5hp24A preventative / planned maintenance advice
 

Hello all from the UK, this is my first post on this forum.

I own a 2002 D2 S8, engine code AVP, gearbox code FBG. Car has done 87000 mls.

I have owned the above car for aprox 18 months and have spent most of that time doing some much needed repair / maintenance work. Timing belt, timing chains and adjusters, oil cooler plastic pipe, gearbox output shaft oil seal, transmission oil and filter change plus plenty of other stuff, I am now looking at preparing for some preventative work on the transmission. I consider myself to be quite a reasonable diy mechanic but am limited by access to equipment. I do all of my repairs outside on the drive (so am limited to summer working) and only have access to jacks / axle stands for getting under the vehicle.

The gearbox has no perceptible issues at the moment, everything seems good. What I am looking at is how to keep it that way for as long as possible.

Do I?

1. Just do regular transmission fluid and filter changes and leave the box to do what it is going to do?

2. I have a new "front lower" valve block assembly which Nat Wentworth (Eriksson industries) put together for me. This is a mixture of new and used parts but importantly the block itself and the pressure regulating valve are new. I am hoping fitting this will prevent or at least delay the pressure spike problem which then damages the A clutch drum. That said, there seems to be an opinion that facelift models don't suffer from this problem. They suffer other problems but not this one. Is that correct? any opinions much appreciated.

3. A much more expensive preventative procedure and one I would not be able to do myself.
Having the gearbox removed and replacing the thrust roller bearing that fails behind the oil pump. Opinion seems to be that this is a week link and if / when it fails will lead to a cascade of other failures. Clearly the expense of removing the gearbox may mean that it;s more cost effective to just wait for the gearbox to fail and then do a full refurb at the same time. Again, any thoughts and opinions much appreciated.

Thanks Frank

The impressions of a guy who's had FIVE of these gearboxes need to be rebuilt?

The FL and PFL cars both lose transmissions at roughly the same rate. They just have different failure modes... Hunt-and-thump is mainly a PFL issue.
However, the A-baskets and the "reverse" assembly both had material-design flaws throughout the run... and both those flaws are made worse by the pressure-spike issue which was present throughout. I have had more FL cars with bad transmissions than PFL.

If you have a "cherry" FL car, I'd think the "pressure moderator" fix to the valve body/regulator is well worth doing. It's your best hope. If you are using approved fluid I don't think "more frequent" flushes help much. The thing that breaks isn't the fluid-- it's the basket mechanisms. The bad fluid is a symptom, not a cause.

Just one guy's opinion.

Thanks Oxnardo ting

All advice is much appreciated.

Sorry
Oxnardo Ring (ting typo).

No. I have put the updated valve into both my facelift D2s, 2001 and 2003 and both really needed it. The 2003 S8 at 107K miles had such valve body wear that I replaced the lower VB casting. Maybe it sat in traffic, stop-and-go-ing a lot or something, the 17k mile VB was worn worse on it than the 2001 A8 at 165K. I'd used a trans additive in the A8 but I do not think it had anything in it to reduce the steel-on-aluminum wear in that pressure regulator bore.

In both cars, spooky shifting, harsh downshifting and even a couple freewheel-bang events went away once the pressure regulators were updated.

I prefer the TransGo valve to the re-bored and oversized valve option because I think the scarf seals protect the bore, but it should not matter much over 50K miles or so. Once the valve body is reamed oversize the transgo valve is no longer an option. But you already have this part. If it's got an oversized main pressure valve in it, I'd install it as-is. If not I'd get the TransGo valve and install that before putting it in the car.

Cheers,
-Joel.

Hi Joel, thanks for your reply.

The valve body I am planning on installing is a brand new casting with the updated (slightly longer I believe) pressure regulator valve, a genuine ZF part.

I did consider taking this valve out and fitting a transco valve. I kind of moved away from this as I thought the transco is more designed to take up some of the wear in a used casting. Ideal really for updating your original casting if you were re-useing it.

As mine will be brand new I thought the genuine update would be a better option. What do you think?

More than happy to fit a Transco if there is a benefit.

That was the situation on my 2003 S8, I put the TransGo valve into the OEM valve body but felt the valve body was excessively worn and that bugged me, so I took it apart again, replaced the valve body with a new casting and put the TransGo valve into that. As I said I think the scarf seals will reduce wear on the aluminum bore. Maybe not, if the new ZF valve has some oil grooves it might be all the same. I actually added some oil grooves to my TransGo but that is because I own a lathe and can't keep my hands off of it. If your target is 50K miles you probably won't see a difference between the two, or maybe the updated ZF part also prevents wear as well as the TransGo.

Since it is a $4K or more trans replacement I felt some suffering and $200 was well spent to make the trans as solid as I felt I could. I was lucky to have attended to it before it blew itself apart.

Thanks jfrahm, information much appreciated.

Basket design flaw
 

Here's a recent pic of a transmission Gabor just finished for me from a 2000 A8 SWB.
This shows the fracture zone along the stress line on the A Basket. The newer replacement design has a lot more material in this area to eliminate this design weakness.
https://cimg9.ibsrv.net/gimg/www.aud...ddddd607c0.png

Thanks for the picture. This is exactly what I am trying to avoid.

On a more general note, when this happens it's clearly a gearbox rebuild job but does it cause any other damage? I.e. will the cooler get contaminated with debris etc?