<VV> First extended drive -PG shift harshness issues

[FrankCB at aol.com]

Stephen,
    While all that Seth states is quite true (as  always), I'll bet that the 
problem is the leaky short rubber hose connector  leading from the metal pipe 
directly to the connector end of the vacuum  modulator.  This is underneath 
the car where it has been exposed to all  sorts of leaky oil, road debris and 
who knows what else!  So if it were me,  I'd check that FIRST for leaks and 
deterioration.  If that is NOT the  problem, then go on to the other items that 
Seth mentions.
    Frank "been there, done that" Burkhard
 
In a message dated 7/6/2007 11:18:58 AM Eastern Daylight Time,  
Sethracer at aol.com writes:

In a  message dated 7/6/2007 6:41:55 A.M. Pacific Daylight Time,   
contactsmu at sbcglobal.net writes:

Oh, I  forgot one  thing.  As I come to a stop, the PG downshifts like   
a  horse is kicking the back of the car, but not every time (70% of    
the time?).  Ideas?


Stephen - I don't know how much you  know about the PG. The 2-speed has to  
upshift and downshift under  differing loads. A full-out sprint onto the 
highway  
means a hard  upshift under full throttle at about 45mph. A smooth drive up 
to 
35   will require a soft shift at 18-20 mph. The way the trans knows how hard 
 
to  shift is the vacuum modulator. It adjusts the shift hardness  depending 
on 
how  much vacuum is present in the engine intake. A high  vacuum, like a soft 
throttle  during a slow acceleration, causes a  soft, slow shift. Stomp the 
throttle and  vacuum drops like a rock.  As the engine accelerates, vacuum 
remains 
low and a  hard shift is  specified. So a leak somewhere in the line from the 
metal  cross-over  tube (the vacuum source for the modulator) to the 
transmission   modulator will cause the modulator to think a low vacuum 
condition exists  
in the  intake and a hard shift is needed. This occurs in either  upshifts or 
downshifts.  In your case, the PG thinks you have  "kicked-down" the trans 
into 
Low gear to  accelerate - hence the hard  downshift. From the metal 
cross-over 
tube (which can  also leak at  the carb bases where there are two short hoses 
providing the seal)   to the bent metal tube that runs into the transmission 
area 
and the hose  onto  the modulator itself,  you have to check hoses and  
connections. Since they  are vacuum connections, Chevy thought they  would 
never be 
subjected to anything  BUT vacuum, so no clamps were  installed. Of course, 
it is 
possible that the  modulator itself has  failed, but they are pretty 
reliable. 
The more common  failure mode  is for the modulator to fail internally and 
let 
ATF be sucked  into  the engine. That results in pinging, because of the low 
octane of the  ATF  and smoke out the exhaust.  Another piece of good news is 
 
that they are  quite easy to replace. So check all your connections  first, 
then 
make sure that  the throttle linkage is in proper  alignment as it connects 
through the  throttle bellcrank on the  trans. Then, if it persists, try 
swapping 
the  modulator out with a  known-good unit. If the problem goes away, you may 
 
want to put a  brand-new unit in. -  Seth Emerson 







************************************** See what's free at http://www.aol.com.