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help, no front brakes
sdh2903 - 28/5/12 at 07:06 PM

Filled and bled my brakes yesterday for first time using an eezibleed. All good, couple of little seeps that nipped up no probs. Tried the pedal, good but still a touch of sponginess.

Today, complete with able assistant, went for the old fashioned approach. Started at the rears all dandy. Go to the fronts hardly any fluid and with pedal pressed. Disconnected the inlet pipe to the t piece and the same, trickle of fluid even when pedal pressed.

I am running Wilwood master cylinders. 0.7 rear, 0.625 front using a bias bar which is set even.

Has anyone got any ideas? I think it must be either bias bar needing adjustment or I have a knackered cylinder.

britishtrident - 28/5/12 at 07:12 PM

Have you got allowed enough ( ie a bit of float ) side clearance between the clevises and the tube welded to the pedal.

sdh2903 - 28/5/12 at 07:15 PM

quote:
Originally posted by britishtrident
Have you got allowed enough ( ie a bit of float ) side clearance between the clevises and the tube welded to the pedal.


How much is enough? I have around 3 or 4 mm each side.

austin man - 28/5/12 at 07:19 PM

What rear brakes have you if they are discs the calliper usually traps air in the system. Sounds like air is getting in to the system, Master cylinder seal may have gone

sdh2903 - 28/5/12 at 07:33 PM

They are disc all round. 318is front calipers, mk4 golf rear.

The rears feel spot on the calipers are gripping and the wheel won't budge when the pedal pressed.

The fronts are barely gripping the disc when standing on the pedal.

pmc_3 - 28/5/12 at 07:49 PM

Stupid question but easily done, calipers on the correct sides? bleed nipples should be at the top

sdh2903 - 28/5/12 at 07:56 PM

Yep all on right sides nipples all at top.

I think that the issue is definitly with master cylinder/bias bar due to the fact I'm not getting fluid to the front t piece (or very little any way).

rusty nuts - 28/5/12 at 08:06 PM

Sounds very much like the push rod for the front master cylinder may be too tight? Try giving it a bit of slack

tomgregory2000 - 28/5/12 at 08:31 PM

quote:
Originally posted by rusty nuts
Sounds very much like the push rod for the front master cylinder may be too tight? Try giving it a bit of slack


I'll second that, not allowing the push rod to fully return and therefore not opening up the transfer ports and not allowing the fluid through to the front brakes

sdh2903 - 28/5/12 at 08:41 PM

Hadn't thought of that good shout, car is away tomorrow having a geo setup so will hopefully try it tomorrow night.

matt_claydon - 28/5/12 at 09:08 PM

Careful here, if the bias bar has too much slack - allowing full travel on the m/c you're bleeding, then if that circuit fails you may never get any pressure into the remaining circuit before the pedal runs out of travel. You need just enough slack so that in normal conditions the balance bar can apply the pedal force fully to both cylinders without binding, but not so much that if you remove the pushrod from one or other cylinder (or open that hydraulic circuit) you can't still obtain full pressure in the other circuit. If your setup can't be adjusted to suit then you may need to do something clever with the linkages just while bleeding.

[Edited on 28/5/12 by matt_claydon]

Dusty - 28/5/12 at 11:42 PM

Usually a mistake to start with the bar square on to the rods. Set with the bar forward to the rear cylinder and back on the front cylinder side. Gives much longer stroke available for the fronts. The rears tend to go solid on a small movement of the pedal and the fronts need a much longer stroke.

[img] Bias set
Bias set [/img]

[Edited on 28/5/12 by Dusty]

britishtrident - 29/5/12 at 06:05 AM

Never jack one of the pushrods out it is courting problems the pus rods must come fully back or you will get a brake circuit jammed on with hydraulic lock because as the brakes warm up the fluid expands and if the piston in the master cylinder is not fully back it will be unable to vent back to the reservoir.

On a master cylinder The port that links the cylinder with the reservoir is called the recuperating port, on Girling pattern cylinders it is closed off within the first mm of piston travel.

britishtrident - 29/5/12 at 06:14 AM

quote:
Originally posted by sdh2903
quote:
Originally posted by britishtrident
Have you got allowed enough ( ie a bit of float ) side clearance between the clevises and the tube welded to the pedal.


How much is enough? I have around 3 or 4 mm each side.



I would reduce that to about 1 mm but it is not what is causing your problem.


Disconnect the pipe at the master cylinder and put a bleed nipple in, give it a quick bleed -- a couple of presses and hold the pedal down should be enough.
If the pedal is now solid you know the master cylinder is OK

Dusty - 19/6/12 at 12:51 AM

'Never jack one of the pushrods out it is courting problems.'

If that's my pic you are referring to can I point out the pistons are level at rest and it's supposed to show them on their stops in their cylinders. The pushrods are adjusted to unequal length to yaw the bias bar to provide for the different fluid volumes usually needed between front and back. I would be very surprised if front and back required the same fluid pressures and/or the same fluid volumes. Almost inevitably piston size and travel will be different, front and rear and thus some initial yaw of the bias bar is needed at rest.