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Wiring a P38 Borge Warner transfer box


Tom.H
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Hi guys

Just wondered if anyone knows anything about the Borge Warner transfer box used in the P38?

I’ve got one in my challenge truck and need to work out the best way to wire the high/low switch in.

All I know is that with a P38 the Becm controls when the transfer box is ‘allowed’ to change. The actual physical change is carried out by a motor.

Therefore I see it as just an electric motor.

Am I being stupid :blink: Does the motor just require a two way switch and the correct power to turn and move the selector?

Tom

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I'll go and look for more detailed information, but the Transfer motor is controlled by it's own ECU, which interlinks with the BECM, naturally. However, it's an interesting point to establish if there are in fact two signal wires from the BECM which 'allow' the ECU to power the motor in either direction.

As far as the motor itself in concerned, there is a position switch incorporated in the assembly which signals back to the ECU. This signal switch will not only say when the output shaft is in the correct Hi or Lo position, but also whether the shaft is either side of the correct position. That's 3 possibilities for Hi, and another 3 for Lo.

I don't know why it's quite so picky, but I think we should assume BW thought it best to be this precise, so, if you want a successful implementation, we should take note of this, and design a switching circuit accordingly.

The simplest way is to incorporate the ECU, would this cause you to despair, or are you already managing other ECU's?

Regards.

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Cheers for your help

The transfer box is the only component I have from a P38 range rover. I have neither the ECU for the transfer box or the DECM or any other ECU on my vehicle

I have the two way p38 sliding gear selector which is what is normal used to switch from high to low although I cant see if being much use if I dont use it alongside the ECU/DECM.

In fact I am thinking of changing it back to a normal ZF4HP22 single one when I know what I am doing.

Obviously this is far more complex than I first thought

Tom

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The Transfer box ECU should be easily available second hand via a well known auction site, or RR breakers.

I suggest you want one from a car that had a manual gearbox. AMR6460 is for a manual box, AMR6459 for an Auto box.

New boxes are probably less then £250 inc VAT, but do check.

Your reference to "the ‘two way’ p38 sliding gear selector which is what is normal used to switch from high to low" suggests that came from a car with an automatic gearbox. I suggest that in your situation, whether your car has an auto or manual box is immaterial, as your transfer box switching doesn't need any autobox to transfer box interconnection. The Hi Lo switch in a manual boxed car is just a switch in the dashboard.

Obviously this is far more complex than I first thought

Yes - it's what makes a 38A such an interesting and rewarding car :-)

I have culled the Transfer Box pages from the ETM.

These show I mis-remembered the outputs of the position switch, shown on page B6-8, but the principle was there.

Those switches are actually a single device with a stepped carbon track 'printed' on a plastic disk. The carbon track can only work an electronic circuit, I would not trust it to operate the coils of a normal relay.

Note that some of these pages show details for the Autobox, which I think you can ignore.

As well as the ECU, you will need to wire in a Neutral switch, and a Vehicle Speed sensor, which is on the Transfer box. You might be able to hardwire default inputs to the ECU connection points, but to do so would increase the risk of misoperation, and subsequent damage.

The Neutral switch already exists on a manual box, if you are using an auto box you might be able to use the existing XYZ switch.

Before going any further, you mention possibly using an alternative box.

What are you using for axles?

The 38A boxes put the propshafts down the left of the centreline, all other Land Rover boxes put the propshafts down the right of the centreline. Obviously the axle differentials have to accommodate this.

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The motor can easily be turned with a battery and two wires, so no ECU needed. Depending on the rotation you want, you just switch the wires.

It should be fairly easy to wire a switch for this.

Have you wired a challenge truck for this? I haven't, so experienced input would be useful.

As I have already pointed out, BW go to a deal of trouble to position the output shaft within close parameters, so it will be of great interest to see if this has proved to be a waste of time, especially on a challenge truck, where the transmission can expect to be worked fairly hard.

Remember there is no limit switch in the motor to cut the power when it reaches its mechanical end position, so any manual switch will have to be non-locking, and Double Throw (to reverse the motor). A switch for an electric window might be suitable, but you would still have no idea where the transfer gears were positioned. I suggest that 'half meshed' would be a bad idea.

The current loading for the motor is both high and inductive, the switch will not control this directly, and live.

At least two relays will be required, as both power leads need to be switched. Changeover relays would be no good, because these would always leave power to the motor.

Regards.

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I haven't wired anything like that, no. You do have a good point about the aligning of the input shaft, I completely forgot about that... I really need to stop giving advice in the morning <_<

Yeah, you'll probably need the ECU then, unless there's an easy way to detect when it's in right.

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  • 2 weeks later...

Still thinking :blush:

I’ve just been reading the overhaul manual for the borg warner transfer box.

I believe the manual transfer box ECU takes 4 Inputs before it powers up the motor and moves selector fork.

  • Ratio control motor position
  • Range selector switch
  • Vehicle road speed
  • Gear lever neutral

I don’t see a problem with the first two inputs as they already exist in the transfer box.

The vehicle road speed sensor is mounted in the transfer box. Does the input go directly to the transfer box ECU or does it first go through the BECM and then onto the ECU?

In fact I may be making things more complex than they need to be.

The ECU prevents low being selected if the vehicle is going faster than 15mph (I believe)

If the sensor works with a reluctor ring surely it receive no input if the vehicle is stationary. Does this mean I can leave this input and just make sure I only press the high/low switch when the vehicle has stopped

If I am going to use the ECU from a manual box how can I give an input to the ECU that the gear lever is in neutral?

I guess there can only be two possible inputs to the transfer box with the gear lever, Neutral/In gear.

What type of signal is the ECU expecting? Would it be possible to give a similar input just by a two way switch?

Cheers

Tom

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I see I made a mess of the pages I posted before, duplicating pages 4 and 7, and therefore missing pages 5 and 8. Apologies for that.

I can't edit my post of 15th March, so have included the two missing pages here, just to make the record complete.

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Neutral Switch.

I did include the diagram for the neutral switch (B6 page 7), which shows it switches an earth, so that diagram answers both 'type of signal' and 'not via BECM' with regard to the neutral switch.

There is an anomaly here, the text description of the Neutral switch (B6 page 2) says the signal is passed via the BECM. The diagram shows the signal as going directly to BOTH the Transfer box ECU, AND the BECM. I would follow the diagram rather than the text.

If I am going to use the ECU from a manual box how can I give an input to the ECU that the gear lever is in neutral?

You specify the ECU from a manual box, but not which type of gearbox.

Both the Manual gearbox and the Automatic gearbox switch a straight earth via the Neutral / XYZ switches.

B6 Page 7 for the Manual gearbox. B6 Page 8 for the Automatics XYZ switch.

Vehicle Speed Sensor.

The diagram (B6 Page 3) again shows the direct connection to the Transfer Box ECU.

It does not show the signal type, but as you have the VSS anyway you can supply the correct signal.

If the sensor works with a reluctor ring surely it receive no input if the vehicle is stationary.

Does this mean I can leave this input and just make sure I only press the high/low switch when the vehicle has stopped

We don't know. The ECU may be looking for a complete electrical circuit, to test the VSS is connected, THEN looking for a signal through that circuit.

The inference here is that if the VSS is disconnected the ECU may refuse to power the motor.

It's only a two wire connection, BUT they are shielded, so I'd expect to see the the resistance of a coil from the VSS when un-powered, with either a varying DC or AC voltage from the VSS when moving. This to change frequency rather than peak value to indicate the actual speed.

Note the ECU supplied voltage may be around 5VDC, with the speed induced variations on top of that.

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Hi Tom.

Why are you using the P38 'box as opposed to the standard Borg offering? Is there an apreciable difference? I'm not trying to be clever, I've got the choice between these two boxes myself, and had been intending to use the standard one, in preference to the 'leccy weird thing.

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I wasn’t even aware that borg warner transfer boxes were used in other land rovers.

The reason I am using the one for a P38 is because it’s offset to the opposite side to land rover axels.

Which means with a rear mounted engine the props will line up the diffs on a standard axle.

I am still up for the idea of a different box, especially as I’ve just found that the viscous coupling is sized (£300)

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Late RRCs had them too, but it's offset differently.

I'm guessing the box sends a VSS signal once the gears have lined up. I don't know how proficient you are in electronics/microprocessors, but making your own 'ECU' for it in that case wouldn't be exactly rocket science - as long as the box isn't signalling the gear is in place, you keep rotating the motor.

Still pure speculation though, haven't had one to fiddle about with, although with all this talk about them it's tempting :D

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  • 1 month later...

I keep on putting this behind me.... However I really need to get it sorted?

David: It seemed in your previous posts that in my circumstance you would recommend I use the transfer box ECU for a manual box.

I am aware that one of reason was because the range switch on a manual is done via a button whereas on the auto it done my moving the gear selector over to the ‘low gate’

Are there any other differences between the ECUs apart from this, It seems as if they need exactly the same Inputs.

It seems I can achieve all the inputs apart from one..... Gear position

As my vehicle runs an auto box from a Discovery 1 it doesn’t have an XYZ.

The XYZ switch on the P38 auto box reads of the selector shaft, which moves when the driver changes gear with the selector

I was thinking I could just buy a complete XYZ switch for a P38 auto box and imitate the movement of the selector shaft by moving it by hand. This would allow me to give the correct signal to the transfer box ECU (That neutral is engaged).

I don’t know whether using an XYZ from a manual would make it any easier to achieve the neutral signal required by the transfer box.

Would this work or am I off my head??

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Hi not the answer you are looking for but have you considered a mechanical, or cable link, try turning the shifter by hand(or grip with a mole grip etc) to get some idea what is needed. Ian Ashcroft

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I keep on putting this behind me.... However I really need to get it sorted?

You don't help yourself by picking it up and then putting it down, because you lose track of the detail. Also it doesn't help anyone else, like me, to help you because it's not our priority. I certainly haven't bothered to remember what you are doing and why. This creates the danger that advice given 'now' is not compatible with something you mentioned at the beginning.
David: It seemed in your previous posts that in my circumstance you would recommend I use the transfer box ECU for a manual box.

I am aware that one of reason was because the range switch on a manual is done via a button whereas on the auto it done my moving the gear selector over to the ‘low gate’

Are there any other differences between the ECUs apart from this,

I don't know, I haven't compared them, I've never owned an Auto.
It seems as if they need exactly the same Inputs.
Possibly so.
It seems I can achieve all the inputs apart from one..... Gear position
OK.
As my vehicle runs an auto box from a Discovery 1 it doesn’t have an XYZ.

The XYZ switch on the P38 auto box reads of the selector shaft, which moves when the driver changes gear with the selector

I was thinking I could just buy a complete XYZ switch for a P38 auto box and imitate the movement of the selector shaft by moving it by hand. This would allow me to give the correct signal to the transfer box ECU (That neutral is engaged).

All that seems logical, BUT...

I wonder why you need the full complexity of an XYZ switch as you aren't using it to control the auto box?

In fact, looking at the crib from the manual you have supplied, Neutral is indicated by 0 Volts on the Y line, X and Z being disconnected. So if all you want to indicate is neutral you need a single manual switch to apply an Earth to the Y line when you want the transfer box to move. In this respect it seems the same as the neutral switch on the manual gearbox.

I don’t know whether using an XYZ from a manual would make it any easier to achieve the neutral signal required by the transfer box.
There is no XYZ on a manual box, just a single switch to say the box is in neutral. Again, the XYZ does MORE than just signal neutral to the Transfer box ECU, the XYZ ALSO signals the individual gear selections to the Auto gearbox ECU. This misunderstanding is what I mean when I say you don't help yourself by leaving the job halfway through.
Would this work or am I off my head??

I'm not whether 'this' refers to the preceding text or the following diagrams.

I'm not sure what the diagrams are saying. One appears to be a direct crib from a Manual, if it's been modified I didn't spot the changes. The other is just two lists, again, I don't understand what it's trying to tell me.

HTH

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  • 6 years later...

Hi Tom,

I know a few years have passed but are you still playing with the rear engine truck? I am just about to start a similar project but using a complete GEMS P38 4.6 driveline.

I will need to use both Auto box and transfer case controllers and feed the rellevant inputs and get them to communicate with the engine ecu.

 

How did you get on with your transfer case control? A pic attached of the wiring mess I have to sort out. Currently getting engine ecu unlocked so I can run without security (or any other inputs) from the BECM.

I@m sure there will be some fun and games but it may make it easier if I can locate other folk who have gone the same route.

 

Happy New Year to all.

 

Bob Tail

DSCF3836.JPG

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  • 4 years later...
 
 
   I have seen conversations about p38 gearbox also a have the same problem I use p38 rover but I design in other way using different kind of computer to control the engine I get stuck on how I can bypass the gearbox because in the gearbox there two wire for high and low and other four wire small how may I do to use this gearbox to run well pls help me. This below is the wire come from transfer box and motor also I try to connect with it's own ECU I get only sign from level display mode.

20210212_142305.jpg

20210212_141641.jpg

20210212_141224.jpg

Edited by Vicram
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  • 2 months later...

Hello ! First post, but my first google search brought me right here and been lurking ! Love this place ! Bit of a necro thread I know, but .....

Anybody able to point me into a direction where I can get plug and pin details ? Had my car standing at an Indy and when I got it back the plug had disappeared :(.  Been driving with the box complaining and no low range, but we have a Landy Club event in two weeks and would like low range back for the proposed off road location. I can source the plug, just need pointers on pin outs and how to connect if you can guide me please !

Quote

20210212_141641.jpg

 

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