Trans has a little under 9k miles since rebuild by a well know shop here in Texas. Truck is completely stock. What I found was the front speed sensor unplugged and also the vent clogged with mud. Would those cause pressures high enough to blow the front seal? The truck moves on its own when I fill the trans, but leaks it all out in a matter of minutes. I was hoping I could just change the fluid (brownish red), filter, and forward clutches. Does that make sense?

 

the vent was clogged.

 

Clogged vent will cause the seal to blow out pretty quick. It needs to come out and inspect for any damage. If its trying to drive forward in neutral, then the forward clutch is welded together. Could be from the low fluid level, or you could have more issues. Such as pump damage, spun front pump bushing, etc. Forward clutch rarely fails, and its almost always caused by low pressure or low fluid.

 

It acts completely normal when the fluid is full. I drove it once when it was a company truck and it drove fine. I bought it, but before I could take delivery of it, my coworkers took it and left it in a pond saying the transmission went out. I had the truck towed to the front office, filled the trans and started it. It didn't move so I just assumed it needed a new trans. Towed it home and about 2 years later I decide to fill the trans up again and this time I notice the transfer case was in Neutral. I drove the truck 40 feet to my car port and proceeded to drop the trans.
I'm hoping I can get away with just changing the clutches and steels...no bushings, seals, or hard to install parts.

 

At a minimum I would be replacing; front pump bushing, inspecting the pump gears, and the cast in pump crescent, front pump seal, possibly the torque converter if the neck has ANY damage where the seal, or bushing ride. Further, tear the unit down and inspect ALL bushings. If this trans has over 100K miles on it you are going to find that the sun gear tube bushings are worn, and potentially the center support bushing. The 80E is HARD on those bushings I just mentioned. It's best to replace them ALL. You can also substitute a C6 pump bushing for the case bushing and gain significant surface support area for the output shaft. The inner, or small, pump gear is known to have wear where it engages the tangs on the torque converter. Inspect those inner gear flats VERY carefully. New pump gears are cheap, and are a smart investment.

Your statement " I'm hoping I can get away with just changing the clutches and steels...no bushings, seals, or hard to install parts" is possible but in no way practical, or prudent. If you have the trans out, now is the exact, perfect, time to replace bushings, seals, and anything else that needs attention. Cutting corners while you have it out now will mean you may get to pull it a 2nd time in the near future.. Do it once, do it right.

When you get it apart inspect the internal diameter of the direct drum where the center support sealing rings ride. Any damage inside that drum IS going to be a problem later. At my shop we will only install the 1 piece (non scarf-cut) teflon sealing rings. We will NEVER use the factory hard plastic sealing rings under any circumstances. If you find your direct drum has grooves cut inside where the rings ride, you can purchase a new drum, or have the drum machined and a Sonnax bushing pressed in that restores sealing ring mating surface integrity. We machine our drums in house and put the bushing in. Also, if there are grooves in the direct drum, inspect the sealing ring grooves on the center support for wear and/or damage as well. If the ring lands have contacted the inside of the drum due to worn bushings, you may find that the sealing rings will bind in the grooves. This is a big problem that will necessitate a rebuild very shortly if you miss it. Also, the BIGGEST problem that we see with 80E's is loss of reverse..... So, while you have it apart-replace the reverse band!

I know you said it was rebuilt <9K miles ago, but I would not trust in anything anybody has told me unless I was there to witness it myself. What you have been told may, or may not, be true. Once you get it out, YOU need to visually inspect it all yourself, or take it to someone who is knowledgeable on these units, and have it gone through again. Also, do not forget to check for the presence, and condition of, the dowel pins on the back of the motor. Missing, or pins that are pressed too far into the block will cause rapid pump wear, destruction of the torque converter neck, and failure of the pump bushing and/or seal.. The dowel pins are another area people rarely think about until it destroys a pump, and takes the trans out with it. PLEASE post back and let us know if you tear it down. I will support you in any way that I can. Pics are AWESOME for other people who want to learn about these units.

 

You're completely right, now is the time to do a full rebuild on it. I do know for a fact that it was rebuilt less that 9K ago. It's in the truck's history report and was done at a well known transmission shop (I believe Century transmission).
There is some damage to the converter neck, it has a deep scratch all the way around it near the base. Front seal seems to have a little lip cut out of it too. Looks like I need to decide if I can tackle the rebuild or take it to a local shop.

 

Sicksilverado I pm you . If you could please get back to me asap need to ask You some questions thanks

 

I know this thread is about 6 months old but hopefully you guys can help out.

Did an LS swap with 4l80e in my Silverado. Got a donor trans from a 1996 C2500 with 81k miles. Before I swapped it in, I changed all the external seals (extension housing, output shaft, shift shaft, front seal, TCC o-ring, etc) and put a brand new Circle D 3200 278mm stall converter in it. Did the base 4l80e segment swap in the Green/Blue PCM. Put it in with brand new trans cooler lines (no kinks or restrictions) and a brand new radiator from a 1 ton 454 truck with external stock trans cooler added in front.

Took the truck for a drive yesterday and did a decent pull and next thing I notice smoke in the rearview and it wasn't rubber burning. Pulled over and it was puking trans fluid from the converter area. Towed it home and pulled trans. Front seal was blown out. Inspected everything. Pump drain and vent on top of trans were clear. Converter bushing was fine with no scoring. Bushing had not floated forward either. Torque converter snout was smooth with no wear. Put another new seal (National 4598) in it using #1 Brown Gasket Maker around the edges this time. Let it sit overnight and drove it this morning about 20-30 miles. Checked it with my inspection camera and I can see the seal pushing out again.

I have logged my drives since the swap using my VCM Scanner and the temps have been hanging 150-160* warmed up. No abnormal shifting/harsh shifting. Any ideas why this seal wants to work it's way out?
I'm pretty sure the original seal I took out was the one from the factory with 81k miles on it. It didn't push that one out prior to the swap.

Literally the only thing changed is the converter and external seals and the vehicle it's in. Any ideas?

 

did it have the seal retainer over the seal ?

 

4L80E's don't use a retainer on the seal.

 

You hit the nail on the head.

 

Currently experiencing the exact same issue with a trans built by a reputable guy in “Texas”. Trans was bought about 3-4 years ago and just getting the truck it’s in running. Will drive fine for about 20-30 minutes, then start to get that trans fluid smell. Put it on the lift and sure enough, coming from the pump seal. Trans and triple disc converter are both from said shop.. any advice on where to start looking would be great! Will change out the seal first and obviously inspect the bushing and converter snout mentioned above. Would like to diagnose first before I bug the shop that built it. Thanks in advance for any advice