Still no brakes - ARRRRRGH!

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J

Jock666

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No brakes - lets refresh story:
2000 model Mk1 FL TD4 ABS manual.
Initial fault: worn discs & soggy pedal - car driving perfect otherwise.
Cure - New front pads & discs - wind back pistons slowly - then NO brakes - pedal to the floor! no leaks anywhere
Next - bleed them - no difference.
Next - 2 x New Lucas (not recon) front callipers - still the same
Next - replacement master cylinder (used) - after removal check inside servo - dry - no leaking fluid.
Next - another 2 New rear brake cylinders (long story) - and bleed all 4 corners - no leaks and yep - you guessed - still the same - pedal goes straight to floor...
With engine off - pump the pedal there is a brake on all 4 corners - start engine, get boost - no pedal
Anyone ???????????:
 
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I know this may sound silly but , clamp 3 flexy hoses and bleed the 1 left until all air is out take off next clamp and bleed that and so on did this to a bmw once worth a try
 
Hi - does not sound silly - has worked on many an occassion - however we use a vac bleeder on all our vehicles, never had a problem with it. This time we ran close to 250ml through each corner with full vac, so should be ok. The fact the vehicle is exactly the same as it was the 1st time the problem appeared is the baffleing one. The only part not changed, and according to many folks never needs to be, is the ATE ABS pump - but I fail to see how that would produce these symptoms - only other thing it could be and its a very long shot is the 2nd m/cyl is also faulty!
 
Never ever had a prob with vac bleeder or pressure bleeder - only prob with pressure bleeder is if they spring a leak you get luvelly brake fluid everywhere.
 
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Is there a flexi hose on the way out?

They show them sevles in a couple of ways.

Brakes Binding can mean that they have broken down inside and are acting like a one way valve, allowing presure on, but not letting it off.

The other, is where they Balloon under prsure, and not by much to give the impression that there is air in the system.
 
I would pump some fluid the other way through the system (same now it's all clean) or at least get a hand vac pump and suck the fluid through. Can the abs module be put into bleeding mode? That's an interesting question..
 
Jock666 said:
No brakes - lets refresh story:
2000 model Mk1 FL TD4 ABS manual.
Initial fault: worn discs & soggy pedal - car driving perfect otherwise.
Cure - New front pads & discs - wind back pistons slowly - then NO brakes - pedal to the floor! no leaks anywhere
Next - bleed them - no difference.
Next - 2 x New Lucas (not recon) front callipers - still the same
Next - replacement master cylinder (used) - after removal check inside servo - dry - no leaking fluid.
Next - another 2 New rear brake cylinders (long story) - and bleed all 4 corners - no leaks and yep - you guessed - still the same - pedal goes straight to floor...
With engine off - pump the pedal there is a brake on all 4 corners - start engine, get boost - no pedal
Anyone ???????????:
Click to expand...


This isn`t unusual when you have relined the brakes.
As long as you have a firm pedal without the engine running you should be okay.
If you are holding your foot on the pedal with the engine running the pedal will sink to the floor.
As the brake linings and pads bed in this will improve.

With the engine off, pump the pedal a few times to get rid of the servo assist
and then keep your foot on the pedal.
If it still sinks to the floor you have problems which could be,Master cylinder,fluid leaks,and as somebody else said a ballooning brake hose.
I have heard of the Master cylinder seals be pushed back when the brake piston are pushed back in.
I always undo the bleed screw when I do mine.
 
Appreciate the replys folks - does not seem to be too much input though!
Ref last reply - trying to get my head around comment that: whilst running pedal will sink to floor - why/how does this happen? where does the fluid go? which should be under pressure at all times when pedal pressed upon. As shown when we sit at traffic lights with foot on pedal - it would be very noticeable and worrying if it gradually went to the floor.
Stripped old master cyl and was in perfect condition - seal had not flipped.
 
The fluid is not going anywhere,the boost from the servo is.
Diesels have a separate pump for the brake assistance,not a vacuum from the engine.

If you have a solid pedal with the engine off,you don`t have a problem.
If you are unsure get it to garage.
 
OK. Makes sense. However.....for last hour we've been driving up and down the lane - engine off - pump air out of servo=solid pedal - OK. Start engine - foot on pedal light force drops to floor! let it up drive hit brake (sort or hard) takes tremendous force almost as if no servo there and slowly, scarilly stops - next time press pedal goes straight to floor.
Is this sounding more like a servo fault now? or could it be related to this>
Just put Hawkeye on - and 3 failed abs sensors! whats the chances ???? after testing them its confirmed - 3 failed with zero ohms and 1 with 1.5 ohms - 1 shows as working when driving with Hawkeye.
 
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Been following this with interest, it does sound like to much travel on a front calliper or wheel cylinder, or still air in the system are the back shoes adjusted ok ?. What I would do is clamp all the flexi hoses off and see if you get a pedal with engine on if so release one at a time and re check, if no pedal then when all clamped it at least it points at servo/master fault
 
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If you have the engine off with the servo empty(pressing the pedal repeatedly)
Now if you press the pedal do you get hard resistance?
If you then start the car does the pedal sink slowly to the floor?
If yes then you have brakes and also servo assistance(which is just that "assistance")

The ABS fault is likely to be ABS pump or module. It would be unlikely to be a failure of 3 sensors.
Disconnect individually and test the resistance.

As I previously posted it is best to open the bleed screw when pushing back the caliper pistons,thus avoiding any damage to the master cylinder and ABS pump by forcing back fluid the wrong way.
 
If the pedal is still spongy,raise the back end of the car up and then bleed again in the correct sequence.
The old fashion way with an assistant.
I myself use a Gunson pressure bleeder,with a wheelbarrow wheel supplying the pressure.
 
Brakes were again bled manually, in correct sequence - no difference. All 4 sensors were checked for resistance and with the Hawkeye when moving - testing just confirmed that 3 were faulty and 1 was good with 1.35ohms.
Pedal hard when engine off and air removed from servo - yes goes to floor when engine started. Vehicle is unsafe to drive as the pedal a) initially requires too much effort to stop and then when you have eventually pulled it up it goes to the floor. Having 4 other makes of TD 4x4's and cars on the road, and driven many hundreds of diesels over 25 years (at car auctions) I have never ever experienced any brake reaction like this before.
 
Won't be anything to do with Abs sensors...

I think you must have air somewhere. Have you pressure bled the system partway through? Ie made sure no air in mc by bleeding at outputs. Then bleeding at abs unit, then at the flexis and finally at the wheels?

Does the pedal improve by clamping some of the hoses?
 
Just one other thing...

You are bleeding LHfront, RHfront, LHrear and RHrear, this is what is on RAVE and is different to virtually every other car.
 
Worth a try as it might help eliminate the cylinders and the calipers. If the pedal is soft with them all clamped then the problem lies in the mc or abs.
 
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