Bleeding Brake Problem

[RenesisRaceBuggy]

The servo would never have been the issue with a pedal going to the floor unless the linkage was broken tbfh.

I would clean all the lines off with solvent, wrap them all with paper towel - especially around the fittings and pump the brakes a few times to see if a weep shows up.

Are you certain the new bleed screws that you fitted to the calipers are the correct ones? Some have different tapers to seal at the bottom, there's an odd few that sit on a shoulder, etc - didn't damage a seal pushing the pistons back when cleaning the calipers?

[qwakers]

to add to that list, check all the banjos for a extra copper washer.

[warpc0il]

We had some very strange problems with a car many years ago that was suffering from one front brake locking on.
We rebuilt the caliper, which was dual-piston, so no sliding pins to seize, and it didn't make any difference.

Very long story short, we discovered that the flexible hose had an effective one-way valve inside, either from a piece of debris or the liner had collapsed. With the line removed and on the bench you could blow through it either way no problem.
However, if you put the airline blower on it and wiggled the hose, it would suddenly block and could hold the 110psi from the compressor, in the return direction. A new hose totally cured the problem.

Not that this specific issue could relate to your symptoms but it does show that strange things can happen, that don't fit any of the usual patterns.

[warpc0il]

to add to that list, check all the banjos for a extra copper washer.

It's not uncommon for aftermarket lines to have thinner banjos than oem.

If these are fitted with the oem hollow bolts, rather than matching bolts, then the bolt thread can bottom before the copper/alloy washers are compressed.

Some people will then deliberately fit two washers under the banjo to take up the slack - which is a bodge job.

[qwakers]

and always leaks air, if not fluid.

[Ashman]

I had the idea it might be the flexi lines pretty early on. I tried with standard lines and the braided ones and the issue remained the same. Also the bolts that are on the car now with the braided lines are the bolts and washers that came with the lines.

It's so frustrating that i've tried pretty much everything and should have found the problem by now but haven't. It's taken me the best part of nine months almost and i've still not fixed a simple thing like the brakes. It was supposed to be a quick couple weeks and back on the road.

[boosted]

Blimin bonkers this,. Throw away suggestion...disconnect the abs eleccy plug from abs module and see if pedal? I know its had a tested abs module fitted but maybe loom fault ???

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[ChrisHolmes]

although the pedal is fairly hard, it will still go to the floor immediately. am I the only one that sees a total contradiction in this statement? If the ordain is fairly hard how can if also still go to the floor immediately.

[Conan]

although the pedal is fairly hard, it will still go to the floor immediately. am I the only one that sees a total contradiction in this statement? If the ordain is fairly hard how can if also still go to the floor immediately.

I read it a little differently.
I thought there was firm pressure there although the pedal still went straight to the floor
As opposed to no pressure and falling to the floor easily.

[Ashman]

I should have worded that better. The pedal isn't just light, it does have some pressure behind it but not much. When you pump the pedal it gets harder and harder but you can still push the pedal to the floor with a bit of force. As soon as you stop pumping, even for a few seconds, the pedal will get lighter and instantly push the floor. You then need to pump the pedal back up again in order to build up the pressure. Even though the pedal gets harder it's still not enough to stop the car.

Blimin bonkers this,. Throw away suggestion...disconnect the abs eleccy plug from abs module and see if pedal? I know its had a tested abs module fitted but maybe loom fault ???

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That is a good idea, i haven't tried that yet.

[boosted]

Fingers crossed...

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[Ashman]

Nothin', still the same.

[Ashman]

What would the car be worth in it's current state? I haven't given up on it yet but i do tend to think about things way in advance.

[qwakers]

not a lot im afraid.

[warpc0il]

Bigpete might have an interest in spares/repairs.

As you're only a couple of hours down the road, for a flatbed truck or trailer, it might be worth giving him a call to see if he can fix it for you, or make you an offer.

[Ashman]

I think i've finally nailed the problem. I replaced the servo and master cylinder one last time, got a neighbour to help bleed the system and check brake pipes etc. and between us we've now got braking pressure. I think it still needs to be bled again because it has a lot of air in the lines from the master cylinder swap but it actually stops when driven now, although it was only down the street and back. I have 2 other problems to solve though not as bad. The first is the brake lights are staying on so i'm guessing a switch on the brake pedal somewhere, and second is the front left wheel locking up which is likely an abs sensor. It's getting there though and i can't thank you guys enough for the help, all 9 months of it

[Plan3tBob]

get a lump of wood or a jack handle etc and wedge the pedal down for 24h.

when you release the pedal check the fluid level, bet its dropped. brakes now 100% bled with a perfect pedal the lazy man way.

[Plan3tBob]

Try parking the car nose down on a slope.
Engine running, press firmly on the brake pedal and hold for 30 seconds.
Release the pedal slowly.
Repeat until there's no further improvement in the pedal resistance.

This works by encouraging the air in suspension to collect together a form bubbles that are large enough to rise in the oil lines and gather behind the piston in the master cylinder. The slope and the slow release allows these bubbles to pop-up harmlessly in the fluid reservoir.

It only works when you can create some pressure and it can make all the difference.

Because there's nothing required, other than access to a slope, it can be repeated at any time in any of our cars.
Sometimes it's all that's needed to get back a firm pedal.

[Ashman]

That's something i can do on the day of it's mot.

Is it possible to buy a front left abs sensor alone or only as part of a complete bearing? I bought one but it's literally just a wire and all the searches come up with the same wire. Seems odd to me to change the wire and not the actual sensor.

[ChrisHolmes]

The sensor is part of the hub bearing as far as I know.

Have you been looking here viewtopic.php?f=58&t=35629&sid=712a3cc3 ... 52aab69dc9

[Ashman]

I'm not authorised to read that forum.

I should really get a membership... DONE

[ChrisHolmes]

Welcome to the club, finally!

[Ashman]

Yeah i should've done it ages ago

I got a new wheel bearing today with the abs sensor, hopefully this will solve the locking front left wheel.

[PeteH]

I'm very interested to see if this works. I'd have thought that if the sensor was faulty you would get far more symptoms than just a wheel that locks when braking. I'd expect the speedo to be confused. I'd expect the ecu to throw various wobblies. I'd expect all the traction control and DSC lights to be illuminated. And I'd expect the the handling and braking to be odd, as the electronic systems get confused.

To me, a locking wheel when braking implies a malfunctioning abs valve unit. Not that I want to suggest that you get back to swapping braking components, now the system is finally bled.....

[Ashman]

The abs and tc lights are on but i did think that could be because we've been fiddling with it on axle stands. I suspect they will go out (hopefully) once it's driven. I scanned for codes but all i got was a U0073 so i think my reader may be complete sh*t. I did try turning the steering lock to lock a few times but it didn't work.