Gearbox failure at 90,000mls

[Spannerrash]

As many of you will know I put the car up for sale for about a week or so and then took it off the market as I needed to lend my intended daily driver to a family member. No problem I thought, I'll run around in the S8 for now and then re list later.

Well, the S8 had other ideas. Whilst driving home one afternoon I made a very low speed right turn into my street. I came off the break and onto the throttle only to hear the engine rev but no drive. Then suddenly a very aggressive thump, so much so, she span a wheel or two momentarily. She then seemed to drive fine the next 300 meters or so onto my drive.

There are no faults stored in any of the control units and the PRNDS display has never lit up to indicate limp mode.

The next day, simply running the car on the drive without moving it, the gear selector worked fine. In reverse all OK, in drive all OK. That is until the gearbox warmed up. Then she started thumping as you put her in drive. Reverse is OK.

I took her out for a short drive the next day and she worked perfectly fine for about 20 minutes. Then the very same thing again. So, I think this is only an issue when the gearbox oil is warmed up.

My suspicion is the skinny "O"ring on the A clutch drum is worn or split. Possibly as a result of a collapsed thrust bearing on the A drum. This is then allowing the oil to pass when it thins out.

I would much appreciate any other theories you might have and appreciate any help.

I don't think there is any point at clutching straws with oil changes etc. The gearbox is done. How badly done, no one knows until she is stripped. My initial starting point is to drain the oil, remove the pan and see if there are any signs of metal. This would obviously indicate more excessive damage and maybe even a broken A drum.
A conversation with Mackies alludess to a possible 6k repair bill (for a full gearbox rebuild) and that as an additional problem, some of the parts needed are now getting hard to find.

If the damage is limited to the A drum then it is possible to just repair that and re-fit but that really depends on what you find when you drop the pan. Any signs of metal and realistically the gearbox will need a full strip.
I'm collecting parts at the moment as I seem to have the mentality that as long as I have the parts, she will always be repairable.

There is a major part of me that wants to do this job myself. Working on the drive though on axle stands is gonna make that a very interesting project. What's the worst that could happen. I end up with a car that won't drive and then sell for parts? An engine alone seems to be worth more than the full car at the moment. I can also take the opportunity to replace the Orings and pipes at the rear of the engine which are difficult to access otherwise.

To that end I bought a used 5hp24 from a BMW, X5 I think to practice stripping down through the winter. After purchasing a few special tools I found this to be not a big deal at all. Clearly there is more too this than simply stripping and re-fitting new parts as there are clearances that will need to be checked but I think it is doable.
Even if I don't do a full refurbishment I'm sure I could install a full new "A" Clutch assembly quite easily. This lives behind the oil pump and is quite easy to access once the gearbox is out of the car.

So, multiple options and I'm not sure which way I'll go yet.

There is also the economic element that needs to be considered. A repair of a car worth 6k at a cost of 6k clearly raises question of my understanding of basic maths. If the net result is zero then it makes no financial sense. Especially when the car is worth somewhere near 3k in parts.

If I do the repair myself on the drive I calculate the repair at being aprox 3k. I have already spent 2k on the parts I need. I will need to purchase an engine hoist and a hydraulic lift table. This is gonna be about another £800 but could be sold on after the job.

There will be no quick decision on this as I am also keeping an eye on the classic car market and indeed the wider economy in general. Both of which are not doing too well at the moment. I believe the situation in Ukraine could also deteriorate over the next couple of years and the added risk of Trumps tariffs will also impact our economy.

I am practicing a wait and see policy at the moment.
I will keep you updated.

[MikkiJayne]

I suspect your diagnosis is correct. Surprising it hasn't gone in to limp mode though. Normally slipping will cause a 'gear ratio incorrect' code which then causes limp and a thump in to drive. I would be inclined to put a MAF in it at the same time since you're so deep in to it already. The MAF is used to generate the engine load signal to the TCU, and if that is giving plausible but incorrect readings to the ECU that can cause hard shifts and break the A-drum.

Its worth seeing if you can get hold of a Transgo valve for it as well. This replaces the stock all-metal pressure valve with one with piston rings so compensates for any wear in the bore of the valve, which can also cause hard shifts and break the drum, although it does sound more like a spontaneous failure rather than an induced one.

Doing it on the driveway is unpleasant but possible. It sounds like you're planning on taking engine and box out together, which is sensible. That can be done with a pallet truck if you have access to one, rather than demanding a hydraulic lifting table. An engine hoist is a must though. When splitting and reassembling, take the engine off the gearbox, not the other way round, preferably with the gearbox strapped down to a pallet or pallet truck. While the engine weighs slightly more, its centre of gravity is right in the middle where you would expect it to be, unlike the gearbox where its just behind the driveshaft flanges. This makes it very tricky to manuever in to place, whereas with the engine on a balance beam its much easier to wiggle that in to position.

[Spannerrash]

Thanks for the info MJ.

Yeah I was planning on dropping the subframe complete with engine and gearbox. I'm in no rush so I can remove bits that wouldn't ordinarily need removing in order to make the job easier.

I have a transco valve but haven't decided if to use it or not. I had an email conversation with Natt Wentworth at Ericssons in the US and he seems a bit 50/50 on Wether I should us it or fit a brand new valve body which I have.

I am not planning on doing anything with the car this year. I have allot of other projects on the house I need to prioritise if I want to remain in a stable relationship. As said previously, I also want to see what direction the classic car market is heading in.

It may seem dumb to some but as long as I have the parts she will always be repairable and if I don't use them, there will always be some value that I can claw back out of them.

I am an electro mechanical engineer by trade so I believe I have the skills to do the job myself and really want to but at 59 years old, I'm not sure my back will thank me for it. It may be that in the end I get the car and my spare parts transported up to Mackies. With genuine Jf parts already paid for, maybe they'll do it for somewhere in the 4k range.

I'll keep you all posted but it will ultimately depend on where the market goes.

[Spannerrash]

A couple of typos. Transgo and Zf. What a dummy. That will teach me to preview before posting in the future.

[Ronin]

I would really like this documented on the forums if you're going to DIY it.
A handful of owners work on their D2's, and pretty much no one does this level of work on their drive.

[Spannerrash]

If I end up doing it myself on the drive I will absolutely document and post. I'm sure I will need the support and encouragement.

I would like to do it as a "WITW" kind of thing as really enjoyed reading MJ"s. Weekly or monthly updates maybe.

It will be a while off yet but I will keep you all updated whatever my decision. It's the financial viability that is really bothering me at the moment so essentially it makes more sense to have a go myself.

[Spannerrash]

Sorry guy's but I just thought of something else I would like your opinions on. It may have an impact on my financial calculations.

I roughly value my car with a fully working gearbox at about 6k. Would this same car sell for a higher premium if it had evidence of a full mackies gearbox rebuild with receipts?

Bear in mind that mackies now only give a 12 month warranty. To be honest I found that a little disappointing. Why would a company need to reduce the warranty period? My only assumption has to be that they were getting too many warranty claims. If nothing else it's not a good look.

[Ronin]

If you're definitely selling it, a piece of paper from Mackie's is a way to go.
If you're going to keep it, I would do it all properly yourself.

[MikkiJayne]

Wether I should us it or fit a brand new valve body which I have.

I'd put it in the new valve body. Best of both worlds then - you solve any other VB-related things, and the pressure valve will never wear out.

I also want to see what direction the classic car market is heading in.

I have a feeling D2s will always be 'rare but no one cares' because of complexity and lack of parts. Look at the E39 M5 now - you could buy at least two very nice S8s for the price of an M5 because BMW look after their classics. Maybe when we're down to a handful they will become worth something like the Ur-q and the V8. Not betting my pension on it though!

I spend what my D2 needs (and then some!) because I love it and will never sell it. I'll never ever get that back.

[Spannerrash]

It really is a tough call. It seems I am not as connected to my car as some of you guys are to yours. I need to remind myself that I was about to sell the car because of becoming frustrated with the whole NLA fiasco. There is absolutely no point in even rebuilding it myself if I then sell it shortly after.

If I spend 3k to do it myself, I still have a car only worth about 6k. So only a net gain of 3k. I could gain that same 3k over time by simply stripping and selling the car for parts. I would then still have all the gearbox parts to sell on.

It is also a major indicator for me that I am even thinking this way. Logically and financially. To think this way is trying to be practical about something that is purely emotional.

That said, we all have hobbies, usually spend lot of money on our hobbies and mine is working on the car.

It's a dilemma that I am going to have to wrap my head around. As you can see, I flip flop from day to day.

For now, other stuff to do.