No 3-4 shift at WOT

["Mitchell D. Murray" <MitchellMurray@compuserve.com>]

On Thu, 2 Jul 1998 16:00:41 -0400 (EDT) Mike Ewasiuk wrote in part:

>Ever since I bought my Ty last June I thought that the transmition was
>going since it would hesitate before shifting into 3rd at WOT and it would
>not shift to 4th at WOT.  

>Does any one have a easy fix for this, does the chip need to be replaced,
>I have not opened the CPU to look at the chip yet, I am planing on doing
>that this weekend.

The chip does not control the shifting for Syclones and Typhoons -- they
use the 4L60 transmission.  The 4L60E electronic transmissons ARE 
controled by a computer -- but they are NOT used in Syclones and Typhoons.
Only the lock-up of the torque converter is controled by the computer in
a Syclone or Typhoon.

Opinions will very on this subject -- but it is likely that your
2-4 band in the transmission is overly worn -- which
means you need a transmission rebuild -- I would recommend a factory
rebuild transmission from a GMC dealer for your Typhoon if you want
to retain the shift feel of the stock transmission.
Syclones, Typhoons, Corvettes, and some Comaros and some Firebirds came
with versions of the 4L60 transmission that have valve bodies that
allow full throttle upshifts from 3rd to 4th. Many other models of
vehicles were produced with the 700R4 and 4L60 that did not have
the ability to shift 3-4 at full throttle.

As the 2-4 band wears out, the transmission will stop performing the
3-4 shift at Wide Open Throttle (WOT) -- the transmission will
often seem to work OK except that the 1-2 shift will seem a little
harsh and the 3-4 shift at WOT will be lost.

Below is a partial repost of an e-mail message about this from last year
which has a little more information.

On Sat, 20 Sep 1997 23:30:45 -0400 (EDT)
j00n (Turbo262@aol.com) wrote:

>For those of u who had the same problem that i had....i found out why it was
>happening.  My truck wasn't shifting into 4th @ WOT, and i couldn't figure
>out why.  Well, when i took my truck in to get the tranny rebuilt, i
>mentioned it to the dood, and he told me that the valve body has control over
>that.  He told me that the only 700R4 that were supposed to do this was
>theVette, a nd i indicated to him that the Sy/Ty should also have the same
>valve body.  So, he said it was prolly cuz the clutches for 4th were
>completely shot.  He said it did have the correct valve body.  Well, i
>finally got a chance to get the truck goin that fast, and it now shifts into
>4th @ WOT.  So that might be the problem for other trucks that don't shift
>into 4th @ WOT...cuz he said if the clutches weren't  strong enuff, the
>tranny will go to the gear that can hold the power.

The shop manual shows that during the 3-4 shift the only clutch that
gets newly applied is the '2-4' band.  The other clutches just remain
being applied or get released. (The 'forward clutch' remains applied,
and the '3-4 clutch' remains applied, and the 'forward sprag cl. assembly'
gets released).

So it seems that all we have to do when we start getting no shift
from 3rd to 4th at WOT is to pop out that bad 2-4 band and put 
in a new one and go.
(Unfortunatly, to get at the 2-4 band the trans has to come apart --
so we might as well replace the other clutches.  But it is still
nice to know what is probably causing the problem).

Mitch Murray
Syclone (VIN 1144)