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Hi guys,

So I recently bought a '91 Dynasty (3.3/4speed), did a full tuneup and the correct fluid/filter change using atf+4, then drove it home (150 miles) with no problems. Today I had to change the coolant bypass hose, and disconnected the battery just because, and then after reconnecting, left to drive to work, and it upshifted into 2nd and stayed there. Before anyone suggests I need a new trans, as I know the reputation of these A604's, anything I can do to remedy this? Since these are electronically controlled, I thought perhaps disconnecting the battery did something, as I had no issues prior to this other than occasional harsh 1-2 upshift when cold. Any tips on what to look for, where to look for it, etc. would be greatly appreciated. Thanks.
 

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Virginia Gentleman
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Have you checked for fault codes? That's where I'd start.
 

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Discussion Starter #3
Have you checked for fault codes? That's where I'd start.
I don't have a scanner to do so. However, after posting this, I disconnected the battery for about a half hour and then reconnected it, drove home from work and it shifted perfectly. Hit 4 different stop lights, and each time it did what it was supposed to as far as upshifting/downshifting, with not so much as a harsh shift...but the last stoplight, I took off and it went to shift into second, revved up like it was in neutral, then hard shifted into 2nd and went into limp mode again. So this is why I'm confused..it shifted perfectly 3 different times and then does this the 4th time? FYI my TCM is indeed the old style, and I'm wondering if replacing with the updated '92 version would fix this.
 

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If the problem is low fluid pressure, an updated transmission computer will deal better with that. But without scanning it, you won't know if the new computer will help.

Some faults occur have to occur once and the transmission goes into limp home mode. These are hard faults. Other faults are soft faults and have to occur several times before the transmission goes into limp mode. The fact it drops out of gear concerns me.
 
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The 1992 TCM was different than 1990-1991. I'm not saying that this is your problem, but smooth sided TCMs have been obsolete for about 20 years.
There may also be internal transaxle wear issues.
The finned TCM with the latest and greatest software version is desirable.
TSB 18-24-95 covered this. See p. 4 for the correct TCM part # for your application. Looks like 4796122:
http://www.robskorner.info/faqs/tsb/18-24-95.pdf
 

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Sorry to hear this, good luck. I am glad my LeBaron LE has the 3 speed A670.
 

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Discussion Starter #7
If the problem is low fluid pressure, an updated transmission computer will deal better with that. But without scanning it, you won't know if the new computer will help.

Some faults occur have to occur once and the transmission goes into limp home mode. These are hard faults. Other faults are soft faults and have to occur several times before the transmission goes into limp mode. The fact it drops out of gear concerns me.
Any tips on how/where to scan and check for codes? It's just odd to me that it shifts fine and then suddenly has a problem, but with resetting, will shift fine again a few times.

The 1992 TCM was different than 1990-1991. I'm not saying that this is your problem, but smooth sided TCMs have been obsolete for about 20 years.
There may also be internal transaxle wear issues.
The finned TCM with the latest and greatest software version is desirable.
TSB 18-24-95 covered this. See p. 4 for the correct TCM part # for your application. Looks like 4796122:
http://www.robskorner.info/faqs/tsb/18-24-95.pdf
I read somewhere else on here that '92 model TCMs are the only newer/updated versions that can be swapped in, unless you can find a '91 and older one thats been replaced..and that TCM # 4796124 would also work ('92 minivan, finned version with newer software)?
 

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No, you can't swap a newer TCM. They are specific to a year/range. In 1993 they began using reflashable TCMs (a finned box instead of a plain box). However, you cannot retrofit these in an earlier car.
However, Chrysler offered a reflashable TCM for the earlier years. What you need is a finned TCM with software 4796122. The software should be shown on a decal affixed to the finned TCM box. If you are looking in a junkyard or eBay, the donors are 90-91 3.3 and 3.8 powered AC (Dynasty, short New Yorker), AY (Imperial, NY Fifth Avenue) or minivan. 3.0 powered cars won't work as a donor.

The only way to get the codes from the TCM is to have a dealer or some other shop with the proper scanner to access the TCM and pull the codes.
Unfortunately I've experienced the "it drives OK for a while after a rest" type problem. In my case it never freewheeled though. The fact it losses all gears is not good. A total electrical failure or whatever sensor failing should still leave second and reverse functional. It certainly would not hurt to try a newer 4796122 TCM, especially if you can find a used one cheap as if can still be used even if you have to have the trans worked on.
 

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I know when I had my 1990 Imperial and my 1992 New Yorker, I could not swap the TCMs between the cars. I tried and ended up with a non-shifting transmission.
 

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Discussion Starter #10
No, you can't swap a newer TCM. They are specific to a year/range. In 1993 they began using reflashable TCMs (a finned box instead of a plain box). However, you cannot retrofit these in an earlier car.
However, Chrysler offered a reflashable TCM for the earlier years. What you need is a finned TCM with software 4796122. The software should be shown on a decal affixed to the finned TCM box. If you are looking in a junkyard or eBay, the donors are 90-91 3.3 and 3.8 powered AC (Dynasty, short New Yorker), AY (Imperial, NY Fifth Avenue) or minivan. 3.0 powered cars won't work as a donor.

The only way to get the codes from the TCM is to have a dealer or some other shop with the proper scanner to access the TCM and pull the codes.
Unfortunately I've experienced the "it drives OK for a while after a rest" type problem. In my case it never freewheeled though. The fact it losses all gears is not good. A total electrical failure or whatever sensor failing should still leave second and reverse functional. It certainly would not hurt to try a newer 4796122 TCM, especially if you can find a used one cheap as if can still be used even if you have to have the trans worked on.
So I've gotta find a '90-'91 with the updated TCM...

Sidenote: Today I drove to work and the car had reset itself it seems, as I did not disconnect the battery this time, just parked it last night..and today it shifted just fine other than occasional kinda rough 1-2 upshift, but not consistent, other times it shifted 1-2 smoothly..and drove to work just fine, not going into limp mode at all. So I'm very confused...perhaps an updated TCM will solve this new issue?
 

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Discussion Starter #11

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Yes, if it has that part number that is the latest software for your car.

Rough shifts are often a sign of low pressure.
The new TCM may shift oddly at first until it it learns your transmission. On these early ones there is no quick learn with a scan tool so you just drive it.
 

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Discussion Starter #13
Yes, if it has that part number that is the latest software for your car.

Rough shifts are often a sign of low pressure.
The new TCM may shift oddly at first until it it learns your transmission. On these early ones there is no quick learn with a scan tool so you just drive it.
Sounds good, I'll give it a shot and see if it helps the problem. Thanks so much for the input and help! What causes low pressure? Leaky seals I assume? It only seems to shift rough sometimes, not always, and its always the 1-2 upshift. Again, it drove close to 200 miles home to Lake Tahoe from Northern CA with no issues or any shift problems, so it's so bizarre to me that its acting this way so suddenly.
 

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I had work done to my trans a few years back and the mechanic was intent on filling the trans with more fluid than recommended. The trans had all kinds of issues with shifting until I reduced the fluid level. I believe with my trans the fluid level has to be at operating temps, cycled thru all the stops, and then check.

Perhaps another level check if not done properly?
 

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Sounds good, I'll give it a shot and see if it helps the problem. Thanks so much for the input and help! What causes low pressure? Leaky seals I assume? It only seems to shift rough sometimes, not always, and its always the 1-2 upshift. Again, it drove close to 200 miles home to Lake Tahoe from Northern CA with no issues or any shift problems, so it's so bizarre to me that its acting this way so suddenly.
This sounds like a connector/wiring issue.
 

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Discussion Starter #16
I had work done to my trans a few years back and the mechanic was intent on filling the trans with more fluid than recommended. The trans had all kinds of issues with shifting until I reduced the fluid level. I believe with my trans the fluid level has to be at operating temps, cycled thru all the stops, and then check.

Perhaps another level check if not done properly?
I've heard about how finicky these are with that, and have been monitoring it. So far, its at the correct level still.

This sounds like a connector/wiring issue.
Perhaps? Not sure what to check though.
 

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The problem is this latest issue sounds like it could be a sensor however the post earlier indicated the transmission freewheeled which is not an electrical fault.

I think the previous owner knew the transmission was flakey and got rid of it. You need to get it scanned because you'll spend more time and money throwing parts at it and never knowing if the transmission is any good or not.
 

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If this is the original A 604 from 1991 and it is determined that the trans needs work, most trans shops will switch it out for a reman 41TE and not want to spend the money putting in all of the upgrades into this transmission.
 

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If this is the original A 604 from 1991 and it is determined that the trans needs work, most trans shops will switch it out for a reman 41TE and not want to spend the money putting in all of the upgrades into this transmission.
Unfortunately I'm not sure if it is or not. Ordered the replacement TCM, will share after if it makes a difference or not.
 

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This sounds like a connector/wiring issue.
My thoughts as well. After 26 years, connector pins aren't so grippy anymore, particularly the kind Chrysler used back then on the A604 input and output speed sensors.
 
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