Well, here's my problem. When I'm driving along easy (you know, trying to get halfway decent mileage, ha) the trans seems to shudder, almost like the engine skips a little in third gear. Mostly when its getting ready to shift into 4th and when I'm in town in a 30 mph zone. Doesn't seem to matter whether the O/D is on or off. But if I drive it a little harder it shifts fine, goes into 4th no problem. Doesn't seem to slip. If I gas it when the shuddering starts it doesn't rev way up like if it was slipping, it will downshift or go into 4th (or lock the t/c, which ever comes first), depending on how much throttle it's given. Only mods are K & N cold air intake and Summit dual exhaust. Just turned 100,000. I don't race it or beat on it and only tow occasionally.

Any ideas? Thanks

 

100k - still on the original spark plugs? Which engine, please.

 

Not sure about plugs, i've had the truck a year and haven't changed them. Engine is 4.6. If the plugs were the problem, wouldn't i get the shudder in all gears?

 

Not necessarily. The symptoms of a low grade misfire show up at low rpm's and light throttle openings, that's when the PCM is telling it to run super lean. Your K&N and the exhaust mods only make it worse unless you get a custom tune. I would recommend you change the plugs, use only OEM Motorcraft.

 

I'll give that a try. Looks like a pain to get to some of the plugs, not like my old 351M plow truck ('84 F150 4X4) and 360-powered wood hauler ('70 F250 4X4).

Thanks

 

Got the plugs changed. Put Motorcraft Platinums in it (thats what came out). Still have the tranny issue but at least I've got new plugs so I can check that off the list.

 

sounds like some minor slipage to me. It's doesn't rev way up when you gas it, because your also increasing line pressure. Under the light excelleration, your starving your clutch of fluid, and they must be getting warn and allowing some slipping. These clutch packs in the 4r70 are smaller then some light cars ! It sucks, but its what we got (just blew mine out not too long ago, and got finished with a rebuild/upgrade). If you go with a rebuild, you can stick a couple more clutchs in the pack to give it a little more hold (only use Borg-Warner). Some other mods to try and help these trans live longer are out there too.

When was the last time fluid was changed ? A full flush, not just what's in the pan ?

 

Change your transmission fluid. Probably will fix it. This is a generic problem with the 4R70W. It is the torque converter mechanical lockup slipping. Or at least that is what it was on my 95 Mark VIII and from the Mark message board, it happened to almost every owner. Changing the fluid fixed mine. The shudder felt like driving over a railroad track.