Shaking/vibration under load in OD

[Talon762]

86 Jimmy, 355/700R4/NP208 stock axles no lift

Drives great in all gears including 4th until the torque converter locks up, then whenever you apply more than 10% throttle (approx) the whole vehicle starts to violently shake until you let off the gas or downshift (truck will do 65-70 with no vibrations so its only when the TC locks up)

Engine/trans mounts look fine but I intend to replace them just in case.. any other ideas?

 

[Wes Harden]

change your trans oil. Has the trans gotten hot, maybe towing or something ?

make sure it dexron 3

 

[Talon762]

change your trans oil. Has the trans gotten hot, maybe towing or something ?

make sure it dexron 3

Changed the trans fluid about a month ago when I did an oil change, old fluid looked fine and didnt smell burnt to me, I've never towed with it but I've only owned it a year so I'm not sure how hard it was used by the P.O

 

[Wes Harden]

is shudder is new? how many miles on fluid?

 

[Talon762]

is shudder is new? how many miles on fluid?

Less than 50 on the fluid, I've put maybe 200 on the whole truck since I've bought it, and 90% of that was driving it to work (top speed of 35 so never enough for the TC to lock) the shudder was there the first time I drove it on the highway shortly after buying it but I attributed that to the bad harmonic balancer which was replaced to no effect

 

[Wes Harden]

mine did that I thought it was a trans problem more than once turned out to be fuel delivery. ethanol and a carb with low rpm in forth. I put a holly red pump with return to tank, set at 6 psi. Upped the needle and seat from .107 to .147 dia and 1 set stronger spring under main metering rods. I raise the float level but I have since lowered it once and am considering lowering it 1/32nd again.

 

[Wes Harden]

even an inexpensive micro pump, w/o regulator, was enough to improve drivability, but they didn't last.

 

[dyeager535]

Should be able to very lightly apply the brakes while maintaining speed to get the converter to unlock while cruising. Still have to ensure that is happening (Tachometer is helpful here), I could never tell by sound the unlock was happening in my rig.

If its the TCC causing the issue, you'd know once it unlocks from the brake apply I suppose.

 

[ccj8008]

Add some friction modifier to promote proper lock-up on your torque converter: https://www.napaonline.com/en/p/BK_7652883

You may want to pump out your transmission fluid via the radiator cooler lines first for a proper transmission flush.