thing: it's not in the maintenance scedule. The only manual that says something about it, is the one that happens to be the most detailed on the front brake. It's the French one, which has been composed in close cooperation with Honda France.   
Avant d'assembler l'étrier, il faut s'assurer qu'il pivote correctement. Au bessoin, graisser l'axe après démontage.
In translation: before assembling the caliper, make sure it swings correctly. If needed, grease the pivot pin after disassembly. If needed, if.
I agree however on cleaning where the piston moves. It's a known dirt collector. But the pivot pin?
Again, it's dead easy to check if it moves correctly. If so, you can leave it alone. It's well sealed. Mine has never been apart and still swings as new, after over 46 years and 138.000 km...

[Bodi]

The maintenance schedule never imagined the machine would still be running after 45 years, what it says is meaningless for tasks not scheduled - many do need to be done. Like the brake pivot. It's a 99% certainty that the original lubrication and the original O-rings are no longer useful if this was never serviced. For example, wheel bearings are not on the schedule and you're an idiot if they haven't been checked since new.

On topic, there are a few places that air gets trapped in the brake system. Spongy lever is due to air in the system unless your soft lines are completely wasted.
If the MC isn't leaking, and you see a little gush from the small relief hole (visible with the reservoir cap off) in the first bit of lever movement - the MC is OK.
If the caliper isn't leaking, assume that it's OK. As you've cleaned the seal groove well that is not a problem if fluid doesn't leak past it (but a crudded up groove only causes poor pad retract or a fluid leak, not a spongy lever feel).
Air gets trapped in the caliper and the brake switch tee. I remove the caliper and suspend it with the banjo the highest point. Then I pump the piston out with the lever as far as I dare, hopefully not to where it falls out. Then force it in all the way with a C-clamp, with the reservoir cap back on to avoid gushing fluid all over the paint, and shake/tap the caliper now and then to dislodge any tiny bubbles stuck somewhere in there. Pump it out slowly again (the bubbles should float in the fluid and not be pushed back into the caliper if you go slowly), undo the tee mounting bolt and slowly push back in with the clamp while shaking, tapping, and twisting the tee around with the soft line to the MC straight up when you tighten the clamp. Let it sit a while then very very slowly pump the piston back out and crank it back in quickly all the way - remember that reservoir cover for this one! That should/will get all the air bubbles up and out through the MC relief hole.

[bryanj]

Delta you must be lucky or no road salt or no winter riding.
Here in UK when the bikes were still being sold new the most common fault of bad brakes was the pivot siezing followed by the small hole in master followed by pitted pison/seal groove in caliper.
Yes we only stripped them when tight with caliper split but that was regular at over 3 yrs when first mot due

[Deltarider]

The maintenance schedule never imagined the machine would still be running after 45 years, what it says is meaningless for tasks not scheduled - many do need to be done. Like the brake pivot. It's a 99% certainty that the original lubrication and the original O-rings are no longer useful if this was never serviced. For example, wheel bearings are not on the schedule and you're an idiot if they haven't been checked since new.

That's quite a statement, Bodi, and I'm afraid it's directed at the wrong person, seen not only my personal experience but also of others I know. I check the movement of that pivot pin each time I'm there, like when replacing pads, cleaning the caliper, etc, without taking it apart. It's so easy to check and if you think, you have to take it apart anyway, then... where is the end? Also my frontwheel bearing is still original. I can perfectly check its movement and I do it each time the wheel gets a new tyre and is dynamically balanced by pro's with me standing by. I specifically ask their comment. Again without taking things apart. Can't you? It's in every manual.
@ Bryanj. You're right. I never ride in winter. A friend of mine once did and regrets it to this day, since he forgot to rinse his K3's OEM 4-4, which turned out rusted when he opened the garage the next spring. Nowadays min temp for me is 15^o Celsius.

[maxheadflow]

Make sure that the caliper pads are parallel to the disk.  The way to tell is that the caliper will twist some when the lever is pulled in.

[scunny]

get a syringe 50 cc from your local bunnings, with a bit of  tubing, bleed the caliper using suction. works great.

[Kevnz]

Update; proved by substitution that m\c is OK, put it on another bike and brake is fine. Didn't even need to bleed. Now have absolute minimum setup on the bench; m\c, ( one from the other bike, which was fine) braided hose straight into caliper. Took an absolute age just to eject the caliper piston. Dismantled caliper and cleaned the groove and bore, so piston moves freely in the body. ( Had already done that when I rebuilt it, but double check) Reassembled and same thing. With the two caliper parts bolted together and the pads touching, you can pump the lever until piston moves a bit, retracts when you release the lever, but no bubbles come out of the bleed hole in the m\c and the lever is still spongy. I'm at a total loss now. Frustrating in the extreme.

[RAFster122s]

I wonder if the aftermarket seal is contributing to the spongy lever?

[dave500]

dont have the pads touching,push the caliper piston all the way back and wedge something between the pads,try bleeding it now then testing.

[Kevnz]

dont have the pads touching,push the caliper piston all the way back and wedge something between the pads,try bleeding it now then testing. Did that previously, metal plate same thickness as the disc.

[Kevnz]

I wonder if the aftermarket seal is contributing to the spongy lever? That's pretty much the last thing standing, but how would that cause the symptoms I'm experiencing? It's not leaking, the piston moves and retracts.

[Deltarider]

Have you given it enough time? I hardly ever needed to bleed. Just position the bike thus that eventual air can find its way to the top. Lever pulled halfway ofcourse and a night is enough. Worked for me.
Slightly of topic. I keep postponing it, but I have to renew the brake fluid one of these days. Can I top up with 5.1?

[Remcod]

Are you sure that the tiny hole in the reservoir is open?

Verstuurd vanaf mijn SM-A415F met Tapatalk

[Trevor from Warragul]

I had the same thing happen, and it turned out to be the bleed nipple not quite tight enough. Turned it until it was ridiculously tight & the brake was fine.

[Deltarider]

I had the same thing happen, and it turned out to be the bleed nipple not quite tight enough. Turned it until it was ridiculously tight & the brake was fine.

That is very, very risky. Besides, if there was a leak, it would show.