GM Archives - Page 8 of 10 - Transmission Digest
IMA (Integrated Motor Assist)

In an effort to improve fuel economy, drivability, durability, and cost, many changes have occurred to automatic transmissions over time. In the last decade however, the proliferation of new models has been unending. Step-type transmissions have ratcheted up the gearing from old-time three- and four-speeds to five- through seven-speeds.

Magna Powertrain Transfer Case, RPO Code NQF

We finally had a big-enough snow this year to bring out the people with 4WD problems. This one was a 2008 Chevy Silverado 2500 HD.

It was from a tire distributor that has a number of these particular trucks. Their technicians had been trying to fix the issue of having no 4WD by putting various parts on it. They said that they had replaced the transfer-case motor and buttons.

I started out with the usual road test, scan and lift check to verify the problem. Sure enough, there was no 4WD and the transfer-case control module (TCCM) had every code possible stored. I thought I’d clear the codes and start out fresh.

Saturn VT25-E Ratio Error

A 2005 Saturn Vue experiences erratic ratio control (gear position) and ultimately sets a trouble code P1882. Once the code is cleared, the transmission starts to shift again, for a short time. The code then reappears and the unit returns to a fixed gear position.

After it was determined that the issue was not computer related or valve-body/solenoid related, the transmission was removed and disassembled. Damage was found in the drive variator (pulley), and there also was seal damage.

The New 7-Speed Tremec TR6070 Manual Transmission

This is truly a world-class vehicle. It features new technology, design and manufacturing methods that go way beyond the familiar C5 and C6 Corvettes. These cars have come a long way from the older fiberglass models, using an aluminum space frame and many carbon-fiber body parts. GM has invested a fortune in development and design in a totally new LT1 aluminum-block engine (Figure 3) that produces 450 horsepower and 450 lb.-ft. of torque from the 6.2-liter displacement. Zero-to-60-mph times are in the four-second range, and this is from the stock motor. Higher-performance versions of the new LT1 will be released for the top-of-the-line Corvette models. The most-striking feature of these vehicles is a seven-speed manual transmission, the TR6070 (figures 4 and 5).

Magna Powertrain Transfer Cases, Part 2

In last month’s article we identified and explored the basics of the Magna Powertrain transfer cases found in late-model GM trucks. In this article we take an in-depth look at one of the three series of models available: the MP 1222, 1225 and 1226 models, using RPO (regular production option) code NQG.

Understanding the significance of the RPO codes on GM vehicles will make parts ordering simpler. Figure 1 shows the variations and descriptions of the NQG series of transfer cases. As these units are used in K1, K2 and K3 models of trucks, there are differences in input and output splines, chain size and number of pinions on the planets. These variations provide the torque capacity necessary to cover the different engine/transmission combinations for light-duty, heavy-duty and super-heavy-duty applications.

GM Release-Bearing Installation

The design of the release fork on many GM applications can contribute to a common installation error.

Unlocking Some 55-50 Valve-Body Mysteries

Let’s start with identifying the AW 55-50 valve body and the differences that matter when you’re choosing a replacement valve body. There are four castings, which can be identified by either a letter cast into the valve body just to the right of the S4 solenoid or a blank spot.

Tests Confirm Uneasy Feeling about Diagnosis

When was the last time you had a customer bring you their vehicle – along with a part – and ask you to install it? On occasion, I have a customer ask me to do just that, and it is often large, used and costly to purchase new – such as an engine, transmission or differential. This was the case recently when my friend Jim had his 2002 Pontiac Grand Prix GT towed to our shop; he also had a used automatic transaxle delivered from a local, reputable used-parts supplier.

Serviceability Report: Chevy Cruze

This is another in a series of reports that asks a simple question: Do the automotive engineers look at “ease of service” when designing a new car?

Issues Pop Up During Emissions Check

How often have you had a customer with a high-mileage, 20-year-old vehicle say, “I just need it to last one more year”? With the average age of vehicles on the road more than 10 years, I am seeing more “20-somethings” coming in my bay for TLC.

A customer recently brought in her 1992 Oldsmobile Cutlass with a 3.8-liter engine, 138,000 miles and a failed emission report. In our metro Denver area, we all must pass our centralized emission test – or we cannot renew our license plates.

4L60-E No move after rebuild

The transmission rebuilder accused the R&R man of breaking the pump during the installation process. The R&R man was certain that he had done his job correctly and that the rebuilder must have done something wrong during the rebuild. To help pinpoint the problem, a pressure gauge was installed into the line-pressure port. To everyone’s surprise, the line pressure was normal. This meant that not only was the pump not broken but also the PR valve was not stuck open. This also meant that the transmission would have to be removed from the vehicle and at least partially disassembled.

Bitter Cold: Sometimes It’s the Root Cause, Sometimes It’s Not

Here in Denver, when the snow flies and the mercury plummets, we all like to press “4WD” on our dashboards and blast out into the blizzard. When our rigs stay in “2WD” and slide into the gutter – that’s when I get the phone calls. The following two customers called me the same morning recently, and we came to two very different conclusions after diagnosing their inoperative four-wheel-drive (4WD) systems.