Seeing the Forest AND the Trees - Transmission Digest

Seeing the Forest AND the Trees

They say that the proverbial phrase “I couldn’t see the forest for the trees” means that a person or organization cannot see the big picture because it focuses too much on the details.

I have seen this phrase used after days of diagnosing a transmission problem without resolve, yet the cause is staring you in the face. You are so deep in; you no longer can see the obvious.

With the 6L80 being out on the road for the past 15 years, they are coming into the shops more frequently. They are beginning to take the place of the 4L60-E transmission. Although that is a tough act to follow considering how many 4L60-Es were manufactured from 1993 to 2013. I wonder if anyone knows that number? Not to mention how many were remanufactured. 

Figure 1

Getting back to the 6L80 transmission, with the years they have been on the road; we now see the types of failures for which they are susceptible. Things like converter clutch failures, output carrier lube failures, 4-5-6 clutch burnout, 4-5-6 clutch hub with the output carrier shaft snapping or twisting (caused by shift overlap programming issues or output carrier failure). Cracked 3-5-R drums and 1-2-3-4 clutch piston. Or pressure regulator valve bore wear, AFL, TCC Reg, and compensator feed bore wear are also on the rise. 

With 6L80 transmissions having TCC issues, the TCC Reg valve in the valve body is usually looked at first. If this is OK, the decision must be made to inspect the TEHCM or pull the unit and look at the turbine shaft O-ring, the PR valve, the TCC control valve, and converter limit valve in the pump. Removing the unit is the usual choice over replacing the TEHCM. And when the turbine shaft O-ring and valves in the pump are good, a visual inspection is made with the upper ring on the turbine shaft and the bushing in the stator, particularly the one on the converter end of the stator support shaft. When all these items are good, and nothing is discovered, the torque converter is replaced. When that does not work, the TEHCM is replaced. And when that does not work, the inspection cycle repeats itself.  

Figure 2

But here is the catch in seeing the tree that is in the forest. The stator bushing can look good when it is not. This is where one can be easily fooled. The turbine shaft must be in the stator to get a better visual of the bushing condition. 

Bushing clearance is 0.001˝ for the first inch and .0015˝ for each additional inch after that. The bushing journal on the turbine shaft for the stator bushing measures approximately 1.117˝ in diameter. The clearance should then be 0.001˝ for the first inch plus a tenth more: 0.0001˝, which works out to be 0.0011”. This would be the absolute tightest observable clearance between the journal and the bushing. The reality will be a clearance closer to 0.0015˝ to 0.002˝. 

If you look at figure 1, there is far more clearance between the journal and the bushing than 0.002˝. This excessive wear will compromise the hydraulic converter circuit as the converter “off” and converter “on” pressure will mingle (figure 2). So, as you can see (all pun intended), just looking at the appearance of the bushing will cause you not to see the forest for the trees. 

Figure 3

By the way, there is nothing worse than finishing a rebuild where you are tightening up the pan bolts according to torque spec and the bolt head snaps. Not just once, but two or three times. Well, this is yet another personality of the 6L80 transmission. The pan bolts used here are quite small (M6 x 16mm) and do not tolerate much corrosion because of it. Look at figure 3, and you can see how the corrosion takes place at the base by where the pan would be. Water collects in this area and deteriorates the bolts. Some are worse than others, so you can build a few units and never have an issue. But then, the one that needs to go Friday at 5 pm, you have three breaks. 

You May Also Like

Sherlock Holmes Approach to an AB60 No-Move Situation

The effectiveness in diagnosing automatic transmission malfunctions is an art form. Although there are similarities among the wide varieties of transmissions on the road, each transmission has its own peculiarities. Aside from having mechanical, hydraulic, and electrical hardware systems to contend with, software/programming issues and various vehicle platforms make diagnostics much more difficult.  Using scopes provides

ab60

The effectiveness in diagnosing automatic transmission malfunctions is an art form. Although there are similarities among the wide varieties of transmissions on the road, each transmission has its own peculiarities. Aside from having mechanical, hydraulic, and electrical hardware systems to contend with, software/programming issues and various vehicle platforms make diagnostics much more difficult. 

GM 6T40 Pump Identification Guide

The 6T40 was introduced in 2008 for General Motors front-wheel-drive cars in the Chevrolet Malibu and has gone through several changes throughout its three generations, specifically in the pump area. The 6T40 is closely related to the more lightweight 6T30 and the heavier duty 6T45 and 6T50. Generation one started phasing out during the 2012

The Manifold Pipeway

The Honda six-speed transmission has been on the bench of many specialty shops for one reason or another (figure 1). But, for those of you who have yet to lay your hands on one, mounted on the upper side of the unit is one of the largest, if not the largest solenoid and pressure switch

8L90 Vacuum Testing

Below are the diagrams for vacuum testing GM 8L90 transmissions. Note: OE valves are shown in rest position and should be tested in rest position unless otherwise indicated. Test locations are pointed to with an arrow. Springs are not shown for visual clarity. A low vacuum reading indicates wear. For specific vacuum test information, refer

4L60E Harsh 1-2 Shift

The 4L60E transmission platform has been in service from 1993-2015; that’s 22 years. It amazes me when a transmission that has been around for this long can throw a new twist on a common problem and blindside you. Let us have a look at the systems and potential problems in a 4L60E that can cause

Other Posts

Integration becomes synergy for Sonnax and Rostra

Klynt Baker, the recently appointed president of Sonnax and Rostra, says that his responsibilities aren’t two aftermarket companies owned by Marmon Holdings. Baker says that Sonnax and Rostra have integrated their operations to the point that there are indeed two brands encompassed in a single business. Related Articles – Dealing with the increasingly common pin-fit

Look for the little details: Three transmission repair case studies

Below are three examples of trucks that came into transmission shops, yet either did not have a transmission problem, or had a simpler issue than it originally seemed. Read on for the stories. Related Articles – Podcast: Talking CVTs with Transtar, part 1 – Back to square one: When a transmission replacement doesn’t fix the

techspeakfeature-1400
The 6R140 torque converter: Common fault codes and how to rebuild

There are many reasons for converter clutch slip codes to occur in vehicles equipped with the Ford 6R140 transmission. One is bore wear in the valve body with any one of the three valves related to converter clutch apply and release. Low line pressure could be another. But there is a third that is inherent

Tech-Speak-July-Figure-1
A 10L80 with a buck and bang

A 2018 Cadillac Escalade ESV AWD 6.2L using a 10L80 transmission came in to Stroli Motors barely moving forward, making a banging noise in the center of the gearbox. Reverse was good. Keith from Stroli pulled two codes from the PCM: P0300 for Random Multiple Cylinder Misfire Detected; and P175E for Shift Limiting Active. P175E

Tech-Speak-June-Figure-1-1400