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904 lockup converter slipping issues:
https://www.slantsix.org/forum/viewtopic.php?t=62760		 Page 1 of 2
Author:  BamaFan95 [ Mon Aug 27, 2018 1:35 am ]
Post subject:  904 lockup converter slipping issues:
Hi, everyone. Recently been having issues with the lockup on my '85 D100. It has the A904 lock up transmission. I guess it's a very early date O/D. I recently changed the transmission fluid (Dexron III) in the truck and I know that can open up a can of worms: and unfortunately, it did. Fluid surprisingly was very clean, though. Nice red color. I will say that the lockup on this truck has always been kinda finicky (occasional hard bang when locking up), it's just really aggravated now with new fluid.

The transmission shifts 1-2-3 perfectly. No slipping. But when the converter lockup tries to catch, it will shudder or make a grind sound until you let up on the throttle some and it will lock up. Also: this only happens when the transmission is hot after driving for half an hour +. If the trans is cold, the lock up works perfectly with no abnormal noises. Even when the converter is locked; if the trans is hot and I hit a hill in it and really put the torque to the transmission, the lockup will begin slipping again and making noise.

With that being said, does this just sound like a bad converter or something? Like previously stated, it shifts flawlessly (except for an unrelated linkage adjustment issue that results in short shifts at light throttle). The problems only exist when the converter tries to lock. Could I go with just having the converter replaced, or should I just have the trans rebuilt entirely? Thanks guys, for any input.
Author:  Brian [ Fri Aug 31, 2018 4:27 am ]
Post subject:  Re: 904 lockup converter slipping issues:
Disable the lock up function and see how it is. My 86 D150 had a metal relay mounted right behind the starter relay on the inside of the fender. All the relay did was ground the wire to the solenoid on the trans. I unplugged it. I'm guessing the 85 model is the same. If I'm wrong someone correct me :wink:
Author:  BamaFan95 [ Fri Aug 31, 2018 12:27 pm ]
Post subject:  Re: 904 lockup converter slipping issues:
Quote:
Disable the lock up function and see how it is. My 86 D150 had a metal relay mounted right behind the starter relay on the inside of the fender. All the relay did was ground the wire to the solenoid on the trans. I unplugged it. I'm guessing the 85 model is the same. If I'm wrong someone correct me :wink:
I looked for it, but couldn't find anything on mine. I thought these transmissions were completely mechanical in this era of Ram trucks? Maybe I'm wrong? From what I've heard from several people is that it's controlled by engine RPM, or the kickdown linkage, or something along those lines. Seems to be the lockup giving trouble, though I'm not sure. Every time it tries to lock up (trans hot) it makes weird noises and shudders.
Author:  Brian [ Fri Aug 31, 2018 4:57 pm ]
Post subject:  Re: 904 lockup converter slipping issues:
The ESC computer bolted inside the drivers side fender controls everything on the 86. Maybe yours is mechanical. Not sure. :|
Author:  Reed [ Fri Aug 31, 2018 8:32 pm ]
Post subject:  Re: 904 lockup converter slipping issues:
Brian- please post some pictures of your electronic solenoid controlled lockup trans. There have been reports for years of 1987 model year trucks being equipped with computer controlled lockups in the transmission, but never and documented sightings. In virtually all slant six lock-up transmissions the lockup feature is hydraulically controlled, not electronically controlled.

The 904 is a three speed transmision, not an overdrive. The lockup torque converter eliminates some slippage, but it is not a fourth gear.

It IS possible to disable the lockup feature on a hydraulically controlled transmission. It involves pulling the valve body and a minor modification, but it can be done. However, frankly, I don't recommend it.

Are you sure it is the lockup and not another orn transmission part?

Have you adjusted the bands?

I have found this diagram extremely useful in diagnosing what part of a 904 transmission has failed:

Image

This is something you find in a factory service manual, which you should get for your truck.

You might have worn front clutches.
Author:  matv91 [ Sat Sep 01, 2018 4:39 am ]
Post subject:  Re: 904 lockup converter slipping issues:
On the driver side pan rail of tranny is number. Post it. http://slantsix.org/forum/viewtopic.php ... it=lock+up
Author:  BamaFan95 [ Sat Sep 01, 2018 5:28 am ]
Post subject:  Re: 904 lockup converter slipping issues:
I am fixing to take the truck out for a spin. I will take a video right quick and post it here. The only time it does it is when the lock up converter tries to lock and it makes lots of weird noises. I didn't adjust the bands. I will be right back with a video. Thanks, guys.
Author:  matv91 [ Sat Sep 01, 2018 5:43 am ]
Post subject:  Re: 904 lockup converter slipping issues:
Flow test http://slantsix.org/forum/viewtopic.php ... =flow+test about half way down that page, page 3 bulletin no. 21-14-79. That is standard test any year .
Author:  matv91 [ Sat Sep 01, 2018 6:34 am ]
Post subject:  Re: 904 lockup converter slipping issues:
This is lock-up story,heat related. After 40 mile drive on hot days, lock-up would engage at idle in drive some times stall engine. Ran good cold,passed flow test. When metal gets hot it expands,allows leaks between circuits. In this case pressure from another circuit was leaking in to the apply circuit for lock-up.By passed radiator cooler used after market in line cooler instead.No problem after that daily driver 8 years ago 100000 miles. This was for testing purposes but it worked. Just left it that way
Author:  BamaFan95 [ Sat Sep 01, 2018 7:33 am ]
Post subject:  Re: 904 lockup converter slipping issues:
Quote:
This is lock-up story,heat related. After 40 mile drive on hot days, lock-up would engage at idle in drive some times stall engine. Ran good cold,passed flow test. When metal gets hot it expands,allows leaks between circuits. In this case pressure from another circuit was leaking in to the apply circuit for lock-up.By passed radiator cooler used after market in line cooler instead.No problem after that daily driver 8 years ago 100000 miles. This was for testing purposes but it worked. Just left it that way
Thanks for the info. I will look into that. Here is a video of mine. I apologize, there is some wind noise in the video so it's hard to hear, but when mine starts to act up, it makes a grinding noise. Pulling hills (with the lockup engaged) when hot and it'll slip and grind as well.

Here's the link: https://www.youtube.com/watch?v=-Ibw3Rej4Sg
Author:  Charrlie_S [ Sat Sep 01, 2018 9:57 am ]
Post subject:  Re: 904 lockup converter slipping issues:
My 88 diplomat has a lockup issue. If you are on the throttle at the lockup point (45mph) after trans is warm, it will chatter, just like a manual clutch. It gave me a hard time diagnosing, whether it was the clutch or misfire. My trick is to ease off the throttle right at the lock up point. It will occasionally chatter at higher speeds during hard throttle, but not to kickdown point.
Author:  Reed [ Sat Sep 01, 2018 10:59 am ]
Post subject:  Re: 904 lockup converter slipping issues:
If you are having a lockup issue, my first thought is to install a stiffer spring in the lockup valve body that will raise the lockup point a bit. Or, if you are feeling adventurous, try disabling the lockup completely as I detail how to do HERE.

I don't advocate disbaling the lockup. I think you are better served fixing the problem. But if you want to give it a try, go for it.
Author:  BamaFan95 [ Sun Sep 02, 2018 7:49 am ]
Post subject:  Re: 904 lockup converter slipping issues:
Thanks everyone for the replies. Yes, I definitely want to keep the lockup feature. It really helps out this little engine. Not sure how I'm going to approach this issue, but at least I now know what my options are. Thanks again, everyone!
Author:  matv91 [ Sun Sep 02, 2018 3:51 pm ]
Post subject:  Re: 904 lockup converter slipping issues:
http://www.slantsix.org/forum/viewtopic ... tc#p276058
Author:  BamaFan95 [ Mon Sep 03, 2018 1:34 pm ]
Post subject:  Re: 904 lockup converter slipping issues:
Quote:
http://www.slantsix.org/forum/viewtopic.php?f=20&t=39894&p=276058&hilit=ktf+tc#p276058
Thanks for the link. I tried to click on the links provided in that thread for the upgraded lockup springs, but they have expired. Can you provide me with an updated link to these stiffer spring kits? Thanks, in advance.
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