If I have a 75k transmission, and it has no issues, could I get away from replacing Drum A by simply replacing the valve pressure regulator? I have read and watched videos online about that regulator causing the transmission to fail, so simply replacing it would prevent that for the lifetime of the transmission. Is this true?

I'm not saying I'm not willing to do the drum swap, but if it's not really necessary once the regulator is swapped, why do it?

 

The drum is weak. Replacing the valve will not change that, but it may reduce the chance of failure. If you replace the valve and the drum begins to fail at some future date, stop driving and do the repair. I replaced the valve in my 97 XK8 and sold the car with over 90K mi. If you're going to depend on this car for primary use it's a more complicated situation.

 

I don't know for certain that the A-drum is weak (its made just like other drums in the transmission), but the main pressure valve design is still an issue and I kind of doubt that any of the available upgrades really address the issue. I installed a Sonnax upgraded valve body in 2013 pre-emptively thinking that would prevent the dreaded A-drum. I don't know for sure that it bought me the extra ten years, but yeah, this past summer, the A-drum eventually blew at 125K miles. I took the valve body apart and the Sonnax unit was actually worn much worse than I remember the original valve body was 40K miles ago. The valve itself doesn't wear, its a harder material, but rather what wears out is the soft aluminum of the valve body housing itself. If the main pressure valve section were sleeved with steel or maybe plated with Nikasil like the engine cylinders, then we might not have this issue. And whether a worn pressure valve bore causes the A-drum to break apart or not, its still going to cause other performance issues.

You have basically three options for the main pressure valve upgrade. As I interpreted the description, the Transgo valve was a direct install and just changed where valve piston rides on the walls of the bore to an unworn section. That didn't sound good, but a lot of people swear by it. The Sonnax valve you send in your lower valve body unit, they ream it out to eliminate the wear and install a larger diameter piston. That sounded like the best option so that's what I chose to do ten years ago. Or lastly, you can buy a brand new lower valve body housing and what ZF calls their 2nd generation valve piston. But whichever way you go, its still a soft aluminum housing.

I'm still slowly putting mine back together again with an upgraded A-drum from Kuhle. This time, I've gone with a new lower valve body unit and 2nd generation valve from ZF. I only manage to find a couple of hours per weekend and much of it has been spent shopping for special tools, making special tools or trying to figure out workarounds to do it without the special tools shown in the ZF workshop manual. Fingers crossed that it works or I guess I'll be posting a lot of lovely spare parts for sale if it doesn't. A 2000 XJ8 with 125K miles unfortunately is worth less than it would cost to have a shop rebuild its transmission so I understand your desire to postpone the seemingly inevitable. You could remove the valve body, take it apart and inspect without removing the transmission. If its worn, then a repair or upgrade is certainly worth doing. How many more miles or years it'd buy for the A-drum, no way to know. Doing both is more certain, but cost-prohibitive at shop rates and DIY is challenging to say the least.

 

The ultimate transmission upgrade is to buy an XJR. 😄

Of the 3 X308’s, my wife’s 00’ XJ8 is the only N/A car we have. We’ve had it since 21k miles at the end of 2013 from the original owner. Anyways, ever since we’ve had the car, I engrained in her that when she starts the car up cold not to quickly put it in gear. I told her that she has to wait until the RPM’s come down to about the 800rpm mark before shifting which is about 10-15 seconds. If you think about it, when the RPM’s are up at the 1200-1500 RPM mark and you shift it into gear, it’s like doing a neutral drop on it and that’s what kills these already fragile transmissions. I talked to our ‘go to guy’ which is a long time transmission shop owner/tech since 1978 (!!) and he jokingly said those A drums are made out of recycled beer cans. 😂😂😂

 

So what you're saying is, in short, changing the regulator and/or the drum might only increase transmission life by a little? So is there even any real semi-permanent fix?

To be fair, I only plan to use this car for 2-3 more years until I have enough to LS swap it.

 

I think the pressure regulator, the best you can do is put it back to the way it left the factory. If the original lasted 80K miles, then its replacement should last another. However that A-drum has already taken a pounding and the snap ring groove may already have cracks and be weakened. Just doing the valve body may not buy you much time if the A-drum has already been compromised and the only way to know is to take it all apart and inspect it. If you go that far, you might as well replace it. But if you upgrade the A-drum to the new one from Kuhle it probably won't break the same way no matter what. And if you go that far, you might as well rebuild the whole thing, which is what you are trying to avoid.

 

What do you think is the best option if I only want to use the transmission for a couple years then?

 

I'm assuming you have no symptoms now. Is it time for a fluid service? If so, go ahead and drop the pan, remove and inspect the main pressure valve bore. If its worn, then choose one of the replacement options and put it back together with new fluid and filter. Maybe $300-600 DIY depending which route you take. If the fluid and filter have already been serviced recently, then with 75K miles, I think I'd just drive it and take my chances.

If you are already having some symptoms then probably some damage has already been done, in which case rather than spend the time and/or money to rebuild the ZF transmission (I'm at like $1,300 in parts and supplies alone as a DIY project - not a cheap fix nor a quick one), take out a personal loan and move up your LS swap plans by a three years. Whether you spend money on a transmission rebuild or interest at the bank, you won't get your money back but more importantly you certainly won't get your time back.

Worst case you do nothing, drive it till it breaks, maybe 18 months from now, then borrow a little bit and move up your LS plans by 18 months. Or chances are it runs fine for another three years and you're all set.

 

This is great advice, thanks for your time and insight. Yeah, there are absolutely no symptoms on the transmission right now. Runs smooth as a kite. The fluid hasn't been changed so I guess I'm gonna have to do that. I'll inspect the pressure bore and update on what I find. Thanks again.