I came across an XK8 with a dead 5HP24 in it, which is a common problem in x308 cars as well. The post 2003 XK8 and XJ8 cars had the 6HP26 which seems to be a lot less troublesome. I am reasonably confident that 6HP26 will bolt up to the AJ27. The potential stumbling block would be getting the electronics to work.

The "easy" way out would be to find a wrecked car with 4.2 engine and 6HP26 and swap the engine along with the trans and requisite electronics. While it should be possible to get all of this stuff to work, I am not sure as to how "easy" this swap would be, i.e. whether it would require swapping instrument cluster, various other ECUs and re-wiring most of the car.

Powertrain Control Solutions seems to have a standalone controller capable of controlling the 2nd gen 6HP transmission (6HP28). These transmissions seem fairly robust, and therefore available at reasonable prices. It looks like there is not much demand for them. I am wondering if I could bolt on the 6HP28 in place of 5hp24, wire the standalone transmission controller and call it a day. I know that the 5hp24 transmission controller has a habit of asking the engine computer to reduce torque in certain cases, it also relays any OBDII transmission codes to throw via the ECM. The 5hp24 brain also likes to chat with ABS controller.

If a combination of factory ECM for 4.0, 6hp26 (or 6hp28) Transmission controller and ABS controller that all work together existed, that would make this swap an easy job.

As a side note, I am wondering if the 4.2 ECM can control the year 2000 4.0 engine or not. If it did, I could swap the 4.2 ECM and 6ph26 transmission controller and reuse the 4.0 engine.

 

With all of the electronic difficulties to overcome you would probably be better off rebuilding the 5hp24 with all of the updated components, new a-drum, new valve body and shift solenoids.
In the end it would probably cost less than to do a conversion. Rebuilt with the updated parts the 5hp24 is a pretty reliable unit.

If you want to try for it I would recommend you go to JagRepair.com - Jaguar Repair Information Resource and download the wiring diagrams and trace out the control circuits. You may find that without rebuilding the wiring harness with new sections the modules won't plug and play. As a minimum you are going to have to program the modules to work together.

 

The only reasonable way out is to fix this transmission. There are complete rebuilt units available for direct swap. Separately, there are a number of rebuild kits that vary in scope for all manners of repairs (check eBay). My understanding is that the one design flaw is a specific valve directing too much fluid pressure and destroying the A-drum. There is a better designed valve available that should make a rebuilt transmission last for the remainder of your ownership. This is sort of a worst case. There are also other possibilities involving control module, shifter cables out of adjustment, even a brake switch, etc, that are much cheaper to fix. This is where a code scanner comes in to tell you the specifics, besides providing a way to search this forum for more exact details.

Altogether, these are not terribly expensive cars. If you want a 4.2L 6HP26, then go look for one. Something will eventually turn up. Overall, these modern transmissions are designed to work as a package with the engine, and the rest of the car's electronics, really (think CAN bus, etc).

The other option is to drop a GM engine/transmission in the car. Check vendor Jaguar Specialties.

Best of luck, keep us posted.

 

I answered in your other thread, but will re-post here for the sake of the discussion.

Short answer is not to bother with it.

Long answer is you would more or less need to transfer all the major modules and wiring from a 4.2 X103 into the 4.0 X100...

I mean Instrument Cluster, ABS/DSC components, J-Gate, PCM, and all the wiring associated with it, plus most of the wiring in the engine bay as well. And even then you will have to electronically assume the identity of the donor car in order to be able to reprogram any modules. i.e. when you connect the IDS or WDS it will have to read the VIN of the 4.2 X103 that all the parts came from...

Not worth the effort...

 

Indeed they are. Sadly the asking price and labor to install comes close to the market value of the car.

My symptoms are: slowly creeping forward, reverse works fine. They seem to be consistent with the broken "A" clutch drum, but I'll know for sure once I yank the trans and take it apart.

If I decide to keep the 5hp, I'd probably go for ZF kit and ZF clutches, steels and revised "A" clutch drum from ZF. Some aftermarket parts are not perfectly true to size. While you can make them work, you will need to do a "proper" remanufacturing job, complete with lots of measurements and running the trans of the testbed, which I don't have. With aftermarket parts some machining may be required. ZF parts tend to be a direct bolt-on, no machining required, provided you get the correct kit for your trans (they vary by Brand and manufacture date).

Ultimately the root cause of the problem is the valve body wear. Once the pressure regulator wears enough to start misbehaving, the oil pressure starts to spike, which in turn causes broken "A" clutch drums. It seems that with respect to the valve body my options are:

1. Get replacement valve body housing from ZF. I suspect that this will be expensive.
2. Machine the pressure regulator valve bore oversize and install oversize plunger. There seep to be at least a couple of options from Sonnax and Transgo (5hp-24-pr). The former looks the same as ZF part, the latter seems like a redesigned part with O-rings. I am not sure which one is the better options.

P.S. The car has 140K on the odometer. If it lasts another 100K after less than a grand in parts and a few days of labor, I'll be pretty happy.

 

That 5-speed has lasted 140k, you should already be jumping with joy. The main reason these cars end up getting parted is a blown tranny, real shame

 

Click the link below and check out Post 8 and post 22 of the below thread - also check out Gus's site Jagrepair.com. Eriksson Industries in Ct can rebuild the 5HP24 for $2295


https://www.jaguarforums.com/forum/x...-p1747-173644/

 

I am not the first owner of the car, so I would not be at all surprised if the transmission were rebuilt at some point in the past.

Clearly just replacing the A clutch drum is not a permanent fix, because it fixes the symptom without addressing the root cause. I am wondering what is the best, most "permanent" fix for the root cause, i.e. the valve body wear causing the pressure regulator to malfunction. I remember reading that there was a revised piston from ZF, there are also aftermarket options. I am wondering if boring the hole oversize, pressing in a brass sleeve and reaming it to the proper size would be a more permanent solution than all the silliness with piston swapping and oversized bores. Aluminum is a fairly soft metal, unless you take special measures to create a hard-wearing surface. Boring the hole oversize clearly won't do that. If the original bore wore out around 100K, I see no reason why an oversized one won't, unless you change piston material or design.

Does anybody know what the valve body plungers/pistons are made of, steel or aluminum? Steel (or hard coated aluminum) vs. raw aluminum makes a seriously shitty friction pair. If that is indeed the case, I am not at all surprised at all the grief with 5hp24 failures and rebuild comebacks.

 

The original pressure regulator valve that I removed from my 99 XK8 is hard coated aluminum. I changed it to the Transgo design, which unlike the upgraded ZF replacement valve, has two flexible seals that ride in the bore section that is prone to wear.
The transmission upper valve body developed a crack a thousand miles later(delay in engaging drive and losing drive at a stop) and was replaced ($105 from Ericksson). I also updated the A drum and axial bearing between B & C clutches, even though both appeared to be in excellent condition. 8.5 qts of ATF and back to traffic.

 

What caused your valve body to crack?
The only time I heard of one cracking was due to an engine overheating.

 

The crack in the upper valve body (see picture), along with pressure valve spiking, (& subsequent A drum failure), B/C Axial bearing and reverse piston issues are the main problems with the 5hp24. The upper valve body crack seems unusual, but it is unfortunately common. Whether its a design, casting or pressure caused, it can be fixed without removing the transmission and is the "best of the bad" problems that you may have with the 5hp24.

 

I am not sure how engine overheating would cause the transmission valve body to crack. I'd be curious to know, though.

I suspect that the valve body cracking was a result of the pressure spikes, which in turn was caused by the main pressure regulator not working right once worn out. if you keep whacking an an aluminum baffle filled with oil with shockwaves, eventually the baffle will fail. Not unlike an engine failure after hydraulic lock.

 

Was the $105 a new empty valve body or a reconditioned one? Did you move the transgo piston to it?

I am a bit hesitant to replace the original piston that had no seals with an aftermarket one that has seals. There is no doubt in my mind that the piston with o-rings/seals will not allow the fluid to leak through the gap between the bore and the piston. Which, in the transmission that was originally designed for a piston with seal (GM comes to mind) would be fine, until that seal blows. I am suspecting that the ZF engineers designed the valve body with the assumption that some fluid will indeed leak through the gap. If we close the gap with o-rings, no fluid leaks by and the pressure goes up. Which could create a whole bunch of new problems, like cracked valve bodies that weren't able to hold the extra pressure.

Hard coated aluminum has excellent wear characteristics. That's why the piston remains intact and the bore in the valve body wears out instead. I doubt that the inside of the bore which the piston rubs against is coated with anything. It's just plain aluminum (casting-friendly aluminum alloy to be exact). The wear characteristics of plain aluminum surface are not good. That's why I was thinking about reaming the bore oversize and installing a sleeve in the bore. If the sleeve is made from from steel or hard wear-resistant brass, it will maintain the piston-to-bore tolerance a lot longer than plain aluminum.

5hp24 works fine when new. The problems start once things wear out. Having a wear-resistant sleeve would extend this "working as new" state for longer.

 

The 'upper" valve body is only accessible after the entire valve body is removed from the transmission. It is on "top" of the main valve body and easily removed on the bench. The $105 was for the new ZF body only (pictured). Scott at Ericksson said the new units don't appear to be failing like the originals. The eight valves and springs are quickly transferred from the defective unit.
Transgo has been in business for a long time and I like the idea of the square cut seals in a wear prone area. The seals are the same design as used on the "A" drum shaft. The Transgo pressure valve has a different shape and spring from the original ZF design. It is located in a removable "lower" valve body and is even easier to update, since the main valve body remains in situ.
I'm not aware of any complaints with the Transgo pressure valve.

 

One of our customers brought in their 99' XJ8 because it overheated almost to the brink of destruction. Fortunately it was ok after cooling off and I repaired the overheating situation. Apparently there's a very fine line between the coolant temp being ok and engine locking up, rods knocking or blown head gaskets. There was no engine damage fortunately on this car. I went to test drive the car but something clearly wasnt right about the way it shifted. I don't remember what it was doing but comes to find out that the valve body had a rather large crack on the topside of it. The transmission oil cooler runs thru the radiator and that's how the valve body cracked on this car. We changed out the valve body with another spare we had and all was well afterwards.