TF727 suddently started slipping

[Guss]

Hi guys,

On my 70's Challenger, made a little acceleration, all was fine. Next acceleration litteraly 10 seconds later, and all forward gears started slipping bad !
I struggled to get back home.

Reverse is still tight.
Now takes a while to get into drive. when it does, it's lazy, super lazy!
Oil is still bright red, no weird smell, up to the level. Overfilled by 0.2" on the dipstick actually. Maye that's bad ? you tell me.
Shift linkage is fine.
Kickdown rod is fine and bottoms out when WOT.

Could you please let me know if the following operations are correct in order to diagnose the issue :

- Perfom an oil pressure test - are the following pressure I should read correct ?

• At idle:
  ~25–50 psi
• At WOT:
  ~75–125+ psi

- If the pressure is good, should I look for burned clutches ? But then why would it slip so much, all of a sudden ? And why isn't the oil smelly and burnt too ?

- If the pressure isn't good, from easiest to hardest :

• check if the filter isn't clogged
• check if the pick up tube hasn't simply dropped in the pan, or blew its seal ? or is cracked ? any check for any air sucking related issue.
• Valve body issue such as loose bolts, bad seal, debris clogging the foward clutch circuit ?
• Pump issue =: blew a seal or something ?

I'm far from beeing an automatic trans expert, and never done a TF727 before.
Thanks for your help !

 

[terrywalker]

I'm going to ask a silly question here. Did you or someone else service the transmission? The reason I ask this is this. Was the correct transmission fluid put in the transmission?
Terry W.

 

[Guss]

Thanks terry,
I have been driving the car for a few hundred miles with the oil in, and it worked perfectly. Looks, Smells and tastes like ATF to me

I'm thinking loss of oil pressure due to clogged valve body/filter/pickup tube or a lip seal failed on the pressure plate for the forward gears.
I'll go get my hands dirty now - try to understand what's happening.

 

[Guss]

Well I was very wrong.
If I have reverse, I have good oil pressure since reverse needs way... way more pressure than forward!
I tested oil pressure for no reasons... But at least now I know how to do it on an 727.

So next thing, I pulled the pan, and discovered my foward clutch laying in it.
It is all clear now !

At first I was a little bummed.... Now it's been an hour, brain has accepted and ... I'm actually excited to rebuild a 727 !

 

[terrywalker]

Glad you found the problem. I had a friend years ago who rebuilt automatics for his job. We got together for a couple of evenings and rebuilt mine years ago. I think the friend, who I last saw several years ago, he had dementia then, has since passed away. I learned alot from him about automatics. BTW, he was the one who told me putting the wrong tranny fluid in can lead to failure of the clutches and band materials.
Terry W.

 

[Guss]

Terry,
Thank you / Sorry about your friend.
Will for sure fill in the right ATF in it!

 

[Challenger RTA]

Your 'Guide' to the 727/904 transmission

Your 'Guide' to the 727/904 transmission

Often I or anyone for that matter asks to find out what type of transmission they have in their old mopar. There are hundreds, if not a thousand, of threads on this website identifying, discussing or assisting with this process, troubleshooting or repair. Because of this large number of...

www.forbbodiesonly.com

 

[Xcudame]

Before you rebuild it, spend the money on the two books below! I've rebuilt dozens of torquefites and still use these books for excellent reference.

 

[moparleo]

Agree with above. Educate yourself. Excellent resource books also get the Factory Service Manual for your car. Transmission section goes through the FactoryService procedures. I will attach a link for free Manuals and other Mopar info.
Save the link: -> Resource Library – MyMopar

 

[Mopar Nut]

The books @Xcudame posted and the MyMopar library that @moparleo posted are excellent resources.

 

[moparleo]

Proper transmission fluid level In a 904 or 727 is on level ground.
Warm up to operating temperature.
Set parking brake.
Place transmission in Neutral.
Proper level is 1 pint below full.
I see that you have an aftermarket pan.
If it is deeper than the original pan, make sure you have the proper filter and spacer to place the filter deeper down into the pan

 

[Guss]

Thanks a lot for your answers ! That helps !
Pulled the trans off of the car. Easier than expected actually.

I'll be rebuilding it, ordered the Tom Hand's book.
Found great YT video's as well.

Now I'd like to understand why the clutch burned.

• Could it be because my oil level was a little high ?
• The oil cooling circuit looks like a rat nest. It goes from the trans to the main rad, then get's to another aftermarket dedicated rad, then comes back to the trans. i'm sure the oil is quite cool .... I'm also sure it affects the pressure. Could this be a cause too ?
• Maybe the clutch adujestment in the drum itself ? Too loose or too tight ?
• Another "usual thing" ?

From my understanding, this car hasn't really been driven for about 16 years, so maybe the clutch has also gone bad over the years...

Thanks a lot guys, trully appreciate you taking the time to answer my questions.
Will order a full rebuild kit for the trans now.

 

[Ricks72Chlgr440]

Thanks a lot for your answers ! That helps !
Pulled the trans off of the car. Easier than expected actually.

View attachment 140113

I'll be rebuilding it, ordered the Tom Hand's book.
Found great YT video's as well.

Now I'd like to understand why the clutch burned.

• Could it be because my oil level was a little high ?
• The oil cooling circuit looks like a rat nest. It goes from the trans to the main rad, then get's to another aftermarket dedicated rad, then comes back to the trans. i'm sure the oil is quite cool .... I'm also sure it affects the pressure. Could this be a cause too ?
• Maybe the clutch adujestment in the drum itself ? Too loose or too tight ?
• Another "usual thing" ?

From my understanding, this car hasn't really been driven for about 16 years, so maybe the clutch has also gone bad over the years...

Thanks a lot guys, trully appreciate you taking the time to answer my questions.
Will order a full rebuild kit for the trans now.

Good for you for pulling the trans and preparing for a teardown! Tom's book will be a big help. Sounds like the transmission cooler setup is fine. Running a secondary cooler after the radiator is quite common, and will help the transmission stay cool. This is especially important if using a higher stall converter. Transmissions that have sat for a long time can certainly have problems with the seals getting hard and the clutches disintegrating. Not unusual. Our cars are made to be driven and they don't like sitting for long periods. You will find it quite simple to rebuild your transmission with basic tools. My first 727 rebuild was when I was in the military stationed in the Philippines. There was a typhoon coming and I had some time so pulled it apart and rebuilt it on a dining room table! My wife was very understanding, which was very much appreciated! The only thing I could not do was to replace the bushings but I did all the seals, thrust washers, and of course the clutches & bands.