I inherited a working 904 transmission along with a lot of other parts for a 1969 Barracuda project car. The transmission came out of a late 80's Dodge van, along with the 318 engine. The seller did not know anything about different engine/transmission models. In checking to see if it is a lock up TC, I counted the splines on the input shaft at 27. According to a Mopar Tech Archive article, this makes it a non-lock up model. However, it also has a short non-splined section on the front of the input shaft and a hole in the center of the shaft. According to another thread on this forum, this makes it a lock up model. How can I tell for sure, and what are my options if it is a lock up model? Use as is (performance not an issue)? Some way to trick it? Other? Thanks.

I can't answer your question as applies to application, but will add this...

I would not put a used torque converter in there being it is all apart now.

Cheap insurance in my mind.

definitely a lockup, cant find my notes on the spline count

I was under the impression lock up TC's needed a computer to make them work. I now see this is the case for late model drivetrains, but back in the 80's, TF's had fully internal hydraulic lock up controls. Since high power/torque is not an issue, it appears the lock up 904+converter I have can be used as is.

I believe so & I saw some info way back on modding that system which might not be needed for your app but FYI it is out there somewhere

Yes the early lockups were hyd. control totally and it was not a very good setup/application from what I remember of the Lebaron and Gran Fury I had.

a friend has a torque converter shop---he says the lock up clutch is becoming the fail point---when he built a 28 chrysler 5.7 hemi--he had me looking for a 518 out of an early dakota without a lockup converter---he said it only saved 300 rpm over a regular setup and he is driving that set up now....bob

Thats right as the early lock-ups were hydraulic and used gov pressure and a spring to determine the speed it locks up. The later ones are electronic and controlled by the PCM which controls a solenoid that can block or bleed off pressure. I dont remember what year the started with the electronic ones. I think it was around 1986 but dont remember for sure. Ron

My 86 D150 has a lockup converter.Can it be deleted without a full blown rebuild?

A999 lockup transmission. The good news is that they have the lower first gear for a bit faster launch. The bad news is that there is a TSB for shudder on these as the lockup occurs. Unfortunately the parts for the fix are no longer available. This kit has the fix built into it:
http://www.ebay.com/itm/A904-A727-SUPERI...135.m2548.l4275
I used it for the shudder fix, tossed the rest. Used the Transgo shift kit TF2 to do the normal shift kit fixes on the transmission. I did this 4 years ago and it is still running well.
If you drop the valve body, it will have a growth on the top side that channels the fluid to the lockup circuit so valve bodies will not interchange to the 904.
BTW, I did change the the torque converter as was suggested before.
Craig

There are physical differences between the two transmissions. A full blown rebuild to non lockup is not possible, you will have to swap transmissions.
Craig

They used hydraulic lockup until about the time they started putting fuel injection on the trucks. Cars asin M-bodies had the non electronic one until they were discontinued.
You can lockout the lockup but if you don't want it you're probably better to start with a transmission that never had it to begin with.

Good info, I have two, van and truck 84 or 85. I guess I'll rob the low gear sets and stick them in an early trans. What is the best 904 case? You can use a toggle switch to turn on the lock up, did this on my 92 diesel, it eat tps switches like candy.
Wait, that was over drive, never mind.

I checked with my local transmission shop pro about the lock up TC. He said it will work, but might result in the dreaded low speed shudder when locked up. He said he could drop the pan and add a ball check to defeat the lock up feature if I don't like it.

Using the correct fluid will often stop the shuddering on converter lockup. Try the newer +4 fluid.

If it doesn't, a change to a heavier spring in the lockup valve will raise the road speed at which lockup occurs and prevent shudder.

Back in the day, the lock up convertor snout was prone to cracking under load.
I broke one with a slanty six...in a Mirada.

I would not put one behind a decent motor.

I have an 86 D150 and it has a one wire electrical plug going in thru the main case close to where the tail shaft bolts on to the main case of the trans. It has one solenoid mounted to the valvebody. Im told this confirms its a lockup trans. Hope that helps!

If its a round connector at the left rear of the trans then yes it sounds like it is lock-up. I believe that model also uses a relay for the lock-up as they called the relay a part throttle unlock relay but it locks and unlocks the converter and the relay is controlled by the PCM (eng controller). The relay should be mounted on the firewall and it sends power to the lock-up solenoid in the trans as the solenoid on that one is grounded in the trans as it only has the one power wire to it from the relay. Ron