Hey all,

I've got an 01 Excursion 7.3 Limited RWD with 350,00p miles that's been leaking transmission fluid from the bottom of the bellhousing. Now I read about the input shaft seal likely being the leak so that's where I headed and I've got the trans sitting on my garage floor and I'm looking for some advice.

Does the quality of seal matter for the input shaft or can I just get one from rockauto/local parts store? I assume I should replace the dipstick o-ring and the TC o-ring while I'm in here, but should I consider replacing the the whole torque converter?
My FIL was the previous owner since 120k and has said as far as he knows, the transmission has never been taken off, aka original seals and converter. The truck only ever had issues shifting when it was running low on fluid from the leak, normally runs perfect even when towing. It's stock except for a downpipe and tuner.

My plan is for relatively light towing, I autocross a 2023 Mazda Miata and will tow it to events, and maybe tow a camper or boat on occasion, meaning I really won't be towing more than 6000lbs at the heaviest.

 

The quality of every part matters, especially in 2025, especially when the part in question lives between the engine and transmission (labor). You can buy from the rock, just make sure to get a quality part. If you buy whatever is on the shelf at the local parts store you can be sure you are getting chinese garbage that will leak. They will have options for good parts but they will have to order it in for you and it might only take a day or two. I just bought a 2003 Silverado SS (let the bowtie hate commence) and the guy had just done a front diff rebuild on it. I'm sure he used a Do-It-Again Dorman axle seal as it is already leaking fluid. I always try to get Motorcraft parts for my Ferd and (legit) AC Delco parts for my Chebbies. Anything less is not asking its BEGGING for trouble in 2025 where an alarming percentage of parts are complete junk right out of the box.

I can't say what to do about the trans as I manual swapped my Excursion several years ago and never looked back, but I'd at least throw a quality rear main seal at it and replace the up pipes with bellowed up pipes from KC Turbos or whoever you like.

 

Appreciate the reply! I found a proper Viton seal on ebay and found the teflon ring that goes on the stator shaft as well. I've decided not replace the torque converter (don't fix it if it ain't broke, it runs great) but I did order a FelPro rear main and Ultra-power bellowed up-pipe kit as well. I didn't even know the up-pipes were an issue on these trucks. I've also got a new dipstick o-ring, new pan plug and pan gasket, and new filter to throw in it. I thought about the output/driveshaft seal but that can wait considering how easy it is to get to with just dropping the driveshaft.

Do you have any idea at what mileage I should rebuild the turbo? I have no idea how much shaft play it has but I figure I'll find out when I do the uppipe and can wiggle the turbine wheel. In the future I plan to rebuild the turbo and upgrade the compressor wheel, but I've got an upcoming family trip where I need the Excursion as we will have six people and luggage to haul around. Don't want to put too much on my plate at once right now, just need to get her back on the road and not pouring trans fluid.

I've got a two post lift, the trans was actually easier to drop than most of the cars I've done, with the exception of the top passenger bellhousing bolt and the sheer weight of the trans. Hopefully install is as easy as removal.

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Oooooof eBay.... the #1 source of counterfeit/garbage import auto parts under the sun. Do not pass go, do not collect $200. I suggest cancelling that order or throwing them in the lake once you get them and buy brand name parts from a reputable vendor. I'm no auto trans expert but it feels kinda dumb to put a 350k mile tq converter back in it. YMMV.

Turbo... I'd say if it don't need it don't worry... if it needed it you'd probably know. But also there's never anything wrong with preventative maintenance on a rig with 350k.

 

Also I'd ditch the Fail-Pro rear main seal for something without the word "fail" in the name. As for the dipstick tube, the o ring wont help you because the holder flange inside the pan is totally smoked and the new o ring will just fall out. That's the failure mode of all of them. there are good and permanent fix kits you can use to replace the idiotic OEM design. I used the one from 7.3 dipstick dot com. If you aren't pulling the engine I think that one is the best one.

 

Ebay is all about the vendor. In this case, a very well reviewed physical diesel transmission repair shop out of El Paso that only sells transmission parts on Ebay. But who knows, maybe it'll leak in a year. The only Viton seals I could easily find were being sold off websites I had never heard of, this was the most reputable source I could find that would also have it here by Friday. I was told by a trans mechanics that if the OEM converter is not slipping/having issues, they would suggest not touching it for now, especially over a rebuilt unit.
Have you had issues with Fel-Pro parts? They are my go-to for high quality seals and are generally considered to be so among all of my car and truck friends. I've had issues with Motorcraft seals in the past (even ones ordered from the dealer) and tend to stay away from Motorcraft, I've never had an issue with a Fel-Pro gasket but everyone has their own experiences. And I was talking about the transmission dipstick, however, my engine dipstick tube could probably use to be done at some point as well, so I'll look into that. I've been slowly cleaning the built up gunk off the engine and transmission anytime I'm under it in an attempt to pin point any actual leaks. There is an engine oil leak somewhere, but it's just a couple drops after it's been drive, so not a big current concern.

I honestly wouldn't be surprised if I end up needing to have the trans replaced in the next 100k and it seems like every rebuilt/new trans comes with a new upgraded torque converter so I'm holding out on that (hence my hesitation to put a $400+ new torque converter in it). This is my quick and dirty "drop the trans and do all the cheap **** so it doesn't leak anymore" plan. I figure a deeper overhaul is in my future, likely where I pull the cab up and off the frame and really get in and replace every gasket and tube, etc.

 

I consider myself a hardcore DIYer, have many cars, I race at the club level with my friends and we do all the work on the car. My inner circle of friends are all more hardcore DIYers with more cars than me. One owns an auto shop, one is a professional mechanic turned service advisor for another auto shop, another is the commercial accounts manager for an O'Reilly, selling parts to auto shops. We all avoid Fel-Pro because we have all had problems with them.

Your logic about the converter and a new trans coming with it may be valid, again I am not an auto guy so I can't give good advice. The Silverado SS is the first slip n slide transmission I have had in nearly a decade... From reading this forum for years it sounds like to get 350k out of a 4R100 is an impressive feat anyway! It must have had continuous timely maintenance for it's whole life.