I have a 2003 XJ8SE 224k miles that I have owned for the last 10.5 years, which I bought it with 900 miles on the clock. For the last 40k miles the gearbox (ZF6HP26) has felt like it was about to pack in. The symptoms included:

1) the "lurch", which occurred mainly when the oil was hot after a long journey. It seldom happened when the oil was cold. Specifically, upon re-starting the car, it would hesitate in selecting the early gears and then slam hard into fifth, or occasionally fourth or even third, where it would remain – happened fairly frequently.
2) whining caused by multiple clutches engaging simultaneously on start-up – happened occasionally
3) loss of power from gearbox braking whilst accelerating – happened a lot
4) weedy acceleration in general, which made the car feel both gutless and fragile – happened all the time.

My mechanic advised a new/recon gearbox; the local Jag specialist the same; and (for the lurch) the forums appear to advocate a software re-flashing with seemingly mixed results. I figured I would drive it until it packed in - albeit very gingerly! I happened to be Googling this again about a month ago and came across a supplier in Keighley, Yorkshire (BA Transmissions Limited) that claimed expertise on our box. The key problem with our boxes - they claimed - is weakness in the valve body design.

To cut a long story short, I went there yesterday and had my valve body overhauled. Having been fascinated by this whole topic for the last six months, I asked to watch the thing from start to finish. The process took about five hours, with the first hour being the cool down of the gear box.

In order to understand what went wrong with my box, it is worth describing how the valve body fits together. Imagine a sandwich with the bread slices cut very thick, with a thin slice of cheese in the middle. The “cheese” is the interesting bit: the gasket. The gasket is a sheet of steel that has gasket material printed on both sides – it looks a bit like a circuit board – and it separates the upper and lower halves of the valve body. The gasket material means that even though there is a small gap between the steel of the gasket and the steel of the upper and lower valve body halves, when the gasket material is intact there is an effective seal.

This is the bit that had failed in my box. Specifically, the gasket material had worn off near the bolt holes, creating unexpected gaps allowing the pressurised oil to travel down the wrong channels. This clearly accounts for my problems 1, 2 and 3 above. I reckon 4 was caused by low levels of transmission fluid – we put in a lot more than came out (we put in 9L). I don’t know what the cause of this was – possibly the gearbox oil change about 18 months ago by my mechanic was done incorrectly. I noted yesterday that there was a requirement to fill the box to the brim when cold and then start the engine and fill again – possibly they didn’t do that.

Interestingly, also, there was no swarf on the sump magnets, which the mechanic said was a sign of low/no clutch wear. I am hardly a boy-racer and I do mainly motorway/highway mileage, so it is ironic, therefore, to think that I could have replaced the box with a reconditioned one that was actually more worn than mine, and at 5-7 times the cost!

In addition to carefully cleaning out all of the gasket material debris from the valve body halves and replacing with new the accumulators and the filter/sump – and here’s the interesting bit that I think is unique – they spent about an hour rubbing off all the gasket material using a whet stone, thereby ensuring that the steel of the gasket is in complete contact with the valve body halves at all points. Having refitted everything, the mechanic then spent 15 minutes re-training the Mechatronics, doing hard accelerations and decelerations on the hilly roads near the workshop.

Anyway, the difference is staggering. It feels again like I have got back the car that did 0-60mph in 6.1 seconds when it was new. Having spent hours and hours searching the web for a solution to my problem and having never seen this particular remedy before, I bring it to everyone’s attention in the hope that it will be of help to somebody.

All the best

Mike

 

very interesting report, thanks
was it just the gasket or was there work at the valves too ?

 

Hi Nebelfuerst

I asked the same question: what about the valves? We have all read that the pressure regulation valve wears and leads to unregulated pressure spikes that crack the A-drum in ZF boxes. Apparently our box is not so susceptible to this (unlike the five-speed), but in any case, my fault codes were not indicating this, so the advice was to leave well alone.

Certainly the A-drum failure appears to be preceded by a delay in engaging forward gear when selecting drive followed by a thump when it engages. As I understood this "symptom", it is not the same as my "lurch". In the "lurch" the gear selects immediately but then struggles and thumps into fifth (usually - see above).

I am no expert - to be clear. I have just read a ton of different posts on the internet!

I suppose time will tell as to how definitive is this solution. But - hey - I just did a one hour drive today to my brother's. I have the beast back! No hesitation, just full-on acceleration from my Lazarus car!

Best wishes

Mike

 

Fascinating, thanks.

You should publish this on the UK forum.

I have just looked them up: http://www.batransmissions.com/commo...-transmission/

 

Hi Meirion1
Thank you. I don't know how to do the post. Happy to do so, if you can tell me how.
Mike

 

Err........I am no expert but:

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I have never done this and it may not be possible-maybe someone more knowlegable will be along soon.

Good luck

 

As seen here in this thread from our UK meet held at the UK's A1 ZF gearbox specialist

Page 7 from post 125 ( pics can be seen )....

https://www.jaguarforums.com/forum/u...=transmissions