Master Cylinder/ Brake pump

[bigboystoys]

Hi I'm riding a 98 S4 spec1. had some brake binding problem so I took apart my calipers/pistons for servicing. I took apart the master cyilnder/brake pump as well to service the piston and the 2 seals. my difficulty started when I assembled back the master cylinder and start to prime the system. with only the master cylinder installed (brake lines disconnected from M/C), I pumped the lever few times, but no fluid came out of the M/C outlet port. I realised that the brake fluid level in the reservoir is also not decreasing. Initially I thought maybe the seals are worn and there's leakage, but somehow it doesnt make sense that almost no fluid is being pushed from the piston to the outlet port. I tried a slightly different method to prime. I pumped and hold the lever. After this, I'd seal the outlet port with my finger and then release the brake lever. After few successive pumps, fluid starts to flow from the outlet port. I know this method is merely to force the fluid to be sucked down from the M/C compensating port during the release stroke. But the greater problem is, there's no way I could have the brake system primed with the lines disconnected. Neither is it feasible to prime the M/C first and then do a ultra quick connection of the brake lines. I think you guys know what I'm talking about. My experience with priming a brake system is I could just install the M/C, brake lines, calipers and just loosen the bleed screw (at the caliper side), and start pumping the M/C away while maintaining the fluid level in the reservoir. I'm perplexed by what's happening to my brake system now. I even changed the M/C piston and seals. I asked an experience mechanic friend over the phone and he suspected that the M/C cylinder bore has enlarged beyong the seals' tolerance. I'm not too convinced by that actually. I could be wrong. Anyone has similar experience? Care to point out my ignorance of the honda brake system? Sorry that my post is a bit windy. Needed to provide the necessary info (or what I deemed necessary) to have the best picture painted. Thank you all

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[spenx75]

Try fitting everything back without priming 1st. With the bleed valve loosened, do like wat you said, pump and hold the lever. Seal the loosen bleed valve with your finger and then release the lever. Do this repeatedly to prime and it should work.

I had this problem of fluid not flowing too after replacing all the internals of my brake system. . . I did the 'pump, tighten bleed valve, release, loosen valve, pump, tighten valve. . . ' and got the fluid flowing.

[bigboystoys]

is this 'priming' problem same with all S4 ?? or is it an isolated case?

one thing i realised is, i've always worked with bigger bore master cylinders.. and the brake pump bore is only 5/8" ... so i'm not sure if the smaller bore will have a much stronger suction during the lever-release phase...

[kaozie]

the rule of thumb when bleeding any brake lines is to bleed the nearest joint to the furthest...
the problem you gave seems to be an air-lock... very common when you over-hual the master cylinder...
the fastest way to bleed brake lines is to force brake fluid into the system with compress air... most bike shops will have the equiptment...

[bigboystoys]

i thought when we bleed, we start with the furthest first? that is my understanding all along, i could be wrong

the rule of thumb when bleeding any brake lines is to bleed the nearest joint to the furthest...

finally figured out what's the problem...
turns out that it's not really the master cylinder's fault..

when the brake lever is installed, it pushes the plunger that pushes the piston inside the master cylinder slightly (but enough to give me headache)..
now that the piston in its 'free' position is already slightly engaged, i believe the primary seal in the M/C is just behind or even covering the compensating port of the M/C
thus during the priming phase, the piston can push the fluid albeit only very slightly... here's where the problem started, during the retract of the piston, it will pull the fluid back until the main seal retracts past the compensating port. when the seal is past the compensating port, fresh fluid from the reservoir will be drawn down to fill the M/C.. but of course, in my case, the primary seal either did not make it past or it is just so slightly past the compensating port that no fresh fluid is being drawn down... hence my problem of the M/C not being able to push fluid..

i discovered it when i took out the brake lever and realised that the piston is able to retract all the way till it touches the inside of the circlip that is holding it within the M/C... so what i did was to prime and bleed my brakes without the brake lever... it worked just like how i expected it to be...
after i'm done with the bleeding, i simply install back the lever...

however, i still have some doubts over the brake lever problem which disallow the piston to fully retract and draw fresh fluid.. maybe in its fully bled state, the amount of fresh fluid to be drawn down is so little when my pads are worn every time i braked, that it really didnt matter that much...

now i'm left with one more headache, IS MY BRAKE LEVER ORIGINAL??? haha
any kind souls that rides a Super4 Vtec Spec 1 can let me confirm my doubts? with that i mean i have to remove your front brake lever and either fit into my brake pump or i'll fit my 'original' lever to yours...


Thanks for reading this long windy explanation... hopefully nobody runs into this stupid problem of mine... i'll be glad to help if anyone that's into DIY runs into problems

[aaa3237]

Thanks for sharing bros.

[EJ]

from what i learnt during my army days as a VM and currently from what i see at work they bleed the hydraulic brakes on the super jumbos, they start off from the nipple furthest from the brake pump. i don't know about bleeding the nearest from the pump, cos this is frankly the 1st time i've ever heard about it.

[EJ]

anyway,

Typically, one starts with the wheel furthest from the master cylinder; almost always the rear passenger wheel, then goes to the rear driver's wheel, front passenger wheel, and finally the driver's front wheel; but see the technical manual for the vehicle in question for proper procedure.

i got this from Wikipedia after a quick search using yahoo. that should clear some doubts.

[bigboystoys]

thanks for clarifying...


i've always bled from the furthest first... then make my way to the master cylinder... but i always doubted myself.. so after bleeding the master cylinder.. i'll check the caliper side again for air... haha..

but i'm proud to say that the brakes i've bled so far has been top notch... not the slightest spongy feeling... really build confidence under heavy braking...

[andiorama]

i had similar problem....after investing in good brakeline hose, fluid, brakepads and a new caliper and a new pump kit, together wif a new discbrake. ONLY to find out that, the root of my problem was!!!! the brake lever=( hahaha!
but hey, atleast i DIY and learnt alot abt the braking system=)

its always better to bleed furthest from the M/C. i asked an engineer about it=)

[bigboystoys]

i had similar problem....after investing in good brakeline hose, fluid, brakepads and a new caliper and a new pump kit, together wif a new discbrake. ONLY to find out that, the root of my problem was!!!! the brake lever=( hahaha!
but hey, atleast i DIY and learnt alot abt the braking system=)

its always better to bleed furthest from the M/C. i asked an engineer about it=)

what was the brake lever problem?
something broken? unable to actuate the master cylinder properly?

pls share so that we all can learn from this

[suhasingale]

I am planning to clean my master cylinder pump - just want to know if it is necessary to do brake bleeding after rebuilding back the mast cylinder?