I have a 93 Blazer that I bought a few years back. It is a 4wd with the 4L60E overdrive trans. Last spring, it would not shift out of first gear. It would shift if I manually shifted from 1st to 2nd, but from 2nd to 3rd would be like if I put it in neutral. So I talked to a very reputable trans builder in my area and he had me check out all the soleniods, etc. Everything checked out fine so I wound up removing it and having it rebuilt. I just installed it last week and it's still doing the same thing. It won't shift out of first while in drive, etc.

I am at my wits end and was hoping someone could steer me in the right direction. I searched the forum before I wrote this and could not find any similiar problems. Is there a fuse that feeds the trans that might be blown? The speedometer works so I am assuming the VSS or speed sensor is working fine. Is there more that one speed sensor?

Any help would be appreciated!

Thanks...

Tom

 

I had a simliar problem on my ford thunderbird. I actually found out at the throttle cable there was a shift linkage tha was broken, so when driving the throttle also controlled whent he trans shifted, something that had to do with pressure or something...anywhay they fixed the linkage and adjusted all those cables by the throttle. Maybe u might have a cable from the trans thats attached there too. Check that out, i know it might be a long shot but worth a shot

 

Check this site out for how to adjust the "TV" cable.


http://www.tvmadeez.com/article/index.php

 

The 4l60E is electronically controlled. No cables. The computer gets information from the engine and decides what gear to go in. I would take it to the transmission shop and have them put in a break out box. It's a computer that the trans tech uses to control the transmission and can activate any solenoid and make the tranny go in any gear. I replaced a 4l80E that would only run in 2nd even after being rebuilt and it was the wiring harness inside the tranny that was bad. Lucky for us. LOL If it had been wiring in the truck, that would have taken a while to trace back!

 

Here is some background I received from a friend of mine that might be helpful to someone. I am going to hook it up to a Snap on Tool next week so I'll post my results...

Is there a single power supply to the trans? (fuse issue)
Should be only a PCM fuse. If the fuse is blown you would only have 2nd and reverse, according to the solenoid logic.

Is there a separate computer that controls the trans or is it in the central ECM?
Not entirely sure for that year, but it is most likely One computer for engine and trans.
(Powertrain Control Module)

I know you have shifted your trans with switches is that an option to eliminate the trans as the problem?
You can possibly 'manually' override the computer and control the trans by Grounding the appropriate
solenoid wires to the trans, you would need a service manual for the schematic .This would be a good check to verify that the trans is OK and point you in the direction of your computer's
output. First thing I can think of is that the computer may be 'seeing' a high throttle opening due to a bad TPS or
incorrect reading, this can cause Very late shifts. If you can grab a good scanner tool, that would help to see what's going on
while your driving this thing. You want to be able to watch the VSS and TPS readings and if possible the shift "requests" from
the computer.

I don't have any logic, is that available?
The logic works like this:
The general shift algorithm (my homebrew one is similar) needs at least the following basic inputs to provide outputs (listed in Order of importance):
-VSS (higher vehicle speed = higher gear)
-TPS (high throttle = late, hard shift)
-MAP (low vacuum reading = hard shift)
-engine RPM (used primarily when TPS gives a full throttle condition and also a threshold value to prevent overrevving the engine)
-coolant temp sensor (cold temp prevent TCC lockup and cause slightly later shifts)

Outputs from the computer are 'Grounds' sent to the shift solenoids listed below:
'A' ON, 'B' OFF = 1st Gear
A' OFF, 'B' OFF = 2nd Gear
A' OFF, 'B' ON = 3rd Gear
A' ON, 'B' ON = 4th Gear


Could it be the VSS? The Speedo work fine?
If your speedometer is working then the vehicle speed sensor on the output shaft is working properly.

 

Ok... Quick update. I plugged the truck into Snapon scan tool and it claims the VSS is bad. So I changed the VSS and still no shift. I checked the wires from the VSS to under the dash and they were fine. I understand that there is a 'buffer' that translates the signal from the VSS before it hits the computer. Has anyone heard of this???

Thanks...

Tom