4-3 Downshift Rough

[Dfishrmn]

I have recently noticed a rough downshift from 4 to 3 at lower speeds. It is fine when kicking it in to passing gear except for a lag or plateau before it starts to accelerate. At lower speeds it seems to have a hesitation then just jumps to 3rd, even at a normal downshift (coming to a stoplight, etc.) Kinda hard to explain the feeling but is not normal. This just started happening after I installed a 14" Magnaflow muffler on an otherwise stock exhaust. Bill said there was no need to re-program because of this mod so don't know what is wrong. Maybe a coincidence with the Magnaflow. I am running the shift firmness at +10 on all shifts, besides that no modifications to the custom 87 performance tune as far as shifts are concerned. Tranny had a complete flush 10K miles ago at 35,000 mi. The downshift doesn't rattle your teeth but is annoying! Also wonder why it has the "flat spot" mentioned previously when downshifting in heavier acceleration situations. I would appreciate any input!

[Jackpine]

I think you DO have custom tunes, is that right?

I'm a bit surprised at your +10 shift settings. Bill sets up the shift pressures to be about optimum in his custom tunes, and I've left mine at 0 - the shifts still feel like a "boot" in the rear to me. Bluejay, long time user of custom tunes over on the f150Forum uses only a +6 firmness setting I think on the 3-4 shift.

But, you're talking about downshift, which may be a whole new thing. I wonder if the torque converter is staying locked longer than it should? Possibly try adjusting the TC unlock in the positive direction for 4-3 downshift? It won't hurt anything to try, and I'd try a setting of +5. (You can go all the way to +/- 10 at 3-4, 4-3 upshift/downshift).

If that doesn't work, I expect the Mad Doctor will have to work his magic.

- Jack

[Dfishrmn]

Originally Posted by JackandJanet

I think you DO have custom tunes, is that right?

I'm a bit surprised at your +10 shift settings. Bill sets up the shift pressures to be about optimum in his custom tunes, and I've left mine at 0 - the shifts still feel like a "boot" in the rear to me. Bluejay, long time user of custom tunes over on the f150Forum uses only a +6 firmness setting I think on the 3-4 shift.

But, you're talking about downshift, which may be a whole new thing. I wonder if the torque converter is staying locked longer than it should? Possibly try adjusting the TC unlock in the positive direction for 4-3 downshift? It won't hurt anything to try, and I'd try a setting of +5. (You can go all the way to +/- 10 at 3-4, 4-3 upshift/downshift).

If that doesn't work, I expect the Mad Doctor will have to work his magic.

- Jack

Yes I have the custom 87 Performance. I'll give the TC unlock a try and let you know how it comes out. I'll back the firmness off a bit too just to see how that works. Thanks for your input Jack!

[Dfishrmn]

Just an update here. I tried increasing increasing the 4-3 unlock by 5 and it seemed to help. I then upped it to +8 and that helped a little more. It still is noticable but not near what it was. I'm a little concerned about increasing it any more than that. Thanks for the input Jack!

[Power Hungry]

The thing to be careful with is to avoid crossing the unlock points past the lockup points. This can cause erratic converter operation. If you raise the unlock point, also make sure to raise the corresponding lockup point around the same amount.