Weird 4l80e problem.

[CarolinaOBS]

Ok i have a 96 suburban 454/4l80e combo. I have recently noticed the truck uses transmission fluid (about a quart a month driving about 400 miles a month), i cannot find a visible leak. Truck has a random occasional harsh shutter upon accelerating from a dead stop, or cruising at low rpms. Occasional(rare, usually after a shudder previously mentioned) HARSH 1-2 shift. Cruise control doesn't work , sometimes on highway won't lock the tc up unless you manually shift from 3 to OD then it locks up. Most of the time everything works fine and it shifts normal and tc locks up, but cruise will not work no matter what. But these issues happen at random times.

note: the transmission was rebuilt at some point in its life

please help.

 

[burnhedge]

Is it 4wd? Missing fluid may be in the transfer case.

Sent from my SCH-R970 using Tapatalk

 

[Christian Steffen]

If it is shifting real hard and not locking, it is probably throwing a code that doesn't illuminate the CEL. Do you have access to a scanner?

 

[rhino]

Check the brake switch. It would account for no lockup and no cruise. If that isn't it, look at the TPS. But I bet that brake switch is it. The only place the fluid can go is in the radiator if it isn't going on the ground. But.... my bet is the brake switch is stuck on, causing no lockup, overheating the trans, causing it to blow a little out of the vent.

 

[CarolinaOBS]

Check the brake switch. It would account for no lockup and no cruise. If that isn't it, look at the TPS. But I bet that brake switch is it. The only place the fluid can go is in the radiator if it isn't going on the ground. But.... my bet is the brake switch is stuck on, causing no lockup, overheating the trans, causing it to blow a little out of the vent.

this sounds like a probable issue, i recently had to put a new brake booster in and may have damaged the original brake switch. Ill just get a new one.
Transmission is 2wd. maybe its leaking from the front of the pan where theres a little oil from the rear main of the motor, ill double check to make sure it isn't dripping there, i just put a new radiator in the thing.

If it is shifting real hard and not locking, it is probably throwing a code that doesn't illuminate the CEL. Do you have access to a scanner?

Whenever the issue arises yes it shifts hard with what feels like TC chatter when it shifts. I have a nice scan tool and hooked it up, throwing no codes or pending codes?

 

[Christian Steffen]

I bet rhino is correct. When the transmission reaches the set limit for temperature it probably reduces the shift times, increases the line pressure, and locks the tc really early to reduce friction and heat buildup.

 

[mykytiuk]

Had some of the same issues shifting. Took to a tranny shop and spent $800 replacing sensors and solenoids and such. Worked for a day. Took it back and spent another couple hundred fixing wiring and a "bad" sensor that was put in. Worked for another day. Enough of this!!! Read a few things and the TPS was mentioned a couple times. Put a used one on and instant fix! Also had a leak that I couldn't pinpoint until I left it idle for about a half hour on clean concrete. Tiny leak under pressure.

 

[Tzfbird]

The TPS is the most or tied with VSS for the most important sensors regarding electronic transmission operation.
I had a bad TPS pigtail on a '95 S10 that caused random Torque Converter locking/unlocking and erratic up/down shifts. It took testing and replacing multiple sensors before I figured it out. A test with a meter would test good everywhere but when the pigtail was connected to the sensor it was not making a good connection between the male and female pins. That fight lasted almost a year of off-and-on work and could have been fixed for $5 in about 15 minutes.

 

[Supercharged111]

A cheap crappy Harbor Freight scanner will display live TPS data.