option B install

[laney]

Hi all does anyone know of a mechanic who would install a shuttle valve switch with option B mod done to switch. I was going to do it my self but work has got in my way and I don't have the gear to power bleed the abs system I need someone in Brisbane thanks for any information.

[clintooo]

Hi

I did option B last weekend. If you are just removing the SLS with the pump in situ you don't need to bleed the brakes.

It is a bit of a pain. Probably took me 2 hours all up, as the SLS bolts had a heap of thread lock on them and you can only get about 1/8th of a turn due to access, so it takes you a while to get them out.

but doing it that way, doesn't introduce any air into the system, so I didn't need to bleed the brakes.

[laney]

Thanks clintooo but it needs to come of as I am replacing some o rings and e clips that I ordered from falcon works in America.

[clintooo]

no probs. it will be easier to get it out at least :)

[Brenton.T]

You'll have a hard time finding anyone to do plan b. Mechanics wince at the thought of the liability that goes with changing anything to do with the electronic side of brakes. Even though they'd only be making an electrical path more direct, and it is a tried and tested method, most of your average workshops won't touch it. I'm in victoria, and I've heard of one place that does it, but they charge about $800.00 just for the plan b install.

All that being said, if you can find the time, you don't need any special gear to power bleed the system. Just a couple of spanners. It is a little bit messy, but all you need to do is loosen the pipes on the abs pump one at a time while someone pumps the pedal inside. Then tighten and repeat, and then do the calipers as normal.

Clintooo is right about the thread locker as well. If you're removing the whole unit it shouldn't be a problem though.

Hope that helps, all need to do now is find the time and will - and that can be damn hard.

[Pedro_The_Swift]

going back 6 years,, I did Option B around the first weekend I drove it home,
Bleeding was done by a twin wire cable and switch into the fuse box to get the ABS pump to operate,, still no concerns after 6 years,,,, :cool:

[sierrafery]

Bleeding was done by a twin wire cable and switch into the fuse box to get the ABS pump to operate,,
I've seen this "method" with activating the ABS pump relay to bleed brakes mentioned before but IMO it's a false impression that it has anything to do with the tester managed power bleeding as the pressure will go only to the inlet valves circuit which is N/O and the N/C outlet valves will still be closed so nothing additional to the pedal bleeding as long as there's no command to open the outlet valves...it's like you'd try to inflate the air springs by bridgind the compressor relay without feeding the air supply valves to open

[Pedro_The_Swift]

no doubt,,
but it works? and after 19 years of-- 3 disco's I'd have a fair idea if it didnt work,,

and please dont tell me I was lucky!! This is the Big Silver Lemon after all,,, ;):D

it may be the only thing that STILL works -- (after the first fault of course...) :angel:

[sierrafery]

I didnt say it doesnt work, what i mean is just that it has nothing to do with the tester bleeding cos it bleeds only the IV circuit between the modulator and calipers which is covered by pedal bleeding anyway :cool:

[sharmy]

find a flat road, put in low range first gear, turn hill decent on, get up to speed and take foot off accelerator and let it do its thing, do it a couple of times and it seems to bleed the abs unit. it worked for me.

[steve_a]

I didnt say it doesnt work, what i mean is just that it has nothing to do with the tester bleeding cos it bleeds only the IV circuit between the modulator and calipers which is covered by pedal bleeding anyway :cool:

ABS is a fail safe system, pull the power to the block and you get normal brakes. That means that the paths from MC to each caliper is open.
Thinking on the fly, for the ABS function typically the valve for the locked wheel is closed (and vented?) to stop it from locking, carried out on a per wheel basis, the idea being is automated cadence braking on each wheel, with pressure supplied by you/pump. ABS mode.
ETC is the pump supplying braking to a wheel, so I guess if you want to brake FR you close FL,RR,RL valves and engage pump.
HDC is probably more like ABS with the pump replacing your foot.

I'm thinking from that to bleed the block you want to operate the pump to bleed the pump body and relief. If everything is open then I guess relief area may not get it, unless on over pressure.

FWIW, I've actually bled the block itself with a contraption to control all the valves and pump, but that was very specifically done to clean power steering out. Back on the car I used the relay bypass to bleed and didn't find any issues what so ever.
Other times I've used the relay bypass and nanocom to bleed, and again the pedal has been great afterwards.

[sierrafery]

Sorry, i disagree, IMO you misunderstood things a bit(and forgot about EBD which is the most complex of all ;)), there are 2 circuits in the modulator, the IV(inlet valves) and OV(outlet valves)...the IV circuit is N/O so that's the fail safe side of it for normal braking cos they close only in active braking mode(EBD, ABS, ETC, HDC) while the N/C OVs are opened by the ECU to achieve the desired action with pressure management according to the situation, better read again the system's description and operation mode.
I edited the modulator's diagram and what's with red is the pedal circuit on one side (same on the other), that circuit is opened all the time with the exception of situations during active braking when the ECU closes them to reduce pressure on that caliper/s and eventually opens OV's, there are many scenarios(each situation is described in the modulator's description in RAVE or in WABCO documents, i'm not gonna paste the whole thing here)

If you unplug the modulator or something fails only that red(IVs) circuit is open the OVs are closed, with tester the pump will be activated and the OVs opened too so then there will be full flow within the modulator otherwise the expansion chamber is islolated, if you bypass the relay this will not open the OVs only start the pump and the flow will be only between pump and calipers through the IVs so if you want a perfect job you'll use both methods pedal and tester bleeding(better at the same time which means activate that circuit with tester while you push the pedal) but if you want to use only one of them then pedal bleeding is more efficient than tester bleeding cos with tester the circuit between the modulator and master cylinder is not covered only between the pump and calipers... that trick with HDC can help but only if it's followed by another pedal bleeding otherwise the air which eventually was pushed out from the OVs circuit has no way out

this system is more complicated that it appears :cool:

[ozscott]

What do you think of Option B Sierra? I can't recall if you have commented before about it. Apologies if you have already. Cheers

[sierrafery]

I think is that option B is the perfect fix for the poor way in which the SVS signal side of the modulator was conceived and built... more modern modulators like they started to put on D3s dont even have SVSs they are taking the brakes on/off input from the brake switch circuit... i invented a way to bypass the whole SVS thing with a relay and two resistors and posted it here some time ago but i was thrown away with it and called idiot even though it was based on a prolonged study of the system and tested on my own car before(still working since then without any issues) but i'm not gonna speak about that again here... what's certain for me is that what ever happens with the system it's well enough conceived as any default mode for any fault will let the IVs open so normal braking should not be affected whatsoever, IMO fitting greater than 5% tyres is worst for the braking distance and system behaviour than my blamed mod and more dangerous in traffic...i explained that in some other thread a while ago.

[ozscott]

Thanks mate. I am interested in why say 10% increase in tyre size adversely affects the system. I suspected that the system is designed with 29.5 inch tyres in mind and any deviation might cause less than optimum performance but I don't pretend to know why.

Cheers

[sierrafery]

Welcome anytime :)... the first part of the theory is here when i was just presuming based on study: https://www.landyzone.co.uk/land-rover/one-job-done-more-to-do-and-its-great.270896/#post-3290851 and some more after i made live tests too: https://www.landyzone.co.uk/land-rover/255-65-or-255-70-pros-and-cons.292220/#post-3620824

[ozscott]

Thanks again. It makes sense. Here is a Wabco tech bulletin that for a bus/truck air brake ABS system that actually refers to design parameters in wheel revolutions per mile - 437 to 591.


https://www.google.com.au/url'sa=t&source=web&rct=j&url=http://www.meritorwabco.com/MeritorWABCO_document/tp0320.pdf&ved=0ahUKEwioutOTs6vPAhUBvJQKHUWPCpUQFggcMAE&usg=AFQjCNH8Pf-VgAmqzozQuvS7CxZBsachsw

Cheers