ABS retro fit

[elbekko]

The P38 valve block has the master cylinder built in.

RAVE has all the schematics:

[Bigj66]

22 minutes ago, Snagger said:

I think it’d work if you have the ABS release return line and ETC supply line valves locked closed (or replaced by plugs).  I think the master cylinder is part of that valve block, thought I may be mistaken - I can’t go and take a look.  It may be a separable module.  It could be a real can of worms for legal issues, though.  A simpler power brake system from an non ABS vehicle would probably be the safer way to go.

Yeah, it was just something I was mulling over.

Do you mean a similar unit but without the ABS? What model used that?

[Snagger]

I don’t know of any nonABS power brakes on Land Rovers.  I think you’d have to look at other marques.  While the ABS/ETC block of the later Defenders and the D2 is separated from the pedal area, the master cylinder is conventional and uses a vacuum servo - as far as I know, these Emended parts are the same as on non-ABS Defenders.

[Bowie69]

You can get DIY hydroboost brakes, which is what you are talking about, e.g.

https://www.ebay.co.uk/itm/Universal-Hydroboost-Brake-Power-Booster-Kit-w-Astro-Van-Bracket-/162356068470

Not sure there is one for a LR though  

[Bowie69]

Oh, hang on: https://www.powerbrakeservice.net/newunlarohy.html

https://lrautomotive.com.au/contents/en-us/d4944_Hydroboost_kit.html

But having said all this, the RRC brakes always feel better to me than other vehicles, I am not sure this is just down to the hydroboost, but could possibly be the pedal arrangement and its proximity to the valve block/master cylinder. When there's a servo in the way, the rod becomes a lot longer and more wibbly 😛 

[Bigj66]

28 minutes ago, Bowie69 said:

Oh, hang on: https://www.powerbrakeservice.net/newunlarohy.html

https://lrautomotive.com.au/contents/en-us/d4944_Hydroboost_kit.html

But having said all this, the RRC brakes always feel better to me than other vehicles, I am not sure this is just down to the hydroboost, but could possibly be the pedal arrangement and its proximity to the valve block/master cylinder. When there's a servo in the way, the rod becomes a lot longer and more wibbly 😛 

The hydro boost uses hydraulic power From the power steering system to provide the additional pressure whereas the Landrover ones use an electric pump.

The firm pedal on the Softdash and later models is due to this improvement over a vacuum assisted version.

[Bowie69]

1 minute ago, Bigj66 said:

The hydro boost uses hydraulic power From the power steering system to provide the additional pressure whereas the Landrover ones use an electric pump.

The firm pedal on the Softdash and later models is due to this improvement over a vacuum assisted version.

Well.......... 

My Audi (that I have had for 20 years....) used to run a hydroboost system, it used the PAS pump to boost the brake, ran at something like 2-3000psi, so very similar to the RRC setup, albiet not electric

I converted to a vacuum set up due to cost of repair for the 'bomb' (same as the sphere you see on RRC/P38 pumps) and have felt no change in pedal from an assistance or feel perspective -it is identical.

 

[Escape]

Some cars (like old BMW 5) came with a hydraulic brake booster, but without ABS/TC. It doesn't really matter what is used to assist braking, either vacuum (engine or electric) or hydraulic pressure.

You could fit the pump, accumulator and master (with the complete valve block) of an ABS vehicle but not use the control unit. That would give you brake assist, a fail safe system but no ABS or TC. It would be a lot of work and probably not cheap unless you have a donor vehicle.

If you're not happy with the brake feel, why not use an electric vacuum pump instead of the engine vacuum? Easier to tune to your desire and independant of engine revs. You could change the master and/or add an adjustable pressure regulator to the rear for even more flexibility. This is exactly what is being done to some Lotus Esprit when the first generation ABS system starts to act up. With very good results.

Filip

[Bigj66]

1 hour ago, elbekko said:

Disabling TC is just snipping a wire. ABS is a bit more difficult, without power the system only has the emergency backup braking on the front brakes.

Maybe you could rig the valves to just open with the ignition feed or something, but it sounds sketchy.

So the output valves to each corner are normally closed in a power off condition with the exception of half of the front circuit? When energised the solenoids open to allow fluid through until the ABS senses a locked wheel and shuts the supply to that wheel off?

So as long as there is power to the system the solenoids will keep the valves open and in the event of a power failure, the front secondary circuit will still operate?

Disabling the ABS input from the wheels should keep the entire system open circuit all the time then unless there is a power failure.

[Bigj66]

16 minutes ago, Escape said:

Some cars (like old BMW 5) came with a hydraulic brake booster, but without ABS/TC. It doesn't really matter what is used to assist braking, either vacuum (engine or electric) or hydraulic pressure.

You could fit the pump, accumulator and master (with the complete valve block) of an ABS vehicle but not use the control unit. That would give you brake assist, a fail safe system but no ABS or TC. It would be a lot of work and probably not cheap unless you have a donor vehicle.

If you're not happy with the brake feel, why not use an electric vacuum pump instead of the engine vacuum? Easier to tune to your desire and independant of engine revs. You could change the master and/or add an adjustable pressure regulator to the rear for even more flexibility. This is exactly what is being done to some Lotus Esprit when the first generation ABS system starts to act up. With very good results.

Filip

To fit the P38 system without ABS enabled, you’d need the wiring diagram for the electrical circuit and I’m assuming that’s all part of the ECU?

[Bigj66]

25 minutes ago, Bowie69 said:

Well.......... 

My Audi (that I have had for 20 years....) used to run a hydroboost system, it used the PAS pump to boost the brake, ran at something like 2-3000psi, so very similar to the RRC setup, albiet not electric

I converted to a vacuum set up due to cost of repair for the 'bomb' (same as the sphere you see on RRC/P38 pumps) and have felt no change in pedal from an assistance or feel perspective -it is identical.

 

I was just going by how my old 4 door was compared to my old mans Softdash and then later my own soft dash compared to my TD5 that has new brakes all round. There was a definite improvement in pedal firmness and brake response with the electric boost systems on the two RRCs compared to the vacuum ones that all seemed to have more travel.

Ive never driven a vehicle with the hydroboost fitted so that would be quite interesting to try.

[Escape]

I think the improvement in brake feel might have more to do with the cars and braking systems evolving over time. Especially the Range Rover, as top end of the range.

As for the P38a system, the wiring is actually rather simple. Rave lists it all, including the diagrams @elbekko posted earlier. All the valves have their default state to allow normal operation of the brakes. The hydraulic booster has it's own wiring, with a pressure switch controlling a relay, independant of the ABS ECU. It was all designed (and rightfully so) to allow as much functionality as possible even if a fuse blows or the ECU fails. So using it without the ECU shouldn't be a problem. You could even wire the low pressure warning lamp to work without the ECU.

Filip

[Hemunro]

We have a Defender 90 and recently the ABS went whilst driving. It has been in a garage for over 6 weeks and they were useless so we have now ordered a second hand ABS pump on eBay. The garage has said they can “re-plumb” it, but then what are the next steps? Presumably needs re-programming. Does anyone have any advice on this? Or has had this done a the cost? We’re completely lost

[Snagger]

By “replumb”, they probably mean remove the ABS system and go to the plain servo assisted Defender system.  That works well, but it will almost certainly have insurance issues and may have some legal issues with VOSA and on MoT tests because they will expect an ABS system to be present.  Worth checking up on before changing anything.  I would suggest changing garage first - find a reputable LR specialist (not a franchised dealer, whose workshops are always appalling) and have them take a look.  The pumps can fail, but it is more commonly a sensor issue (wheel or pump pressure sensor) or a problem with the solenoid pack.  It won’t be a programming issue.

[Bowie69]

MOT won't care, they test the vehicle as presented.