P38 Auto Box

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Haggisbiker
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P38 Auto Box

Post by Haggisbiker »

I plan on taking my P38's V8 out and swapping it to a rear wheel drive Scimitar but need some pointers on the box. The P38 has the ZF4HP Automatic that has the ecu and I know you can convert this auto to RWD only but then it needs a standalone control for the box...between the conversion of the box and the standalone controller seems like a chunk of cash and time!

What auto box will fit to the 4.6 V8 for rear wheel drive use and take what a mild tuned 4.6 can throw at it?



unstable load
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Re: P38 Auto Box

Post by unstable load »

You are making a mountain of work for yourself fitting a 4WD box to a rear wheel drive application. The box has a totally different layout because of the transfer case fitting on the back and you will need an expensive adapter to be able to fit a driveshaft flange.

Pretty much any RWD box will be useable with adaptation, but I'd go with one of the 4HP22 boxes available locally to you. Volvo and Jaguar use them, I believe and possibly BMW.
Ashcroft's has an electronic controller that would allow you to use the more modren electronically controlled 4HP22s, but it's pricy, and building the manual valve body over to an electronic box looks doable.

Head over and take a look here... http://www.classicroverforum.net/index. ... train.101/ there are some smart blokes on there, particularly "eightofthem".
Cheers,
John

Haggisbiker
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Re: P38 Auto Box

Post by Haggisbiker »

Thanks John I did think it would take some work to convert it and then the cost of an ecu...will go have a look at the link you sent me.

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Re: P38 Auto Box

Post by russell_ram »

Kind of as above. What you need is a 4HP22 from a Jag XJ40 (or BMW). They are completely mechanical shift. The RR uses the later 4HP24 which is pretty much identical to the 4HP22 except for the electronics. Then swap out the bolt on bell housing and torque convertor etc from your RR box onto the Jag box and it'll bolt straight up to your RV8 with no issues. OK, the shift maps won't be perfect but it certainly works well enough.
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Re: P38 Auto Box

Post by DaveEFI »

I have an an earlier 'mechanical' 4HP box from a RR here. IIRC, you can fit the tail shaft assembly from a RWD box easily. And of course the valving will be correct for the RV8. Can be collected for a few beer tokens. SW London.
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Haggisbiker
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Re: P38 Auto Box

Post by Haggisbiker »

Thanks guys for the info BMW box on EBay my only concern is that the HP22 were rated between 100 - 380Nm of input torque the Gems 4.6 in stock did 380Nm and the later Thor pushed 407Nm.

If my Gems is slightly modified it may kill the HP22 unless I get it uprated like Ashcroft can offer.

Will PM you about HP22 as have one that is tired on my 110 V8 so it may be of use.

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Re: P38 Auto Box

Post by harvey »

Haggisbiker wrote:
Wed Jul 25, 2018 1:36 pm

If my Gems is slightly modified it may kill the HP22 unless I get it uprated like Ashcroft can offer.

unstable load wrote:
Tue Jul 24, 2018 11:28 pm

Head over and take a look here... http://www.classicroverforum.net/index. ... train.101/ there are some smart blokes on there, particularly "eightofthem".

I'm pretty sure "eightofthem" can upgrade HP22 boxes to HP24 spec and he can build a box to your requirements.

James 33
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Re: P38 Auto Box

Post by James 33 »

I have a BMW Zf4hp22 fitted to my V8 trike with a Chimaera 400 engine. Works well and the overdrive 4th with lock up torque converter makes it good for cruising. I did use the deeper Range rover sump but over this winter I have swapped it back to the BMW sump as it didn't have enough ground clearance and only a matter of time before I holed it. Used the RR bell housing and Torque converter.

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Re: P38 Auto Box

Post by DaveEFI »

It's just a bolt on job to fit a tailshaft and housing from a RWD 4HP to your box, and at least then you have the correct internals for your engine. Early versions of the 4HP fitted to the RR etc are cable shift which makes fitting to something else easier.
There is a RWD version of the 4HP for the RV8, used on Sherpa ambulances.

If you'd like a cable RR 4HP, I have one here you can have from free. SW London. It has been lying around a while, but was good when bought.
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Re: P38 Auto Box

Post by unstable load »

Isn't the 4x4 tailshaft longer than the 4x2 boxes due to the transfer case requirement?
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Re: P38 Auto Box

Post by DaveEFI »

The main body of the box is the same for all. The transfer box bolts on to that. As does the tailshaft housing for RWD. I assume the tailshaft for RWD fits the splines on the mainshaft, same as the transfer box does. So should be easy enough to fit.
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James 33
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Re: P38 Auto Box

Post by James 33 »

Pretty sure to convert a 4wd box to 2wd requires a complete strip down. That's what I read anyway. Better of getting a 2wd box like I did and just change the bell housing.

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Re: P38 Auto Box

Post by DaveEFI »

James 33 wrote:
Wed Jan 23, 2019 9:40 pm
Pretty sure to convert a 4wd box to 2wd requires a complete strip down. That's what I read anyway. Better of getting a 2wd box like I did and just change the bell housing.
Ah - OK. I was told different.
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Re: P38 Auto Box

Post by Eliot »

Certainly on the GM Hyrdamatic boxes - the physical tailshaft is a different length between 2 and 4wd, necessitating a strip down.

Cant comment on the 4hp stuff, but I've always read that you get a jag/bm 4hp and swap the bellhousing over.
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Re: P38 Auto Box

Post by unstable load »

The rear shaft on the 4x4 box is longer where it goes into the transfer case and (I think) the case is different at the back to allow the transfer case to bolt on.
There are also a few different bellhousings between the various Land Rovers, but the P38 would all be the same.
Cheers,
John

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