Lock-up Torque Converter Not Locking Up

[Deano]

My 904, I believe is having a bit of trouble. It has always locked up almost as soon as the trans shifted to third, just cruising along. A week or so ago, I was on my way home from work and it did lock up, but I kinda goosed it to get going a bit better and the car shook HARD. Dash, steering wheel was shaking like I took an jackhammer to it. But it stopped when I let off the accelerator. Didn't really know what to think about it at the time. Took around a 75-80 mile 'round trip yesterday and the converter never locked up once while we were out in it. Don't know if the tranmission fluid and filter needs to be changed and everything will be okay, or a new converter is in the future.

To the best of my knowledge, the fluid and filter hasn't been changed. I know that I haven't. Yet.

I bought a new filter and a gallon(?) of dex/merc fluid. I know that the dipstick says use only dexron fluid, but I didn't really know if this stuff was exactly what I need or I need to get another type.

 

[Aspen500]

Fluid that meets Mopar ATF+4 specs is fine. It far exceeds the Dexron stamped in the stick. Should say on the back of the jug what manufacturer specs it meets.

The shaking is a classic symptom of a slipping TC clutch as it tries to lock. Most likely a leaking TCC piston seal, which is inside the converter and not replaceable in the field. Sounds like it came on suddenly, kind of points to the TC seals or a pressure leak in the trans from a seal or even a valve body problem.

 

[AMC Diplomat]

That should be fine. I run ATF+4 but I have an 87. I'm sure you'll get a lot of different answers. I'd throw a bottle of lubegard in there if it's acting up. This stuff actually works and isn't snake oil:


You can get a quart-ish out of it if you pull the neutral safety switch first. At least it will pour out of one hole and not rain all over the ground. That's if you want to take the chance and hope it doesn't break.

Some older 904s and aftermarket brands have drain plugs on the torque converters. Yours probably won't. I'd recommend getting a pan with a drain plug. This way you can slowly replace all the fluid a few quarts at a time. Beats paying someone who has no idea what they're doing to flush it.

@Camtron has a pan kit for sale FOR SALE - A904/998/999 Deep Trans Pan Kit

probably worth making him an offer

I forget how many quarts you get out with a pan drop. It won't be all of it. Maybe 3 or 4. A shop manual will have better answers for your model year

 

[AMC Diplomat]

Fluid that meets Mopar ATF+4 specs is fine. It far exceeds the Dexron stamped in the stick.

On some Mopar boards people insist on running Type F in a 904. I just shake my head. Glad to see someone else suggesting ATF+4

 

[Mikes5thAve]

If it is lockup falling and is causing drivability problems its a bit of work but you can disable it to get some more life out of the transmission.

 

[MiradaMegacab]

What to use for trans fluid

I had an extreme amount of clutch particles (from the TC LU friction plate) clogging the filter several times in the above thread…
As mentioned, you can disable the Lock Up function in the valve body. That’s what I did an the transmission worked for several more years.

 

[GregG48213]

never locked up once

The lock up feature is there just to increase fuel mileage. If the car drives okay otherwise, and the mileage is acceptable, then leave it as is.

 

[LSM360]

Dex/Merc is fine. I doubt you'll even get four quarts out. Sounds like TC shudder and probably time for a new converter.

 

[Ash_Whole]

ATF-4 has the friction modifiers in the fluid. Dextron/Mercon transmission has the friction built into the clutches. ATF4 in dex/merc trans is fine, not the other way around. wont die right away, but change it to the the right fluid sooner than later.

TypeF is a welfare version of ATF4

 

[Mikes5thAve]

Dextron is what the majority of 904s use so there's no problem with that.
Ideally you'd want to stay consistent but there's probably been a mix in there for 30 years.

 

[Ash_Whole]

Dex is a fluid from GM. why would Mopar use a GM fluid when they have their own?
i worked at dodge for years through the 90's as a transmission tech, they dont even sell Dextron

 

[AMC Diplomat]

Dex is a fluid from GM. why would Mopar use a GM fluid when they have their own?
i worked at dodge for years through the 90's as a transmission tech, they dont even sell Dextron

Early Mopar automatics used GM fluid because it was cheaper.

I think it goes Type A, then AQ-ATF, then Dexron, some type Fs, then ATF, then the numbered ATFs

 

[LSM360]

I'm no expert sooooo, I asked one of the family members and owners of Dewey's Transmissions in Melbourne FL. They have been in business for over 47 years and rebuilt TONS and TONS of torqueflites. He said just use "Dex/Merc" in torqueflite. That's what I've done ever since. I know, I know, F Type firmer shifts and lots of other opinions but I defer to an actual expert who has literally opened up 100's if not 1000's of these transmissions.

 

[Mikes5thAve]

Dex is a fluid from GM. why would Mopar use a GM fluid when they have their own?
i worked at dodge for years through the 90's as a transmission tech, they dont even sell Dextron

Maybe it was more common and they didn't have their own to use at the time. It wasn't until the later 80s that they started to say use 7176 ATF Plus or Dexron II.

Attached pic is a mid 80s M body dipstick.

 

[LSM360]

That's right Mike, I forgot it use to list on dipstick. I'll have to look at my FSM and see if it says same.

 

[Mikes5thAve]

Good question.. The 87 manual says ATF PLUS Type 7176.

 

[Deano]

Okay. Now I'm faced with another conundrum. I bought AFT+. Now I'm wondering what type fluid is in the converter. I'm sure you not supposed to mix fluid types. Am I correct? Really don't have the knowhow to remove converter and drain it. Should I just go ahead and drain, replace filter, and refill, or what?

 

[Mikes5thAve]

If it was mine I'd put Dexron in it but at this point it probably doesn't matter because it's probably seen both over the years and like I said the newer dipsticks listed both types.

Being a 78 it might have a drain on the torque converter. My 79 had one.

1985 manual says Dexron II so that side of it changed in 86 or 87.

 

[Aspen500]

I seem to remember lock up converters not having drain plugs.

However,,,,,if you pull the small cover off the converter shield and rotate the engine you will see the plug (if it has one that is).

 

[Deano]

Probably go back to O-O-O-O'Reilly's and swap to Dexron, just to play it safe. So if it does fuck something up, I can say, "I only did what the dipstick told me to!"