shudder

[forklifttech]

hoping for some help, feel kinda smoked as i am a mobile heavy equipment mechanic. here it is, 1988 gmc suburban 4x4, 350, auto, 4" suspension lift, 35" tires, quad shocks & dual str. stabilizer.
wicked vibration through front of truck @ certain rpm's, only under load(slight accelerating), only @ exact rpm & or speed. slow up one mph, or slightly touch gas pedal, vibrations gone!! never did this until a few months ago, always lifted w/ these tires, always rode great.
i have replaced motor mounts, tranny mount & u-joints in rear drive shaft. replaced rotors, calipers, pads, checked & regreased wheel bearings. replaced drag link & both ends. checked the entire front end, everything is tight. had tires balanced & rotated. shocks not new, but highly doubt they could cause this. from reading various posts, i am leaning toward the trans. (700r4) causing this, nothing i have done has even touched on this problem. not wasting $$, truck needed those parts, just really starting to lose sanity @ tracking this prob. down. any help to look in the right dir. greatly appreciated. john

[Carsick]

did you ever resolve this issue? My brother and friend are having the same problem with a '92 gmc van and 91 gmc pickup, both 5.7 litre's.

Problem is only under load, even at a stop. He puts it in drive, foot on the brake, slight pressure on the gas and it starts to stutter/vibrate. Much worse at 60mph.

There are no computer codes coming out. Thoughts anyone? Thanks in advance.

[MagicRat]

Well, for the forklift guy, I think the problem is in a bent or twisted driveshaft.

For Carsick, I do not think you have a driveline problem. Your engine may be running rough, (needs a tune up) or there is internal damage in the engine or torque converter

[Carsick]

It actually turned out to be a clogged fuel filter. He sure replaced a lot of parts before getting it right, and all because of $5 fuel filter. I told him to go buy a Toyota, which didn't go over very well. Thx for the reply.