transmission problem

[ZYGOTE]

Recently purchased a used 94 Silverado, X-cab, 4X4, 5.7, auto, w/3.42(?) rears and aftermarket tow package added by the PO.  Truck has 110K miles.  Just returned from a trip towing a loaded car trailer (5-6000 lbs) 1500 miles round trip.  Towed entire time in 3rd gear ('D' not 'Oh-D').  However, there were two or three times when I inadvertently had the truck in Oh-D when returning to interstate speed after fueling, but quickly realized my mistake and had it back in ‘D’ before going any distance of more than a mile.  With the recent hot weather (90+) and no trailer, the truck now hesitates from a stop (feels like slippage or ‘grabbing’) and seems to ‘search’ for the right gear at speed causing a moderate to severe shaking of the truck.  The ‘searching’ is especially worse with the cruise set at about 50 on long, slight hills.  Any suggestions?  Thanks.  MLS

[bassdog]

First, welcome to the forum. Glad to see another Pre-Vortec owner here

Few possible suggestions here; not 100%

Inadvertenly driving in OD won't cause those problems, I have done it towing as well.

The sliipage sounds like the "bands" need to be tightened, but the moderate to severe shaking off the truck...have more questions.

Is this in OD when this occurs? If so, yes you will be searching for the right gear on hills and such at that speed. I run "D" until ~65 on the highway, then throw in in "DOH- OD". I have also felt the rear shaking, in "OD" at about 70 - 75 trying to accelerate up a hill. I can only think of three things it could be. Converter, u-joints, or "searching" to down shift from the lock-out.

That moderate to severe shaking should be looked at, mine isn't that bad.

 

Hope this helps some.

[tfpary]

First off, I don't think there is anything, including "bands", that is easily adjustable on the 4l60e. I would change the fluid and filter, and see what happens then.  I am no transmission expert, but it sounds like there may be some junk floating around in the fluid, creating havoc in the valve body. Just a guess.

good luck!

[Guest Friz]

Even better than changing fluid and filter, have it flushed.

My mechanic calls it a "Transtech". It costs about $70.00 to do. That will flush out all of the old fluid, much better IMO than just a filter change.

Does the fluid smell burnt or appear to be black on the dipstick?

 

A few years ago, I saw a mechanic come into the yard of his shop with a pickup in tow. He had obviously overheated the tranny with the load and we could actually see smoke coming out from the vent.

He unhitched, put the tow vehicle on a lift and hooked up a 5 gallon bucket of tranny fluid to the input of the transmission and an empty bucket on the outflow. I'm talking about the lines that go to the cooler here.

He let the truck idle and ran it through all the gears (while on the lift) until all the black, stinky fluid was pumped out.

He said that that same thing had happened before and that this "flush" saved the tranny.

As far as I know, it still runs fine.

This was an old TH-350.

[ZYGOTE]

UPDATE:  (and boy, do I feel dumb, however...)

Back to Auto Mechanics 101 here for me.  Did a little more trouble shooting by way of manual shifting of the transmission, applying the brake while adding power, etc.  Shakeing occured in all gears but went away completely at mid to high rpm.  Found the problem to be MOST prevelant at lower rpm's (est 2500 or so) no matter what gear.  Began to suspect engine problem, specifically fuel or possibly spark delivery.  Changed filter, no change.  Removed/regaped plugs and inspected wires; no change. Removed distributor cap and rotor...HOLY SH*T, Batman!  Where'd all that carbon come from?  Cleaned rotor, filed carbon from contact point, reassembled and test drove.  Voila, problem fixed.  Have new rotor, dist cap and set of plug wires sitting on the workbench for installation tomorrow!

Thanks to all who offered advice and shared their experiences.  For me, I must remember the basics of fuel and  spark delivery.  

MLS