� GEARSJuly2008

Welcome 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

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

PLAYING WITH FIRE

by Jon Rodriguez

4L30E Pump Interchange

Figure 1

GEARS July 2008 �

experienced code P1811 — trans-mission component slipping — in both front- and rear-wheel drive GM transmissions, and the 4L30E is no exception. The cause is wear in the regulator valve bore, which reduces clamping force on the deli-cate woven carbon converter clutch material.

Parts DifferencesThis isn’t going to be an in-depth

look at the theory of both pumps. Instead, we’re going to focus on how to identify the two systems’ parts, and what you need to change. For those of you who want the “whys” answered, we’ll discuss that at the end of this article.

CAUTION: Never attempt to cross the bellhousing, pump plate, and pump body. When making this conversion, all three of these components must be the non-PWM style. These components are completely different; mismatching them will damage the transmission. Refer to figure 1 to identify the differ-ent parts.

The one part that can be modified to work with either system is the input shaft. The fluid passages in both shafts are identical (figure 2). The one differ-ence is the PWM-style shaft doesn’t have an orifice check valve at the con-verter end (figure 3). If possible, you should use the on/off-style shaft with the valve already installed, but if it isn’t available, you can install a new valve into the PWM shaft. The check valve is the same as the one in a 4L60E and is available from your transmission parts supplier.

Never use a shaft without the valve; that will cause extremely firm TCC apply and will damage the TCC clutch material.

One final difference involves the torque converter itself: The PWM con-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

3.5L engine.The other part of the system is the

TCC solenoid. Since an on/off-style lockup solenoid has a resistance of 18-20 ohms and the PWM solenoid has a resistance of 9.5-10.5 ohms, always use the PWM style solenoid or the computer will set code P1860 (TCC solenoid elec-trical circuit).

An important consideration is how lockup will feel after the changeover. TCC apply will be firmer than it was with the PWM system. Always discuss this with the customer before the conver-sion; don’t wait until you’re finished to explain the difference. If you explain it beforehand, the customer will expect the difference and appreciate your efforts; waiting until later, your explanation starts to sound more like an excuse for a condition you weren’t expecting.

Why It WorksFigure 5 shows the differences in

the pump gasket area. The on/off pump is missing the additional machining groove for the enable valve in the PWM pump. This won’t affect gasket sealing or hydraulic operation.

The other difference is the addition of a front seal drainback hole that leads straight to exhaust in the overdrive sec-tion. This is actually a better design, because there’s less wormtrack area for crossleaks to allow pressure to get behind the front seal and cause front seal popout.

Now let’s look at the hydraulic operation: Figure 5 shows the TCC solenoid signal hole is in the identical location in both pumps. The difference is instead of the solenoid signal oil actuating the enable valve, the torque converter clutch control valve, and the isolator valve, it now has only one responsibility: to shift the on/off con-verter clutch control valve to the apply position.

The spring behind the TCC con-trol valve applies 4.5 lbs at working height. With the valve’s signal land being 0.12”, it’ll take about 38 lbs of signal oil to switch the valve.

With the help of G&S Transmis-sions in Garden Grove, CA, we moni-tored the TCC solenoid duty cycle in a 2000 Trooper with the PWM-style pump and converter. The computer started to signal the solenoid at about 40 MPH, and quickly rose to 50% duty cycle. The duty cycle remained at 50% through third and fourth gears.

Figure 2

Figure 3

� GEARSJuly2008

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 more than 50 RPM, but usually slips under 5 RPM.

Second gear oil provides TCC solenoid feed; basically it’s mainline pressure. Using our solenoid dyno in the shop, we found that at 90 PSI — which would be a light throttle cruising pressure — it takes a 45% duty cycle to achieve 50 lbs of signal oil to the actuating side of the TCC control valve. That’s plenty of pressure for our 38-lb valve to stroke. Voila! Lockup. From that point, as line goes up, the duty cycle will need less signal to engage lockup. That’s okay; we still end up with lockup fully applied.

The computer has two codes for lockup ratio problems, and duty cycle isn’t involved with either one. The

computer will only set code P1811 when the slip is between 250 and 800 RPM for seven seconds, and it has to occur three times in a row.

The other code is P0742 — TCC stuck on. This code will only set if TCC is commanded completely off and TCC slip is between –20 and 40 RPM for two seconds, while throttle opening is above 20%. That isn’t a condition that this modification should affect.

That’s it. Lockup will work beau-tifully and line pressure will run the same as it did with the original pump. As always, good rebuilding practice dictates that all mating and mounting surfaces be flat and torqued to specs. You shouldn’t have any other problems

with the pump area.

I hope you enjoyed this first edi-tion of Playing with Fire as much as I did researching and writing it. If you have an interchange question you’d like to see addressed here, drop us a line and we’ll see about presenting it in a future issue.

Until then, remember: If you’re going to play with fire, make sure you pay attention and know exactly what you’re doing. That way you won’t get burned!

“A Special thanks to Raffi at ITC of Fresno, CA for his help with this article.”

Figure 5

Figure 4

4L30E Pump Interchange

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