Just noticed this in my 2002 Ford F150 Supercrew with a 4R70W transmission.

Somewhere around 45-55 mph, just before the transmission shifts up to 4th gear, there's a slight shudder that feels like it's coming from the transmission. Think a little like driving over a washboard. This only happens under light acceleration and goes away when moderate throttle is applied forcing a downshift to build RPMs, then it doesn't shudder on the next upshift. Only seems to affects shifts between 45-55 mph and only under light throttle.

I've read that this is a known issue for 4R70W transmissions and torque converters and Internet solutions abound––complete fluid flush and filter change (it was done around 20,000 miles ago so it's a little early for a change), add a Ford friction modifier (although I'm familiar with these for differentials not transmissions), switch the Mercon V transmission fluid, replace the torque converter, have the transmission rebuilt, or live with it.

Take note that the truck doesn't shift hard on any gears, has never towed anything, and has been well-maintained. It really feels like something is slipping and catching and when a little power is applied, everything locks up the way it should.

What say y'all, hive mind? Any suggestions?

ETA:

Based on further reading, this could also be indicative of a failing coil pack or spark plug. No codes being thrown so I'm at a loss as to diagnose whether one is going south.

Without being there to diagnose it myself, I'd guess torque converter shudder.   I believe this is the case due to the steps needed to make it do that––light acceleration (unlocking TC, no downshift); between 45-55MPH, which puts you right at 1500-1900RPM in OD, ballparked, is the average "lockup" speed for most OE converters.

This can be caused by a lack of fluid, bad solenoid or not enough line pressure.

It sounds to me like torque converter shudder. This is a common problem on many Ford automatic transmissions. The cause is due to Ford's stupid sloppy ass programming that allows torque converter slippage when it is supposed to lock. I recall it was done so old geezers don't complain about harsh driveability. The slippage is a major problem in 3rd gear and overdrive when the TC is commanded to lockup. The stock programming also unlocks the converter when you tip in your throttle, which is why the shudder goes away when you stab the throttle.



Band-aid fixes include changing the fluid, adding more friction modifier, use a Dr. Shudder mechanic in a bottle product, etc...



Permanent fix: New torque converter and change the programming to eliminate all slippage when the torque converter is supposed to lock (usually SCT or another aftermarket tuner can do it).



 

Gotcha... I guess I'll live with it until I decide to have the transmission rebuilt, then have a new TC put in at that time.

Well, not willing to leave well enough alone, I took the truck over to the recommended local transmission shop this past Saturday and had all the fluid flushed, changed, a new filter installed, and everything inspected. The transmission service didn't fix the issue. In the opinion of the mechanic at the transmission shop, the transmission is in great condition and isn't the cause of the issue. He said he believed it was a misfire. At that point, I was leaning that way as well.

Later that day, I took dear ole' Dad, a former mechanic from his youth, for a ride and he thought it was a vibration, not a shudder, and he said his opinion was that one or both u-joints needed to be replaced.

That seemed to make sense, but I was stuck on misfire.

Then, we had a bit of a cold weather snap and the "shudder" really got worse, especially at highway speeds and under throttle.

I stopped by my local mechanic's shop and grabbed a tech for a test drive. We didn't make it far before he said "coil pack and spark plug"––the problem was no CEL! Other than expensive testing there is no way to tell which coil pack is failing until a code is thrown.

So, this morning, I set about to get the PCM to set a code... after about three laps on Interstate 45 of 15-20 miles at 85 miles another, bucking all the way, the CEL came on! EUREKA! P0301 Cylinder #1 Misfire!

So, while I sit here typing this, it's at the shop getting a new coil, spark plug, and an oil change. I'd do it myself but it's cold outside and it's hard to work on a truck and surf ARFCOM simulanteously (although not impossible).

Another common problem with Ford modular V8 engines is misfires. My 4.6 2V constantly sets off P0300, P0301, P0302, P0303, and P0304 - but guess what? No shudder or bucking at any speed or gear.



It sounds like a misfire might be the cause of your shudder, but the fact that you only feel the shudder in overdrive at 45-55 MPH suggests it is the torque converter clutch. Hopefully the new coil pack fixes it. Ford coil packs are overly sensitive to moisture and easily short out.

Just picked the truck up from the shop and took it for a drive down the freeway.

Thought I felt a few misses, but nothing like what it was doing before. Also noticed a lot more responsive throttle and more power on take-off. Evidently, in this case, it was the coil pack.

I went back and looked through the previous owner's maintenance records on this truck.

At 101,000, coil pack and plug on #5.
At 135,000, coil pack and plug on #3.
At 148,000, coil pack and plug on #7.
At 165,000, coil pack and plug on #8.
Now, at 176,000 coil pack and plug on #1.

I'm just going to set aside a little cash over the next few months and have the remaining original coil packs replaced when the next one goes out. My mechanic was very specific though––don't waste your time with non-Motorcraft coils. Bite the bullet and pay $90 each rather than being cheap and buying the aftermarket.

All total it was a little over $170 for coil pack, new spark plug, an oil change with filter, and labor.

Given the issues with spark plugs breaking and the threads in the heads stripping out, I think I'll let the professionals with the tools work on this one.

If the threads in the head strip out (common problem with Fords), get Timeserts.