GM 8L90 #7 Check-ball: The overheat that saved the day - Transmission Digest

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.

Figure 1.
Figure 2.

When this took place, the Lube Override Enable Valve bore was cast shut as well as the channels feeding the valve. No modification was made to the spacer plate. This #7 shuttle ball seats against the Lube Override passage while the transmission is operating in Park, Reverse, Neutral and Drive ranges. With the #7 ball in this position, Regulated Lube fluid enters the Regulated Lube/Lube Override circuit to hold the Lube Flow Regulator Valve in the regulating position (see Figure 3).

Figure 3.

When the transmission enters a high-speed default gear, Lube Override pressure is routed to both the #7 ball and the Lube Flow Regulator Valve to ensure Converter Feed Limit pressure enters the Regulated Lube circuit.

By removing the #7 ball along with casting shut the Lube Override Enable Valve bore, the Lube Override circuit has been eliminated entirely. It no longer has any influence on the Lube Flow Regulator Valve (as seen in Figure 4).

Figure 4.

Since this took place in 2015, many rebuilders have become accustomed to building later units not using this ball, especially since the spacer plate didn’t change in the area over this ball. So, when an earlier transmission comes into the shop to be rebuilt, leaving the #7 ball out is an easy oversight to make.

When this happens, Regulated Lube pressure will drop as it flows into the Lube Override circuit and exhaust out at the Lube Override Enable valve, as Figure 5 illustrates below. This also robs lube pressure going to the transmission which can cause a catastrophic failure.

Figure 5.

What saved the day for one sharp tech when this happened recently was that he noticed that transmission temperatures increased rapidly on a road test getting higher than normal. When he returned to the shop, he pulled the cooler return line to check the flow and it was good. This put them back into the transmission to examine the cooler return circuit through the valve body. This is when they discovered that their unit needed the #7 ball. The overheat saved the day!

Read more stories from our Technically Speaking column series here.

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.


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.

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 – Shift Pointers: Nissan’s no throttle response – Jatco/Nissan JF011E critical wear areas and vacuum test locations – ZF 6HP26: A torque calculation

Shift Pointers: Nissan’s no throttle response

Nissan vehicles using continuously variable transmissions (CVTs) are notorious for defaulting to a no throttle response when the vehicle is engaged into gear. There are several malfunctions that can cause this protective failsafe feature to be initiated. A brake switch (stop lamp switch) stuck on, a double-footed driver, blown or incorrect brake bulbs, and wheel

Other Posts

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

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

Back to square one: When a transmission replacement doesn’t fix the problem

The subject of this article is a 2002 Ford Ranger with a 3.0L V6 engine and 5R44E transmission. There were 191,622 miles on the vehicle when it arrived at our shop. The owner said that the transmission was not shifting correctly and the OD lamp was flashing. Related Articles – Watch: Replacing a transmission and