I've read that there are two problems with this transmission that combined cause a catastrophic failure. 1) a weak A-drum and 2) something about the valve body that causes excessive pressure. The second is somewhat vague.

My Jaguar lurched once back in October or early November. It was sort of unusual circumstance, happening as I began to accelerate again after having stomped on the brakes to avoid another car that cut me off. I didn't think much of it at the time because it didn't trip any dash lights and continued to drive normally. But around Christmas I was in my doctor's office complaining about a pain in my neck going down my left arm and shoulder and my doctor started asking me if I'd been in an accident. I had not and couldn't remember anything, no trips or falls or anything. It was only within the last week that it dawned on my that the Jaguar's lurch may have been enough to cause whiplash. It didn't seem very violent at the time.

Anyway, now I'm concerned about the Jag's transmission doing that again. I'm wondering if replacing or repairing the valve body is in order to prevent lurching in the future. Would fixing the valve body improve the life of the A-drum? I'm guessing the A-drum may still be intact because the car has been driving normally for 2,000 miles since that incident.

 

The 'A' drum and valve body have again become a topic of conversation. While it appears clear that a worn valve causes, or at least contributes to the drum failure, it is not clear if replacing the valve body is an effective preventive measure. While it would seem that the valve body could be removed/replaced with only the pan dropped that, also, has not been definitively clarified . . . at least to me. Then there is the question of only replacing the valve or the complete valve body.

If a low cost valve only with only dropping the pan is a viable solution there will be a lot of folks lining up to do or get that done.

Stay tuned for further discussions.

 

That does not sound like the same thing. The worn vale body causes a lag of several seconds when shifting into D. Anyway, here is the recent thread:

https://www.jaguarforums.com/forum/x...e-valve-88615/

 

I had both symptoms in the ZF 5HP30 transmission of a 1993 BMW 540i I once owned. The problem started out as a delay/lag in the gearbox actually engaging when 'D' was selected. Then after a few months it progressed to the next stage, where the gearbox wouldn't engage with 'D' selected-unless you revved the engine, at which point there was a sickening lurch/thud as the transmission suddenly engaged drive.

At that point I had the gearbox checked over, the valve body & checkballs overhauled/replaced & new fluid/filter fitted. After that the lurching stopped & the gearbox behaved as normal.

The problem with an old high mileage gearbox is that the 'A' drum may well have been weakened by both mileage & the hydraulic pressure spikes from the worn valve body & valve.

Overhauling the valve body will cure the pressure spike problem for now & the future life of the gearbox, but there are no guarantees that the 'A' drum hasn't already been weakened-especially if it's got to the stage where it's lurching into engagement with a thud. However, as you only have to remove the gearbox sump pan to access the valve body, it's not too difficult to overhaul.

You don't have to remove the gearbox to reach the valve body-they are always at the bottom of an autobox immersed in the fluid, because right above them are the main geartrain assemblies so the only place for the valve body to go is in the gearbox sump pan & to be bolted on from underneath.

The valve body on my BMW ZF 5HP30 gearbox was removed with the transmission still on the car & the ZF 5HP24 is of a similar design & layout.

 

The other thread describes replacing the "main pressure valve". I've never observed any symptom of a delay engaging from park to drive. But is this "main" valve involved in shifting all gears? In my instance, the car was clearly in some gear and then lurched when shifting into another gear. I'm not aware of which gears, just that I was doing 45mph or so, hit the brakes and had come almost to a complete stop when the danger was averted and moved my foot from the brake to the accelerator pedal and the car lurched into motion again.

 

If it were mine, I would do nothing unless it happens again and a transmission fault is displayed.
Is it possible that you pushed the gas pedal to the floor and when the transmission downshifted the sudden acceleration snapped your head back?

 

Indeed. I keep trying to recall the incident in my mind's slow-motion replay and wonder if I was actually tapped from behind by another car, but there's no damage to the rear bumper cover and I'm probably prejudiced by all that I've previously read about these Jaguar gearboxes.

 

Well, I guess its starting. On Tuesday I experienced a delay of between five to ten seconds when shifting into reverse and its lurched a couple more times when accelerating from a stop. I think I'm going to put it on the lift this weekend and go ahead and pull the valve body for inspection.

Anticipating the worst, I've checked pricing on rebuilt valve bodies with Sonnax overbored pressure valves from $300 to $900. I can't imagine why there would be that much difference. How do I know if I ought to buy the cheaper or most expensive vendor? Reputation? What questions do I need to ask? A local supplier at the top end of that range has two in stock for exchange.

 

You can just ask the vendors directly as to why there's such a price differential between the suppliers. The vendor of the top-end priced units should be able to explain what has been done to the valve block to have it priced at that level. They may have replaced more than one part...

Bear in mind that fitting a new valve block should cure the original symptoms of hydraulic pressure spikes acting on the 'A' drum, but there's no guarantee that the 'A' drum won't fail at a later date as it may have already been weakened.

Having said that, even with a new transmission fitted which has the stronger updated 'A' drum, you'd still have needed to have the valve block overhauled anyway so that the original hydraulic pressure spike fault doesn't start acting on the new 'A' drum as well.

Either way, the first starting point is the valve block & then 'play it by ear' once this has been done & the gearbox refilled with new fluid & also a new filter while the sump pan is off.

 

Keep us informed. I have to do this to a replacement tranny that I am putting in my XK8 once spring arrives here in Minne-snow-ta. The A drum went kaput last fall and it has been in the garage ever since.

B

 

I spoke on the phone today with an acquaintance of mine, a man I met years ago through a local Corvette club, who works at a transmission repair shop. Luckily he was very familiar with the ZF valve bodies. He used to rebuild them at the shop where he previously worked, tho the shop where he works now they just buy rebuilt VBs from their supplier instead of doing them in-house.

His opinion was that the vendors offering them at low prices had to be cutting corners as there is some pretty expensive testing equipment, machinery and significant labor hours involved in doing it right. He explained a bit of the process including how they reamed out the valve bores (not just the main valve, but any that were worn), then they had to calibrate them because the larger valves would require a different spring rate to achieve the desired pressures. He seemed to think that around $700 was a fair price as that's what he pays wholesale.

He believed that my symptoms indeed indicated the VB was wearing out. He was also of the opinion that replacing the VB now is a good idea and the probability is great that it would postpone the demise of the dreaded A-drum by many thousands of miles (assuming of course that it has not already been damaged). He did figure tho that eventually, just normal stress on the A-drum will do it in.

 

When mine starts doing this, I will get the tranny off the junkyard, replace the A drum, and the VB, and bolt it into the car. I will get another tranny as soon as I experience ANY delay in engaging the gear (D or R).

Total cost about $1500.-

 

I removed the valve body this weekend and inspected the main pressure valve. Indeed there was some serious wear inside the bore. It had worn a sort of a lip in one side of the bore. Working the valve in and out, I could feel it moving across that edge and so likely, with sufficient pressure on it, in certain circumstances I could see it hanging up. Taking the valve piston out and shining a flashlight inside, I could see the wear and feeling with a small pick, it was very obvious that it went around about half the bore. And to top it off, another part of the valve body had a crack in it. It probably started from an overtorqued bolt and was about an inch long. It probably was not in a location that affected the performance but it might if it kept growing.

So I've ordered a rebuilt valve body from Sunbelt at $450 plus $100 core. I was impressed with their online video showing their process and since they do nothing but valve bodies, no other transmission parts, they don't service transmissions, just valve bodies, that they may be able to do a good job while keeping the price low. Fingers crossed (for luck).

 

What mileage on the car? Any picture with the damage is welcomed!

 

Good update Phil, you did you take any shots of the problem. I think you're the first on here to actually confirm the valve block is the root cause of the A drum failure. One of the more valuable threads for owners....

 

It's not the first time that worn valve blocks have caused serious damage to the main gearsets on ZF autoboxes. The problems in the ZF 5-speeders go back to the early 1990's when they were first introduced on the BMW 540i in 1992. That had a similar affliction whereby wear in the valve block body & in certain plastic 'checkball' valves would cause uncommanded fluid pressure spikes that would blow clutch drums...

Because BMW adopted the 5-speed autoboxes several years before Jaguar did, the problems that are now surfacing on high-mileage Jags with ZF transmissions had already happened several years earlier to certain BMW models.

Same goes for Nikasil engines...

Even the old 4-speed ZF autoboxes had problems with valve block wear that would cause the forward clutch drum to partially engage in 'N' or 'P', due to fluid seepage past worn valve bores in the valve block. As the engine idled in Neutral or Park, the partially engaged clutch drum would eventually wear out it's multi-plate clutches & require a full transmission overhaul. Symptoms were the car creeping forwards slightly in 'N', unless the brakes were applied.

This happened way back in the late 1980's on ZF autoboxes & the cure back then was a redesign of the valving on later gearboxes, while owners of earlier gearboxes were advised not to let the engine idle for long periods in 'N' or 'P', or at traffic lights for example-the fault could be 'contained' if the gearbox was left in 'D', so long as a gear was engaged & the clutches were fully engaged rather than partially engaged & slipping...

 

Does it appear that the known valve body weakness' of the ZF transmissions was resolved or at least mitigated over the years from '92 through '02?

 

On the old 4-speed ZF autoboxes the valving was improved in the late 1980's to reduce fluid seepage past worn valves causing partial clutch pack engagement in 'N' or 'P'.

I'm not aware of any formal production line changes to the valve bodies by ZF on the 5-speed autoboxes. As the problems only started to emerge after several years of use & high mileages, the gearbox design was being superceded by the later 6-speed units as the problems started to show.

So it was probably too late in the production run of the 5-speed autoboxes for any major design changes, & so the usual course of action was for ZF to offer uprated components which could be retro fitted during the servicing & repairs of older transmissions.

The problem for ZF was that they started to introduce new gearbox designs at shorter time intervals, so by the time the 5-speeders started to show problems ZF were then gearing up to manufacture the newer 6-speed autoboxes.

 

How hard is it to remove and replace the valve body ? Is this a tranny out exercise ?

 

Appears that it is a simple removal after the transmission pan and filter are removed.