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Various little 4R70 Trans issues


Well-Known Member
July 2, 2018
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Year, Model & Trim Level
98 Explorer V8 AWD
Dora the explorer
Ok bought my 98 explorer 5.0 with 141k and did a trans fluid filter change when i got it because fluid was dark. No metal specs in the pan or anything. The transmission shifts buttery smooth normally. First issue is when completely cold and get in and don't let it warm up at least 1-2 minutes it will hold second gear and you have to "convince" it to shift to 3rd, but once it finally shifts for the first time no more issue. When I give it just a few minutes to warm up its completely fine. Also another issue, when the truck is not quite fully warm, if you get on it the 2nd to 3rd shift can be a bit slow. Other issue is sometimes only when cold it will clunk into reverse. I don't really have any issues at all when the trans is warm. I've noticed that these issues have actually been becoming LESS frequent, which is good. Any ideas what would cause them. I have put around 1,500 miles on since the fluid change.

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Mass air flow sensor and engine coolant sensor will give similar symptoms when failing. Transmission shift strategy relies on several engine sensors even ABS. Do a complete diagnostic work up before throwing parts at it. Good luck

My truck used to do the delayed 2-3 shift the first time it was driven in the morning, but oddly it cleared itself up after a few months.

Mass air flow of all things? My truck cranks long on start up alot and every once in awhile when i come up to a stop, it will attempt to idle at 400 rpm and almost shut off. Are these also indicators of a mass air flow issue?

Long start can definitely be a symptom of the engine coolant temp sensor.

Really? I guess ill look into the coolant sensor, and clean the MAF sensor while im at it

It gets the mixture wrong because it vastly under/over reads the engine temp. It’s like starting a carbed motor without the choke.

Have you had it scanned for trouble codes? May have pending codes also. Need more than a 20 dollar code reader to do a proper job of diagnostics. Really need a live data stream to see how things are working together. I’m not familiar with the apps and Bluetooth for smart phones capabilities but many on here are.

Well the truck recently got a code for the cam syncro sensor, which was broke off in the syncronizer, which then ruined the syncro as well, so I replaced those two things, which got rid of the code for that, which it starts somewhat better (i still think it takes to long) doesn't try stalling anymore at idle like it recently started doing. No improvements on the shifting, and i notice more so, if you go easy on it when cold it wont have a shift issue but if you get anywhere around 2.5-3k RPM when it isn't fully up to temp, it will hold, and then let off and will shift

I've fixed all the vacuum leaks, or at least the ones I know of, and so far I have no codes, idles better now, and hasn't done that goofy 2-3 shift thing since. Also shifting in general seems to be nicer. I still do have the clunking in reverse more so when cold, idk what that could be, i think the sound is coming from the front of the truck, a clunk, maybe front driveshaft u joint? Sometimes if i go to drive and then N to R it wont clunk as much.

Check your front and rear driveshafts, the front d shaft at the t case is suspect for your Reverse clunk since you said its coming from up front

Our trucks no longer have a downshift control rod. Transmission shifting is controlled by the throttle position sensor.

If this sensor output is a tad high, delayed upshifts will result. The PCM "thinks" you have the pedal depressed further than it is, so it is holding the passing gear downshift.

Just another thing to check. TPS resistance should rise steady with no spikes.

Output voltage of TPS should be < 1v at idle, should rise steadily with no spikes to 4.6v at Wide open.

The EGR 401 code came back and with it the cold 2-3 shift problem started happening again. Look at "Sting of codes 5.0 explorer" thread for more info.

One thing i have noticed that i failed to mention is that when your slowing down sometimes can notice 1 of the downshifts i'm assuming 3-2, and pretty much only when it's cold. When this thing is fully warmed up, it shifts like a dream, no issues then. The warmer the day- the less the issues happen.

My reverse clunk is only when its cold, so can i rule out the Ujoints? Also there is no delay, it kicks into R right away. Its like a "clank" sound, doesn't happen in drive. If i go to drive before shifting to reverse it goes into R a little bit nicer. I need to figure out whats going on with these, cause i will be taking it to college this fall, and need it needs to be sorted out. I have some very small exhaust leaks, along with EGR issues p0401, but i just can't see that that would be the source of the problems. Also, when it holds second gear, if get off the gas the rpm's will drop, and when i get back on the gas, it grabs 2nd again. No slippage, it acts as if i have the shiftier in 2, without the engine braking. Yes i'm rambling, but i want to figure out if these problems are minor or major.

Check your front driveshaft for play at the CV joint.

Ok, And for the 2-3 shift, i have read stuff about a 2-3 accumulator spring breaking, or the accumulator itself or something. These can be fixed by dropping the pan and valve body i believe from what i read?

Yes, and with high mileage, it's wise to replace all of the solenoids, the accumulators, besides the fluid and filter. There's more that can be done, but those should be part of any pan drop of a trans with 150k miles or 10-20 years age. The VB is the most important part of the transmission, and the one thing an owner can work with readily. There are many other parts applicable to the VB, Sonnax has a bunch highly recommended, plus kits for shift improvements, those springs of course too.

The clutch parts can last indefinitely if the VB is working very well at all times. When the VB begins to have issues, then the clutches wear out very fast, and that's a full R&R the trans, big job. Take great care of the VB, don't skimp on parts or put off anything for later. Do what you can as soon as you can, go slow and be patient, it takes a long time to do it right.

4R70W 2-3 Shift Problems
This may be the problem? And i would probably want to do springs and stuff while i'm in there depending on the cost.

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4R70W 2-3 Shift Problems
This may be the problem? And i would probably want to do springs and stuff while i'm in there depending on the cost.

That is only an issue with certain rebuilt units. With age, all of the solenoids and accumulators, and their seals, are due to be replaced. It's fine to leave them all alone for twenty years etc, but once there is a symptom, that's a good(or bad) sign that it's time to give more attention to the transmission.

If you drop the pan and plan to do just the filter, and find nothing odd about the fluid or debris, it probably needs more than the fluid/filter. So be prepared to be able to catch and save the fluid of you have to go into it again. ATF is not cheap any more, $5 a quart seems to be the low end price.