This document provides information about interchanging the four-valve PWM-style lockup pump for the 2000-2004 Trooper and Axiom 4L30E transmissions with a two-valve on/off-style lockup pump. It describes the differences between the parts, how to identify them, and what parts need to be changed. It also explains why this interchange works from a hydraulic operation perspective and discusses lockup feel and diagnostic trouble codes.

1. PLAYING WITH FIRE
by Jon Rodriguez
4L30E Pump Interchange pressure and converter charge
issues.
2. Torque converter clutch regulator
valve wear. The pulse width modu-
lated apply of the converter is con-
trolled through the converter clutch
regulator valve. You’ve probably
W
elcome to the first edition
of Playing with Fire. In this
new series, we’re going to
cover the most common interchange
questions that we receive on the ATRA
HotLine.
Interchange is an important subject
because of the risk verses reward factor
that comes into play. Sometimes a dif-
ferent style part can be less expensive,
more plentiful, and in some cases such
as this one, improve the durability
of the transmission. All of which can
make the job more profitable. The risk?
Virtually none… as long as you handle
the interchange correctly.
In this edition we’re going to look
at how to use a two-valve, on/off-style
lockup pump in place of the four-valve,
PWM-style lockup pump in 2000-2004
Trooper and Axiom 4L30E transmis-
sions.
There are two common reasons for
pump failure in the PWM-style pumps:
1. Pump gear and cavity wear. Any
galling or clearances above 0.003”
between the outer pump gear and
pump body, or between the inner
pump gear and crescent, aren’t
acceptable. Using a pump with
wear in these areas will reduce
pump volume and cause line Figure 1
4 GEARS July 2008

2. experienced code P1811 — trans- 3.5L engine. The spring behind the TCC con-
mission component slipping — in The other part of the system is the trol valve applies 4.5 lbs at working
both front- and rear-wheel drive TCC solenoid. Since an on/off-style height. With the valve’s signal land
GM transmissions, and the 4L30E lockup solenoid has a resistance of 18- being 0.12”, it’ll take about 38 lbs of
is no exception. The cause is wear 20 ohms and the PWM solenoid has a signal oil to switch the valve.
in the regulator valve bore, which resistance of 9.5-10.5 ohms, always use With the help of G&S Transmis-
reduces clamping force on the deli- the PWM style solenoid or the computer sions in Garden Grove, CA, we moni-
cate woven carbon converter clutch will set code P1860 (TCC solenoid elec- tored the TCC solenoid duty cycle in
material. trical circuit). a 2000 Trooper with the PWM-style
An important consideration is how pump and converter. The computer
Parts Differences lockup will feel after the changeover. started to signal the solenoid at about
This isn’t going to be an in-depth TCC apply will be firmer than it was 40 MPH, and quickly rose to 50% duty
look at the theory of both pumps. with the PWM system. Always discuss cycle. The duty cycle remained at 50%
Instead, we’re going to focus on how this with the customer before the conver- through third and fourth gears.
to identify the two systems’ parts, and sion; don’t wait until you’re finished to
what you need to change. For those of explain the difference. If you explain it
you who want the “whys” answered, beforehand, the customer will expect the
we’ll discuss that at the end of this difference and appreciate your efforts;
article. waiting until later, your explanation
CAUTION: Never attempt to cross starts to sound more like an excuse for a
the bellhousing, pump plate, and pump condition you weren’t expecting.
body. When making this conversion,
all three of these components must be Why It Works
the non-PWM style. These components Figure 5 shows the differences in
are completely different; mismatching the pump gasket area. The on/off pump
them will damage the transmission. is missing the additional machining
Refer to figure 1 to identify the differ- groove for the enable valve in the PWM
ent parts. pump. This won’t affect gasket sealing
The one part that can be modified or hydraulic operation.
to work with either system is the input The other difference is the addition
shaft. The fluid passages in both shafts of a front seal drainback hole that leads
are identical (figure 2). The one differ- straight to exhaust in the overdrive sec-
ence is the PWM-style shaft doesn’t tion. This is actually a better design,
have an orifice check valve at the con- because there’s less wormtrack area
verter end (figure 3). If possible, you for crossleaks to allow pressure to get
should use the on/off-style shaft with behind the front seal and cause front
the valve already installed, but if it isn’t seal popout.
available, you can install a new valve Now let’s look at the hydraulic
into the PWM shaft. The check valve is operation: Figure 5 shows the TCC
the same as the one in a 4L60E and is solenoid signal hole is in the identical
available from your transmission parts location in both pumps. The difference
supplier. is instead of the solenoid signal oil
Never use a shaft without the actuating the enable valve, the torque
valve; that will cause extremely firm converter clutch control valve, and the
TCC apply and will damage the TCC isolator valve, it now has only one
clutch material. responsibility: to shift the on/off con-
One final difference involves the verter clutch control valve to the apply Figure 2
torque converter itself: The PWM con- position.
verter uses a woven carbon clutch; the
on/off style uses a standard paper clutch
(figure 4). Since we’re going to convert
lockup apply to an on/off style, there’s
no need to spend the extra money on
the woven carbon-style clutch. In fact,
the woven carbon is more delicate than
the paper, and could be damaged if used
with a firm, on/off apply. The paper
clutch style converter can be ordered
by using the Rodeo Application with a Figure 3
GEARS July 2008 5

3. 4L30E Pump Interchange
50% is low,
because the freshly-
built transmission had
a solid lockup and the
computer saw that
the clutch was fully
engaged at 50%. The
computer will con-
tinue to increase the
duty cycle until the
slip drops below 50
RPM. On the PWM
application, the clutch
is designed to slip no Figure 4
more than 50 RPM,
but usually slips under 5 RPM. computer will only set code P1811 with the pump area.
Second gear oil provides TCC when the slip is between 250 and 800
solenoid feed; basically it’s mainline RPM for seven seconds, and it has to I hope you enjoyed this first edi-
pressure. Using our solenoid dyno in occur three times in a row. tion of Playing with Fire as much as
the shop, we found that at 90 PSI — The other code is P0742 — TCC I did researching and writing it. If you
which would be a light throttle cruising stuck on. This code will only set if TCC have an interchange question you’d like
pressure — it takes a 45% duty cycle is commanded completely off and TCC to see addressed here, drop us a line
to achieve 50 lbs of signal oil to the slip is between –20 and 40 RPM for and we’ll see about presenting it in a
actuating side of the TCC control valve. two seconds, while throttle opening is future issue.
That’s plenty of pressure for our 38-lb above 20%. That isn’t a condition that Until then, remember: If you’re
valve to stroke. Voila! Lockup. From this modification should affect. going to play with fire, make sure you
that point, as line goes up, the duty That’s it. Lockup will work beau- pay attention and know exactly what
cycle will need less signal to engage tifully and line pressure will run the you’re doing. That way you won’t get
lockup. That’s okay; we still end up same as it did with the original pump. burned!
with lockup fully applied. As always, good rebuilding practice “A Special thanks to Raffi at ITC
The computer has two codes for dictates that all mating and mounting of Fresno, CA for his help with this
lockup ratio problems, and duty cycle surfaces be flat and torqued to specs. article.”
isn’t involved with either one. The You shouldn’t have any other problems
Figure 5
6 GEARS July 2008

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Driveline and Chassis Technology