Final drive fluid test?

[Doyt W. Echelberger]

Thanks for the reply, Dave.  That supports a post I found in the archives 
from August 8,1995, which I will copy to you (below). The author (German) 
suggests one way that the fluids might mix.  I'm going to look at the car 
today. I'll get under it and see if I can pinpoint the source of the drip. 
Thank you.  Doyt

In a message dated 95-08-25 17:40:45 EDT, quattro at vulcan.gep.ge.com (Vikram 
Mittal) writes: >Does someone have a cross-sectional diagram of the 
autobox-differential. >I would like to put an end to all this speculation. 
I have heard that >it is not possible for the fluids to mix and the 
reverse. One mechanic >told me that there are common seals between the 
tranny and differential. >Therefore there is pressure exerted on them from 
both sides and that is >what causes the failure. Now I'm not at all sure if 
this is true or not. > > I think if you look at 38.2 and 38.3 of Bentleys 
('84 -'88 5000) You will note that there is a gasket and separation plate 
for the transmission; and a separate rear cover plate with Pinion oil seals 
for the Automatic differential (final drive).

In addition there is a "weep" hole in the bottom of where the components 
mate. (I would assume it is there to warn a person that one of the seals 
has gone bad. I would think the only way possible that the two fluids could 
mix is if the weep hole clogged and both seals went bad allowing what could 
be coined as "Audi osmosis" of the fluids.

Seems highly unlikely to me. Before I made a fool of myself posting this, I 
called an Audi specialist who has been instrumental in many Audi designs 
and engineering, and he confirmed my analysis. Bottom line, mix or no mix, 
the engineering is obviously flawed. ---peter Audionly


 >>>>>>>>>>>>>>>>>>
At 10:05 AM 12/21/2003 -0500, you wrote:
>Doyt,
>I own two cars with A/T and have made a bit of a study of the "ATF in final
>drive" subject.  Both my cars have about 150k miles on them and still have
>their original transmissions ... both are non-turbo.
>
>Some people say there is no physical way for the fluid swap between AT/diff
>to happen.  Based on what I know of their construction I suspect this is
>true, although I have not dissasembled these units myself.  They are two
>separate units... there is no seal with ATF on one side and diff fluid on
>the other.  The actual problem is fluid loss. Maybe thru evaporation?  Low
>fluid is what kills the differential.  Incorrect fluid level will also kill
>an AT.
>
>The most common leak in the AT would be around the 3 inch round cover on
>the passengers side of the transmission held in with a big circlip.  This
>is the 2nd gear brake band piston cover.  It is sealed with an O-ring and
>the heat of the exhaust hardens the o-ring over time. The piston assembly
>can be removed and the O-ring replaced. It's best to replace the piston
>seals at the same time since they are rubber and harden also. If the piston
>seals have hardened they can affect the shifting, pressure is lost past the
>seals.  This can be done with the trans in the car on the type 44's.  I've
>had this leak in both of my cars and did the seal replacement myself.
>
>If I needed to replace an AT or diff I would look seriously at a used one
>or else ship it out to the rebuilder in Florida recommended by Dave Head
>... assuming he's still in business.  I'd sooner pay the shipping cost than
>take a chance on anyone locally ... this is after asking around and not
>finding anyone who would recommend a rebuilder in Central OH.
>
>If anyone knows of an actual incident where ATF leaked into the final drive
>(or the reverse) I'd like to know about it.
>----------------
>Dave C.