440-T4 / 4T60 Fluid, Pan, Filter, Pan Gasket (to replace or not to replace).
85,000 miles.

Hello there:
If there are a few gurus out there, I’d really appreciate your advice as I’d like to keep this transmission/car going and take my time going for second and third opinions about a rebuild or refurb of the trans which I cannot afford at this time. My concerns/considerations follow here. Your comments and suggestions are very welcome and much appreciated.

1) I’ve heard folks say changing all of the fluid in an old dirty tired transmission could cause additional slippage and/or actual failure by removing dirt/friction from the trans fluid or by kicking up the dirt from the filter and elsewhere. Both ideas seem plausible to me…and I’m inclined to changing both fluid and filter from the pan, no flush. Comments?

2) I’d like to change the trans filter as part of regular maintenance and because some of the trans fluid was replaced. I’d have to remove the oil pan (if I’m not mistaken, pan removal also provides access to a couple of accumulators – transgo kit, more on these later) or I could leave the fluid and the filter as-is (if it ain’t broke, don’t fix it).

3) The oil pan has an unbroken rib along the face of the pan rail. The rib goes around the bolt holes and according to the filter kit that I purchased, a neoprene gasket is needed for this type of pan with a ridge (19 bolt holes). So far, it has not been easy to find such a gasket available for sale.
a. Is there a good source for such specialty NEOPRENE gaskets, I’ve check in a few places? Is it possible there is a reusable gasket avail? Typical retail solutions fail here.
b. I’m wondering if replacing the pan would solve the problem. If the rib on the face of the existing pan rail is seated into a matching depression in the transmission housing or if a new pan with a flat face would sit flush against the transmission housing and completely eliminate both the ridge and the need for a neoprene gasket. I would check for the depression in the housing but I expect the existing gasket is original (it is not of cork and the exterior edges are brittle) and will crumble or crack if the pan is removed to inspect.
c. I’ve seen paper gaskets in a couple of catalogs. Have no idea what this is.

Right now, my plan is to figure out the gasket, use ATV if I can't figure another solution, change the filter and the accessible accumulators and whatever fluid comes out when the filter is changed. Then at the next oil change, if the car is still operating?!, I’ll change 1/3 or 1/2 of the remaining fluid by pumping it out.

Betty thanks you, and I thank you!!!

Here are the details/history about the trans:
The automatic transmission is tired. A couple of months ago, I started hearing a Clunk upon shifting into reverse. (I could have caused the problem by not stopping completely between D and R when parallel parking, doh!). The clunk seems to happen less when I’m pulling out of parallel parking as compared to after the car is warmed up and I’m parking it. In September, a slow leak in the trans cooling lines (rusted out) appeared. The leak was repaired and at that time, about half of the trans oil was pumped out and replaced w/Castrol Dex VI. The filter was not replaced. The car was subsequently taken on a local drive, then a day later for an additional 4 hours of mixed highway and stop and go traffic.

The transmission seems about the same as before the fluid was changed, maybe a little smoother…still occasionally thumping down into lower gears at low speeds. Also, when upshifting at lower speeds there will sometimes be a delay and a push/surge as the clutch/gear fully engages. May be taking a while to get out of third but I’m not sure if that is a new issue or just me finally paying attention to when we get into 4th. I had installed a new vacuum modulator but then went and reinstalled the original. The swapping of new and old vacuum modulators had no noticeable effect on the above issues. I adjusted the shift cable (push button adjuster) for a softer shift per a YouTube video (lower rpm) and this has helped significantly with the downshift thumping.

It is possible that the trans fluid had never been changed before September…it was dirty and brown brown brown. (according to the maintenance manual the trans fluid should have been changed every 15,000 miles if driven in city traffic where temps regularly exceed 90F). I’m in the city but the temp isn’t that bad except a couple months in the summer and there was lots of highway miles in there too. In any case, I am very familiar with the car and do not recall ever asking for the trans fluid to be changed.

Thanks again!

The Amateur.

It closer to 89,000 miles...

Get a filter kit and the required amount of Dex VI; do not use any of that dual purpose fluid. Make sure you have a very large pan to collect the fluid. You leave bolts in the pan so that you can basically drop the pan at the corner and control where the fluid comes out; it is still going to be messy; I recommend getting some large sheets of corrugated paper from large boxes to help keep the floor clean. I was able to let mine drip a day to prevent as much dripping on one as you work under the car. Make sure the car is supported on jack stands or ramps; I am paranoid so I also have something under the car as well just in case it falls off the stands. My filter kit for the 98 Buick came with a new pan gasket but stated if the original gasket was XXX (can't remember now) to use the original pan gasket so that is what I did. The only thing I did that I wish I hadn't was there was this gasket coated tube that the filter slides into that presses into the aluminium body; it was a PITA to remove the old one and I don't think it was necessary to replace it; if I had known ahead the PITA it was going to be, I would never have started, once buggered it had to be replaced. Have some clean lint free cloths to help with the drips; I think these things could drip for a month.

I would think the gasket would come with the filter kit, check and see at the auto parts shop you use. I think I purchased mine at AutoZone.

It is the clutch material bonded to the clutch discs that locks the clutch packs when the servo is engaged. If the clutch discs are worn that much, then it is time to have the trans overhauled or replaced with a certified rebuilt one. Go ahead and drain the fluid, it can break down over time and it is also the lubricant for the sun gears etc in the trans, replace the filter, clean the pan before reinstalling, fill the trans, check level, etc.

Actually it was Advance Auto and I used a 20 percent discount.

8668028 seems to be the gm part #

If I had entered that number into google then I'd have found the flat neoprene gasket avail. Of course I kept searching based on the trans model number and not the part number...learning curve.

I still want the fancy one with the grooves and the rings but whatever this flat one is the one indicated by the part number so will give it a go.

The part appears to be available at advance auto -- thank you kimberly.

Now i'm off to find some videos about installation of the accumulator kit.

I would check to see what comes with the filter kit; usually the filter kit will have the gaskets need to replace the filter since you have to drop the pan to replace the filter. At least my filter kit came with all necessary gaskets. Or maybe I am confused on what gasket you mean. In my case, I was told to reuse the gasket on the pan unless it was damaged.

Hi there:

I found the felpro gasket TOS18668 at summitracing and i'm getting ready to order some supplies.

Would you have an opinion or experience with high mileage fluids like castrol transmax? I've read a few threads about transmission fluids but haven't found much info about the high mileage type.

I'm planning to make the next couple of changes with Dexron VI synthetic blend as I already have 4qts of it in the case with the old fluid. Then after most of the old fluid is out and if the trans is still happy, I may begin incorporating some of the high mileage fluid as it includes additional cleaning agents.

I'm considering skipping over the Dexron VI and going straight to the high mileage stuff which seems to have a more conventional base oil...some folks say that using synthetics in an old transmission could cause slippage.

Maybe I should start a new thread about high mileage fluids. I'm definitely planning to begin using a high mileage motor oil.

Your comments are very welcome, appreciated.