Violent shudder, need help

[dpmcvittie]

Hello, new here and truck is as well. Bought 3 months back
Specs: 1985 Silverado SWB 4x4{125000mi} 400 sbc Carb4bbl {6000mi} AT TH400
Problem: Recently while driving from a stop to around 50 at a steady acceleration no noticeable shudder. It's when cruising at 35-45mph and try to ease into acceleration it violently shudders in the mid-section to motor area, not in steering wheel or rear end or tire wobble. When it does that if i punch the throttle it accelerates out of it. I was talked into thinking distributor and vacuum advance, had shop replace that to no avail. No noticeable grease spots around axle's, pinion or transmission. Distributor did nothing. Ive been thinking mounts, driveshaft or angle protrusion. Its not lifted but additional lift springs added. Any clues? Thanks in advance

 

[87scotty]

Tires mine did that when i bought the truck it was the tires mixed with bad alignment new tread and a tape mesure alignment got her straightrned out

 

[dpmcvittie]

Well initially thought that but began out of blue 2 months after I bought the truck. I did figure something out yesterday, it only seems to do it in overdrive, in drive no.

 

[87scotty]

double and triple check all your ujoints

 

[Trixxterr]

Well, when you come up with a fix post it up. I have this exact issue, on my 2001 Tahoe 2wd, 5.3, 4L60E. I'm all ears. Been dealing with this for two yrs.. doesn't do it all the time..

 

[CSFJ]

Well initially thought that but began out of blue 2 months after I bought the truck. I did figure something out yesterday, it only seems to do it in overdrive, in drive no.

If you have o/d the you don't have a th400 trans. The th400 is a 3 speed. Most likely, you have a 700r4. My 87 v20 started doing the same thing right before I stopped driving it. Felt transmission related to me, same symptoms, shudder in o/d, ok in drive. Didn't bother to look any further into it, as I'll be replacing it with a manual trans when I put the truck back together.

 

[yevgenievich]

Torue converter clutch shudder? Disconnect connector on the side and see if it still does it. This will disabale lockup, but not good to keep it unplugged without additional cooler as trans will get hot in the highway without lockup. Assuming 700r4 or th300c trans.

 

[Rusty Nail]

^ that's right.
TCC.

 

[dpmcvittie]

Thanks, Ill try right after my turkey dinner on thursday, im off till wednesday after that.

 

[Rusty Nail]

Umm...that truck was not factory equipped with a Th-400.

I'm operating under the assumption that you have erroneously identified your equipped parts.

 

[dpmcvittie]

Correct. MD-8 is the casting number so Im assuming its THM700R4. The motor was swapped as well, its a 400 SBC and its 4x4.

 

[wzschirnt]

Hope you got this figured out and forgot to tell us.
If not, FYI - Ford (!!!) converters did this lock-up shudder thing a lot. Auto parts stores sell "Shudder Fix" for them and it seems to work just fine. Pour it in and run it. If fluid is old, change it also. Give it a try.

Good luck.
walt z.

 

[glockholiday]

Spark plug wire arcing? Causing a miss fire. They'll do it more under low rpm load. If it's been a while, plugs, wires, cap and rotor are a cheap investment.