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Transmission Pan Drain Plug + Undercarriage Coating

shima

shima

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Hi all,

Now that I've handled the brake leak, my next maintenance job is changing my transmission fluid and filter. Then I'm going to coat my undercarriage for winter.

Transmission Question:
My pan doesn't have a drain plug. I looked through a bunch of old threads on the forum and found some folks talking about the B&M drain plug kit (https://www.amazon.com/80250-Automatic-Transmission-Universal-Drain/dp/B00029WR78). That is going to be my plan unless you all think it is a bad choice? How many of you guys run larger aftermarket pans that came with a drain plug?

Undercarriage Question:
I plan on painting a bunch of stuff underneath with old motor oil to protect it from snow / general winter BS. Aside from the frame and axles, what should I make sure to cover? Also, should I wash under there before I paint, or leave the dirt on there?

Thanks for any and all input, I really appreciate it.

Drew
 
First, if you are going to install a drain plug I’d get one that has a magnet on it to see if there’s any metal on the plug when you remove it. Some pans already have a magnet glued to them though. Second, if you’re changing the fluid it’s a good idea to change the filter too, which of course requires pan removal.

For the undercarriage I’d pressure wash any accumulated mud/dirt off it first then spray away - just keep it off of the exhaust.
 
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I've used that plug kit before. It works just fine. However, you need to make sure you find a spot where it doesnt interfer with anything on the inside (like the filter). Also try to factor in that you dont want to have anything catch this plug, and you dont want it in the way if you have to lower the transmission on a jack. Ended up using a front corner on mine. Works best if you can find a deeper flat spot, but its never going to allow you to drain all the fluid. It sticks up at least 1/4 inch inside, and that leaves a lot of fluid still in the pan the next time you are dropping it. Also: make sure you apply some oil resistant sealant (permatex black works) to the nylon sealing washers and each side of the steel pan, helps it not leak.

Going with an aftermarket aluminum pan is pretty popular, but its not required. Added oil capacity, added cooling, better drain plugs, and usually have a bung for a temp sensor too. They have a lot of advantages, but usually cost is $100 to $150. I would do the plug kit for now, and think about doing the pan later.
If you do go with an aftermarket pan: make sure you get a quality heavy cast aluminum unit. The stamped steel or thin aluminum ones will bend at the flange surface, and then never seal correctly again.

For your draining: If you have some sort of suction device that you can run down the dipstick tube, use that to drain out about 4 or 5 quarts. Should leave the pan mostly empty. If you dont.... prepare for a big mess when you pop the pan off. Also make sure you dont bend the flange when you drop and reinstall the steel pan.
 
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mechted said:
I've used that plug kit before. It works just fine. However, you need to make sure you find a spot where it doesnt interfer with anything on the inside (like the filter). Also try to factor in that you dont want to have anything catch this plug, and you dont want it in the way if you have to lower the transmission on a jack. Ended up using a front corner on mine. Works best if you can find a deeper flat spot, but its never going to allow you to drain all the fluid. It sticks up at least 1/4 inch inside, and that leaves a lot of fluid still in the pan the next time you are dropping it. Also: make sure you apply some oil resistant sealant (permatex black works) to the nylon sealing washers and each side of the steel pan, helps it not leak.

Going with an aftermarket aluminum pan is pretty popular, but its not required. Added oil capacity, added cooling, better drain plugs, and usually have a bung for a temp sensor too. They have a lot of advantages, but usually cost is $100 to $150.

For your draining: If you have some sort of suction device that you can run down the dipstick tube, use that to drain out about 4 or 5 quarts. Should leave the pan mostly empty. If you dont.... prepare for a big mess when you pop the pan off.
Click to expand...

Hahahah yeah I've heard it is a nightmare. I told myself I was going to buy a lot of kitty litter to help out.

$100 to $150 hmmm... :thinking:. I might have to put myself through the nightmare at least once to see whether it is worth it. The advantages are nice though e.g. better cooling.

Thanks for the tip on permatex black, I didn't think about that at all. I was thinking of doing a low corner on the back side of the pan, but really gotta get under there and check thoroughly before deciding I guess.
 
If you have a Th350 ,and some salvage yards with some old vehicles in your area,you might be able to find a 1972 or older Th350 pan that had a factory drain plug..
I have brazed a 1/2" x 20 thread nut to a few transmission pans so a oil drain plug from a small block V8 can be used for a drain plug..
They sell some with a magnet built into the drain plug too..

I just picked a spot where nothing inside was in the way and brazed the nut to the bottom of the pan,that way it wouldn't interfere with anything inside..

It sucks to drain the tranny pan when it has no drain plug.."If you have a big tray like one you put your wet boots on,you can use one of those to catch the splashover--I take off all the pan bolts but one up front, then loosen the last one a few threads, and pry the pan down,that helps funnel the fluid into a drain pan,and pray the 3+ quarts doesn't splash everywhere and give me a dexron shampoo..

ATF does work for undercoating but it'll wash off in short order...
Oil drained from a diesel engine will stay on much longer and the soot in it keeps it in place better--a good run down a dusty gravel road after the oil is applied also helps to make it stick longer..
Some guys here use linseed oil as a anti-rust coating on frames and underbody areas..
 
I got my transmission pan off a couple of nights ago. I had a big Home Depot 5 gallon bucket and a regular-old oil drain pan. I caught most of the fluid... :D

It just now occurred to me that I probably will have to tap threads into the transmission pan when installing this aftermarket drain plug. I've never done it before, so I'm doing some reading on Google and watching YouTube videos. Do you guys have any tips for me? I wanna do it clean and correct the first time around.
 
Are you sure? I assumed that the kit you posted, you just drill a hole. One nut goes on the inside, and the nut with the shaft and nylon washer goes through the outside. Then the drain plug screws into that shaft and nut.
 
Abusfullofnuns said:
Are you sure? I assumed that the kit you posted, you just drill a hole. One nut goes on the inside, and the nut with the shaft and nylon washer goes through the outside. Then the drain plug screws into that shaft and nut.
Click to expand...

I am not 100% sure, and I hope that you are right! I don't own taps and also don't have a vice setup in my garage. :eek:
 
I would not under coat anything on vehicle that I own. Clean it, paint it, keep it clean. Undercoating it is a good way to trap water, dirt, salt, other crap between the under coat and the body. Before and after you put it on.
 
kgblazerfive said:
I would not under coat anything on vehicle that I own. Clean it, paint it, keep it clean. Undercoating it is a good way to trap water, dirt, salt, other crap between the under coat and the body. Before and after you put it on.
Click to expand...

Does this apply, even if using something like old motor oil? I know some of those "intense" under coating products can trap moisture and cause more problems than they are worth, but do you think motor oil would do the same?
 
Under coat it with motor oil?

First question would be why oil? Its not going to stay it will wash off first rain storm. Oilly things dont make it easy to work on. How will you tell when it is leaking where it is leaking from ? :D

Paint and keep it clean then paint it again when the paint wear off.
 
Abusfullofnuns said:
Are you sure? I assumed that the kit you posted, you just drill a hole. One nut goes on the inside, and the nut with the shaft and nylon washer goes through the outside. Then the drain plug screws into that shaft and nut.
Click to expand...

I have the same plug kit. Yep, the above is correct.
Bonus is the thread for the tiny plug is the same as a temp sensor sending unit. I replaced the tiny golden plug with a temp sensor.
 
You don't tap threads intobthe pan for the plug installation. I recommend that you put a small dab of silicone on the threads of the drain plug retainer nut. I use loctite, but if you don't have any, silicone is better than nothing. Just trying to keep the nut from backing off.
If you do decide to try a different pan, make sure that it won't interfere with the front driveshaft.

I have heard of spraying the oil on, guys back east talk if it. I would think that it may have to be diluted some to spray...
Careful around the brakes. I would probably recommend that you don't wash it with hot, or soapy water after the oil coating, to minimize how much needs recoated. If you are not going to paint the bottom of the body soon, spray it with oil, too.
 
I'm like, I wonder if this is too thick for the step bit. We'll find out! :haha:
 
The crazy thing is...it's almost always not too thick. They work so good that it breeds bad habits. I feel better that it's not just me. Solidarity.
 
I've heard people back swearing by oil undercoating. We don't need it out west. If I did do something like that, it would be clean oil, not used motor oil with the combustion byproducts in it. Just sounds like a good way to ensure the truck burns to the ground faster if there's a stray spark or short in a wire.

A quart of cheap oreillies motor oil is $4.00. One quart may be plenty, maybe a non flammable light machine oil would be even better. Maybe even the silicone grease spray stuff would be cleaner and easier to apply at home?
 
Got my pan off.

View media item 32121
There were a decent amount of shavings on the magnet.

View media item 32123
After cleaning the pan, I took off the old filter. The freaking o-ring is stuck up inside the tranny!

View media item 32124
I swear, some truly dumb s*** seems to always happen when I try and work on my truck. Everything's a hassle! :doah:

So far, my only tools to get that o-ring out are a hammer, a small (micro) flathead, and needle nose pliers. I'm not getting very far...
 
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