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rustylog. 06-25-2021 12:55 AM

4L80E transmission on 1996 Chevy P30 Chassis
I started changing my transmission fluid. I got a flimsy fiber replacement transmission gasket for the pan with my transmission filter. I was advised that the original Chevy pan gasket I have can be reused, but it was leaking badly on one end and less on the other. The original Chevy pan gasket looks very well made and looks great after 25 years, but I might be making a mistake to use it. However, it might work if I use a sealant on the gasket.
My questions:
1. I saw a sealant called Right Stuff, made my Permatex, is it any good and/or what do you recommend?
2. Do I put the sealant on both sides of the gasket, on just the ends or all over?

Iíve never done anything like this before, but I believe you can teach an old dog, even at 83, new tricks. By the way, 10 transmission shops said they could not work on rvís and others could not do the work for 3 or 4 weeks at $350 to $450.

Thank you in advance for any comments, Rustylog.

R.Wold 06-25-2021 03:50 AM

When I use a gasket sealant, I only put it on the pan side of the gasket so that when it comes time to remove it I can take the pan to a bench or parts washer. It you put it on the transmission (or other component) side, you’ll end up under there scraping.

Anything made by Permatex should be good, but there are different products for specific applications.

You might find a good OE type gasket by shopping around, or even going to a chevy dealership. Cost will be more but results will be better.

Argosy 06-25-2021 06:42 AM

I wouldn't reuse a leaky pan gasket, it's going to leak worse.

Did you get a decent brand filter? If so even if it looks flimsy I'd use it, there are a lot of bolts in a trans pan.

Clean the pan well, including the flange, with a solvent. Use a light coat of sealer on the pan flange only, it needs to be compatible with tranny fluid, not all are. Nothing on the gasket to trans surface, next change you want it to release easily when you drain it.

A good trans pan gasket's holes will be slightly smaller than the bolt diameter so you can put all of them in on the bench and they won't fall out while you're installing the pan. Hold it close enough to the tranny to start a bolt at each end of the pan and it will stay up while you start the rest.

It's easy to over tighten the bolts in a thin sheet metal pan, that's why there are so many. Snug is all you need.

Mark_K5LXP 06-25-2021 08:53 AM

The OE gasket is pretty good, I've reused them when they're in good shape. I'm not a fan of the cork gaskets either, they can probably work OK is the surfaces are decent and maybe with some added gasket sealer goop. For a once and done (like you don't expect to ever have to tear into it again) then this may be a good solution. My thought is if you like the OE gasket, why not just buy another one? They're not cheap but they check the box for ease of installation and longevity.

Mark B.
Albuquerque, NM

LETMGROW 06-25-2021 08:54 AM

Normally these gaskets are reusable. However you are working with a gasket which may be 25 years old. I would replace the gasket with a new OEM gasket and not use any sealer on the surfaces.
Place a straight edge on the pan surface where the bolt holes are. If the bolt holes are raised above the pans surface they should be tapped back flush with the pan's surface. These holes can be distorted with over tightening the bolts. These bolts have to be snug but not "Wheel bolt" tight.
I believe "Fel-Pro" offers the OEM style gasket and may be available from a local auto parts store. NAPA may have it under part number ATP11485 but you need to confirm this is the correct part number. This is for a 17 bolt pan. It's not the cheapest way out but if the pan is straight and all surfaces are clean you will be leak free.
One other tip: When I tighten these pan bolts I start at the middle of the pan and alternate from side to side working toward the ends of the pan, tightening a small amount at a time until I'm satisfied all the bolts are snug.

GypsyR 06-25-2021 11:33 AM

Whenever I see added sealant on a pan gasket I assume it was an act of amateur desperation. That probably didn't work. Clean mating surfaces with just a gasket is the correct way to go. As already said, if the surfaces aren't flat you won't get a seal. The bolt holes tend to sink in on the pan from being overtightened. That desperation thing again.
The original reusable factory gasket is best. They don't last forever but do last through many uses. If your pan has distorted bolt holes no gasket is good enough though.
I like the "paper" gaskets it sounds like you have. They are a little less tolerant of major surface imperfections then others but work really well and last other than that.
"Filter kits" from most parts stores come with rubber gaskets. I like to throw those in the trash. They work OK but tend to split and crack as they age.
Cork annoys the crap out of me. It's good for surface imperfections but it keeps compressing. Tighten all the pan bolts, take a breather and retighten them. Come beck ten minutes later and they need tightening again. A month, six months, a year later, you can retighten the pan bolts forever with a cork gasket. Cork is a main cause of people overtightening and distorting pan bolt holes.

The Right Stuff is about the best quality RTV you can buy. Unfortunately RTV does not stick to oil or oily surfaces. So unless you can get both surfaces absolutely clean AND dry it won't help. On an automatic transmission in the vehicle this is VERY hard to do. I've watched them drip for weeks with the pan off. Literally. You can slap a gasket on where there's some transmission fluid dripping or whatever and it won't be an issue at all.

donr103 06-25-2021 10:06 PM

Do yourself a favor.. go back to store and you can order the better gasket.. never reuse 25yr old gasket.. does your pan have a drain bolt..? I only change filter in trans only once.. and Change trans oil based on color and time.. pink ok.. starting to turn.. like climbed big mountains.. change just oil through drain.. 5yrs change though drain.. if trans starts acting different.. complete filter and oil change to rule out these cheap items.. most of the time the better gasket cost more than fitler.. if you are pulling a toad.. every yr.. or if starts to turn..but that just another opinion. Good luck is great you are doing.. get grand kids off space games.. let hem help..get back to us and let. us know If did end up using gasket in the kit.. I coat both sides of gasket and let get sticky.. it will hold pan up until you get 1 bolt in each side.. then coat each bolt [ I use copper RTV. Both sides of gasket and bolts] pull temp bolts coat.. then run shop trowel all around not to remove but smooth out and seal rim.. you will never have to do again.. by the way.. what color was it..? Did you find anything in pan? When was last time it was changed ? Do you have a magnet in pan? Do you pull anything ?

rustylog. 06-27-2021 02:55 AM

Thanks for the 4L80E Transmission responses
1. RWold I decided not to use gasket sealant. The original gasket was installed without it. I figure it is possible to put it in unevenly and I could cause a clump.

2. Argosy You said you wouldn't use a leaky pan gasket. Well, I changed my mine and decided to reuse it. The replacement gasket I got is 1/16" thick and very flexible. The original gasket is 1/8" thick plus it has unbroken beading completely around both sides. I used a magnifying glass in bright sunlight to check the beading and screw holes. The original gasket is made out of hard rubber and I couldn't find any nicks, cuts or squashed beading. Plus I recall that when I tried to take off the bolts on the ends they were looser than the bolts on the middle sides. The pan was leaking only from the ends. The Chevrolet Motorhome Chassis Service Guide states to tighten the bolts from 12 to 13 ft lbs on page 8-5 for non-4L80E transmissions. It took me over a week to find out GM recommends the bolts on the 4L80E be tightened to 18 ft lbs. I have to put the pan back in between two beams that make a tight fit. That means the pan won't fall if I let go.

3. LETMEGROW You said normally gaskets are reusable and will not need sealant. I agree with you, especially how to tighten the bolts.

4. Mark_K5LXP I don't have cork. You are right the OE gasket is not cheap.
I got a price of $44.99 w/o tax and shipping from NAPA, and higher from a few others.

5. GypsyR See No. 2 about my gaskets. Based on the original gaskets good condition I plan to use it without Right Stuff sealant. I had to remove a lot of grime off the original gasket to make certain it makes a good seal. You are right about the transmission leaking fluid for a long time. It has been leaking for over a week with the pan removed. See No. 6 below.

6. donr103 I don't have a drain bolt on the pan. See No. 2 about gaskets, I decided to reuse the original gasket. The Chevrolet Motohome Guide mentioned above states on page 8-7 the transmission holds 7.3 liters or 7.7 quarts. I measured the trans fluid from the pan and got about 4.9 quarts plus another 0.53 quarts that leaked out slowly over 8 days, which means about 5.43 quarts of 7.7 quarts in the system have leaked out so far. I am in Southern California and I believe the 95 to 100 degree days has helped more fluid leak out.

The first 4.9 quarts were dark gray. I have the stuff in 2 liter plastic soda bottles. The 0.53 quarts that leaked out slowly over 8 days has a dark red color you can see through. The pan has a square metal magnet in a minor depression that had no pieces of metal on it. But there was a dark gray paper thin layer over the bottom. I've gone over 95,000 miles but very few in the last 5 years.

I have found out about another controversy. Some say that adding new transmission fluid to a transmission that still has some old fluid in it would cause sludge to form which would damage the transmission. GM says on page 8-9 of the Chevrolet Service Guide: "Automatic Transmission Failure Immediately After Servicing." If there was no known prior abuse, the new transmission fluid is not at fault. What has probably happened is that a certain amount of highly oxidized fluid remained in the transmission converter and cooler lines. The old fluid and new fluid will not mix. They settle out as sludge or varnish, causing valves to stick and/or plug oil passages and screens. When this happens, the transmission may malfunction or fail completely. The best way to prevent the problem is to follow the manufacturer's drain intervals for severe operating conditions such as trailer towing, mountain driving, and stop-and-go city driving."

DARN. How do I know if the remaining 2.27 quarts in the transmission are highly oxidized. To play it safe it seems I'll have to find a way to remove it from the converter and cooler lines.

LETMGROW 06-27-2021 06:52 AM

There are a couple ways you can solve your problem.
When I dropped my pan I cleaned it then drilled a 1/2" hole in the pan. I bought a 1/2" fine thread drain plug at the local NAPA parts store and a 1/2" fine thread nut. I ground two grooves into the nut, placed it in the pan and screwed the drain plug tightly into the nut to hold the nut into place. Then I spot welded the nut to the pan being careful to not cover the area where I ground the grooves in the nut. The grooves will allow fluid to drain below the nut so the pan is nearly completely dry. The grooves have to face the pan bottom to accomplish this. This makes removing the pan much easier and cleaner than trying to balance a pan with a couple or more quarts of fluid in it.
You can also buy hand or battery operated pumps with a long plastic or vinyl hose which can be inserted into the transmission dipstick tube and draw fluid out into a drain pan or other container. This might be your better option at this point in time. We used one of these battery powered pumps in my repair shop and it not only saved a mess but time as well before removing a pan to change the filter and clean the pan.
You may need to draw the fluid out of the pan a couple times before you get the fluid to the point where it looks clean. The torque converter and transmission cooler will hold quite a bit of fluid. After pumping the fluid out, measure the amount you drained out and pour that amount of new fluid back into the transmission. Start the engine, shift the transmission back and forth from reverse to drive several times then check the fluid level and color. If it's convenient for you you could take your RV for a short drive so the transmission shifts through all the gears and fills all the clutch packs, governor etc.
If you are happy with the color of the fluid you are done. If not keep repeating the process until you are satisfied. If the fluid looked burnt or exceptionally dirty when you first started the service you might even want to change the filter again. This would be your call. Personally I don't like discolored fluid. If you get the fluid clean and it starts looking discolored in a short while it's usually a sign of a looming failure as something is wearing internally, usually the friction surfaces on the clutch discs.
They do make machines designed specifically for transmission flushing but they are expensive and not something a do it yourself'er would normally buy. Larger shops or truck service centers may have one of these machines but I'm sure you will pay dearly if they take the time to do the job right.
That's all folks. LOL

Mark_K5LXP 06-27-2021 10:09 AM

There are some DIY hills to die on but flushing a tranny isn't on the list. The local oil change place did mine, they just hook the machine up to the line going to the cooler, they run the requisite amount of new fluid through and check the box. Going forward one can do a periodic drain and fill and keep up with it, but for a swap from Dexron III to VI I would pay for a flush.

Mark B.
Albuquerque, NM

rustylog. 06-27-2021 03:17 PM

LETMGROW you made me think about 2 ideas.
1. Looking at the transmission I see two coolant lines connected to the transmission. I hope correctly that the upper line takes the trans fluid from the radiator into the transmission and the lower coolant line goes from the transmission into the radiator. Therefore, I plan to disconnect the lower line and connect a hose from it into a gallon container of new transmission fluid. Then I can turn the motor on and put the transmission in drive for 30 seconds. Hopefully, this will flush the 2 coolant lines, radiator and converter. The trans oil will fall down into the area where the pan had been removed. By my calculations I have 1.27 quarts of trans fluid still in the system that should be flushed out with 1 gallon of new trans fluid.

2. I found a site on google stating how to determine the state of your transmission oil. You place the trans fluid from your dip stick onto a clean white cloth or paper towel. Red is great, light brown is good, and dark brown is serious & black is terrible. I tested my fluid from a dark gray bottle and it was light brown, which surprised me.

I've read that a backward flush could be bad for the transmission. So the flushing method described in No.1 hopefully will be good.

3. LETMGROW, I don't need to install a transmission fluid drain plug. I plan on selling the RV in the very near future.

donr103 06-27-2021 04:29 PM

On my cars and big van, they don't have drain bolt.. simple.. go to harbor freight and get a oil change vac pump.. you will never have to climb under and Change again.. it looks like a tire pump with plastic reservoir on it.. holds about 3 gals?.. comes with many tubes.. because the van trans stick is a mile long.. I got extra 1/4 in plastic tube.. ice maker line.. added that to pump.. just pull dipstick.. put in plastic tube.. and suck out oil.. it's a lot easier and you will get most of oil that way.. just run it 2 or more times.. what ever you like and suck out 2 or more times.. that way you will get 99% don't have to get dirty and so simple.. can be used on most cars that have dipstick and great for flushing brake fluid.. very good for changing out p/s oil.. don't get dirty.. I love it.. when I last time you changed p/s oil.. oh and reservoir is clear enough you can see how bad old oil is.. it has a spout on it to make pouring back into jugs to recycle.. keep us posted.. I even use it to change out diff oil.. put tube in fill plug suck out old oil.. and boom.. just add new, no pulling cover on and off.. I do it so often I don't worry too much about what little old oil stays in.. when is last time changed diff oil?.

donr103 06-27-2021 04:38 PM

On last line.. I have a typo.. no pulling diff cover on and off to change oil.. and should have noted.. since you already changed trans filter.. you don't need to pull pan for along time.. just suck oil out to change.. it's nice once and a while you pull trans pan and diff cover for inspection but I don't unless there is a problem.. I suck out oil and Change so much I hardly ever pull cover.. van Is 30yrs old.. OEM p/s pump and trans and diff and master cylinder and abs system.. I keep it changed so much.. runs better than new..

Isaac-1 06-29-2021 09:53 PM

Make sure you get the right filter, early and late 4L80E's used different filters that looked a lot alike, The biggest difference visually is the late filter has indentions on the bottom, and I think the filter neck is a different length. I think you probably have an early transmission, though the early / late split was near when yours was built (I think 98, but it might have been earlier) They also differ in where their oil cooler ports are located, which is the easiest way to tell an early from a late 4L80E from the outside.

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