Re: [DML] More on Auto Transmission and the Transmission Governor

["Mark Hershey" <dmcinfo@xxxx>]

Sorry, Bob. Your info on the ZF4 is both interesting and entirely correct;
I just didn't read your post carefully. Have had lots of private E-mails on
A/T and other "D"questions and have had to skim 'em all a little; I've
probably been more confusing than helpful in answering their questions :-(

And many thanks to all of you who have written such kinds words thanking me
for this info. Some of you don't even have auto transmissions! This DML list
has helped me countless times and I can finally say I've at least partly
returned the favor.

Like Bob said... I, too, would like to know what components have actually
failed in the field. About half convinced that really poor factory solder
jobs account for more intermittent failures than anything else. And there
seems to be more intermittent failures than firm ones, judging from
feedback. Perhaps we should do an Egroups survey and see what symptoms are
reported. Might get a few new clues....

My sample of five or so is statistically way too small to draw any
conclusions. Interestingly, I haven't seen any comparitor chips fail yet,
although I expected to from the design. So far only electrolytic capacitors
(all five governors, 10 capacitors total) and driver transistors (three out
of 10) have actually failed. All 10 capacitors failed Open, so the governor
continued working fine under normal conditions but events like cooling fans
coming on or locking the doors while driving would introduce transients and
the comparators would sometimes (but not always) get confused. In one
reported case cooling fans would come on and sometimes the car would
downshift to Second, then upshift again just fine a couple seconds later!
Other than caps and drivers, a resistor that controls downshift seems to be
under rated; two were cracked and one showed signs of overheating. General
flakey operation seems improved by adding bypass caps (a parts addition,
technically not a failure).

The governor is, as you say, quite simple and with a very few changes could,
I think, be made reliable. Keeping my fingers crossed on my most recent
mods; so far (about 10 days), so good. Getting hot here in Dallas so we'll
be doing a little stress testing. :-)

I wish I had the time to do a micro controller....a PIC micro and a small
a/d convertor connected to the existing governor's "alternator" could do it;
just don't have the time to do the firmware. The hysteresis loop would be
the only tricky part of the programming---the speed/throttle position
voltage the causes the comparaters to drop out a solenoid to upshift is
higher than the voltage that causes the comparator to release the same
solenoid. You sure don't want the transmission chattering in confusion right
at the voltage threshold point! You can see this on the D(with a working
Governor) by letting the car coast and noting the vehicle speed at point of
downshift is considerably less than the upshift speed. Guess the Micro could
be programmed to keep track of rate-of-rise / fall rate and set a
acceleration / deceleration flag or something to help determine when to
energize/de-energize the solenoids. Oh, well, reckon this isn't the place to
go designing a replacement... but hey, it would be cool to program your own
personal upshift/downshift curve with a laptop in your front seat...

\\ Mark

----- Original Message -----
From: Bob Brandys <oehcs@xxxx>
To: <dmcnews@xxxxxxxxxxx>
Sent: Tuesday, July 04, 2000 9:21 AM
Subject: Re: [DML] More on Auto Transmission and the Transmission Governor


> You are correct about the Ds trans computer.
>
> I compared its design to that of the the ZF4.Bosch computer. I really
like the
> Ds design because of its simplicity.