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Tranny shifts down when engine warms up.


11 replies to this topic

#1 deesdog73

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Posted November 27, 2012 at 10:52 pm

Just purchased a 94 LHS (3.5L w/42LE transaxle) for $1000. I knew it was gonna have issues, but with only 69,XXX original miles on a clean engine & decent body & interior, I couldn't pass it up.When I first take off & for the first few miles it shifts like a champ, but as the temp gauge gets to (or sometimes just below) it's normal operating temp, the transaxle will downshift itself (rather violently w/light wheel lockup if you are 'on' the throttle). I haven't had an opportunity to test how long of a cool-down period is required before normal shift capabilities return. I'm going to change the filter & flush all the fluid & replace with ATF+3 or +4 as a starter, I'm hoping that someone here has had or heard of this occurrance & might be able to share their knowledge or advice. I personally prefer older vehicles with as few wires as possible, but my wife really liked it & she already knows I'm capable of working on it (whether I like it or not) so any advice or help would be greatly appreciated. Thank you in advance.

#2 valiant67

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Posted November 28, 2012 at 05:17 am

I assume you mean it's dropping into second gear and staying there (which is limp home mode).
If that is the case, there will be an error code (or codes) stored in the transmission computer. You need to find a scanner capable of accessing the transmission computer to read those codes.
The fresh fluid is a good idea and may help, but without knowing the error codes you could be looking at anything from a simple fix to a worn out transmissions.

#3 deesdog73

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Posted November 28, 2012 at 09:11 pm

Thank you valiant67. Would a standard OBD I scanner be able to access the transmission codes, or does it take a more specialized scanner? & if so, is it going to be something I can find & purchase myself, or would I be better off taking it to a shop that would have that type scanner. Haven't had very good luck with the shops in my area & hate chancing gettin' burned a second time if I don't have to.

#4 valiant67

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Posted November 28, 2012 at 10:42 pm

It has to be a fairly advanced OBD I scanner, most won't do it. I have a SnapOn MT2500 that works with OBD I cars and can access the transmission computers.

#5 brycmtthw

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Posted November 29, 2012 at 01:07 pm

I had that problem with a Grand Caravan of that vintage... It turned out to be a faulty speed sensor.... But a shop told me that and replaced the part FO FREE!

#6 deesdog73

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Posted December 9, 2012 at 02:43 pm

Ok, here's the latest update on the LHS. I changed the fluid & filter & replaced both the input speed sensor & the output speed sensor a week ago. I let the car run at idle until it reached normal operating temp to make sure the fluid level was ok & there were no visible leaks. After all that, I took it out for a test drive, drove it about 15 miles & it shifted perfectly. The next day my wife was driving it & as soon as it got up to normal operating temp it went in to limp-home mode. We've been driving it the same way (i.e. start it up cold & take off) since then & it's kept doing the same thing. Today, on the other hand, I started it cold & took off & it went in to limp-home mode after it reached temp (about 5 miles) & I drove it that way for 15 miles at low speed on backroads, but after letting it sit for a few minutes at the places I went to, I took off on the backroads expecting it not to shift, but it shifted perfectly for the entire 20 mile trip (not just the first 5). So, I'm going to try letting the car reach operating temp at idle in park before driving it & see if that is a way to bypass whatever is causing the problem, as well as narrow it down so I can give a more specific list of symptoms when I take it to a shop. Again, if this sounds familiar to anyone else's experience, please let me know what you found out as I'm preparing to take it to a shop & I want to be as prepared & knowledgable as I can be when I walk in the door. Thanks.



#7 valiant67

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Posted December 9, 2012 at 03:48 pm

Ask any shop to provide you these things:
1) The exact error code they read from the transmission computer
2) The CVI values (a measure of wear)
Then you can post that information here along with their diagnosis and hopefully someone can comment on this.
It's been my experience that cars that drop into limp mode warm will often suffer from a low fluid pressure related issue. Sometimes fresh fluid and an upgrade to the latest transmission control software will address the issue.
However, there are 30+ individual faults that the transmission computer can record so without the codes it is all a guess.

Edited by valiant67, December 9, 2012 at 03:49 pm.


#8 deesdog73

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Posted December 9, 2012 at 05:21 pm

Thanks valiant67, I'll ask for that info & post back when I find out.



#9 78LilRed

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Posted January 3, 2013 at 11:19 pm

Go to any local parts store and they can scan it for free...come back and report any codes

 

Not sure on the 1st Gen LH, but on 2nd gen a faulty cam sensor can also cause this issue...



#10 ImperialCrown

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Posted January 4, 2013 at 06:32 am

 Most PCM engine code scanners won't read pre-OBD 2 TCM codes.

Being a 1994 OBD 1 vehicle means that a more advanced and specific scan tool/plug-in cable is necessary. It will probably require a shop with the right tool.



#11 78LilRed

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Posted January 4, 2013 at 07:14 pm

I read on www.dodgeintrepid.net that AAP and AZ can read the OBD1 tranny codes.....I have no proof though



#12 raymondo112

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Posted January 5, 2013 at 02:32 am

Well it kinda stinks I didn't see your post before you did the fluid and filter changed, because I would have highly recomended with the filter down you replace the solenoid pack it is on the inside and you have to remove the filter to get it, it is common for it to go bad and cause some symptoms as you describe, also when you pull the pan make sure you reseal it with black RTV as was done with the factory trans filter kits come with gaskets and these pans were not designed for gaskets it causes leaks if you use the gasket.  How bad was the old fluid dark red smelly looked to have any little material in it if so I don't need a scanner to tell you the clutch packs are probably going or gone.  I never like throwing in parts for no reason, it is good to get it scanned but most places will just tell you to rebuild it, the 42 LE in these cars is actually pretty strong but if you run them out of fluid they die, regular ATF causes it to act real crazy wont hurt it unless you keep trying to drive it like that, you could pour in lubeguard using the mixing ratio, ATF+4 is regular ATF mixed with 4 additives, an antifoaming, friction modifiers that are necessary for the clutch packs to operate properly, I am sure there is more, this is what I remember being told in school.  People are probably going to be mad I said that or tell me I am wrong thats ok cause I don't rebuild transmisssions or use Regular ATF customers hate paying more but hey I hate seeing cars comeback.  You can test the solenoid pack if you want to be sure, its just too bad it is inside the pan on this transmission so that means you will loose all your new fluid and I know it is expensive. You will need to use a ohmmeter, and might want to see if you can find a diagram that tells you where to measure it from and what the value is supposed to be.

 

I would say that the trans is pretty much to that point, you are either going to try the solenoid pack or I would get a used trans from a yard and before you put it in pull the pan look at the magnet and look for a lot of shavings if it has it bring it back, if the fluid if dark or has little material in it bring it back get another one.  Problem you will have is 1 getting the car up high enough to take it down, 2 you will snap a few bolts on the engine member getting it off, 3 trying to loosen the bell housing bolts sucks, especially since you have the heater tube running there and you don't want to snap that thing they are dealer only and expensive. 4 you wont believe how much really has to come off to remove the trans, 5 the bellhousing bolts have threadlocker on them so you need a nice big cheater pipe to break the bolts loose.  Its not a fun job, theres worse out there, but it's not fun or super easy. 

 

Goodluck....

 

 




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