The valve body can be removed with the transmission still on the car-you don't need to remove the transmission from the car. Conventional autoboxes always have the valve body at the bottom of the gearbox so it sits in the sump pan, immersed in the fluid.

All you have to do is drain the fluid, remove the sump pan & filter-then the valve block can be disconnected electrically & unbolted from the bottom of the autobox from under the car-the transmission doesn't need to be removed, so it's a relatively easy job apart from the messy fluid bit

 

I have been working with ZF on a few problems with my trans and I posed the question about the Lurching to my contact and this is the answer I got. Before you replace anything read this.

“Good morning Gus,
I have worked with a couple of issues regarding what could be called lurching, this is when almost at a stop and a thump or similar to a bump from the back end is felt. The ZF6HP transmissions have what is called neutral idle control or NIC, this process turns off the forward clutch at stops to reduce engine load and improve fuel economy, similar to shifting to neutral at stops. I’m not sure what is causing the lurch but I believe the dealer is able to disable this function in what may be called a city drive program or something similar. This will not always solve the problem. At times wear may be causing internal oil leaks, some leaks may pass into other circuits causing clutches to bind. In this situation it’s possible a mechatronic may resolve but I have had little success considering the cost of the mechatronic. Having the transmission rebuilt by a shop experienced with ZF transmissions or purchasing a ZF factory reman where all components are carefully checked and updates performed would be the best solution.”
I will be posting additional information on my page shortly… I hope this helps!

 

This only applies to the more modern ZF 6HP transmissions, which are 6-speed units. This was indeed a problem on many cars & the usual cure was a dealer reflash of the gearbox ECU to make operation smoother.

It was also a common complaint on some modern Mercedes with the 7-speed gearboxes, whereby the NIC facility would cause 'lazy' step-off from standstill due to the time delay in re-engaging the gearbox forward clutch. UK road testers had a few 'alarming moments' with this 'facility' when pulling out of small roads onto major fast arterial roads with fast-moving traffic & a sluggish transmission due to it's designer programming for fuel economy

However, the X308 Jags only ever had the older ZF 5HP series of 5-speed autoboxes & were designed before the emphasis turned to fuel economy on the more modern ZF 6-speed transmisions.

I'm not aware of any facility on the older ZF 5HP tranmissions that functions in the same way as the NIC control on the later 6-speed units.

The fact that the lurching symptoms on the X308 model XJ8's usually precede a subsequent major transmission failure on the ZF 5HP series autoboxes, points more towards outright hardware failure rather than gearbox ECU programming-especially as owners report that the gearbox has worked normally for a long time & then suddenly starts lurching, followed shortly after by a full transmission failure where examination during gearbox overhaul & repair had revealed a fractured 'A' clutch drum.

 

You may be correct but it is worth looking in to. My question to him was general but specific Jaguars. I will be direct if it does apply to ZF 5 as well.

 

The later Jags used the ZF 6HP series of transmissions so his description of the symptoms is accurate for those Jaguar models.

However, the older X308 Jags only ever used the older ZF 5HP transmissions & when these start lurching after years of working smoothly, it's usually a sign of imminent transmission mechanical failure.

If it were just an issue of gearbox ECU software programming, then the transmission would exhibit the same characteristics throughout it's working life.

What happens with the X308's with the ZF 5HP transmissions is that owners report sudden gearbox lurching at high mileages, after years of normal smooth gearbox operation.

The 'A' drum & valve body weakness on the ZF 5HP transmissions is a well-known & documented failure now, as ZF themselves acknowledged by introducing uprated hardware parts for retrofit to older gearboxes during servicing & repairs.

 

The valve body is actually quite easy to remove. Links to transmission manuals and technical bulletins describing how have been posted elsewhere on this forum. I had it out in a few hours, mind you, I am not a professional mechanic, reading the instructions, going slow and most annoyingly, cleaning up the messes, drips and spills as I made them (tranny fluid is slippery stuff so its safest to keep a clean workspace.)

Here is the crack that I mentioned earlier.


The replacement is in transit, hopefully to be delivered before the weekend. Wish me luck and I'll report back once its installed.

 

If my memory serves me correctly this photo was taken from a Land Rover transmission.

 

I think this photo is from the OP's own Jag & shows the crack he mentioned earlier in this thread after he removed the valve block...

 

This is the one I was looking at when I was investigating my problem

Link ZF 5HP24 teardown - Page 4
Page #4 Post #58 & Page #6 Post #76

 

Perhaps Gus has seen this crack before and maybe its not so unusual that I found one like it on mine. I kind of doubt it is causing the mechanical fault, but it could become a problem. These parts rely on being torqued together just exactly so to seal against the hydraulic pressure between them. If that chunck were to break off completely, it looks like there'd be one or two out of the umpteen bolts that would not be holding any torque. Even as it is, the torque may not be correct. Also, one of the drums is exposed directly above the valve body and the chunck could bounce around inside and cause damage. I'm wondering if the transmission has been opened before and this was done by a previous mechanic or if it was a factory defect. There's no record of any transmission work among the paperwork but that's not gospel. Any clues I should look for?

 

Hard to tell-enthusiasts like us who spanner their own cars may not always leave a paper trail to document the repairs we do, unlike a proper garage or dealer who have to keep records of the work they do.

When I did the head gaskets on my Bentley last year I found that they had been done before, due to various 'clues' I came across when dismantling the engine-like exhaust manifold bolts not tightened up evenly, with some actually loose. Then I noticed that the cylinder head bolts came undone at different torque settings & the bolts on the ram pipes had adhesive on them to assist refitting.

There were so many clues & loose bolts I discovered during dismantling that it was obvious someone had been there before & done a 'quick repair job', yet there was nothing in the service history to document this & as the car had several previous owners, someone had been doing work on it without leaving a paper trail.

Regarding the crack on your valve block body, it's unlikely that this was a manufacturing defect-although not completely impossible-so there's a very good chance that somebody has been there before to try and sort a transmission problem out.

Maybe that's why they sold the car-who knows?

 

Strange that they both cracked in the same place. I would wonder if it is a defect or as was mentioned improperly installed.

 

the give-away is sometimes apparent with the pan torx bolts, these have a relatively high torque that can leave them marred. I'd inspect these.

I bought a T27 solid tip torx, not the hollow security type after being told by one of the tech directors of the J.E.C that they can 'snap off' when trying to remove them. I think there's upgraded sets been offered over on the XK8 forum to stop this happening.

Drilling and tapping upside down is something I don't want to experience, or having a car stuck because the oil is drained and cannot be serviced from this point without major remedial work.....

 

Probably not so much a defect at manufacture & more like a stress/fatigue crack with age & the repeated heating up & cooling down of the valve block every time the car is used.

Either way, it's a clear failure of the valve block from a casing viewpoint-even before you get to the probable worn bores inside the valve block body itself.

The good thing is that it's relatively easy job to remove & replace the valve block & costs much less than a new transmission-provided the actual transmission gearsets & clutch drums haven't been weakened by the spurious hydraulic pressure spikes.

 

This is what I got back from ZF

The 5HP24 had a wear problem in the VB were the main pressure regulator may get stuck due to a wear ridge and cause an over pressure condition. It’s thought the high pressure would cause the D, G or both and more common the A drum (input shaft assembly) to shear the area above the snap ring in the drum. This is a catastrophic failure and would result in no reverse or no move forward. It will not partially break, either it fails or it’s ok. Several years ago an updated main pressure regulator valve was introduced to prevent this as well as a strengthened A drum. Before jumping into changes look at your prior rebuilds and confirm the parts used. Our 5HP24VBK valve body rebuild kit includes the new valve along with other updated springs. The original A drum inventory has been gone for years, The D,G drum was not modified and current inventory is good. Point being you may already have the updates and not be aware of it. If not its not a bad idea to purchase or reman VB. Casting wear is not uncommon and a noticeable improvement can bee found when worn castings, valves, springs are replaced.

The clunk you felt may have been due to the transmission controller having a moment of dementia. I have experienced some thumps or similar problems when the computer is interrupted during an up or down shift and asked to command an opposite response. Example, during normal driving an upshift was being performed, remember the shifts up/down are a process not just and on/off of the clutches. As the computer was mid shift phasing on one clutch and off the other it was asked to shift down. This would involve a different set of clutches and a change in commands. The computer stumbled as it calculated the change causing a delay and possible incorrect clutch overlap. This could cause the clutches to bind and was the thump you felt.

I will post this and other related info on my page.

 

I plan on taking the valve body out of my 97 XK8 next month to inspect it. One thing I have not been able to deduce from all the discussions is if there are gaskets I should replace when I reassemble.

 

That's a good explanation & I won't disagree with it, because I've had that on occasions in BMW's with the 5-speed ZF autoboxes, where a sudden driver request for a different gearchange pattern has made the transmission 'stumble' as it tries to re-arrange the sequence for selection of the appropriate clutch drums & the gearbox ECU 'hangs' for a second or 2 before settling down again.

Having said that, these cars are now getting old with high mileages on them, so the chances of mechanical wear to the valve block are very high-especially as it's a known problem with ZF.

The faults are being reported by owners who have had the cars for a while & been happy with the gearbox operation. Then they suddenly start to notice a big change in the gearbox operation which is not consistent with their previous driving styles.

Under these circumstances it would be prudent to have the valve block inspected, as sudden changes in the operation of a gearbox that was previously operating satisfactorily & is now behaving 'oddly' with thumps is not normal.

If it is ignored & simply put down to the gearbox ECU having a glitch, then there is a very real risk that an emerging valve block problem-which can be solved relatively cheaply-is ignored until it then develops into full transmission failure & damage to the clutch drums, costing thousands to put right.

These cars are old & with high mileages on them, so mechanical wear is to be expected and if a gearbox suddenly starts lurching & behaving erratically-especially when the valve block problem is known & documented by ZF themselves-then some form of inspection is necessary.

Inspecting and, if necessary, overhauling the valve block on an old high-mileage gearbox which is lurching, will be considerably cheaper than ignoring the fault & hoping it is just a 'gearbox brain glitch', as it may then progress on to full transmission failure which will be much more expensive to repair.

 

The transmission is an area that I have little to no experience in but was forced to learn due to problems with mine. I think my xk8 trans is back to normal only time will tell.

 

VB arrived today from Sunbelt. Looks identical as far as I can tell - all the same part numbers. They've engraved a lot of little markings all over it which I assume indicate possibly what was done and who did it and a date of 1/21/13 in one spot. NO CRACK in this one. Guess I know what I'll be doing Saturday. Wish me luck.

 

What's the total cost, including core charge? How did you identified if it's a late or early VB? Which one is the CDS1 solenoid?

You are writing some history files for the XJ8 users...