Transmission slips out of park!

[NWDave]

I have a 1969 F100 Ranger, C6 automatic, that does not like to stay in park. I have asked around, some guys say the parking pawl or pin is worn out. The prior owner gave me the heads up, that he had sent it crashing through his garage door while tuning the carb.

I set the break, and put the transmission in neutral when I'm fussing with the engine. My transmission seems to be leaking from every possible orifice, so plucking it out to at least change the seals may be in order anyway.

[390xlt]

I had the same problem many years ago with a C4 in a Fairlane. Turned out to be a shifter adjustment issue. It was an aftermarket cable operated shifter, so I don't know how applicable that is if you've got the stock setup, but it might be worth checking.

[NWDave]

Thanks for the info. I did find several posts from people with similar problems with Ford C6 and C4 transmissions. I have the truck up on blocks now for a gas tank change, so I will take a look at the transmission linkage for adjustments.

[Ren]

It's my understanding that automatic transmission equipped Fords of this era with column shifters are well known for slipping from P to R.

I think most of the problems come from the column shift assembly. The big enemy here is gravity. It was a bad design when new, and did NOT get better with age.

Some people say to rebuild the column shift assembly. But why rebuild a bad design when it is simply a disaster waiting to happen all over again?

Some people remedy this by installing a floor shift. All things considered, that is the safest practical solution.

[71cc]

I think that year still uses the ball detent in manual valve. Later went to a case detent " rooster comb" which was a bit more positive. Bad motor or transmission and cab mounts cause issues with linkage.

[NWDave]

I have been considering a floor shift conversion, with a B&M truck shifter. The transmission will come out eventually, as it leaks out the front seal.

[Rcarmody]

I have a 69 F250 w/ C6 auto trans and I had the same problem. One time I put it into park, jumped out to open my gate, turned around and saw my truck going backwards down the street. Thankfully I was able to jump in and stop it before it crashed into the neighbor's car.

My mechanic said it was the steering column. There was a worn down pin inside the shifter, I think. I bought a rebuilt column and it's been great ever since. Locks into park and feels very solid.

The hardest part was finding a rebuilt or new column. Apparently the Ididit columns are not compatible with Ford Steering wheels. I would have had to get an aftermarket steering wheel, which I wasn't into.

I swapped my old column for a rebuilt one from these guys. They were very nice and wired it up for me.
http://www.truckpartscompany.com/

[earnest37]

I discovered the root cause of this problem while rebuilding a C6 for my '73 F250. I was "gifted" a '75 C6 which is almost ready for installation. However, while installing the valve body (VB) I discovered that the manual shift rod will not force the parking rod fully in the park position with the VB installed. I removed the valve body and was able to completely engage the parking pawl into the gear on the rear of the output shaft by rotating the manual shift lever into the park position. I put the VB back in and the problem was still there, no full park position. The rooster comb linkage will not go fully into park because: 1) the slide valve makes contact with a small protrusion on the VB case, or; 2) the lever that operates the slide valve makes contact with the VB housing before the parking pawl rod is fully extended rearward. There is a cone-shaped bulge on the parking pawl rod toward the rear which actually forces the parking pawl into the park position. My potential solution is either: 1) remove and lengthen the parking rod about 1/8" to 3/16" to see if this will solve the problem; 2) remove the small protrusion on the VB which stops the slide valve from moving fully forward; 3) relieve the edge of the lever which engages the slide valve if that is making contact with the VB before the parking pawl is fully engaged. Fortunately I have some extra parts to play with but my thinking right now is to slightly lengthen the rod enough to fully engage the parking pawl as long as it disengages when the transmission is shifted into reverse. Incidentally, this was a MAJOR problem with these transmissions which resulted in a lot of lawsuits against Ford. Many injuries were reported and some deaths. This is a problem which definitely needs a solution. Will post results when I've solved the problem.

[Zorm]

any resolve with this issue???

[Bigcalhoun]

Following up to see if this issue was resolved. Sounds exactly like the situation with a '68 Torino that my father drove off the showroom floor back then. He is passing the torch to me to keep it on the road. This slipping out of reverse issue almost got ugly for me a few weeks ago. I'm thinking I should begin cranking it in neutral as the garage sits at the top of a hill. Lurching into reverse will put it into a parked car or the neighbor's living room.

Fortunately, I haven't experienced this in my '70 F100.

[OldRanger68]

I too have been trouble with my truck jumping into reverse and think I may have discovered a problem. It seems the travel of the upper shift arm (on the column) is different than the lower arm on the trans. I have been trying to adjust the linkage so it kind of works but it seems to malfunction at the most inopportune times. Today with help, I discovered the difference in travel. Now, my engine and transmission were replaced with remanufactured units and I don' know what they came out of. I wonder if anyone knows if there are different lengths and part numbers for the transmission shift arms for different applications/years for the C-6. Any help would be appreciated.

[OldRanger68]

Okay. I measured some different C-6 shift arms and found there ARE different lengths which will make column detents different than transmission detents preventing the transmission to be fully in the selected position, especially at the extremes (park and low). I need to find the correct length for an original 68 F-100 C-6. Any help or information will be greatly appreciated.

...Keith?

[zgerbic]

Just a quick update to this thread...

I had a similar problem with my recently purchased 69 F250. I noticed that the column shift lever moved very easily out of park to reverse. I remember other cars I have driven required pulling back on the shift lever a bit before the lever would move between part and reverse. This one required almost no backwards pressure to release it from park.

I had my column apart and thought I would figure out what the problem was. Once I got the turn signal parts out (replacing them as well) I looked at the shift mechanism. I noticed there is a hardened steel "gate" held in place with two Philips screws that restricted the movement of the shift lever. Note that the image is the back of the column bearing plate so the image is upside down. The hole for the park position would be at the top of the gate. Note other indents in the plate control putting the shifter in reverse and first. Note the grayish ware marks on the gate where the shift tab rubs against the gate. I would not expect to see any real ware between the park hole and the larger shift settings area. In theory, you should need to pull back on the shift lever to get the tab out of the hole so that horizontal area should almost be ware-free.

IMG_3342 C.jpg

The shift arm has a little metal tab that engages the gate and looked very worn, and so allowed the shift lever to move almost by gravity from park to reverse. As you move the shift lever forward and backward you can see the tab move. The right side of the tab is expected to fit into the "gate". The right side tab needs to be long enough to fit into the part hole in the gate in order to hold the shifter in park. Since there is little difference in the height of the left/right sides of the tab, the whole tab just slides across the gate with almost no detent action to control it. In this case you are dependent on the detent mechanism in the transmission to hold the shift lever in park up at the column.

IMG_3345 C.jpg

I used a very small file to change the shape of the metal tab to make it better fit the gate so it would require pulling back on the shift lever before allowing the shift lever to move from park to reverse. Note the sharper edges and how the left side is now much deeper allowing the right side of the tab to better fit into the "gate" when the shifter is released. You can remove the gate and use it to make sure the depth and shape of the right side of the tab allows the right side of the tab to fit into the gate park hole.

IMG_3347 C.jpg

I expect that the factory new metal tab would have been approximately the same as the one I filed. The shift lever works correctly now and even wiggling the lever up and down holds the shifter in the park position. This fix also makes the other selector settings work correctly.

While there may be other problems related to the transmission side of the shift linkage, this fixes the column part of the problem and may be all that is needed.

Regards

[zgerbic]

I noticed a bit of an optical illusion in the last photo. It is easier to see if you enlarge it and assume you are looking upward at the image. The left side is filed down while the right side sticks out farther so it can slip into the "shift gate". As mentioned earlier, the image showing the gate is upside down since the gate ends up facing the dash so it can engage with the column shift lever. The park slot is then at the top.

Ultimately you want the protrusion from the column shift shaft to fit into the shift gate slot you see at the bottom of the gate in the first photo. That is park. This is what keeps the weight of the column shift lever from dropping from park into reverse.

Thought I would clarify these points.

[basketcase0302]

There are a few issues that weren't discussed above.

1) Ford had a major recall on ALL their C-4's back in the 70's due to a parking pawl issue causing them to slip into reverse, (the pawl issue was discussed but not the recall). Maybe possible the C-6 had similar issues, (but my C-6 in BC #16 never gave me any issues for a few years I drove it after rebuilding).

2) Look real...hard at the two plastic bushings where the hard linkage attaches to the steeering column and at the transmission. I'd found these worn before causing a lot of slop that caused me issues.

3) Look really hard at the body bushings, (and cab mounts) as when either of these are worn it will cause major issues with your hard linkage "orientation" and shifting.