Shift Pointers: Reassembling GM pumps with cam failure - Transmission Digest

Shift Pointers: Reassembling GM pumps with cam failure

For the past several years, GM has used a binary positive displacement vane type pump. The compact design allows for it to be utilized in off-axis applications such as the 8L90 transmission and the third generation 6T40 transmission. Figures 1 (above) through 4 display a view of this style pump in the 6T40 applications.

Shift-Pointers-Jan23-Figure-2-1400
Figure 2.
Shift-Pointers-Jan23-Figure-3-1400
Figure 3.
Shift-Pointers-Jan23-Figure-4-1400
Figure 4.

The cam ring is stationary and elliptical in design, sitting in a housing with dual suction and pressure output ports. Not only does this design allow for on-demand flow of volume, it also keeps the rotor balanced, preventing side-loading of the pump drive shaft. With the absence of vane rings, pressure at the center of the cam is used to push the vanes outward to seal against the cam. In time, these vanes wear into the cam, causing a loss of pump pressure.

Read more columns from our Shift Pointers series here.

Russel Mott at AACTION Transmissions encountered this recently with a 2017 Chevy Impala 2.5L that came in with slightly over 100,000 miles to its name. When the selector lever was placed into reverse, the engine would need to be revved up to get it to move. In forward, it would slip. Code P2723 was set for a performance problem with PCS 5 which is used to regulate pressure for the 1-2-3-4 Clutch. When the unit was out and apart, the low pressure caused damage to the transmission. The cam wear was not seen at first so when the unit was rebuilt and put back into the vehicle, the problem remained.

The unit was pulled and a completely different “used pump assembly” was put in. This pump assembly includes the stator support, drive chain and pump that is seen in Figure 1. Once the unit was back in the vehicle, the problem remained. The unit was pulled and gone through again but could see nothing as the pump itself was not fully disassembled. This time, they put in a new pump assembly which resolved the loss of pressure issue. When the pumps were completely disassembled and inspected, sever wear on the inside of the cam ring was discovered, as Figure 5 shows.

Shift-Pointers-Jan23-Figure-5-1400
Figure 5.

During reassembly of this pump, be sure to have the dot on the rotor and cam facing up as seen in Figure 4. Use Figure 6 to see how the pressure plate is properly installed on top of the rotor and cam. And then use the updated rubber coated fluid pump seal as seen in Figure 7.

Shift-Pointers-Jan23-Figure-6-1400
Figure 6.
Shift-Pointers-Jan23-Figure-7-1400
Figure 7.

You May Also Like

GM 6T70/75 slips and delays in first

A 2015 Chevrolet Equinox equipped with the 3.6-liter engine and 6T75 transmission has complaints of a delayed engagement into drive and slips in first gear.

Tech-Talk-Q4-Figure-11-1400

The complaint

A 2015 Chevrolet Equinox equipped with the 3.6-liter engine and GM 6T75 transmission has complaints of a delayed engagement into drive and slips in first gear.

The cause

A generation one 1-2-3-4 Clutch Apply Piston was installed into a generation two transmission. The generation two 1-2-3-4 Clutch Apply Piston apply fingers are .147 in. taller than the generation one piston. This created too much clutch clearance for the clutch pack to effectively hold.

How to fix GM 6T70/Ford 6F50 rattling noise with transmission in gear

A rattling noise is coming from the transmission whenever the engine is running and the transmission is in gear.

Tech-Talk-Q4-Figure-13-1400
The importance of the follow-up road test after transmission replacement

A 2002 Lexus RX300 equipped with a 3.0-liter V6 engine and U140F transmission was brought into our facility with a few concerns. The customer said that “it has a leak, a grinding noise when taking off from a stop, and it just doesn’t seem to shift right.” Related Articles – Sonnax introduces Sure Cure Kit

RR Tech Feature Oct
Tips and tricks for Chrysler switch valve plug testing

As technicians, we are often faced with build issues that can sometimes be frustrating at first. But with a little ingenuity, these frustrations can be turned around and made simple. Related Articles – ETE Reman: Ever expanding – Shift Pointers: Nissan’s no throttle response – Jatco/Nissan JF011E critical wear areas and vacuum test locations In

tascfeature-1400
GM 8L90 #7 Check-ball: The overheat that saved the day

Beginning in October of 2015, GM removed the #7 Check-ball from the solenoid valve control body in the 8L90 transmission (see Figure 1). This was done in conjunction with the elimination of the Lube Override Enable Valve from the upper valve body as shown in Figure 2. Related Articles – ZF 6HP26: A torque calculation

Other Posts

Dealing with the increasingly common pin-fit problem

I want to talk a little bit about a common diagnostic misstep or overlooked problem that is prevalent in the automotive repair industry and seems to be on the rise. Pin-fit or tension can deal us a fit sometimes (pun intended), especially if we do not have the proper tools to determine if this mode

RR-Tech-September-FIG-1-1400
Shift Pointers: Shift rod displacement in a luxury car

When owning a luxury vehicle, one cannot be faint-hearted when the time comes to pay a repair bill. Even if you bought a used luxury car at a very good price, this doesn’t change the price of new components required to make that repair. Related Articles – Podcast: Talking CVTs with Transtar, part 2 –

Podcast: Talking CVTs with Transtar, part 2

Following part one of Andrew Markel’s discussion of the ins and outs of continuously variable transmissions (CVTs) with Dave Hritsko of Transtar, part two of Andrew and Dave’s conversation gets more in depth on the topic, including a discussion on programming transmission modules for CVTs. Tune in to their conversation in the video above. Related

transtar-podcast-1400
Podcast: Talking CVTs with Transtar, part 1

CVTs, or continuously variable transmissions, have long been a hot topic in the transmission repair industry, but we can safely say they’re here to stay. So what do you do when one shows up at your shop? In this podcast, with Dave Hritsko of Transtar as featured guest, we dive in to the ins and

transtar-podcast-1400