93 Suburban strange behavior

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  #1  
Old 01-02-06, 11:50 AM
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93 Suburban strange behavior

My 93 truck with 150K will run fine up to about 50 mph. Then at various hiway speeds with or without the cruise on, as soon as there's a load, like the grade of the road goes up even a little, it will start bucking and vibrating like an out of balance wheel, but worse. Soon as you push the gas pedal slightly, it will stop.

A guy at Advance suggested it was a vaccuum leak to the torque converter; during the summer sometimes my AC vents don't open through the dash and the AC comes out the floor. Not consistently, but it happens, so he surmised there's a vaccuum problem.

If someone could make a suggestion or two, I'd appreciate it.

Tranny about to go? Rear end clunks a little when you shift, but it's been doing that for a while.

Thanks to all, and Happy New Year!
 
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Old 01-02-06, 04:36 PM
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Please clarify your symptoms. Is the engine bucking and misfiring, or is there vibration in the steering wheel/chassis?

If it is vibration related, then report back the condition and mileage of the tires. A newly out of balance tire vibration will occur between 50 and 70 mph and will cease when thrust(acceleration) is applied.
 
  #3  
Old 01-02-06, 06:28 PM
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What is happening is the torque convertor clutch solenoid is engaged, and when you either tap the brake pedal or accelerate, it disengages. So, what you are experiencing, is the engine output is being disrupted by something, which when the extra load is applied, the problem is amplified. My bet is you are due for a tune up. You either have a bad plug wire or plug. Could have a bad cap and rotor also. Replace the plugs, wires, cap and rotor. I believe your problem will no longer exsist .
 
  #4  
Old 01-02-06, 09:59 PM
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Lugnut, I'm not sure. I don't think it's the engine. I believe it's the steering wheel / chassis. This engine isn't missing. Has power like a new truck all the way up, til you settle in on the Interstate and come up on a grade.

Tires should be able to go another 10K or more, good shape. I'm using a reputable tire shop/service and they say I'm balanced. I'm going to take them for a ride out on the interstate next chance I get.

Cracked rim, maybe??? I forget who suggested that.

Mr. D, did new plugs wires cap rotor @ 100K, when it was running fine and just did it because of the mileage, and couldn't really notice it was running better. I think I've had this problem for about 6 months now.

Oh, above 80 mph the problem is gone along with my mpg......

Thanks!
 
  #5  
Old 01-03-06, 03:37 AM
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question

Do you have a center bearing in the drive shaft? If so check it out and also U joints and shaft itself.It is a stab in the dark but it is cheap.Also jack up front of truck and grab tires and see if any play is in might be worn front end parts.
 
  #6  
Old 01-03-06, 04:13 PM
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I'll stand by my first post. Keep in mind that it is not a question of a "reputable" shop, nor is it about an objective statement about the alledged condition of your tires. Either you just paid to have them balanced or you did not. On a 50,000 mile tire, the remaining 10k are prime candidates for being out of balance. In fact, tires are generally only shop balanced when they are new (and are mostly balanced right off the shelf) , then never again. Sadly, it is when you wear the first 30,000 miles of rubber off, that the tire becomes unbalanced. Very few people balance old worn tires and that is when they need it the most.

It will be hard troubleshoot until you begin to narrow down the list somehow or another.
 
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