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TD5 Defender with ABS: bleeding problems?


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Hi, There! I'm having trouble with the brakes on my 10-year old Defender. The problem started when I changed the brake fluid as part of the 96,000 mile service. Having pumped most of the fluid from the reservoir through a bleed nipple, I topped the reservoir with fresh fluid and bled through to each nipple in turn (furthest first). Following the bleed and before starting the engine, the pedal came up hard in the first inch of travel, as expected. This is when the fun started......

Starting the engine with pressure on the pedal results in it gently sinking to the floor. In use, each application of the brakes stops the car, but after double the usual pedal travel. Diconnecting the vacuum from the servo gives a perfect firm-pedal-but-no-assistance braking experience.

The servo held vacuum, but suspecting an internal fluid leak, I changed it. Things got a bit better, but not right. Next was a new master cylinder: I couldn't really think how a master cylinder fault would only show itself with servo vacuum applied, but I was getting desparate by then. The new master cylinder has made things a bit better but still not right.

Inbetween these ridiculously expensive purchases, I have put litres of fluid through the system using the pressure and 2-man methods, one nipple at a time and front/rear simultaneously.

I am now leaning toward seal failure in the ABS modulator as the only remaining plausible explanation. The ABS works when tested and has no warning light, although the problem does persist even with the ABS current limiter removed.

Has anyone experienced similar symptoms? Reading the brake-related forums suggests not, but i'd be grateful for advice before taking out a second mortgage and buying another ABS valve housing.....

Cheers!

Gavin

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I'm not sure about the Defender with ABS (not had one,) but I know that there was a routine on the VagCom software for the Audi A3 I used to have, there was a procedure for running the ABS modulator through it's paces as part of the brake bleeding routine, I suspect that there are places - cavities? within the modulator that need to be emptied of trapped air that can only be done by a diagnostics routine.

Of course, I could be speaking into my trousers here, maybe a grown-up will be along shortly.

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Yes, NanoCom is a Land Rover specific diagnostic tool which can be used as stand-alone or in conjunction with a computer.

I've had mine for about 3 years now and never even noticed the "DEF ABS" screen :blush: but here it is -

post-13593-065825800 1285753803_thumb.gif

So maybe that's your solution.

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  • 4 weeks later...

Just an update on the ABS problem.....

There were no handy Nanocoms around, (but thanks for the tip - it's on my Christmas list) so I took it to my local garage (Binnie and Juggins in Needingworth, Cambs - Highly recommended). They found an ABS bleed programme on their generic Fault Code Reader. As it turned out the ABS was returning codes for both rear inlet valves being shorted, amongst other less specific failures. The result of this was that they were unable to do the bleed, but were convinced that sticking ABS valves could create the sinking - pedal symptoms I was experiencing. I got an up-to-date part number from Land Rover (who wanted £1887 plus VAT for a replacement(!!)) and phoned round a couple of recommended ABS specialists; none could help.

I have now removed the ABS completely. Hydraulically I've made up pipes from the front and rear ports on the master cylinder that feed 2 T-piece comnnectors (Available from EuropaSpares or Demon-Tweeks) mounted either side of the clutch pedal mounting. Each of these then feeds the individual wheels, the fronts all the way to the connection with the flexibles under the wheel arches, and the rears to the in-line connectors at the back of the engine bay.

Electrically, I have disconnected the ABS ECU and removed the 30A current limiter from under the drivers seat which powers the pump and relay. I have cut the wire to the TC warning light and connected the ABS warning light to an ignition controlled 12v source. This puts both these lights out. The red brake fail / handbrake light is not so simple. The warning panel logic brings the light on when the voltage on the supply wire goes to (or near) 0v. Best bet is to cut the wire, or bare some insulation, and solder a 1k resistor between the 12v source used earlier and the bare wire. This holds the input at (or near) 12v (light out) unless the handbrake or low fluid switch connects it to earth. In this case the resistance prevents excessive current flow.

My only concern now is that the car is fitted with ABS-specific master cylinder and servo, but no ABS. Does anyone know how the master cylinders differ?

Apart from that, though, a complete success, with the firmest feel to the pedal ever. I've told the insurers, who thanked me for the info, but havn't changed the premium or anything.

I'm in the process of dismantling the old ABS valve housing (I couldn't help myself.....) so if anyone wants pictures or details of this or the wiring mods or plumbing I did, just let me know!

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