GM 6L series no-movement conditions: Analysis and repair tips - Transmission Digest

GM 6L series no-movement conditions: Analysis and repair tips

I am certain that many have experienced a no-movement forward, no-reverse or abnormal pressure condition with a GM 6L series transmission, especially since they are one of the most popular unit families in shops today. So, let’s examine some conditions and causes along with a few diagnostic tips for troubleshooting. We’ll go through a few categories of the unit, and a variety of reasons each might lead to a no-movement condition.

Read more columns from the TASC Force Tips series here.

Software or electronic

• During the OE programming or relearn process, a temporary no-move condition may occur. When this occurs, remove the scanner, remove the key from the ignition, then open and close the driver door. Wait 15 to 20 minutes and return; it’s usually good to go.
• An incorrect part number or incorrectly programmed TEHCM may cause a no-movement or no-upshift condition. If you are replacing the TEHCM, always verify that its part number and program file match the VIN.
• No line pressure rise is a common condition caused by a TEHCM line pressure solenoid stuck in an exhaust mode. Line pressure is usually stuck at about 60 to 68 PSI when this occurs, with no RPM line rise whatsoever. Unplugged is no different.

Pump

• A pump TCC control valve stuck against spring blocking apply oil (converter charge) is usually a no-movement condition. This valve may cause a variety of symptoms depending the position in which it is stuck, such as shudder during TCC apply or when coasting to a stop. A tip: this valve can be air checked in-vehicle with the valve body removed.
• If the pump pressure regulator boost valve retaining pin is missing. When pressure is below 30 PSI or less at idle, it may be caused by a missing boost valve roll pin. This condition may have some movement, but it will not be normal.
• Pump pressure relief ball and spring missing leads to no movement and no line pressure. This occasionally shows up in rebuilt pumps.

Valve body

• A Type 2 separator plate on Type 1 valve body causes a no-forward condition. Early Type 1 valve bodies cannot be updated to the later eight-checkball plate. The correct plate (no. 24245720) will use seven checkballs. Line pressure will typically be normal with this condition.
• Type 1 separator plate no. 24245720 on Type 2 valve body causes a no-third and no-reverse condition. Line pressure will typically be normal with this condition.
• A TEHCM filter gasket left out during assembly will cause a no-movement condition. This is somewhat rare and typically has no or low line pressure.
• Clutch select valves/springs being put in backwards will cause a no-movement condition. Improper installation of the clutch select valve may cause either a loss of forward, reverse or both. Valves go in first with springs outboard. A stuck clutch select valve may cause the same problem. Line pressure will typically be normal with this condition.
• Actuator feed limit valve (solenoid regulator valve) problem. A loss of line pressure rise and movement may occur with some aftermarket AFL valve assemblies that malfunction. A quick test for AFL valve function is to determine if the transmission shifts through the gears on rack. If it shifts, that’s generally an indication it’s not an AFL valve issue.
• 1-2-3-4 Clutch regulator valve stuck, no forward. Clutch regulator valves can be confusing and easily missed. The 1-2-3-4 clutch regulator valve issue is usually discovered after the repair/reinstall. The 3-5-R clutch regulator valve is also known to stick and cause no-reverse and shift complaints. Line pressure will typically be normal with these conditions.
• A No. 1 checkball shrunken and out of place can cause no-forward. No. 5 checkball out of place can mean no-reverse. Line pressure will typically be normal with these conditions. Sometimes this is an intermittent condition.
• Incorrect valve body installed. A 6L90 valve body installed on 6L80 is a no-reverse condition.
• Compensator feed regulator valve stuck. This valve, depending on the position in which it’s stuck, may cause delays going into gear or harsh, chattering type of shifts or downshift clunks. Line pressure may be RPM erratic and all over the place as it is fed by line pressure.

Geartrain and unit

• If the sun gear is left out of the front planet, or the front input planet is upside down, this will cause no movement in forward or reverse. Line pressure will typically be normal with this condition.
• A forward piston (1-2-3-4) that may become cracked or have the snap ring popped out because that snap ring is not seated properly (one lug that’s not machined for snap ring opening) or a cracked apply piston missed during repair. The 1-2-3-4 OE piston has such a high failure rate that most shops replace this piston on all repairs with a more durable, heavy-duty aftermarket version.
• Output gear weld broken. This typically has a normally working OSS, but no movement in forward or reverse. Line pressure will typically be normal with this condition.
• 3-5-R drum weld broken/cracked is typically a no- or slipping-reverse condition along with third and fifth gear issues.

Hopefully this will help many of you in the repair of GM 6L45, 6L50, 6L80 and 6L90 transmissions.

Jim Mobley is a Sonnax technical communication specialist. He is a member of the Sonnax TASC Force (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax Transmission Co. technicians.

You May Also Like

Being tuned in: The value of transmission tuning

Tuning a vehicle to optimize its performance is nothing new. This customized process is used to provide fuel efficiency and improve other driveability concerns. Tuning for torque is especially desirable by diesel owners.Those who are proficient at tuning know that the transmission will need serious upgrades to survive the increased force it will receive from

Tech-Speak-Feb-Figure-1-1400

Tuning a vehicle to optimize its performance is nothing new. This customized process is used to provide fuel efficiency and improve other driveability concerns. Tuning for torque is especially desirable by diesel owners.Those who are proficient at tuning know that the transmission will need serious upgrades to survive the increased force it will receive from the crank, through the converter and to its internal components. Those who are tuning amateurs blow out their transmissions by ignoring the physical path torque travels to get to the ground.

Diagnosing an unusual problem: A slow-to-respond solenoid

A 2001 Chevrolet S-10 pickup came into our shop the other day. This job started with a concern of the engine revving high and not shifting correctly. With the truck being equipped with a 4L60E transmission, I expected to find non-functioning third and fourth gears, which is a common failure for these transmissions. Related Articles

Diagnosing Chrysler transmission max line pressure and P0933, P0869, P1745 codes

This article applies to Chrysler RFE, RLE and TES transmissions that utilize pressure control solenoids (PCS) for line pressure control. The subject is a rather common electrical fault that may occur on the PCS line pressure solenoid circuit, which results in max line pressure. Diagnosis and correction of a max line pressure condition may become

How to service the Honda 10-speed transmission

With Honda’s 10-speed front wheel drive transmission (see Figure 1, above) going into its fifth year on the roads, it’s feasible that one may show up in your shop for service. Related Articles – Dealing with PCM fault codes on the Ford 5R110W – Ford FNR5 slipping or no reverse hot – Solving electronic control

Tech-Speak-Jan-Figure-1-1400
Doing the little things right at Habby’s Transmissions

Habby’s Transmissions started as a radiator shop. When Warren Frie bought it in 1975 (keeping the name Habby’s from the previous owner), it took until the mid-1980s until he saw an opportunity in the transmission repair market, and transformed the business. Related Articles – Shift Pointers: Reassembling GM pumps with cam failure – Valve body

family

Other Posts

Sonnax adds new clutch regulator valve kit for Ford 6F35

Sonnax has introduced a new oversized low reverse/overdrive (4-5-6) clutch regulator valve kit (part no. 144740-43K) for Ford 6F35 transmissions, generations 1 and 2. Related Articles – Solera launches Identifix Shop Manager – TransTec extends coverage for 9T overhaul kits – Alto releases spring retainer, filter screw for 68FRE Sonnax says that users can restore

Sonnax-144740-43K-600
Sonnax adds new stator support bushing for Ford 6F35

Sonnax has released a new stator support bushing (part no. 144036B) for Ford 6F35 transmissions, generations 1 and 2. Sonnax says that users can eliminate spinning and premature deterioration and restore critical clearances in these transmissions by machining the bore and installing this bushing. Related Articles – TransTec offers 8HP50/850RE overhaul kit – Alto adds

Sonnax-Stator-Support-Bushing-600
Sonnax highlights 10L/10R solenoid stabilization retainer, 9T clip insert

Sonnax highlights two product lines for helping with heavy solenoids for GM/Ford 10L/10R and 9T series transmissions. Related Articles – Alto adds to intermediate clutch PowerPack line for GM transmissions – Dana offers Spicer end yokes for Allison Transmissions – ATI introduces six-speed Chevy transmission performance package According to Sonnax, the heavy OE LFS solenoids

Sonnax-105740-19K
Sonnax introduces new pump vane for Ford and GM transmissions

Sonnax highlights its line of pump vanes for GM 6T70/75 (Gen. 1), 10L60/80/90 (Gen. 1 and 2), Ford 6F50/55 and 10R60/80/90 transmissions. Sonnax touts this pump vane (part no. 124533) as a cost-effective alternative to replacing an entire pump rotor assembly. Related Articles – Georend Transmission adds Ford 6R140 transmission pan kit – Alto introduces

Sonnax-124533