Re: Auto Transmission Governor Secrets Revealed...(long post)

["jtrealty@xxxx " <jtrealty@xxxx>]

I would like to add that I had trouble with my automatic too. I was 
driving and the car started slipping and wouldn't move in foward or 
reverse. Before that the car was acting funny about shifting but 
nothing I could put my finger on. Upon removing and dissasembling the 
trans I discovered c-1 and c-2 frictions wiped out and the steels 
burnt. The filter was clogged.I cut open the filter and discovered 
that the mesh and the support baffle was assembled in reverse causing 
the pump to be starved for fluid and causing the line pressure to be 
lowered. With the low line pressure the clutches slipped and burnt.
After rebuilding the trans I was able to fully apreciate an
underlying 
shifting problem with the shift computer. After replacing the vacum 
modulater, adjusting the line pressure, adjusting the cable to the 
shift compter,and adjusting the micro switch I gave up and bought a 
"new" shift computer. It seems to have cured the shift problems. I 
have an old shift computer I diseccted ie: I cut up the cables, the 
multi switch and the plug.I can send You the diagrams I made of the 
wiring connections and I am trying to build a test stand to test and 
troubleshoot shift compuers.I am also trying to get the documentation 
that Chrysler Corp had when they used the shift computer in one of 
their imports.I agree that we need a Transzilla but short of that 
there are some things that can be done to improve the shift computer. 
If anyone else on the list has anything to contribute to this effort 
please respond and maybe we can fix this source of problems once and 
for all with an upgrade or patch for all of the unlucky owners of 
automatic transmissions. It's not a matter of if your shift computer 
will fail but when.
David Teitelbaum
Vin 10757
2nd place winner 2000 concours 


n dmcnews@xxxxxxxxxxx, "Mark Hershey" <dmcinfo@xxxx> wrote:
> OK, maybe not everything we'd like to know. But as promised awhile 
back,
> here's enough to explain
> some strange auto transmission symptoms and get started on the
story 
in
> detail.
> 
> First, I'd like to thank Dave Santos and others who have
contributed 
bits
> and pieces of knowledge, experiences, and spare parts to my What 
Makes the
> Governor Computer Tick and Why Most Eventually Fail project.
> 
> Over the years I have experienced multiple failures of the GC and 
have
> gained considerably more experience with them than I intended. Been
> able to repair my own, but experiences reported by other owners 
revealed a
> variety of failures, only some of which I saw on mine.
> 
> To determine what was going on I reverse engineered the mis-named 
"computer"
> and made my D into a test fixture for several possible circuit 
changes. I'm
> working on a comprehensive document but for now here's some of the
> results. I'll also report perodically on how well some changes work 
after
> they
> have more time and miles on them.
> 
> Here is some key info for the technically inclined among us. I'll 
try to get
> schematics and pictures up on
> a forthcoming Web page after I get 'em cleaned up.
> 
> 
> Missing parts:
> Good Engineering practice dictates some preventatve measures that 
simply are
> not included in the original design. I'll describe a few examples, 
but first
> it may help to understand a bit about how the GC works.
> 
> The GC works by comparing a variable voltage derived from a small 
alternator
> attached to the transmission (and reduced by advancing the throttle
> position) to a constant 7-volt source derived from the battery with 
a
> voltage regulator device called a Zener diode. When the variable
> speed/throttle position voltage equals the 7 volt constant voltage, 
the
> first transmission control solenoid valve drops out and the 
transmission
> shifts from 1st to 2nd. Similarly, when the variable voltage 
continues to
> climb to a specific point (about 9.5 volts), the second solenoid 
drops out
> and the transmission shifts to 3rd. All this depends on keeping the 
7-volt
> reference at 7 volts no matter what-- and in a hostile electrical
> environment, that can be difficult. The cheap Zener diode circuit 
used in
> the GC is a typical design, and it appears adequate so far.
However, 
Zeners
> can be forced out of their Zener regulation "knee" by large spikes 
and
> transients. Though they rarely fail with permanent damage the 
circuit can
> behave erratically. Expected symptoms:if your transmission goes 
flakey
> (downshifts erraticlly, refuses to upshift) BUT you can immediately 
stop,
> shut off the ignition, restart the car, and everything is OK for 
days and
> weeks at a time this circuit is a likely culprit. I'm interested in 
feedback
> if that happens to any of you; if so I'll test a design with a 
better
> regulator. For now I'm leaving that as is.
> 
> The main "computer" devices are two integrated circuits technically
> referrred to as op amps configured as voltage comparators. These 
particular
> Siemens Corp. chips are long unavailable but rarely fail. The 
circuit they
> are used in is extremely sensitive; even condensation on the board 
will
> cause the circuit to function improperly. Holding your thumb on the 
board
> while driving around (don't try that one yourself)will even cause
it 
to
> fail! This was the core of my research since the most common GC 
failure
> symptoms are caused by this circuit, that being the car randomly 
downshifts
> from third to second with no cause/effect pattern other than perhaps
> relative humidity. Reason for such instability: two things...First, 
there
> are two electrolytic capacitors ("caps") on the GC board that, when 
new,
> help filter out transient variations (electrical noise)from the car 
battery.
> These caps nearly always fail, just time and transmission heat will 
kill
> 'em. Every single GC I've looked at (5 years or older)had bad caps. 
That in
> itself would be OK, except the comparators depend on a good, clean 
reference
> voltage and without these caps they are less likely to get it. The 
fix:
> replace the caps with more rugged parts (I used tantalum caps seven 
years
> ago, still OK)AND add .1 microfarad bypass caps across pins 1 and 4 
(supply
> and ground)of each of the comparator chips. Yes, all you incredulous
> engineers out there, the Renault designers actually left out the IC 
bypass
> caps!Amazing...Anyway I added these last week so time will tell if 
they
> reduce instability long term. I can, at least, handle the board
live 
on
> rainy days without downshifting :-)
> 
> Also for you engineers, they left out antispiking diodes in the 
solenoid
> driver circuit-- an invitation to intermittent / erratic operation. 
Add
> reverse biased 1n4007's (radio shack)across the transistor output 
leads.
> 
> The number one problem I saw on examination was poor solder joints! 
All
> seven units I have examined (two mine, one Dave's, and various 
Dallas
> friends over the years)had really bad solder job all over the
board. 
Worst
> problem is where the 8-wire cable attached to the two boards and 
where the
> six-wire inter-board jumper cable solders on to both boards.Can't 
stress
> enough how removing the red conformal coating (I used lacquer 
thinner),
> generously fluxing the board, and resoldering everything can help. 
Certain
> it causes many of the intermittent problems.
> 
> Drive Transistors:
> The two transistors that drive the solenoids are RCA units long out 
of
> production. Although they only fail ocassionally, they can be 
replaced with
> a more rugged TIP42 or TIP42C part from Motorola. TIP42Cs can still 
be found
> in some Radio Shack stores and are available from Radio Shack's 
online
> store. Symptoms:car starts out in second gear but shifts OK to 
third, or car
> starts out in 3rd and stays. Note that a blown A/T fuse can also 
cause it
> start and stay in 3rd. Generally these transistors don't fail
> intermittently, so if your car sometimes shifts OK but gets screwy 
on
> occasion, this ain't it.
> 
> Multiple switch
> The multiple or "combination" switch controls backup lights and 1st 
gear
> hold when you move the lever to "1". The switch rarely fails, and 
isn't
> repairable in any case. Just make sure the retainer screw that
holds 
it to
> the transmission case is firmly in place. I'll offer more detail on 
this
> switch's complete function later.
> 
> Well, enough for now...I'll try to write up a more coherent 
description with
> pictures for download. Perhaps Mr. Zilla could be persuaded to offer
> TransZillas with various design improvements. I'd like to see 
someone
> replace the whole circuit board set with an A/D converter driving a 
PIC
> microprocessor and let you adjust shift performance curve via a 
Laptop
> serial port connection. Wouldn't be all that hard to do...
> 
> Bye!
> \\ Mark Hershey
> Vin 2790,now full-time automatic (so far)