hillpc

From another post by me at https://www.audiworld.com/forums/a8-...2891020/page2/


Eriksson said they could send me a replacement upper valve body already welded, but we couldn't be sure about the part numbers, so I sent them mine and they welded it. $135. 1 day turnaround. Nat Wentworth there said they had done quite a few of these. (I was initially thinking JB Weld, too, but didn't trust it with all the heating up and cooling down, plus my doubts about being able to get the valve body clean enough for it to stick.)

He also told me that the plastic manual valve has been known to absorb water (?) and swell, making it stick in the bore. So I bought an upgraded manual valve (metal) from him for $15. Also bought a replacement valve body he'd reamed out and installed an upgraded Sonnax pressure regulator valve in, $125. (I understand this fixes a common issue with breaking the A clutch drum when the regulator sticks in the bore and can't relieve the pressure generated by the pump during a higher rpm blast.)

Also in that thread, tozoM8 says
If there is a crack it will be 2 inches long pouring fluid. You will not be able to Fill the trans if there is a complete crack.

I do have a slight thunk on what seems to be a 2-1 downshift when slowing down for a stop. I have no idea what this is related to.

jfrahm

Eriksson now has that upper VB, the one that cracks. They can supply it new for about that price, shipped which would reduce downtime.
It's good to hear that the crack would have made it hard for me to fill the trans, I suppose it causes so much agitation that fluid comes out well before the trans is full or something. The crack-pouring-fluid Gary said causes low speed problems.

The rough downshift when coming to a stop was one of the things the TransGo valve fixed in both my cars and the Sonnax valve should have fixed in yours IMO but maybe you have another issue, you could consider replacing the lower VB as I did so you get new bores for all those valves. You'd need a TransGo valve as the Sonnax won't fit the new un-reamed-oversize pressure control valve bore.

I am curious about the plastic manual valve, I have not been far enough into the trans to see this guy, hopefully that'll continue :-)
There may be some value in just replacing the whole VB when shifting is strange but the trans has not physically broken anything yet or maybe doing the TransGo valve first since it is cheap and easy particularly if you are replacing some fluid and the filter.

Tozo had some great info and pics regarding fluid and filter changes also and how the new fluid and filter can cause a slug of crud to block passages in the valve body, this suggests not changing the fluid or not much of it on older cars with a lot of crud in the trans pan to avoid causing a new problem. Taking the whole VB out for cleaning might also be a sensible step at the TransGo valve stage if things look bad in there. In my case, having cars where the fluid had been addressed with partial changes over time (S8 probably flushed via the cooler lines before I bought it) they were pretty clean inside and the valve bodies were pretty clean from what I saw. No shavings or anything with a part number on it stuck to the magnets, just metallic paste and the like and clearly I was the first one to have those trans pans off.

jfrahm

I've always used Red Lubeguard based on a long-ago recommendation on this forum. I have no idea if it helps but my 190K A8 trans is still working great (with the TransGo valve since 165K). The Lubeguard has beein in since 90-100K.

Shifting was getting weird at 150K or so, rough downshifts when coming to a stop and some slow 3-4 upshifts, other unusual shift feelings from time to time. At 165K, after I'd already bought an S8 thinking the A8 trans was going to fail, I found out about the TransGo valve and it fixed the A8 right up.

My 2003 S8 seemed to have more valve body wear at under 110K than the A8 did at 165K. That could have been the Lubeguard or maybe the S8 sat in traffic a lot. Or maybe the S8 trans works the valve more, I do not know.