Air bubbles in tranny fluid, Jeep, 1997 GC

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I noticed this morning my Jeep started doing the "dropping idle" in start/stop traffic. It had been doing this for quite a while several months ago, and topping off the tranny fluid helped (as well as cleaning the ICV and TB. I also fixed a huge part of the problem by replacing the cat converter and muffler 3 weeks ago. This eliminated the rough idle/dropping idle, and it's been running smooth ever since. I started the Jeep just now, slightly warm engine. Checked transmission fluid. It was right up to the Max line, and there were air bubbles in it. There was never bubbles in it before. Web searches turned up this: Air bubbles usually means either ATF too low or too high. The transmission shifts pretty sluggish, and it's gotten a little worse in the past week. I'm going to start by getting a tranny fluid/filter change. Would it be safe to wait 2-3 weeks to do a tranny service? Money is tight. Just want to make sure I'm not missing something obvious. 1997 Jeep Grand Cherokee Laredo Tsi, inline 6, not sure which tranny Thanks.
 
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Pulled this from WJ Jeeps. It is technically for the second Grand generation, but they have the same 42re transmission.
Originally Posted By: WJJeeps
MODEL 42RE: 1. Transmission fluid must be at normal operating temperature for accurate fluid level check. Drive vehicle if necessary to bring fluid temperature up to normal hot operating temperature of 82°C (180°F). 2. Position vehicle on level surface. 4. Apply parking brakes. 5. Shift transmission momentarily into all gear ranges. Then shift transmission back to NEUTRAL. 6. Clean top of filler tube and dipstick to keep dirt from entering tube. 7. Remove dipstick and check fluid level as follows: (a) Correct acceptable level is in crosshatch area. (b) Correct maximum level is to MAX arrow mark. (c) Incorrect level is at or below MIN line. (d) If fluid is low, add only enough Mopar ATF +4 Automatic Transmission fluid to restore correct level. Do not overfill.
All that said, I would drive it to get it hot and recheck your fluid.
 
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You want to fix any fluid issues right away. Those are garbage transmissions ... you don't want to shorten it's life any extra with too much / too little.
 

niero

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I'm not sure when it was last serviced, which is reason enough to get it done, I know. I'll drive it and re-check it when it's hot. dlundblad - Thanks for posting that list. Good info. Tranny Services I was going to try it myself but I don't have all the tools. I checked at a few places, and one garage said that you should get it done at a tranny shop, they have a machine that sucks out all the ATF from the converter and anyplace else it's lurking. Never heard of that. Is that machine necessary?
 
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Honestly all you need is a 13 mm wrench and socket,a T-25 torx bit for the filter and an oil catch pan. One bolt near the exhaust bracket gave me some heck so I sacrificed a cheap 13mm and cut it in half. Dont flush it. If it makes you feel any better, I wanted the dealer to do a flush at 100k. They said they wouldnt recomend it and "down-sold" and pan drop to me. (I was a puss then and had the dealer do my brakes too.. dont laugh. Lol) Just do a pan drop. 6 out of the 11 quarts should come out. If you do take it somewhere, make sure they use ATF+4. Many shops think Dex III is the same thing. It's similar, but not the same. *Here's a good how to. I dont think you can view the pics as a guest so you should join this forum too. It has saved me so much money and has allowed me to do 90% of the repairs on my Jeep myself. http://www.jeepsunlimited.com/forums/showthread.php?498015-Trans-fluid-change I recommend using an OEM gasket if you can. They are much better than the rubber ones that come in filter kits. Bought mine for around $16 online and its re-usable. If your transmission has never been serviced, you might be able to use what it already has, but its tough to say what condition its in. The part number should be stamped on the pan.
 
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No, the machine is not necessary. The siphon method (fluid extractor)works great for many (myself included).
 
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The tools you need to drop the pan on 42RE transmission are very simple. 12 or 13mm socket, 3-4" extension, ratchet, plastic wedge and a rubber hammer. For normal street duty these transmissions last fairly long if the fluid is maintained. All you need to do is remove the bolts around the transmission pan and use the plastic wedge and rubber hammer to separate it from the main body. The filter is held on with 2 or 3 hex head screws. Diagrams, filters and reusable pan gaskets are available at most auto parts stores. If your not up for surgery, you can take the easy way out and just change the fluid. Find clear vinyl hose, the largest diameter that you can shove down the transmission filler tube and attach a plastic hand fluid transfer pump, like the $6 Pennzoil 36670 that's at most auto parts stores. Simply pump all 3-4 quarts from the pan and refill with fresh fluid, drive a week and repeat as necessary. We sold one of our 42RE equipped Grands with 268K, still driving around out there somewhere.
 
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A quick google image search shows a trans filter with a neck going into the valve body. If whatever seals that neck to the valve body fails it will suck air in with the fluid resulting in aerated fluid. Read about it before on an F150 forum and that is exactly what happened. A new filter solved the problem in that case. Good luck and get back to us with your solution!
 
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Originally Posted By: double vanos
A quick google image search shows a trans filter with a neck going into the valve body. If whatever seals that neck to the valve body fails it will suck air in with the fluid resulting in aerated fluid. Read about it before on an F150 forum and that is exactly what happened. A new filter solved the problem in that case. Good luck and get back to us with your solution!
This may well be it. In fact, there was an older thread on this very topic that was brought back up by someone who joined this site because they were searching for the cause and wanted to thank the o/p. I will add that the other members were also experiencing a surging or low idle too. May hap yours was related?
 

niero

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Originally Posted By: The_Eric
Originally Posted By: double vanos
A quick google image search shows a trans filter with a neck going into the valve body. If whatever seals that neck to the valve body fails it will suck air in with the fluid resulting in aerated fluid. Read about it before on an F150 forum and that is exactly what happened. A new filter solved the problem in that case. Good luck and get back to us with your solution!
This may well be it. In fact, there was an older thread on this very topic that was brought back up by someone who joined this site because they were searching for the cause and wanted to thank the o/p. I will add that the other members were also experiencing a surging or low idle too. May hap yours was related?
Not sure if you meant me, or The Eric. But I've posted a lot on here about rough/low idle, and dying on idle. (Several issues caused it/made it worse.) Agreed, I think The Eric's idea is right, that a seal is failing. Hopefully nothing too serious.
 
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Originally Posted By: dlundblad
Pulled this from WJ Jeeps. It is technically for the second Grand generation, but they have the same 42re transmission.
Originally Posted By: WJJeeps
MODEL 42RE: 1. Transmission fluid must be at normal operating temperature for accurate fluid level check. Drive vehicle if necessary to bring fluid temperature up to normal hot operating temperature of 82°C (180°F). 2. Position vehicle on level surface. 4. Apply parking brakes. 5. Shift transmission momentarily into all gear ranges. Then shift transmission back to NEUTRAL. 6. Clean top of filler tube and dipstick to keep dirt from entering tube. 7. Remove dipstick and check fluid level as follows: (a) Correct acceptable level is in crosshatch area. (b) Correct maximum level is to MAX arrow mark. (c) Incorrect level is at or below MIN line. (d) If fluid is low, add only enough Mopar ATF +4 Automatic Transmission fluid to restore correct level. Do not overfill.
All that said, I would drive it to get it hot and recheck your fluid.
This. The dropping idle has nothing to do with the transmission, that's typically a throttle body or automatic idle speed port dirt issue. The trans has to be HOT to get a correct fluid level reading, and you have to park it level and cycle through all the lever positions before checking. Just firing it up and checking- no wonder you get bubbles. Odds are your transmission is fine, as long as you keep fluid in them and don't let them overheat, those transmissions are pretty bulletproof. Especially if you remove the ill-advised check valve in the cooler line, it tends to restrict flow and increase overheating.This is what the check valve looks like- it can be removed and the only "symptom" may be slow gear engagement when you first start it after sitting overnight because the fluid can drain back to the pan. That's better than overheating due to a check valve that causes restriction in the cooling line. Start it in neutral instead of park, let it idle 15 seconds, and it will go right into gear. The 42RE gets a lot of unnecessary bad press, I think its a better unit than the AW4 found on XJ Cherokees (which shifts like a worn-out Allison on a 1972 Greyhound bus even when its new). FWIW- its not sucking air past the filter, either. The whole filter and intake is submerged on that transmission, it just doesn't do that.
 

niero

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Originally Posted By: 440Magnum
This. The dropping idle has nothing to do with the transmission, that's typically a throttle body or automatic idle speed port dirt issue. The trans has to be HOT to get a correct fluid level reading, and you have to park it level and cycle through all the lever positions before checking. Just firing it up and checking- no wonder you get bubbles. Odds are your transmission is fine, as long as you keep fluid in them and don't let them overheat, those transmissions are pretty bulletproof. FWIW- its not sucking air past the filter, either. The whole filter and intake is submerged on that transmission, it just doesn't do that.
Thanks, 440Magnum. I didn't realize just starting it up and checking it could cause a problem. Just figured it might read a little low. I'll drive it around on lunch, check it again, and report back.
 
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Could dropping idle be related to the crank position sensor? When mine was acting up, I blamed the transmission at first. This still doesnt explain your bubbles though.
 

niero

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Okay, so I checked the fluid again the proper way. Same thing. Lots of bubbles and now the fluid is reading past the max line. So time for a fluid/filter change. Long story short, I'm not going to have any place to park and work on this for a while. So I'm going to have it done at a shop. One place said $250. There's a rapid oil change shop that will do it for $150, they use a suction machine, but don't do the filter. Is this okay, to not swap filters? EDIT: Just re-reading the thread, and saw where dlundblad mentioned the dealer recommended not flushing it. So we'll use it as a last resort. There's one more place I'm going to try, hopefully it will be less money. Thanks.
 
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niero

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It could be the CPS. But now the idle is good, which is weird. However, I think my tranny is toast. Ran to store via the highway. Checked ATF both before and after I went into the store. Lots of bubbles, and fluid reading way over max. Called local tranny shop. They said that since the tranny fluid is being aerated, it "pushes it up" so to speak (my phrasing) on dipstick. But not lubing the gears. Got home and just as I was pulling into a parking spot I hear the transmission grind. I immediately stopped. Called for a tow truck. Should I have put more ATF in before driving home? Or would overfilling have caused even more problems? I was thinking that, since I had topped it off right up to the max line about a month ago, that should hopefully be enough. I'm guessing my tranny's jacked. I'm HOPING that the transmission is still good but there was a leak somewhere with the filter, so it became aerated, etc, But that's a long shot, I know.
 
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Faulty crank position sensors are hard to diagnose. Like I said earlier, i thought it was my transmission. Folks here chimed in saying to check that out. I was hesitant because it wasn't even throwing a check engine light. Since its been fixed, no more hick ups. Since your fluid is still too high, I would try a fluid extractor and siphon it out through the dipstick tube. With your fluid being too high, its hard to blame anything else. Weird about the grinding noise. Was it just a hick up in the shifting or did it sound like you were trying to change gears without clutching?
 
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