4L80E Trans problem-

Jeff A · June 30, 2004

Problem; trans comes out of lockup momentarily(.5-1.0 second) at cruising speeds,50-70 mph, around 1800-2400 rpm(approx). Only happens when truck is fully warmed up. Have replaced (cooling system)thermostat, and fuel filter.Found some brittle vacuum hoses and replaced them and the PCV valve.All hose routings were checked and are correct. I serviced the trans and found no debris in the pan. The coolant temp gauge reads around 190 when problem occours. I took this in to a shop ,the tech said he scoped the tps and checked other sensors.Found no problem ,and sent me to the transmission clinic.The trans tech road tested it with me and his scan tool plugged in.He says everything looks normal.He feels that the trans itself is fine but it is being "told" to "act "this way.I asked him what would he do about this ? He says "sell it" I'm not going to sell it so here I am. If I drive above 80 mph and below 50 the problem dosent exist. As well as leaning lightly on the gas pedal or back ing off a bit.Its constant throttle pressure that causes the symptom. I have tested the brake switch by pulling up on the brake pedal with the top of my foot while driving.No change. If I slowly press the brake pedal while at speed,it comes out of lockup like it should then resumes when I let off. Any Ideas? Thanks!!

snoman · June 30, 2004

Which tranny does it have? A 700R4 or are you sure it is a 4L80 (there was no "E" version back then)

willscary · July 2, 2004

My '91 8600gvw 2500 has an "E" on the end. The 4 speed w/ OD electronically controlled 4L80E came out in 1991.

snoman · July 2, 2004

The torque converter lock up has long been electricallly controlled. A friend of mine has a 94 GMC 1 ton van with a 4L80 in it. It does not have a electronically controlled valve body like the newer 4L80 E's do so I guess it depends on how you define the "E" version.

muleman44 · July 31, 2004

Hi Guys, I have a 91' Burb with the 7.4 ltr. / 4L80E it does the same thing. I took it to the trans shop for answers, they said it was normal. I asked them before I bought the truck, which truck has the most bullet proof trans made and they said buy some thing with a 4L80E. I tow a 28 ft. T.T. that is around 7200 lbs. and I notice it more when towing than not. Trans temp when towing runs around 220 degs. and engine temp. is around 210 degs., they said this normaland drive it. I drive it daily to work (32 miles one way) and average around 62 mph.