Squeeto

I have put this off for too long. We need a fix for the dreaded thump and hunt issues we have with our transmissions.

This is my theory:

The thump when decelerating:
due to too much slip and sudden torque converter (clutch) dropout and engage

The reason:
Everything is wearing normally but the transmission pump is now not able to maintain
enough pressure to keep up with all the blow by in the tranny and valve body.
We should expect to get more time with the current wear though.
The TCU is doing everything it supposed to lock the TCC, but the VB responds too slow.

The fix idea:
mod the valve body to make the TC respond quicker for lockup
-this reduces the slip
note: increasing the pressure is not a good idea, high line pressure exists already

The hunt:
hunt is the huge excursions out of the 0 to 128 specified slip range
-PWM N218, ESD-4 solenoid is told to lock
-system oscillates
the valve mod helps this too
tps mod cures this (hopefully)
-I will post the throttle position sensor mod that I did in a later post.

The valve body mod:
provide faster application of oil flow to lock clutch and possibly provide better back draining
see following pics for details

<img src="http://pictureposter.audiworld.com/125817/tcc.jpg">
<img src="http://pictureposter.audiworld.com/125817/vb.jpg">

Opinions please.

Squeeto

Yes, but that is proprietary information.

CalG

I like your initiative!

The fluid restictors are just small plastic buttons, color coded to indicate passage (orifice) diameter. I am sure that a ZF repair facility would be able to supply any combination of elements, not only the ones that come in the VB rebuild kit.

Presently, I have the VB out of my 99 on the work bench. Lot's of little pieces. And since the casting is cracked, Your observation that more pressure is not a good thing, plays out. More pressure= more cracked castings.

IF I had a copy of the VB repair manual from ZF, I might reassemble this VB with "oversized" orifice buttons. But....without comprehensive information, I feel that I would be guessing about what did what, and went where.

I would not mind at all if the transmission fault and fix would come out of the closet. It's just parts for pete's sake!

Regards

Cal

Squeeto

I see that there are 5 orifice sizes.

ZF Part #1056 327 019 Valve Orifice D=1.0
etc. D=1.2
etc. D=1.4
D=1.5
and D=2.2

If that one orifice (that I show in the picture) feeding the WK-V valve is say D=1.2, it could be replaced with a 1.4 or 1.5 from a new kit or left overs from a rebuild.

I tried the one shop in town that repairs Audi/BMW/MB transmissions and they wouldn't give or save any throw aways for me.

Bangerla

Maybe I was lucky, I changed the fluid on mine and the hunting went away. While I was changing the fluid and filter, I decided to re-torque all of the valve body screws to their specified value. I found quite a few that we looser than they should be. Not sure if this is contributing to the hunting or not.

Squeeto

I have researched a fair amount of information on these transmissions and this is the first time I have heard this. Great thing to look out for! Yes this can account for pressure loss which is directly related to hunting.

Thanks

CalG

The cracked Upper VB casting may be more than an isolated instance.

Recall Notice! ANyone droping the VB should check for failed castings.

'makes me want to pull the "new" VB and have a look.

I need to replace the trans output seal anyway, just maybe...just maybe.

Regards

Cal

Squeeto

This would be much more expensive to replace than plastic buttons or springs.
A good check to make though; added to the list.