brakes, hard time building pressure.

[Clepto35]

I have an 81' honda CB750C and the one thing is keeping me from the road is the brakes are not grabbing very well.

I bled the air out of both calipers  with a bleeding kit and I cracked open the banjo bolts at one point beforehand.  It is a new master cylinder (I believe it might be aftermarket) but there was DOT 4 brake fluid in the system.  I think I got most or all of it out with the DOT 3 fluid.  

Is there a chance the DOT 4 fluid might have ruined the seals in the master cylinder?  Just so you know I did do some work on both front calipers and I can see both of them move and grab the rotor when I apply the brakes and there's no leaks from them.  

I am at a loss for words.  Any ideas would be appreciated!

[rrgunslinger]

http://mechanics.stackexchange.com/questions/718/what-is-the-difference-between-dot3-and-dot4-brake-fluids

Not sure this helps.

[Piute]

   Do your brakes work? before end of play? (doesn't touch grips)
  Your brakes don't have to have direct hard pressure to stop the bike.

[shinyribs]

Is it possible there is air in the system? Sounds like you checked everything else pretty good.

[clyde the ape]

dot 3 & 4 are compatable, shouldn't harm anything.  I would bleed the master first then the caliper.  If its an older line might want to run some fluid through just to make sure.

[Clepto35]

When I apply the front brakes it works almost touching the grips...  I took apart the master cylinder.  I don't see anything jump out at except all the internal parts flying all over the place being spring-loaded!  LOL.

[Clepto35]

It is slightly possible some air still trapped.  But I used a Lisle bleeding kit on both front calipers and got the fluid clear of bubbles.  I wonder if fluid is by-passing seals in the master cylinder or I did a lack-lustre job on freeing up the pistons in both calipers?

[rrgunslinger]

If  you pump the breaks do they build up to where the leaver
is away from the grip and don't bleed off ? If so u either have air in them or your lines are expanding and u need new ones.

Harvey

On Jun 8, 2012 10:39 PM, "Clepto35 [via Honda CB750'S]" <[hidden email]> wrote:

It is slightly possible some air still trapped.  But I used a Lisle bleeding kit on both front calipers and got the fluid clear of bubbles.  I wonder if fluid is by-passing seals in the master cylinder or I did a lack-lustre job on freeing up the pistons in both calipers?

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[Piute]

rrgunslinger wrote

If  you pump the breaks do they build up to where the leaver
is away from the grip and don't bleed off ? If so u either have air in them
or your lines are expanding and u need new ones.

Harvey
On Jun 8, 2012 10:39 PM, "Clepto35 [via Honda CB750'S]" <
[hidden email]> wrote:

> It is slightly possible some air still trapped.  But I used a Lisle
> bleeding kit on both front calipers and got the fluid clear of bubbles.  I
> wonder if fluid is by-passing seals in the master cylinder or I did a
> lack-lustre job on freeing up the pistons in both calipers?
>
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   When I chaged to new S.S.lines and to dot4, push fluids from callipars up to res.a few times keeped thinking air in lines,also pumped and bled,a few times,lever pulls soft ,close to grips but stops great.Paul (my Mechanic )said that so long as it stops the bike don't worry about it,cause there working,
  I didn't rebuild res.,4 new pads,1 new piston(frnt),rubbing alchaul flush.I believe there is always a chance you might have .000009 air in lines,So if not right make it right / safe as you can as I did,I suddently fill one brake not wrking right I'll use the other ,till get to side of road safe to check.

[TOOLS1]

The only way I have found to successfully bleed the breaks on a motorcycle, is to use a pump type oil can with a piece of hose connecting it to the bleeder, and pump the fluid up to the master. Also new braided stainless steel break lines will make a big difference in how the breaks work.
TOOLS

[Clepto35]

Wish there was a way to absolutely identify brake lines are bad as to what you described.  I noticed one caliper piston was pitted.  I am getting new pistons machined.

[rrgunslinger]

Very unusual for the lines to be bad.  Only real way to tell is to replace them.  My front break using the 38 year old lines is like a rock.  Leaver only moves half inch.  Still stops so I don't worry about it. 

Try this, make sure the caliper is level and take the top off,  while looking inside the bowl (don't stick you head over it) very slowly push the leaver (cover tank and such with rags before doing this).  Look for little bubbles coming from the holes in the bottom of the bowl.  My bet is there is air in there. If you see bubbles just keeping working the leaver in and out until there are no more bubbles.  SLOWLY both ways.  If you squeeze it to fast you will squirt break fluid everywhere. I always do this when I have rebuilt a caliper. 
Good luck

On Mon, Jun 11, 2012 at 1:30 PM, Clepto35 [via Honda CB750'S] <[hidden email]> wrote:

Wish there was a way to absolutely identify brake lines are bad as to what you described.  I noticed one caliper piston was pitted.  I am getting new pistons machined.

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[Clepto35]

I will take each individual line off and blow air in them.  If I feel resistance in them (colapsed?) I will replace that line.  Also I am getting new pistons made for the 2 calipers to eliminate that problem.  One of them was pitted pretty bad.