[DML] Re: Improved Automatic Transmission Computer (Long)
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[DML] Re: Improved Automatic Transmission Computer (Long)



 
 
Steve,
 
Great timing.  I was thinking of the same question.  I know I  read about 
someone discussing a digitally controlled Automatic Transmission  Computer (ATC) 
using a PIC computer.  Somehow I think that is overkill, but  maybe its just 
that I'm an analog kind of guy, though.  I have been  frustrated with my ATC's 
intermittent shifting (or not shifting)  problem.  I think I did finally get 
it fixed though. 
 
I previously moved the ATC to the left hand side of the engine  compartment 
the first time I took it out because I did not want to have to keep  crawling 
under the car each time I needed to look at it.  Of course I  believe that in 
reality, IT was never bad in the first place and only started  going bad after 
I fooled with it, which I did because of what I thought was a  weird 
"shifting" problem.  
 
Sometimes, when I am in third gear at medium throttle and medium load and  
"give it more gas" the tranny slips so badly its as if it has been put into  
neutral. I come off the gas and it catches right away.  It does really  happen 
often, especially not that I know how to prevent it.  (To Dave T,  yes I finally 
bought a tranny pressure gauge but of course haven't used it  yet.)   I 
originally thought that it was down shifting into first  instead of second.  A set 
of transmission solenoid LEDs (courtesy of Dave  T's help) proved that that 
was not the problem.  But by that time the ATC  was already out and opened up.  
After not finding the typical blown  capacitors I decide to move it to a more 
easily accessed site because I just  knew I'd be in it again.
 
I did this by carefully desoldering the three wire that connect the boards  
to the generator.  I soldered a shielded two conductor cable to the  generator, 
and filled the rest of the case that housed the boards with silicone  rubber. 
 You can then loosen and reroute the original black cable that  still goes to 
the boards, along with your new shielded cable, back over the  tranny and 
into the engine compartment.  Make sure you use cable ties to  keep the wires 
away from the hot exhaust and any moving parts.
 
Using Dr Dave's theory that when ever something is not working, look at the  
last thing you screwed around with...  The boards seems rather sensitive  
mechanically especially the ribbon cable that connects the two together.   That 
was the first to break.  I found a number of bad solder joints, which  by the 
way looked fine even under a 10x loupe. Originally I did my testing  with the 
car on jack stands so the wheels were off the ground.  I think  this lead to the 
premature failure of my new CV boots so I don't recommend  it.  More recent 
testing was done with the car engine off using a  variable voltage source made 
from a 9 volt battery across a 100K - 10 turn  potentiometer.  This provides a 
0 to 9 volt variable voltage that is easily  adjusted. I connected this to 
the point where the two input diode connect  together.  Of course you'll need 
the schematic to help troubleshoot.   I found that the 1st to 2nd up shift 
occurred at ~ 3.8 volts, 2nd to 3rd up  shift at 7.4 volts.  3rd to 2nd down shift 
at 5.37 volts and 2nd to 1st  downshift at 3.7 volts (which seems a bit too 
close to the up shift  voltage.)
 
Using this method I found that touching or twisting the board would cause  it 
to shift. I also found that the circuit is very sensitive to being shorted by 
 the minute electricity conducted though my fingers and hands so I ended up  
holding the board with a pair of plastic forceps and applying pressure to test 
 for intermittent areas with another plastic probe.  I found several areas  
that seemed to be the most sensitive to touch and position and resoldered all  
the joints in those areas.  Again, the joints looked fine visually.   Also I 
could not seem to get the coating off the boards prior to resoldering so  that 
made it a bit difficult.  I used lacquer thinner but it didn't  work.
 
If I had to make a new ATC I think it would be similar to the one already  in 
place, that is analog.  I would make it on one board so as to eliminate  the 
ribbon cable and I would add protection diodes and bypass / filter caps to  
the IC power as others have recommended in the past.  Shifting could be  
adjusted by fine tuning the comparator resistors.  Not being all that  familiar with 
digital PICs this would be the easiest for me.
 
All comments and suggestions welcome. 
 
Happy New Year!
 
D² & 6530
Dave Delman
 
 
 



Message:  4         
Date: Sat, 31 Dec 2005  05:47:03 -0000
From: "Steve"  <p2freak@xxxxxxxxx>
Subject: Improved Automatic Transmission  Computer

Group,

I've just finished rebuilding the AC mode switch  and tackling the next
item on the work list.

Is there an improved  automatic transmission computer one can purchase
or build?  The  archives indicate some people have taken the computer
out of the  transmission housing and installed it in the engine bay. 
How is it  accomplished?

Please e-mail me off the list if you have a broken  computer that can
be  rebuilt.

Thanks.



Steve
VIN#0442




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