93 K3500 Trans Issue/bad fuel milage

[neura]

So last week I hauled a load of lumber home for the new fence, truck worked perfect, dropped the trailer and drove around through out the day and the next day, cut down a tree and went to haul out all of the branches and the truck started to slip above 40 Km/h sometimes it would just rev like in neutral, sometimes it would shift fine into 3rd and 4th, and lockup the od and be fine up past 100KM/h. limped the truck back home and checked trans fluid, it is up, but brown.... so I am thinking fluid and filter for sure, just it seems more like an electrical problem like the trans temp sensor in the pan causing the issue. this is a 93 K3500 and I can grab another trans for $500, but think it might be worth it to fix this one. and also I dont know if the $500 trans from a 94 would work on the 93.. need to look at that first...

Also thinking it might be time to change the gearing out in the front and rear diffs while it is down since I am down to around 11 MPG now.. I have 4:10 in there now, but have been thinking about going down to 3:46 gears...

 

[bk95td]

You need to get a scan tool connected to see what the computer is seeing. Engine rpm or input speed sensor or throttle position sensor could be not giving a signal or a bad ground.The ground for the transmission is on the rear of the intake manifold,black 10-12 ga. wire. The big main connector on the transmission could be full of oil/trans fluid also.There is a slight possibility that the tcm/computer is bad. Scan tool is your friend.

 

[buddy]

I would suspect the TPS to PCM communication first. Main Line Pressure and Shift Offset pressure is controlled by throttle position and speed, although all pressure curves that I have seen were equivalent on the speed axis, so TPS becomes most important variable. You can probably watch it on a scan tool to see if your TPS input shows an appropriate amount for how far your foot is down on the pedal. If it stays low in the 25% and under area then pressure will suffer greatly

Otherwise the solenoids in these trannys dont cost too much and there are kits to address common shifting/slifting on aged ones that have worn the valves on the solenoids.

 

[bk95td]

When I would loose the throttle signal on my 92 it would shift very hard and have no overdrive and no lockup. That ended up being a bad ecm. It would reset when you shut the engine off.
Input speed or engine rpm would make it not make enough pressure and slip. The input speed sensor could be gunked up with metal filings[it's magnetic]. Remove and clean. Check connectors for bent or loose pins. A loose pin will push out instead of making a connection.

 

[WarWagon]

Paper clip the ALDL and check for codes from the SES light. These 1993 "stupid" computers will not turn on the SES light for codes. Not sure why but they don't. Store them just fine...

 

[neura]

decided I would drop the truck off at the trans shop and have them take a look. well they took a look and more then electronic failures, clutches are slipping, torque is done etc etc.. time for a rebuild or a replacement. I figure a 93 and 345KM on it, probably another used tranny or what do I need to change to say go up to an alison 1000 series? I heard that the bolt pattern is the same, so what would need to be done to the computer/wiring to make the alison work? it seems around here I can find an alison trans for cheaper then a 4L80E, and it is hard to find one for a 91-93 pickup, so if I can't find one out of a 91-93 what needs to be changed on the newer trans to make them work for the 91-93's?

 

[buddy]

Just rebuild what you have. Solenoids are cheap enough and there is the sure cure kits to prevent the problem again. The shop will always paint the worst picture. You could probably drop the pan and replace a couple solenoids for $100 and be good to go. All the solenoids are like $150.

 

[WarWagon]

Local trans shop here will do in and out with full rebuild inc tq converter for $895 plus hard parts. Mine cost $1200 with new OD gearset and all new electronics.

 

[bk95td]

Many crooked tranny shops out there. Their favorite words are"you need a FULL rebuild." Unless severly abused these trannys can last over 300,000 miles.[600,000km]Here's a place that sells the solenoid kit http://www.electricaladvantage.net/4l80esolenoidmasterkitwinternalharness.aspx
I still say there is a input speed sensor or other electrical problem. At the very least get another opinion[with scan results]