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|Diagnosing AT Shift Problems|
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> the tranny wouldn't shift from 2nd to 3rd unless I took my
foot out of it for a moment.
> Even then, sometimes it would take several applications of the accelerator and then
> backing out to get it to shift. ...the engine would rev up like the transmission had
> slipped out of gear. I have 89,000 miles on the rig and it has the 46RE tranny. I am
> taking it in to a tranny shop that I have done business with before (not a dealership)
> in the next week or so. Comments would be welcome.
Taking it to a trusted tranny shop might be the best idea...but here's a few thoughts along the do 'cheap things first' line;
1. Get a clean paper towel and use the tranny dipstick to drop single drops of ATF fluid at four or five places on the paper towel. Clean & good ATF will leave only a faint pinkish ring after a couple minutes of absorbing. Dirty ATF will leave a dark 'bulls-eye' in the center.
2. Overfilling of the ATF fluid can cause symptoms like you tell of.
The fluid level is not supposed to be checked with the engine off ...but with the truck & tranny thoroughly warmed up...on level pavement...with the shifter in neutral. Filling the tranny to the dipstick mark with the engine off and the tranny cold will result in over filling. The manual warns against over filling as particularly bad.
Why might it be overfilled?
If you don't want to spend the $70 at Jiffy Lube, you can do a "T-tech" imitation for $31 (18 qts @ 1.70/qt of 7176ATF from Walmart)
You'll need a buddy's help, two five gallon buckets and one of those manual transfer pumps. Fill one clean five gallon bucket with 18 quarts of new 7176 ATF. Put the suction hose of the manual transfer pump into this one and plumb the discharge of the pump using an adapter into the return line from the transmission cooler back to the tranny. Let the other transmission cooler line empty in the second five gallon bucket. Have your buddy start up the truck and put it into neutral. As the old fluid comes out, pump in the new ATF at about the same rate. If you fall behind, tell your buddy to turn off the truck until you catch up.
Give the old ATF fluid a good looking over for: color, water/glycol that will separate out in a few minutes, and then swirl a magnet around in it and see what sticks to the magnet.
4. Near the throttle cable connection is a second connection for a transmission cable that is involved in shifting. Adjusting the 'cable stop' piece just a few sixteenths of an inch fore and aft will effect how soon the tranny shifts. Yours may have slipped for some reason - but that is a long shot. I certainly recomend reading the service manual/Haynes book tranny chapter before adjusting this. Mark where it is before you start moving the stop. An adjustment here might result in improvement - but only by masking a more serious problem inside the tranny that will eventually get worse.
> A friend of mine has a 99 2500 ISB auto. He's had a problem
> transmission going in and out of lockup in 4th gear, he will be
> traveling at 60-65 mph on level going and the tranny jumps in and out of
> lock-up. I know of at least one more that does the same thing. His
> dealer has replaced the control module and the tps and the truck is
> doing the same thing again. The problem seems to be worse when it is
> cold, but he travels about 40 miles to work and I'm sure the tranny
> fluid has warmed up. Hard to explain this because it's not my truck but
> would appreciate any ideas that might help out.
I've notice that same kinda thing in my 96, w/ automatic and 3:54's. It sort of bothered me when it would unlock very easily in that 60-65 range, but I figured it was in that in between area and the computer is very touchy there. I understand the thing is all computer controlled, and in that sort of "luggy" area, it needs to shift down anyway. If anyone out there thinks this isn't right, I'm also up for ideas. Note: I have rebuilt the tranny, and have the bd extra tight convertor, and hasn't changed this.
If your truck was built in late 95 or early 96 have your computer reflashed to late 96 early 97 standards this should cure the problem. The cost for this is usally free if you are on friendly ground with your dealer. K. Jones (Diesel Performance).
P.S. This also helps the guys who are having problems getting your TC
lockup switch to work properly.
Last Update: March 16, 1999