for a while, my truck has been shuddering after some shifts, and it has recently started slipping. I'll be cruising down the highway at about 60, which puts me at about 1400 revs (3.55's), and it will suddenly "slip" momentarily and then right back, with no change in throttle to entice this. Of course it's not a full shift, but more like a "partial-shift", which I conclude to be the torque converter. Am I on track with this, or out in left field? I'm not very familiar with transmissions and such... btw, I also hear an unusual rumbling sound that seems to be coming from that area, especially at higher rpm. as always, your expertise is greatly appreciated.

 

does your OD light flash?

 

With no OD flashing i would think its the trans wanting to downshift at 1400rpm with the throttle angle. WAG is tc unlock. The 1400rpm is lugging the motor. Will the same happen at a higher rpm cruise?
1400rpm at 60mph is correct? (strange)

I run 355 with a 33in tall tire. (van)

Bill

 

i agree. the main way to get the od light on our trucks is in od with converter issues.

when you say it shudders after some shifts could you elaborate? how much throttle? what shifts?

the 1400 rpm shifts sounds somewhat normal to me but can you also describe the rumbling sound in more detail?

and 60mph in my truck is 1600-1700 and i'm on 35's and 4.10's (nearly equal to stock tires with 3.55's)
to be at 1400 rpms in my truck in OD i have to be doing about 50 mph.

 

OK right off----I AM NOT AN AUTO TRANNY EXPERT!!!!!
Could it be the T.C. unlocking?

 

i ' d check your flex plate!!! thats what mine did! it cracked perfectly around the mounting bolt holes for the crank on the flex plate which the tc mounts to the flex plate. if you take the cover off the bell housing and shine a flash light up there if you can see any shiny metal or a crack up there. Oh ya its very hard to see between the tc and the flex plate. mine was grumbling so bad i thoughts i blew something in the engine it also made the belt tensioner jump like crazy. guys if i sound wrong feel free to chime in just giving my .02

 

there's no OD light, unless I set it manually.

as for the RPM's, I was trying to remember about where the revs usually ride. They're somewhere between 1400-1600 when I'm cruising at about 52-60. This is with 3.55's and 35" tires.

it shudders sometimes after the last couple shifts. it doesn't happen all the time, and neither does the slippage, which only occurs when I'm in OD, cruising somewhere around 52-60 ish. if I remember correctly, the shudder occurs mostly with low to medium throttle. If it get on it pretty hard, it usually falls on its face. other times, it will do good until the next to last shift, at which point it gets weak unless I get out of the throttle. this weak point is usually where I get some shudder.

the rumble is deep and has some vibration, and seems to be coming from the transmission area. gets worse the higher my rpms are, in the last couple gears.

the theory about the flex plate sounds pretty intriguing... anyone else have any experience with that? fordman, did your truck have the slippage as well as the rumble when this happened? were your issues only in the last couple gears?

thanks to all

 

In my experience a cracked flex plate sounds like a rod knocking in the motor. My truck did the same thing yours is doing when my torque converter went out. It took about two weeks of this happening before the O.D. light came on. After this happened I cleared the code twice but it came right back within a day or two. Hope this helps!

 

I doubt if its the flex plate. If your getting slip, and its the flex plate, that would mean that it was broke all the way around, and somehow managed to spin and reset itself. This would be about a 1 in a billion shot. If your cruising down the highway at 60 mph, IN od, just give it a LITTLE more gas. If your rps slide up as fast or faster than the speedo, then its about 95 percent its the TC. If your getting that though, the first thing I would do is wipe of the speed sensor in the rear diff. Maybe its picking up some debris. This is highly unlikely too, but VERY easy to do, and it has worked for some. My TC went bad from the crap stock cooler. Too much heat ate it.

 

My truck is a real dog off of the line and I suspect the TC also. It does have a little shudder from 2nd-3rd.
Since I'm an automatic novice I'm just guessing.

BTW what TC should I use if I do have to replace it?

 

If it was a wheel issue it would happen all the time.
The only time i can run at 1400rpm in OD is with the cruise on.
If i try to run that low of an rpm with the throttle i bounce it off the IVS switch.
Could be a TC issue. Just not enough slip to set a code as of yet. (WAG)

Bill

 

heres a weird thought, he keeps mentioning shutter, and noise. I wonder if any of that is a result of the dp hitting firewall??

 

Or the tranny itself. I have the same DP and it is a tight fit.

 

What's a DP?

BTW, learning already, didn't know the computer monitored the TC slippage. That's good to know.

 

Computer can only monitor after lockup, (when overdrive is engaged) It does NOT monitor in 1 2 3. DP is downpipe