Project P38: Transmission Re-Vamp

GEARBOX: This month, we get Project P38 into gear – with a gearbox replacement.


Ever since we bought Project P38 ‘blind’ – with no test drive – at auction it’s been stuck in third gear ­which, let’s face it, is far from ideal (and most likely the final straw, forcing its previous owner to punt it into an auction I guess!).

For the best part of a year – busy sorting out other jobs on the not insignificant P38 ‘to do’ list – we’ve lived with the gearbox issue, hoping (mechanically optimistically) it might miraculously fix itself, as some things seem to do on P38’s. But (obviously) it never has fixed itself and it’s understandably really sluggish to get moving, not great off-road (where you really need the lower gears to get moving with small throttle inputs) and chomps fuel at an even more alarming rate than most 4.6-litre V8 P38’s on a cruise at 70mph. So, the time had finally come to get the (usually reliable I’m told!) gearbox sorted.

No problem I thought… two options: Fix the current one, or replace the unit. Simples. Wrong! I have come to learn that nothing is ever simple with a P38.

Plugging the diagnostics into Project P38 (such a regular occurrence they should have come with one fitted as standard!) revealed a ‘pressure regulator’ issue, which, in real terms most likely means the pump inside the gearbox is caput, stopping gears being selectable. And getting the unit off, transported, cracked open and fixed by a specialist gearbox repairer transpired to be a very costly job. So, repairing it was out of the question…

As such, the decision was made to replace the faulty unit with a working secondhand ‘box. And that meant finding one.

Ebay threw up quite a few – but, being old fashioned, I’m a bit skeptical buying large, vital items like this from folk I don’t know. So I hunted around for one local to me here in Norfolk, where folk are pretty trustworthy, as a rule.

Using some old contacts, a few calls and a bit of internet research, I thought I’d found a couple and went to have a look at them – only to find they were either the ZF Getriebe 4HP22 unit, designed for the 4.0-litre P38 (and Discover TD5 and V8 models), or they were the (weaker) earlier model ZF 4HP24 unit, meant for the Gems 4.6-litre engine, not my later Motronic unit. The two 4HP24 units have different bell housing mounts and torque convertors and whilst they can be modified to fit, I was recommended to avoid going down this route…

Having drawn a blank and wasted time establishing this, I went back to my new mates, John Kemp Land Rover in Wymondham, just south of Norwich, where Steve, Chris and Shaun turned their vast experience and support to the matter.

As is their helpful, knowledgeable way, the John Kemp boys sorted the issue in no time – finding a ZF 4HP24 four-speed unit only a few miles away the other side of Norwich, from a specialist broker they’ve used before, who only deal in secondhand parts from vehicles that drove in working. Better still, all their parts come with a 90-day warranty too, so they must be pretty confident it’ll work. And, it was only £220 inc. VAT. Which I think you will agree is pretty cheap for any gearbox – let alone a titanic one like this; deal done! Even better, the helpful chaps at John Kemp even lent me their works van to go and pick the ‘new’ gearbox (supplied with the correct torque convertor) up with. How great a service is that…?

Out with the old…

Back at Project P38’s second home (John Kemp Land Rover), ‘super nice’ Steve was limbering up for the vast task of removing the frankly enormous P38 transmission – for his first job on a Monday morning. Ouch.

But, as usual, he wasn’t phased – despite not having removed one of these monsters for some time – tapping into his vast knowledge of the idiosyncratic P38, and set to work straight away; disconnecting the battery for safety and removing the engine fan cover to avoid it getting cracked when the weighty ‘box comes out and the engine lifts up, before raising the ramp to reveal the titanic transmission.

First up, the propshaft is removed from the differentials, before the torque convertor bolts are removed, then off come the lambda wires and the six bolts that hold on the exhaust manifold downpipe cat section (careful; they often snap off). You can then access the lower bell housing bolts (14 of them!), and the gearbox can be slightly lowered down – allowing access to the top bell housing bolts (see on).

The next task is to remove the gearbox cross member (supporting it with a prop first), to get it out of the way, allowing space for the gearbox to come out – after first unplugging the gearbox wiring plugs and disconnecting the handbrake cable from inside the car. You can then access and remove the gearbox mount and remove the gear selector cable and disconnect the inhibitor (ECU) switch. Phew: Half way there!

Steve could then drain all the (stench-ridden) gearbox fluid and disconnect and bag up the gearbox oil cooler pipes, which are hung up out of the way (imaginatively and rather surreally using a rubber glove!), along with the fuel pipes that run by the gearbox. You can then remove the exhaust (cat) downpipe.

Next up, Steve supports the enormous weight of the gearbox and its transfer box, by bolting on a jacking plate to the gearbox mount, attached to a beaten-up, but mighty transmission jack. With this in place and taking the load, the final upper bell housing bolts can now be removed – using the longest socket set adaptor set-up I’ve ever seen, causing me to almost wet myself laughing. Transmission giddiness had set in at this point.

After a final check everything was disconnected correctly and nothing was in the way, Steve called fellow JK technician, ‘duck oil’ Chris over to use a screwdriver to prize the gearbox out. And together they gently lowered the ‘box and transfer unit onto the transmission jack. Et voila! The bloody massive transmission is out – balancing precariously, yet majestically and apparently defying physics on the jack. And this mammoth job only took Steve two hours: I’m impressed, again. The lads at John Kemp really know their stuff, which is so vital with specialist vehicles like Landies, and essential with a P38.

Steve then separated the knackered gearbox unit from the (hopefully not knackered!) transfer box and removes the inhibitor switchgear and breather pipes (which we will re-use) and carefully loads the now drained gearbox into a transportation box and into the works van.

A quick trip up the road to our chosen secondhand Range Rover parts suppliers (Furness Car Company in Rackheath), and there’s the gearbox waiting for collection. Or so I thought. It was a Gems one. Doh! But, no fear, the lads there quickly dug about and came back with a correct Motorinic unit, complete with torque convertor and confidently assured me “all the Range Rovers drive in here, so it’ll work.” Fingers crossed, money changes hands and the 90-day parts warranty if offered and I’m back in the van and heading back to John Kemp in 15 minutes. Result.

Back at base, Steve sets to work servicing the ‘new’ gearbox – fitting a new filter and sump plugs etc. and making sure it’s fully drained of old oil, before washing out the bell housing and torque convertor with oil and re-fitting the inhibitor switchgear and breather pipes from the old, broken unit.

It’s then ‘just’ a question of lining up and fitting the torque convertor inside the gearbox, re-attaching the old transfer box and getting the ‘new’ transmission up on the jack, to offer back up to Project P38. Then Steve went back through the removal process in reverse order to get it fitted, and everything else back in place.

Once back in situ in and checked, the gearbox can be filled back up with oil, with the engine running to help draw it deep into the internals. And we’ve re-selected the Ravenol ATF 6HP Fluid again. It’s an automatic transmission fluid (ATF), produced with a blend of hydrocrack oils and synthetic PAO with special additives and inhibitors to ensure smooth and reliable operation of ZF high performance automatic transmissions as detailed below. It’s claimed to offer a very good lubricating ability even at low temperatures, a high, stable viscosity index, very low pour point, exceptional protection against corrosion and foam formation, good balanced coefficient of friction, compatible with all types of sealing materials, a high thermal and oxidation stability, excellent cooling abilities, an excellent shear stability,lowest evaporation losses and is compatible with all non ferrous components. And all of that sounds good to us – hopefully extending the lifetime of the £220 transmission for a long time to come yet…


I know I keep banging on about it, but I make no apologies – I am so impressed with John Kemp Land Rover. The more I learn about the P38, the more I realise it’s a vehicle like no other I have ever owned – requiring supremely specialist know-how to remedy the multitude of issues it throws up. And Steve and the lads here are so genned-up on these cars, they are never phased by the issues – even on big jobs like a full gearbox swap – using their decades of experience to overcome problems and find solutions. They made the hard, heavyweight transmission re-vamp job look easy – which it just isn’t. Not to mention helping me find a second hand unit too in the first place: They are awesome… not the cheapest, but not OTT and as my grandpa always used to say ‘you get what you pay for – especially with spanner men.’ One thing is for sure, I could not run Project P38 without them, so thanks chaps!

After a couple of weeks off the road, I’ve really missed the old girl and I’m really keen to find out how she drives – with gears! Unsurprisingly, Project P38 is a completely different beast, now she’s not stuck in third gear! It shoots off junctions and roundabouts now, thanks to the lively short first and second gears and acceleration is so, so much better than before with two gears beneath what I’ve been used to. And having a top, forth cruising gear is just awesome – allowing for a far quieter, more refined, faster and much, much more economical cruise. I reckon the £500 it’s cost me to do this job will come back to me in no time on LPG and petrol costs! I only wish I’d tackled it sooner really…

There’s also now no nasty clunk from the transmission when I engage reverse and the gear changes are slick, smooth and pleasing – helped I am sure by the trick Ravenol ATF fluid. In fact, it’s a whole lot smoother than I thought it ever would or could be for an old school torque convertor, agricultural transmission. Sure, it’s no eight-speed double clutch set-up and it’s still an old, simple, noisy beast really – but at least it works well, for now!

Finally, Project P38 is into top gear! So, once we’ve sorted out the oil leak (rocker cover gaskets, we hope), coolant loss (heather matrix O-rings, we hope… not cracked block, please!!) and air suspension (ECU random issues) – we can, finally, be brave enough to venture a bit further off road than my farming pal’s fields (where he’s on hand for a tow if I breakdown). Not to mention take the V8 on a few road trips. And there’s still a few more tricks the old dog has to show you too – including a full ECU re-map by Mark Adams of Tornado Systems next month – so do stay tuned. Meantime, I’m off to enjoy the P38’s transmission re-vamp. Aren’t gears great?!


John Kemp (& Shaun & Steve & Barry & Chris)  @ John Kemp Land Rover (fitting)

Tel: 01953 601440

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