Ford 6F50 3-4 and 4-5 shift flare

[The_Eric]

I've got a gal who had a used transmission installed out of state and by the time she got back home the axle shaft seal was leaking. She brought it to me and I fixed the leak with a new seal but on the road test I noticed a 3-4 and 4-5 shift flare. At first I thought that it might have been related to the battery being disconnected (I replaced the starter too) but after talking with her she said that it did this from the get-go after picking it up.

Is this a common problem, ie hard parts type failure, or is this something that can be addressed with a learn or programming change? My scan tool will reset adaptives but I don't believe that it can initiate any learns for it.

 

[Hall]

Do you still have the vehicle ? If so, put the transmission in Sport mode and go drive it. Is the flare(s) gone ? We had a Fusion with a 6F35 and a flare between 1-2 or 2-3 (one or the other, not both - I don't remember now) was pretty normal (common). When it sport mode though, it was non-existent. In my mind, that's an ECU or TCM issue, not a physical or mechanical one.

 

[ripcord]

It's just as likely a valve body issue. Leaking, sticking, worn pistons and bores in the valve body that the rebuilder did not adequately address are common after rebuilds. Here is a chart from the Sonnax website.

https://www.sonnax.com/tech_resources/491-ford-6f50-6f55-vacuum-test-guide

 

[Brian123]

If so, put the transmission in Sport mode and go drive it.

I did the same thing with the 4R75W transmission on my car, I always drove around with the trans in Overdrive, and the trans was kind of shifting gears and there was no get up and go. I turned off the overdrive, and the car was more responsive, I would only hit the overdrive button if I was cruising above 50 mph. I am cruising on a country road at 50 mph, and the rpms are a bit over 2000 rpms and what is amazing is my gas mileage was the pretty much the same as when I had the transmission in overdrive. These Ford transmissions seem to only like overdrive when you are out on the highway and you are going more than 50 mph. With the trans out of overdrive, I feel like I have 50 more Horsepower, maybe 30!

Now when I did have the car in overdrive and I wanted to really hit the gas pedal, I did take the trans out of overdrive. Around town driving and below 50 mph or 2000 rpm's keep a Ford Trans out of Overdrive!

 

[The_Eric]

Do you still have the vehicle ? If so, put the transmission in Sport mode and go drive it. Is the flare(s) gone ? We had a Fusion with a 6F35 and a flare between 1-2 or 2-3 (one or the other, not both - I don't remember now) was pretty normal (common). When it sport mode though, it was non-existent. In my mind, that's an ECU or TCM issue, not a physical or mechanical one.

Nice thought, but this is in a Taurus wagon and it doesn't have a sport mode that I can find.

 

[The_Eric]

It's just as likely a valve body issue. Leaking, sticking, worn pistons and bores in the valve body that the rebuilder did not adequately address are common after rebuilds. Here is a chart from the Sonnax website.

View attachment 345973

https://www.sonnax.com/tech_resources/491-ford-6f50-6f55-vacuum-test-guide

This is a used unit with an alleged 120k miles on it, but you could be right that the pistons in the valve body are worn/bad.

 

[Hall]

Nice thought, but this is in a Taurus wagon and it doesn't have a sport mode that I can find.

Haha, probably not ! Well, you could replicate it with your right foot. Just do some very hard acceleration runs to change the shift points.