A604 help

I have a '90 Lebaron Convertible with a tranny problem (A604). I know
there are a lot of documented problems with it, but I haven't been able
to find one similar to mine, so I'd appreciate any help...

Bought car July 2004 with 106,000 miles and immediately did complete
tranny fluid change out - fluid was VERY dirty. Replaced filter and
refilled with ATF+3 fluid. Tranny ran great until recent problems.

When car is cold, tranny shifts GREAT through all 4 gears. The problem
happens after the car warms up. First gear operates fine, but instead
of shifting into second it shifts to some kind of neutral instead.
After varying periods of time (15 sec - 2 min) it will eventually
"limp" into second gear. At this time when I manually shift gears, it
won't go into whatever gear I select (R, 2, or 1).
Naturally shutting key off and turning back on resets tranny, but if
the car is warm the same problems happen.

So I replaced the filter again and changed out the fluid, but still had
the same problem.

I took the car to the dealer to read the tranny codes:
Codes appear after attempted shift from first to second gear:
Code 36 - "Fault immediately after shift"
Code 52 - "Gear ratio error in 2nd"
Code 54 - "Gear ratio error in 4th"

Dealer "speculated" that the sun gear was broken and quoted a price for
a rebuild. That lost all credibility with me because why would the
tranny run fine cold if the sun gear was broken?

I found a local guy not too far from me who used to be a CMD mechanic
and he read the codes (got same codes as dealer) and guessed that a
snap ring was broken.

Feeling brave and getting encouragement from co-workers, I decided to
buy the ATSG manual & video and attempt a rebuild myself.
So I've torn apart the tranny, but I've only found one obvious problem
-but it doesn't seem like it would be the cause of my problems. The
OD/Reverse pressure plate (inside of the input shaft clutch assembly)
had a broken piece on the outer ring. It had completely broken apart
from each of the two tabs that it was attached to. The snap rings and
clutch retainer held the broken piece in position, so it's not like it
rolled around and caused any damage, it just remained broken in
position.

In the next couple of days I'll be putting the tranny back together.
But before I do, I'm hoping for some help of things I should
double-check that may cause the symtoms I described above.

Thanks in advance for any help.

-Dave B.

 

It wouldn't. You're right, the dealer is an idiot.

Were the clutch plates excessively worn in any clutch pack common to
2,3, and 4? Everything can look "normal," but if the clutch material is
all gone, it won't work and will feel like its in neutral, especially
when warmed up.

Also, do you have any reason to suspect an internal pressure leak or a
weak hydraulic pump?

 

Thanks for taking the time to reply.

I work with a guy who has rebuilt a few tranny's (not A604) himself and
he didn't think the clutches were excessively worn. There is evidence
of extreme heat on the UD and OD clutches inside the input housing
assembly. The underdrive clutches that are common to 1, 2, 3 show
evidence that they weren't fully engaged at times.

The 2-4 clutch pack is engaged for gears 2 and 4 (that is why code 52 &
54 both showed up on the failed shift to 2nd gear). But these clutches
don't look to be problematic at all.

I haven't found any seals or o-rings that seem damaged, have a gouge,
or are broken, so I don't really have a reason to think there's an
internal pressure leak (not that there wasn't one).
The pump internals didn't show any wear or problems.

I've found on the web that ATSG has a bulletin # 94-28 titled "A604 2nd
gear starts and no upshift, even after ignition cycle". Does anyone
know what this bulletin says?

 

IF both the UD and OD clutches looked cooked, then I'd guess that was
the root of the problem. Glazed and slipping clutches. I'm not
intimately familiar with that transmission, but I have seen cases in
others where clutches with plenty of material left just wouldn't hold
because they had overheated and glazed.

 

my guess is a bad speed sensor. These sensors can get heat sensitive and
work fine when cold then when warmed and expand a bit, get intermittent.
And the speed sensors are known weak points on this tranny. Unfortunately
the only way to test it is with the vehicle warmed and running and an
oscilloscope
on the sensor.

The commercial tranny rebuild shops replace all sensors when they rebuild
these
trannies to avoid trouble like this.

Ted