LC80 (Dec 92) - 'turning ABS off'?

[AndrewCorser]

You mention the brakes pulling all over the place, is this the ABS doing it or do you have a sticking caliper as Shayne possibly had before he got them rebuild.

Unless you already have done so, I would check that the actual sensors are not at fault either

Thanks!

I have had all the callipers replaced, so it shouldn't be that (unless the disks would affect it? They were in reasonable condition).

On the wheel sensors, I got a replacement front one, and we tried it on both sides, but got the same fault codes, suggesting it isn't the front sensors. We also checked the cleanliness and condition of the toothed sensor rotors on the front. At the back we have only checked one of the sensors...but the symptom is the juddering ABS feeling through the brake pedal at 10 mph, AND pulling (one way and then the other) which suggests to me it is related to the front sensing rather than the rear sensors. I suppose I could replace both front sensors with new ones since I have now found those on-line (the replacement one was from Karl and I'm not sure if it was new).

Thank you everyone for your support on this issue! It is really frustrating: at 71, I want this special 30+ year old vehicle to see me through another 30 years, and the only outstanding issue is this ABS!

 

[Towpack]

Hi Towpack, thanks for your useful reply!

Do you have experience with replacing the deceleration sensor? I Have found one on-line from Japan, but quite expensive, so I would like to be sure it is faulty. I get occasional engagement of the ABS around 30 mph, which is apparently indicative of a faulty deceleration sensor...but this is only occasional, and the much more common engagement is at 10 mph, which I understand implies a wheel sensor problem. We have put a new wheel sensor on the front, and swapped that round with the existing one on the other side, and had the same fault codes in both configurations, and since that type of fault allegedly arises from the signal from a dodgy sensor being most obvious at very slow speeds, that would suggest it is not the wiring loom.

Anyway, thanks again for you help!

I've never had to replace anything in the ABS system so far. I was just following the diagnostic procedure in the FSM which suggests a deceleration sensor problem.
The wheel sensors can be tested with a multi meter. Fronts should give 0.87 to 1.27k ohms and the rears 0.7 to 1.1k ohms across contacts. The air gap between sensor head and the rotor can also affect operation and can be adjusted with shims if necessary.
If you swapped front sensors from one side to the other and got the same fault code then surely that means the fault is not the sensor but is elsewhere in the system?
Do you have access to the FSM? It has a comprehensive guide to testing everything in the ABS system and values for voltages at the ECU and resistances for all the wiring and components. As you have found, parts can be expensive so in depth diagnosis is worth while.

 

[Jon Wildsmith]

What fault codes are you getting?

 

[Grimbo]

I seem to remember the loom on the front axle is prone to giving issues and probably now is unobtainable new ...... looms get brittle with age and also wires work harden and get high resistance .....

None of this is a help if you can't narrow down the fault but if the sensors are new the wires to the ecu are a poss cause .

Is it only at 30mph and 15 mph ? this suggests a speed sensor related fault somewhere .... a deacceleration sensor would only measure G load although maybe also getting a speed sense or input from the ECU ......

 

[frank rabbets]

Can you present your car in low range for MOT. It does not have ABS in that mode?

 

[Shayne]

LSV issue ???

Which plug tells abs low range centre locked is engaged and turns abs off ???

Incidentally my 80 came with a broken wire which had been caught in the housing when front diff was replaced , I was really quite astonished that my experimental cutting and cack handed soldering of it fixed the problem .

 

[Towpack]

I'm guessing it's the same plug that sends a signal to the DL ECU and locks the CD, the plug that is disconnected to enable the use of low range with an open diff as I don't get the ABS light up when in low box. Locking the CD with the dash switch brings up the light.

 

[Shayne]

Mine has the same modification Towpack but if it didn't might a poor connection on gearbox plugs cause random abs interference is what i'm thinking .

 

[AndrewCorser]

Thanks again for all the help:I will go through everything in detail directly...
...but Oh No!! Now the braking system has failed completely. This was a very occasional fault, and (luckily) only ever at very slow speed, but now the footbrake pedal goes to the floor, AND HAS NO EFFECT! Quite frightening! Before, after I managed to bring the vehicle to rest, lifting off the pedal and pumping would bring the brakes back. But now, the pedal goes to the floor (with a modicum of resistance, so not without resistance, which I experienced years ago with a broken brake pipe, but with a bit of resistance) and the vehicle still rolls freely forward! Ignition off, and still the same. And with the ignition on (engine turning or not) the brake fault light (the red exclamation mark) comes on for a bit then goes off. The brake fluid in the master cylinder, btw, is still full.

I managed to limp to the garage in low ratio/bottom gear (still no braking from the foot pedal..!) which is where it now is - with the mechanic waiting for me to suggest what the problem might be. Has anyone had this problem?

My thought, given all the previous ABS issues (the ABS light is not on now, once the ignition has been on for a bit) is whether one of the solenoids in the actuator assembly has stuck open. I am not clear, from the descriptions of the ABS system, how the brake pedal can be depressed without any apparent hydraulic leak from the system, and yet the calipers not operate: presumably there is a route in the circulation of brake fluid that enables fluid to be bypassed back to the reservoir.

I had felt that the actuator assembly would be the next thing to service/replace (if I was going to carry on trying to fix the ABS)...but finding one has proved very difficult (my thought being we could put one in place, and service the existing one): I guess that it is mainly a mechanical system, with just an electric pump and the four solenoids.

Is there a hydraulic circuit diagram of the 1992 LC80 ABS system anywhere? That would help with diagnosis!

 

[frank rabbets]

Your brake failure is 99% caused by faulty master cylinder.

 

[AndrewCorser]

Your brake failure is 99% caused by faulty master cylinder.

But we have just replaced that...but then, these days, new items seem suspect!!

 

[AndrewCorser]

But we have just replaced that...but then, these days, new items seem suspect!!

...although, looking back, it was bought from Milner Off Road in November: I would normally trust that supplier...

 

[Shayne]

I vaguely remember cracking the lines at the master an letting it leak very slightly while bleeding all the calipers a usual years ago because i was convinced there was air locked somewhere in the system . Can't actually remember the symptoms but it cured the problem .

My aim was to let more air in making the trapped pocket big enough to move .

 

[Lorin]

...although, looking back, it was bought from Milner Off Road in November: I would normally trust that supplier...

Milner is very cheap for good reason. Symptoms you describe indicate master cylinder. Whether you think OEM quality is overhyped or not, there’s little to match it and definitely not Milner. Fit OEM and be done with it.

 

[frank rabbets]

I don't know what your Milner cylinder is like but the steering damper/shock absorber they supplied to me was about as strong as a bicycle pump. Their online picture of said item showed an OEM one !! Also it was too short so when on full lock was likely to be torn apart or crushed. If you have an original OEM leaky one in otherwise good condition you could reseal it.

 

[Shayne]

Ain't never heard a complaint about anything supplied by Roughtrax Genuine Toyota or otherwise .

Genuine often means parts Toyota bought themselves from Aisin or Denso . We will never know how many parts are outsourced .

On a budget maxspeedingrods is always worth a look . A turbo is the only thing I ever bought from them but being very dubious of a part supplied at more than ten times cheaper than genuine I trawled the internet for a week looking for a bad review in forums or whatever and failed to find a single one .

 

[frank rabbets]

They only sold one turbo Shayne. lol.

 

[Shayne]

Was a long time ago Frank and that turbo got hammered in my tuned black beast without fail , quick search now found this maxspeedingrods.com is rated "Excellent" with 4.4 / 5 on Trustpilot - [Leaving Land Cruiser Club]