View Full Version : for the Brake Pro.... and other

04-22-2008, 09:33 PM
I got some time in front of me and decide to check why a have a spongy brake pedal when I open the rear brake line. So let's start from the beginning, one 3/4 master, two single piston front disc brake caliper, a regulator ( needle valve) 5 ft long ptfe SS braided tubing line, rear 4 pot caliper.

So when I bypass the rear brake the front brake feel right and work well, when I open the rear the pedal double the length of travel , I remove the bolt holding the cliper and have it free floating on the disc , symptom are the same , I think it's setting is *good, check the air, none, so I add a 2lbs check valve since the rear caliper is higher than the master, still spongy.

So I start to think my long PTFE Stainless Steel braided line is flexing and should be replace by a hard line, do you think it could be the culprit ?

04-22-2008, 09:41 PM
If it's a large 4 piston caliper, it could be requiring more than the master can put out. Will the rear brkes lock up, and does the cylinder max out?

04-22-2008, 09:47 PM
is the rear bleeder at the absolute top? if it is not try to remove the bolts and rotate it enuff to put it there and then bleed them.....make sure to leave the pads on the disk somehow, they dont have to be all the way on to bleed them... [smilie=biggrin.gif]

04-23-2008, 12:26 AM
That is a lot of steel braided line. *I would run a hard line. and for the $20 it will cost you at pep boys it should be a cheap experiment

04-23-2008, 07:49 AM
I thought I read that a stainless braided PTFE line will actually expand less than a hard line. The Formula Cross and Extreme had no hard line on the and have good brakes. They will lock up all four wheels. They have two dual piston in front and four piston in the rear with I believe a 3/4 master cylinder. Having pistons on each side of the rotor should not consume any more fluid. Each side should back off half as much as a floating caliper.

04-23-2008, 01:04 PM
plkracer, the rear caliper is one of a front gsx 1100 , I think it use less than one front ( trailer disc brake).

bugpac, yes the bleeder is on the absolute top, I try to bleed it out as you say with the same result.(out of the car , bleeder straight up)

flyerider, that what I think happen, but don't want to tear everything until somebody confirm that it could be the case.

LiveWire , that what I read somewhere to

I think I have no other way than trying the hard line, like flyerider say the hard line are cheap test, just pain in the neck to work with.

04-23-2008, 01:26 PM
Buggito, we are running braided line on all four wheels of our R16's at similar lengths if not *more, and we are not having any issues. I would say a bigger master cylinder would be better maybe 5/8". Hope this helps.

04-23-2008, 01:28 PM
Buggito, we are running braided line on all four wheels of our R16's at similar lengths if not *more, and we are not having any issues. I would say a bigger master cylinder would be better maybe 5/8". Hope this helps.

Make that 7/8, 3/4 is 6/8, and 5/8 is smaller.

04-23-2008, 01:37 PM
[smilie=banghead.gif] *[smilie=stupid.gif] *[smilie=biggrin.gif]

04-23-2008, 01:57 PM
If your line runs up from the master cylinder and then back down to the caliper you might try bleeding it at a fitting that is the high spot because air can get trap there .

04-23-2008, 04:26 PM
Thanks DesertDrifter that one affirmation I was looking to read, I think a bigger master is the solution since I'm sure I have no air and now confirmation that the braided line should be good.
Just need to find one who will work any used ?

04-23-2008, 04:47 PM
Buggito, when you open the rears, soes the pedal go all the way down, or is it spongy? if it bottoms out then i agree go larger, if it doesnt bottom out, then probably some air there somewhere still...

04-23-2008, 04:52 PM
Another test for air (works in vehicles) is to see how fast the pedal returns. If it snaps back quickly, it has air.

04-29-2008, 02:25 PM
Thanks for you help, I found the problem, plkracer got me an idea, I was thinking to have some air but bleed the damn thing since the buggy was build, like other time I removed the caliper out and insure the bleeder was on the highest point, but this time I brake the brake line loose and got the caliper real high, I was using s tick to push the brake pedal with my Bot *[smilie=ashamed.gif] and needed more line, soon I crack the bleeder open I ear some air, I knew I found the problem.

The brake line was above the bleeder and even by keeping the caliper straight the air will still trap, by removing few feet of brake line and raising the caliper two feet higher I was able to bleed it.

One other bad problem solve, than for help and mostly support.

04-29-2008, 03:58 PM
Hey Buggito,

If you still feel like you have a little air in the system, take the caliper off the mount so there is no disc between the pads.

Pump the brake until the pads touch each other and you feel a little pressure on the pedal.

Now release the pedal, hold the caliper low, so the line is the highest point and then work the pads back apart with a flat blade screw driver. *Keep pushing the pads apart until the pistons bottom out in the caliper.

This will force any small air bubbles that may be present in the line back to the master cylinder. *Often you'll see little bubbles come out of the bleeder hole that's inside the master cylinder reservoir.

The idea is to displace as much fluid as possible through the brake lines. *The lines don't have much fluid in them.

This method works really well on motocross bike braking systems.

jumpin jellybean
07-26-2008, 07:17 AM
wow you guys covered almost all ways to take care of this problem:D what about pressure bleeder :confused: that will take care of air in lines:D:cool: