4L80E Dropping out of 4th Gear

my 4L80E was dropping out of 4th gear when I would hit 55mph or 2500 rpm, I called TCI and they said check the pressure, I was at 75PSI well below spec of 150 to 175psi. so they said change pump. I installed a new pump and got 70psi. so I was told to change all the solenoids and the wiring Harness and vehicle speed sensor. I did all of that and the ruck drives worse than ever, it lags off the line and drops out of 3rd gear also and just revs up.

local transmission shop says I need a new tranny at 5k TCI thinks its electrical not mechanical. every shop around town just wants to rebuild it and I say if it reoccurs the same thing will my transmission be free. no one wants to diagnose or fix electronics they want to replace and if it is still electrically bad they want to send it out any way.

the truck is a 1996 k2500, with a 6.5 turbo diesel truck has 150,000 miles on it Transmission has 15,000 miles on it, new motor has 700 miles on it. I didn't need a new motor or tranny, I just wanted upgraded stuff. maybe once a year I might tow something but have never towed anything over 2000 pounds.

I am at my wits end

Can the 4L be manually controlled using a Tech II scan tool? I suspect it can be. A ride-along with a good tech (with a scan tool) might answer some questions.

That said, we always recommend changing the fluid and filter before assuming something more serious.

Forgot to ask... Are any trouble codes being set? If so, what are they?

The Fluid and Filter have been changed, there are no codes. I just ordered a scanner, from the Matco tool truck at the end of my complex, this is a must have tool. the truck isn't my daily driver, but I would like to drive it. what bothers me is how No one wants to diagnose a problem, they just quickly want to replace and move on. what has happened in the Automotive world.

Quote:

---

Originally Posted by Philsky

what bothers me is how No one wants to diagnose a problem, they just quickly want to replace and move on. what has happened in the Automotive world.

---

My neighbor was ready to sell his Suburban because everyone was quoting him an arm and a leg (four or five thousand) to replace his transfer case. He talked to me to see if I’d be interested in it and I asked why they weren’t giving him a quote to rebuild it. Gave him the name of a place and less than $500 later he was back in business.

You should be able to do a little investigative work to locate a reliable transmission mechanic who won't take advantage of you.

Visit a local tire center or auto parts store. Talk to the counter man (woman) or manager and ask about a reliable trans shop. You know a transmission shop will be doing business with the local auto parts store. They should know each other pretty well.

Ask them where they would take their own vehicle for service.

Soooooo.

You have removed the tranny and installed a new pump ??

Are there signs of burnt frictions ???? nasty smelling oil ???

If the oil is clean my first suspect would be the pressure regulator Valve or spring.

If the spring has broken or the valve is stuck this can be the cause right quick.

Did you replace the entire front pump assembly or just the pump rotors ???

The regulator is in the front assembly and easily removed, but the tranny has to come back out and on the bench.

The other possibility could be a BIG internal leak.


If it were mine I would yard it out and rip it down and carefully snoop through it's innards and check all the seals, seal rings, stator support and right on back.

A stuck pressure regulator or spring will sure foul things.

A scored bore/valve can just drive you crazy, and the only way to find the issue is LOOK FOR IT.

Sorry to say, but the real likely hood of a scanner finding the issue is low.

This said, before you rip the thing out and apart (Again) do check the thing with the scanner and make sure the ECM is calling for the shifts and that the solenoids are responding.

The scanner will tell you that.

Now, with all this said there is one more thing to check before ripping it apart.

The Pressure control solenoid (Right rear of the valve body)

Has to wires to it DO NOT TEST WITH 12 volts

If this unit is stuck in its bores or ??? it can cause low pressure.

Easy check is to drop the pan, remove the PCS and look it over.

If the valve looks ok and is not scored the easy way to test it is to swap in a new one.

An electrical failure will normally set a code, buttttttttttttttttttt these can fail and not show a code.

Keep us in the loop

Quote:

---

Originally Posted by More Power

You should be able to do a little investigative work to locate a reliable transmission mechanic who won't take advantage of you.

---

The 4L60E burned up in my wife's Envoy last month. I was able to locate a local racing shop who specializes in transmissions. I dropped the vehicle off on a Tuesday morning, and had it back in my hands Thursday evening. They rebuilt the tranny faster and cheaper than anyone else, and were able to show me the bad parts, as well as explain the upgraded parts they used. I was very, very pleased with the whole experience. Shifts better than ever, and with the upgraded parts, now the lock-up function works like I expected it to!

Just for future reference, Steve at Cantrell Racing in Joplin, MO is the place to go: (417) 659-8071

Casey