Re: TCC lockup on 700R4

[Dig <turbodig@yahoo.com>]

> > My VN Commodore 3.8 V6 has a "Turbo Hydra-Matic
> 700R4" and has just
> > one ECM connection - the TCC Solenoid (I'm sure
> this isn't news to most
> > list members ;-) I had to look at my manual!...
> >
> > My wife mostly drives the VN to work in light
> traffic. I only get to drive
> it
> > when it's playing up, or on a long trip. Last
> weekend the car (apparently)
> > had a problem with unlocking the TCC. When doing
> constant freeway speed
> (say
> > ~ 70 mph) and coming to a hill, there would be a
> point when you'd expect
> > the TCC to unlock to get a few more revs (and
> torque) to make it up the
> > hill. 

Not necessarily... depends a lot on how you have 
the ECM calibrated, as well as valve body calibration.

At this point the transmission seemed to try
> to unlock and
> immediately
> > lock up again, causing an oscillation at about 3-5
> Hz - only cure was to
> change
> > back to 3rd (from OD to D on shifter) until over
> the hill!

You sure this was lock/unlock, or was it just 3-4-3
shuttle? Only way to know for sure would be to watch
the TCC line with a scan tool. (or am I just slow,
and you were doing that?)


> > I swapped the ECU and this didn't make any
> difference - haven't had time
> to
> > check anything else (wife has car!). I'll
> swap/check the TCC solenoid
> tonight:
> >
> > It seems like the TCC solenoid may be pulling in
> and then almost
> immediately
> > letting go - is this common, or do I have a
> hydraulic (ie. auto trans)
> fault?

Well, after 5 700R4s in the Sy, I have yet to kill
a TCC solenoid. :(

It's more likely 3-4 shuttle, rather than TCC lock/
unlock... it's a fairly common mode of failure in
a 700R4. *If* they consider it a failure, that is-
I've had GM garages try to tell me "It's supposed to 
do that". Sigh. That was trans #4.

A good valve-body kit can sometimes remedy the
problem.
I'm not sure what you have available on the other side
of the puddle, so I really can't make a recommendation
on a brand (Trans-Go and Superior are good over here).

Pull the TCC plug from the trans; see if the problem
remains. If it goes away, your problem may simply
be a thermostat running too cool.

I actually saw this on a buddie's Typhoon recently.
He's running a 180 degree thermo with a custom 3Bar
MAP chip, and while driving down the Interstate at
cruise, his TCC would go nuts. On-Off-On-on-off-etc.
Turns out, (after some research and Diacom logs) that
the winter temps were driving engine coolant temps 
down to the 130-140 range... right where the TCC lock
threshold was set to in the chip.  A new winter front 
cured the problem, but reprogramming the TCC lock 
thresholds would have done the same.

Goes to show the damage something as innocuous as a
thermostat can do in a tightly designed system- if
he had continued to drive it with the TCC "shudder",
it would have meant a quick death for the converter
clutch.

Hope it helps...

Dig
turbodig@yahoo.com
'91 Sy (Now with Hartman Racing Trans... good stuff!)
12.53@105.5 | 0-60 in 3.2

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