Back for som emore help since everyone was extremely helpful on my last post. I have been working on my first car for the past month or so and have noticed the transmission slips at times when changing gears. The car is a 1975 plymouth duster with an automatic tran. 225 slant six engine. The plan is to change the tran oil but for some reason i cant locate where to fill it from? or how to change it? would it be similar to a regular oil change? A detailed explination or pictures would be of great help!

To drain it you have to remove the transmission pan. Kind of messy if you are not prepared. Also replace the filter and pan gasket before you button it up.

It gets filled with a narrow funnel through the transmission dip stick tube.

Changing fluid will only help if the filter is plugged. If its plugged the daage/wear is already done Which gears slip? 1, 2 D , R?
Doug

BEFORE you go to the trouble of changing the tranny fluid and filter, check the condition of the fluid. It is highly unlikely that the fluid and filter are your problem. But to someone experienced in this area, the color, feel, and smell of the fluid can tell them a lot about what is going on inside the tranny and could save you from wasting time and money.

And without any previous experience or any experienced assistance, tackling this kind of service can cause more harm than good. In other words, if you can't find the dipstick, you probably shouldn't be tearing into the unit. This board is an excellent source for information, but is not a substitute for a certain level of experience.

I do not mean to be mean spirited here. I am only trying to help you avoid making matters worse.

You said "slips at times when changing gears." Can you define that a little better? What are you doing when it slips? I'm just trying to understand if it's really slipping, or just a "mushy" shift...

EDIT: Here's a pretty good "how to" video IMO. It's on a Mazda pick up, but as he says, the process will be nearly identical on your car. Have plenty of rags on-hand, and that drop cloth. It can be messy a messy job. Don't be under that pan where the fluid can dump on you.
https://www.youtube.com/watch?v=yb_1wbiPz9g

Littleboyblu...if you are describing a “flare” during the 1-2 shift (engine RPM starts to run up a bit during the shift then settles back down as 2nd gear catches) then there is a chance a simple band adjustment will cure it——there is also a chance it won’t and the tranny needs a rebuild.
Adjusting the bands is a two part thing..the front band adjustment is external and easily done. The other requires a pan drop.

Adjust the front band. Adjust the rear when you drop the pan, these steps are important.

one of the single BEST tip[s] i can give, is buy a Factory Service Manual. [FSM for short] that can answer a lot of questions you may have, plus, it will also have pictures to help guide you through many processes in the repair of most systems.
another plus to the FSM, is the fact most systems of 19xx will be the same for years before, and years after the published date, helping you on other vehicles you may encounter along the way.
most of these can be bought in CD form or printed, your choice, and compared to the information contained therein, absolutely stone CHEAP !
you will be amazed at what these contain.

Pick up a FSM and read it and you'll go from novice to expert in a few hours. About 50% of the questions on this board can be answered by looking in the FSM so you'll be answering questions rather than asking them in just a few short hours.

Have you checked the level of the transmission fluid? If its really low it could cause slipping.

This, and check it correctly, meaning warmed up, in neutral, with the motor running...

The discussion about checking trans fluid came up at work the other day. I know it has to be checked while warm, but some said in neutral, some said in park, and some said it didn't matter. Does Mopar, GM, and Ford all get checked the same?

No they do not, and it normally depends on the particular year model of the trans. There is no one universal answer

The fluid level on all Mopar transmissions of the 727/904 family is checked in Neutral, stamped right on the dipstick. CHECK IDLING IN NEUTRAL

I would add, "Check WARM idling in neutral". Or maybe "hot", I can't remember which.

I agree with much of what's been advised. First, check fluid Low fluid will definitely cause slipping! Needing a fluid and filter change probably won't.

Second, I wouldn't dive into this one yourself YET. Kudos for wanting to, but a bit advanced right now. Just learn how to check the fluid and keep it in operating range, I'd say with Dex/Merc.

Third, FSM's are definitely AWESOME. Find a greasy cheap used one on Ebay

So check fluid with trans warm, idling in neutral on level surface, and yeah, parking brake on, and get back to us

How to check the fluid level is usually stamped on the dip stick. Our old Mopars are a little unique in that the front pump is not circulating in park which is why we must check the level in neutral. I have no idea why they did it that way, it seems like a better idea to have the pump circulating all the time.

Iirc it's an artifact of the original 727. They didn't have a park position in the valve body, you started the engine in neutral and used the parking brake to keep the car from rolling. In that design, the pump worked all the time.

With the redesign in iirc 66, they modified the valve body to have a park position, but somehow cut the fluid flow.

this knd of describes it best. The slip is between 1-2. the rpm starts to run high then it settles into second. but for some reason this only happens once during my daily commuting to work. After that, she shifts just fine.
deff. gonna check the fluid as soon as i get home from the office.