ZF 4HP22 step by step.


Active Member
There are already a number of threads on the forum discussing the ZF 4HP22. However I've decided to start a new one which sticks to recording the process of preparing and installing a 4HP22 in a Rover P6B, for the future easy reference of all. I would like to keep this thread on course, but of course comments are very welcome. Obviously every conversion project is going to be a little different, but I hope that the steps I personally go through serve as a useful guide for anybody else who goes down this path. I must warn everybody that I am a complete novice feeling my way through this job, and I am writing this thread both from a novice's perspective, and for novices.

Firstly, a short recap. I have in my possession two ZFs: from a Discovery V8 and a BMW E34. The strategy is to use the bellhousing, torque converter and flex plate from the Disco box, and the tailpiece from the BMW, together with an appropriate selection of other bits to create a suitable gearbox for the P6B. I have already removed the Borg Warner from Brown Rover, so I start the thread at the point of stripping the two ZFs to see what I've got.

The first step today was to remove the bellhousing from each gearbox. Pictured is the Land Rover one, complete with optional extra leaves. To remove the bellhousing, all the bolts you can see in the photo must be removed. As a novice, I found this page useful - http://www.cowdery.org.uk/zf.php. Chris says to leave the pump (newbies: it's the bit between the bellhousing and gearbox proper) in place as you remove the bellhousing. I presume this is to stop the A clutch pack and associated gubbins from falling out, however once you've removed the bolts the pump readily pulls free with the bellhousing, despite your best efforts. This didn't appear to be a problem to me; just proceed slowly and carefully.

In the next photo, you can see the pump separated from the gearbox and still attached to the bellhousing, and the A clutch pack and input shaft poking out of the gearbox. Be careful here; the clutch pack and input shaft will easily pull out and you will end up with a small but confusing pile of gubbins on your workbench.

In the next photo, I have rolled the gearbox onto its side and removed the sump. First, the filter must be removed (3 torx screws), and then you can get to work removing the valve body. You will find yourself looking at a large and confusing array of torx screws. Some hold the valve body on to the gearbox, and some hold the valve body together. The former can be identified by their larger diameter heads. Remove all the larger diameter screws and the valve body will simply lift out of the gearbox.

Elsewhere we have discussed the fact that, unlike the Land Rover, the BMW box does not have an inhibitor switch installed. If a BMW box is to form the backbone of your conversion you needn't panic. With the valve body off it can be seen that the internal part of the selector lever (correct name, someone?) is the same on both boxes, and an appropriately skilled person could tap the boss to install the switch and retainer.

Because I intend to inspect and, if necessary, replace the clutch packs in my donor box, the next step involves removing the gearsets. If you look at Chris Cowdery's page (see link above), you will see that this isn't at all difficult. First, you must remove the circlips, springs and rubber washers that lurk in the galleries above the valve body. Without taking these out, the gearsets cannot be removed. When extracting them be aware that the springs are compressed, and if you are not careful you will have circlips describing graceful arcs over your head and vanishing into the dark corners of your garage, from which they shall never return.

In the next photo I have placed the springs on top of the socket set in positions relative to those they occupy in the gearbox. Four short ones toward the front, five long ones toward the rear. I'm sure this is important, so take note.

In my next dispatch I will describe how to remove the little rubber washers, however first I must figure out how to do it myself. Member eightofthem apparently has a secret method to achieve this, so I'm off to PM him. For now, I'll leave you with this photo of the contents of the BMW box's sump. The BMW was a 120,000 km car, and the Disco had done just on 200,000 kms, but the Disco's sump was as clean as a whistle, and the Beemer's looked like this:

Could do with and Arlo Gurthrie style of photos; color glossy pictures with circles and arrows and a paragraph on the back of each one explaining what each one was or in this case is ie screw locations and dismantling order.
PS great job Warren :)
Good photos Warren. :) Is that material that is covering the inside of the pan metal or friction material or both? Doesn't bode well I would think.. :?

Wow! I don't think I've ever been awarded a sticky before, anywhere on the Web!

It's all friction material as far as I can tell, Ron. Running a magnet through it didn't pick anything up, although I'm not entirely sure whether that was a relevant test.

Graeme, I was hoping that my eloquent descriptions precluded the need for arrows and circles, however I will be sure in future to crank up MSPaint and add them should I feel they could provide clarity for the easily baffled. ;)
Nice pictures Warren.
To get the rubber seals out you heed a pick.
Basically a bent scriber, just hook them out, you need new ones when you rebuild.
Is the RR valve chest the same as the Bemmer?
The last rubber seal( at the back end of the box ) is sometimes an angled one.

Ah! I was under the mistaken impression that there was a method of getting them out intact. Brutal I can do, but I will have to go and buy a scribe.

The valve blocks look totally identical, Jim. Obviously there are internal differences, but I've had to label them carefully so I don't confuse them now that they're out.

Don't hold your breath for my next update to this thread, fellows. I've got a few things to sort out, perhaps with some help over in the ZF discussion threads, before I make some further progress and compile the results into a second proper post. As I said, I'd like to try and keep this thread as clean as possible to help future ZF voyagers, so I'll post any questions elsewhere.
Im impressed with your attitude with this adventure
You appear to be a dab hand at this
Great work
Thank you Gerald. I've been considering this move for at least a couple of years, having already stockpiled the ZF boxes as they passed under my nose. But of course my hand was forced by the self-destruction of the Borg Warner a few weeks ago. C'est la vie. A couple of considerations. Firstly, being a family man with a mortgage I can't afford a professional conversion, so I have to do as much as possible myself, even though I know next to nothing about automatic gearboxes. Secondly, we have discussed this conversion at length, but we are lacking a central resource of concrete information that anybody can use as a guide. Hence my aim is compile a thread of posts here that will serve as a central repository to any other non-experts who wish to undertake the conversion. I do apologise to the likes of Harvey et al if reading my posts sounds like telling grandma how to suck eggs.
WarrenL said:
I will have to go and buy a scribe.

You might be able to make a suitably shaped pick to flick those seals out using an old bicycle spoke - most bike shops will have a box of bent or wrong sized odd spokes in the workshop.

Good work on the strip down so far, I'm looking forward to seeing how it goes.
In my next dispatch I will describe how to remove the little rubber washers, however first I must figure out how to do it myself. Member eightofthem apparently has a secret method to achieve this, so I'm off to PM him.

Looking good so far Warren :wink:
I have missed this post as I have been on our Holliday.
There is no secret as such in removing those pesky seals, if you have the correct tool they come out easy!.
I would be very careful in using picks and self tappers, the aluminium case is easily damaged, and remember these are seals.
Also if you go in too far past the seal, you risk damaging the internals.
My tried and tested method ( and I looked t all other options like picks and self tappers! )
Is to remove the large internal circlip that retains the centre support, then pack the case with newspaper to stop it all from tumbling out of the case, then give the case a good hard tap down on some wood blocks ( directly downwards front first, or at a slight angle.
The weight of the centre support bearing down on the rubber seals will slice them clean in half, hence the need for new ones, and you do not risk damaging the case by picking at them.
Once the centre support is out you can just push the seals upwards into the case.
You do the same with the rear ones as well, only try to save the one angled one if you can as is it more expensive than the rest, and it does come out ok with some long nose pliers.
Good post well done, and keep it up.

Ohh sorry forgot to mention, the valve bodies are different, so be carefull not to mix them up.
They look identical from the outside, but strip them both down and place them side by side and you will see the difference,
More so when you compere the main body and baffle plates, you need the correct gasket for each valve block, as the shift patterns vary between vehicles.
I forgot to PM you, which didn't help. Got distracted by other commitments this week. So, to be sure that I've read you correctly, will tapping the case on wood blocks dislodge the gearsets etc and allow them to be slid out? I carefully removed the seals with a wood screw (taking great care to not damage the passages by twisting it in too far, but I suspect I've only got the top half of them out, and the front gearset is steadfastly refusing to slide out. See the other ZF thread, which is where I posted about this.
Yes Warren, the gear set can be removed with the seals left in place, as long as the large internal snap ring ( circlip )
Has been removed.
Don't forget the centre support is held in place inside the case by two wedges one on each side of the case on the horizontal sides ( looking at it from sat on the sump ),And they are a tight fit. ( you can see the channels where they sit when you look inside the case )
So either pack the inside or have suitable soft items ready to catch the centre support and gear sets, then lift the box up bodily and tap it downwards hard onto wood blocks front first, either on a 45 degree angle (recommended )
Or at the vertical.
With the 45 degree method you have a bit of control when the gear sets let go, as you can slow it down with one hand on the front of the box.
Sorry Warren, I am presuming that you have removed "B" clutch from the case, this is held in place via a small snap ring located on the outer shaft, and below this is a thin washer and an O ring seal.
The snap ring is a fiddle to remove, but don't forget to fish out the washer and O ring before you try to remove " B " clutch or they could jam and become a git to remove.
If you have already removed " B " clutch from the case, then you will be able to see the large snap ring that retains the rest of the internals.
I will have to fire up the laptop and add some pictures, as they tell a far better story than words.
Yes please, do add some pictures. I've removed a large diameter snap ring and a set of friction plates/washers, but without pictures I'm not entirely sure that these constitute what you're talking about. I've got pictures too, but they're at home so I can't post them right now.

Just one thing: could you post them up in the other ZF 4HP22 thread (viewtopic.php?f=1&t=15069)? I'd like to keep this thread as uncluttered as possible to make it easy to follow for future conversions, and use the other thread for thrashing out the nitty gritties. It is my intention to just post the definitive step-by-steps as we solve all the problems.

Well folks, we're well overdue for an update to the sticky thread, but various things have kept me from ZF gearboxes over the last few weeks, and it wasn't until tonight that I finally completed the strip down of the BMW box. If you refer back to my first post in this thread, you'll see I left off with the problem of how to remove the flow restrictor washers from the passages between the valve body and the main part of the gearbox. We discussed various means of removing them, but I found that a big wood screw twisted in a half turn gripped the washers tightly enough to allow removal with a pair of pliers and a block of wood:

Here are the five flow restrictor washers removed from the rear of the box (four more are to be found in passages at the front). Carefully note the hole that holds the deep angled washer.

What follows is largely copied from a post I made in the discussion forum! The A-clutch and input shaft slide easily out of the front of the gearbox, leaving you staring at the B-clutch. With all the flow restrictors removed, a pesky snap ring now stands in the way of further disassembly, but two screwdrivers carefully applied got it out. The following picture shows the clip removed and sitting askew on the shaft - the entire B-clutch assembly will now slide out:

B-clutch removed and on the bench:

Look carefully and you will now see a big snap ring that holds in the rest of the gearbox:

Snap ring removed:

We move now to the tailpiece of the box. Here I'm talking specifically about the BMW box that is donating its rear end to my cause, however once you've removed the tailpiece you will find everything is much the same bar the output shaft and governor.

In my case I had to remove the 30mm nut on the back of the output flange. This required a deep reach socket fixed to an air ratchet to remove, so I must at this point thank my mechanic John for providing the necessary equipment and expertise. (BTW, the pinkish tinge you can see is due to handling the gearbox with gloves I'd been using while spray painting my daughter's bicycle...)

With the nut off, the output flange can be removed and the tailpiece be eased off, exposing the parking gear and pawl, with the governor in behind. I apologise for the crappy photo, but getting my 9-year-old son to act as official photographer so I could keep my filthy hands off the camera was only so successful:

Carefully remove the ten T30 torx screws that you can see hiding behind the parking gear and governor (be careful, the heads are soft!):

Gently tap the end of the output shaft. It will gradually slide forwards through the parking gear and governor, allowing you to remove the entire innards of the box. If necessary, use eightofthem's technique of tapping the box downwards onto a lump of wood, but be careful! Shove a big rag in there to prevent the innards spilling onto your floor in many pieces. Here's what you get:

Congratulations! You have an empty case! In the picture below you can see the parking pawl. Eyeballs and calipers revealed that the parking gear is the same in both the BMW and Land Rover boxes. However the BMW pawl is 6mm thick, and the Land Rover one is 8mm thick, although both look exactly the same from this angle. In my case, the Land Rover parking gear has been chewed up a little, probably by P being engaged while the vehicle was still moving, whereas the BMW gear appears to be in perfect condition. Therefore I will use the BMW gear and the Land Rover pawl, provided there are no issues when fitting the BMW tailpiece. More on that in a future post.

Here on my workbench you can see at far left, the contents of my Discovery box, with B-clutch assembly still attached to the front. The box has slightly separated during removal due to inadequate care on my part. To the right of the Discovery box is the BMW, without the B-clutch assembly. Next right is the Discovery torque converter with P6 flex plate sitting on top, and last right, the Discovery flex plate. I'm pleased to confirm that the Discovery ring gear is exactly the same as the P6, which bodes well for the P6 starter motor. However, all that is a bit further down the track.


Having disassembled my donor Land Rover ZF box as related in the above posts, it's now time to overhaul it, install the BMW output shaft and reassemble it. I do not propose to go into any detail about the overhaul itself because I'm not suitably qualified to do so. If you have taken things this far, then you are already knowledgeable enough, brave enough, or crazy enough to not require my inexpert contribution. The only important step to relate here is that if you are using a Land Rover ZF as the principal donor, you will be swapping its output shaft and tailhousing for the equivalent BMW/Jaguar items.

Installing a BMW/Jag output shaft into the ZF entails complete disassembly of the box as outlined in the previous steps. It sounds daunting, but if I managed it, you can too, provided you take your time and due care. A shout out here to member eightofthem, a bloke who knows his ZFs and has provided me with absolutely invaluable help and advice along the way.

Having stripped the box this far, I suggest an overhaul kit is purchased, and all clutches are thoroughly inspected for worn/burnt out friction plates. The overhaul kit cost me $180 here in NZ, and contained all the new gaskets, seals, O-rings etc to dolly my box up. Importantly, it contains a number of upgraded parts to overcome known weaknesses of the ZF 4HP22. From memory, there are teflon seals for the input shaft and instructions on where to drill a small relief hole in the A-clutch piston; replacement governor support rings for the rear of the box, and a spring to install in the valve body that cures a known downshift problem.

Once again, if you've already stripped your box to install the BMW/Jag output shaft, taking it that step further to install all the overhaul kit is not a big deal. The only problem I faced was not having the correct gear to reassemble the clutch hubs after installing the new seals. This requires compressing the return springs to allow the snap rings to be inserted in their grooves: I ended up taking all my clutches to the transmission specialist who sold me the overhaul kit, and he reassembled my clutches for $40. In the next photo you can see this overhauled clutch's return spring and snap ring, and you will likely understand why a weekend mechanic like me gave up at this point:

Happily in my case, ALL the clutch frictions (including those in the A-clutch, known to burn out on these boxes) were in perfect condition and were able to be reinstalled. All bearings and bushes were in good condition too, EXCEPT for the front pump bush which in both my boxes was heavily worn. I suspect it might be in yours too. The standard overhaul kit does not contain a replacement, but it only cost about $10 in addition.

With your gearbox dismantled on the workbench, you will soon figure out where the output shaft fits into the E-clutch assembly (centre of picture below). The E-clutch is engaged at all times to spin the output shaft, except in 4th gear, when it disengages and allows the output shaft to be driven by the overdrive F-clutch. The output shaft is an easy fit into the E-clutch assembly, except for the securing snap ring, which requires the correct type of snap ring tool.

A couple more views of the output shaft:

After all this is done, you can reassemble your box. You will find that it goes back in in several stages, but for demonstration purposes the next photo shows the entire inside of the box from B-clutch (left) to output shaft (right) all fitted together:

It is a bit of a fiddle getting everything back into the case and sitting correctly. But when you're done, you will have something that looks like this:

The above is a Land Rover ZF 4HP22, with the hard work complete. It has been fitted with the overhaul kit and BMW output shaft, and awaits the reattachment of the following:

- governor and parking gear.
- front pump.
- valve body, filter and sump.

Of course, we also have to fit the tail housing, output yoke, bellhousing, flex plate, spacers and torque converter, but I'll cover that in a separate post as I still have some of these parts away being refurbished.
Well done for the informative thread, going to pick up a 4HP22H from a Jag tomorrow so it'll sit next to all the other parts I've been locating for the old girls return to the road. Looking forward to your next installment. Did you need any special tools to disassemble the box? Thanks again for taking the time to write the thread.
Gidday mate, thanks for the compliment. There is much more to read about in the general discussion thread about the ZF - viewtopic.php?f=1&t=15069 - where you will see that I have made a great deal more progress than shown here so far. I will write up more for this sticky thread in due course, but to do so now will result in things getting right out of sequence due to the higgledy-piggledy way in which the project has proceeded, mostly due to lack of precedence and the need to work things out as we've gone along.

No special tools were needed to overhaul the ZF, at least nothing more exotic than Torx bits (T27 and T30) and a good pair of circlip pliers. However I did capitulate and spend $40 to have my friendly local transmission man install the new seals in the clutch hubs (reassembling those was going to be more trouble than it was worth for a weekend fiddler like me); and a small shop press is handy for pushing out/in bushes, bearings and seals. The correct pliers for the output shaft snap ring helps, and I have to admit that reinstalling the B-clutch retaining ring just about drove me bonkers, but only required two flat-blade screwdrivers and a large quantity of swearing.

The next "proper" post I intend putting up here will detail all the different bits and pieces you need when you go to install your newly overhauled gearbox. Two donor boxes are involved - a Land Rover/Range Rover 4HP22H, and one other that can provide the 2WD rear end. From what we've learned along the way, it seems (at least to me) that the Jag XJ40 box might be the pick of the bunch. The Jag output yoke allows the P6 driveshaft to be reinserted without modification, and member eightofthem has found that the Jag shift cable is the one that works best, allowing the original Rover selector to be retained, also without modification, and apparently allowing selection of all the lower gears (i.e. D-3-2-1). In the discussion thread I've recently posted a picture of all the bits you MUST have from the Disco/Rangie donor vehicle, i.e. the bits that sit between the end of the P6 crankshaft and the ZF torque converter. Overall, the two biggest problems you will encounter are the rear mounts and the speedo drive. Once again, take a look at more recent posts in the discussion thread. My new rear crossmember is a work-in-progress as I type, and Geordie Jim has posted a picture of his different method of skinning the same cat. I've chosen to go with a Dakota Digital conversion kit for the speedo, details of which you will find in the discussion thread. Good luck! I can now see the light at the end of the tunnel and I'm starting to get really excited at the prospect of being able to drive my ZF-equipped P6B very soon!
thanks for the info, yes definitely looks like there are a few possibilities available once the correct type of box is resting in the garage! Do you or anyone out there know what the gear change speeds are for the disco? I've got the ones for the Jag X300 ( which I'll try to capture and post ), so it would be nice to see if they're markedly different before I buy another box, tried RAVE and the internet to no avail. The starter inhibitor as one of your contributors stated - is on the selector, unless I'm looking at the wrong thing....