6F35: A classic bolt intrusion - Transmission Digest

6F35: A classic bolt intrusion

I remember the first time I took a phone call from a shop that had a GM 4L60-E with a complaint that it felt like it was bound up in both reverse and drive. I you got into the throttle a bit, it would move but with a terrible noise. After the Park Pawl was checked and found to be in proper working order, the transmission was pulled to be disassembled for inspection.

In my case, the tech immediately picked up on the problem when he was removing the valve body bolts. One of them did not come out as easily as it should. After he pulled the transmission apart, he saw that the difficult bolt he removed had been screwed into the sun shell.

This became a problem that occurred many times with people working on these units for the first time. A 54.4mm valve body attaching bolt can be easily installed in a location along the transmission’s centerline where a 47.5mm bolt belongs. A bolt intrusion into the gear box planetary system that does not do well.

Recently, we encountered another classic bolt intrusion, this time on the Ford 6F35. There are two different length valve body attaching bolts as seen in Figure 1.

Figure 1.

A talented tech by the name of Steve Regalado discovered in diagnosing a failed unit that a longer bolt can intrude into the gear box. Figure 2 shows the proper location of the shorter length bolt (in white circles around the bolt head), while Figure 3 shows where the longer length bolts are installed (in yellow circles around the bolt head).

Oct-Shift-Pointers-Figure-2-1400
Figure 2.
Oct-Shift-Pointers-Figure-3-1400
Figure 3.

Figure 4 shows the error made with this transmission where the longer bolt was placed into a shorter bolt’s location.

Oct-Shift-Pointers-Figure-4-1400
Figure 4.

It so happens that the threads for the shorter length bolt went entirely through the case (Figure 5) allowing the longer bolt to enter the 1-2-3-4 clutch assembly (Figure 6).

Oct-Shift-Pointers-Figure-5-1400
Figure 5.
Oct-Shift-Pointers-Figure-6-1400
Figure 6.

Figure 7 shows the damage to the frictions and steels that occurred with this intrusion, while Figure 8 shows where the bolt actually dug into the steel.

Oct-Shift-Pointers-Figure-7-1400
Figure 7.
Oct-Shift-Pointers-Figure-8-1400
Figure 8.

With this type of intrusion to the 1-2-3-4 clutch assembly, drive shift engagements and launch will be compromised as well as a 4-5 and 5-4 shift complaint. These symptoms may not present themselves right away. Once it’s been driven for a few miles, allowing for a little time for damage to take place, these symptoms will begin to present themselves.

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