How to: Explorer Auto Transmission Diagnosis - Q & A FAQ

I have had a few inquiries if I might post a kind of "common problems" and diagnosis thread for trannies. This is my attempt to do so. I will not lock this thread but keep adding here (and maybe deleting follow on posts after I have them answered here to keep everything manageable - folks posing Q's with answers will have good ones posted here with attribution.)

So, specific inquiries below will be answered in the top thread and eventually we will hopefully have a comprehensive diagnosis thread here by tranny type is the plan. For now A4LD, 4R44/4R55 and 5R55 as well as 4R70W. More or less Explorers through 2002. Save a lot of answering similar Q's over and over.

A4LD COMMON PROBLEMS

Q1. I have a delayed engagement into reverse (sometimes also into drive). Why is this and how can I fix it?

A. In the A4LD the reverse band is used to engage both reverse and 1st gear. The servo that engages it has a seal prone to leakage, and it also has a rather large volume that needs to be filled and pressurized.

More often that not this is the culprit. Sometimes a leaky seal, sometimes a slow fill because of VB issues. About 50% of the people will find a fix in replacing the seals on the low/reverse servo with either a "double lip" upgrade, or a "D ring" seal kit. Both are cheap (under $5) but you have to drop the pan and valve body to get to it.

Good news? If you can live with it, it isn't doing any harm, just be patient before you goose it.

Q2. I get a loud "klunk" when I shift into reverse. Is this serious? What causes this?"

A2. Generally the "klunk" you hear is caused by worn U joints. The delay in the application of the low/reverse band can cause a sudden engagement, which causes the slack in the U-Joints to be taken up suddenly ..producing that noise. Dangerous? Serious? Hmmmm. Not really. Though the continual "hammering" of the bad joint will only make it worse. Might want to look at those joints, but life threatening? no. Relax.

Q3. I am lacking the 4th gear shift into OD. (The so called 3-4 shift)

A3. In the A4LD, the shift from 3rd to 4th (or the so called 3-4 shift) is controlled by a solenoid. In the majority of cases wherein there is a 3-4 shift lacking, either the solenoid has problems, the wiring to it has a probem, or a screen on some models may be plugged up. Checking the wiring and for voltage at the main feed wire to the solenoids is a first place to check. Many times lack of 3-4 will also have a lack of Torque convertor lockup too. This can add heat to the trans, and the common lack of 3-4 and TCC lockup usually is a good sign of an electrical issue, as neither solenoid is operating correctly. Often this issue may relate to the wiring harness to the PCM (computer). [Brooklyn Bay adds the following good observation: The PCM takes sensor inputs from various places, such as the Vehicle speed sensor, Brake On/Off switch, and Throttle position sensor to calculate when to apply a ground signal to the A4LD's solenoids to apply or not, or in the case of the Torque convertor clutch to lock, and unlock. Often, there could be a driveability problem due to one of these solenoids because of a bad input to the PCM from one of these sensors, and it might be mistaken for a solenoid problem when in fact it is not.]

Q4. I am going through ATF every with no apparent leaks. The transmission pan and rear seal is dry. The front seal appears to be dry. The radiator does not appear to have trans fluid in it either. The driveway is clean under the vehicle. Please help!

A4. The modulator on the A4LD can develop a tear or vacuum leak, and the fluid can be sucked into the engine. While logic would suggest it would be burned as part of the intake gases, it does show up as an overfill in the engine oil area. You can check for this by pulling a vacuum hose from the modulator and looking for ATF in the hose, but if this is your symptom, odds are about 100% you have a bad modulator. It needs to be replaced. It is on the passenger side behind the heat shield with a hose going to it.

4R44E/4R55E/5R55E COMMON PROBLEMS

Q1. My 4R/5R is starting to display an OD light that is flashing, and the shifts are sometimes late, or "soft".

A1. These transmissions use an electronic pressure control (regulator) solenoid (EPC) that works hard to maintain a contant pressure as commanded by the computer. It seems these have a useful life of 65,000 miles on the low side and about 150,000 miles on the high side. In addition, these transmissions were prone to blowing out main control (valve body) gaskets. FORD came out with a technical service bulletin (tsb) on these issues and there is a kit that modifies the VB and changes the separator plate and gaskets. I recommend whenever there is this issue to change out the EPC. It costs about $115. The FORD mods are about $30. This is a good time to upgrade the Valve body too. (See separate Q on this below).

Q2. I have a 5R55E transmission in my late 90's Explorer. I am strating to notice some shifting issues in the shifts between 1-2 and 2-3 ... kind of soft or dealyed and the RPM's will increase a little until the next gear engages. Is this serious? Is there something I should or could do to fix this?

A2. While, in fairness, there can be multiple possible causes for these symptoms, in general a majority are related to either leaking valve body (Main control) gaskets, or an Electronic Pressure Control Solenoid that is getting tired. When I hear of this problem, I generally refer folks to the 5R55E Valve Body Rebuild Diary here in the stickies, and also recommend a "shift kit".

What is a shift kit?

A Shift kit is an aftermarket engineering attempt to fix deficiencies in the original design. In many cases the actual manufacturer will pick up on some of these fixes and incorporate their own in later versions of the design. Overall, the 5R55E is a transmission with weaknesses in the Valve Body that shift kits address nicely. I recommend that if you ever have a need to remove the transmission valve body you have a shift kit installed. I think it will improve the life of your transmission.

GENERAL QUESTIONS

Q1. How often should I change my transmission fluid?

A1. The general answer is one of those "it depends" kind of answers. Remember the manufacturer only has to warranty drivetrain for a finite period. They will give a long interval, and then cover their a**es by saying "In Heavy Duty Applications... blah blah blah.."

One school says change it every 15,000 - 20,000 miles. Another says maybe every 30,000 to 40,000 unless you tow or tend to offroad or use big tires.

If you use yours on streets and highways and do no towing, I think a change every 30,000 to 40,000 miles is fine. Add towing and I am back to 15,000 to 20,000 miles.

Automatic transmission fluid is a rather unique product. The additive properties get destroyed by heat and age. They are important to help keep your transmission from slipping, and at the same time lubricate necessary parts. See how odd that sounds? Did you know that ATF used whale oil as a component part until harvesting whales was banned by international treaty?

Q2. Should I have a "fluid flush"?

A2. More and more we see places (like Jiffy Lube etc) offering a "transmission fluid flush". What they do is hook up a machine and as the old fluid is extracted new fluid is added... sometimes under higher pressures, but not always.

A flush has advantages and disadvantages, the very act is surrounded by a lot of myth and at the same time some good anecdotal information. It is difficult to separate fact from fiction (or friction). I'll try.

When you drop the pan and replace a filter and replace the pan and then replace the fluid lost, you are replacing probably 1/3 of all fluid. It is rather like doing an oil change where you remove the filter and replace it, and drain a quart out of the pan and replace the plug and add 2 quarts to bring it back to full and calling THAT an oil change.

In the A4LD and 4R and 5R the convertor alone will hold a couple + quarts of ATF and cannot be drained unless you do a "flush" prodecure. (The convertor in the 4R70W has its own drain plug).

A "flush" in theory removes and replaces ALL fluid. It can be done with a machine at a garage, or in fact you can do sort of an "engine assisted" flush at home. [link coming].

Ok so the good news was in doing a flush that you replaced ALL the fluid. But unless you drop the pan, the filter didn't get changed. Maybe not a big deal, as filters often have a long life in a healthy transmission, but it is an issue to consider - or follow up with a pan drop and a filter change too.

Ok you ask, so what MIGHT be bad about a flush? Well ATF has a fair amount of detergent in it to keep stuff in suspension. If your transmission had never seen a fluid change in say 100,000 miles a sudden slug of detergent might dislodge crud long rather happily caked in place.... with untoward results - usually in the valve body where tolerances are critical. This is where the truth and fiction game begins.

The general advice that most accept is that if you have a new Explorer, and will be doing regular fluid changes, do flushes. If you have a high mileage transmission that has not enjoyed regular fluid changes in its lifetime, successive pan drops and replacements over a short period of time with maybe one or two filter changes might be a better idea.

Great science to support that? no. SOME anecdotal evidence? yes.


Q3. Are some transmission filters better than others? If so which ones?

A3. It is my opinion that the best filters are the dacron filters made by FRAM called Microfelt. See the following link. [link coming]

Q4. What is the difference between Mercon III and Mercon V beside price?Can I substitute MERCON III in place of Mercon V and save some $$?

A4. Mercon is the designation FORD gives to their requirements for ATF performance. While we tend to think of OIL as OIL.... Pennzoil 5-30 can be mixed with Quaker State 20-50 for example.... ATF is not all the same.

The simple answer is, if your transmission callsfor Mercon V... you cannot subsititute Mercon III. Mercon V has some special "friction qualities" that Mercon III does not. If the manual says use Mercon V, use V.

CAN you substitute Mercon V for Mercon III backwards? Yes, but Mercon V is way more expensive, so why?

Q5. My shop used Mercon III and an additive instead of Mercon V. Am I screwed?

A5. No, and kinda. Mercon III is not synthetic, at all. Synthetics have some advantages in terms of temperture stabilitity and longevity. Mercon V is "semi synthetic". (Not as good as full synthetic, but better han non-syn). It IS possible to add a special additive to make Mercon III mirror the friction qualities of Mercon V.

Is this an accepted practice? Yes. Is it safe? yes. Is this as good as using Mercon V to start with? No.

If you have a transmission using Mercon V (basically anything 96-97 on) and you are going to have the fuild replaced... ask if they will use native Mercon V or just Mercon III with an additive. Mercon V is the better choice.

There was a thread a while ago about Merc III verus Merc V... hee it is:

http://www.explorerforum.com/forums/showthread.php?t=73415&highlight=Mercon

Q5. OMG I accidentally mixed a quart of Merc III into my Merc V tranny. Am I in serious trouble?

A5. No. relax. The main difference between III and V is in two things. V is a mixture of synthetic oils and naturally occurring oils. Is syn better?yeah. Is semi syn better,? half yeah. Merc V has friction additives lacking in III. Is a 10% dilution factor gonna matter? no, not much.

The base stocks of ATF, like the base stock of oils, are interchangeable. Mix and match.

No it will not gel, not it will not thin, no it will not cause a spontaneous fire. And no one will die. RELAX.

Q6. Is it dangerous to overfill my transmission? Will it blow seals?

A6. An overfill, though not a good practice, will not cause internal damage to your transmission. If it was horribly overfilled by several quarts, the aeration of the fluid caused by parts rotating through it would not be a good thing, but would be unlikely to result in any lasting harm. The pump pressures do not change based on the fluid levels once they are adequate to maintain a level the pump can suction from. So you do not need to worry about higher pressures because of an overfill. Seals will not be blown out. Now seals that normally are above the fluid level, if submerged, may leak fluid, but that will stop once the fluid level is returned to proper levels.

Q7. I just dropped my pan and found this odd plastic plug in it (may have an O ring on it). WHAT IS IT ??

A7. Relax. At the factory they plug the fill tube with these and once they assemble the vehicle the plug gets pushed into the pan when they fill the tranny. NORMAL. (Breathe..... in... out.... yer ok.). Normal.


Ok this is it for now, much more to come. Stay tuned

What about questions like: Is my 5R55N completely sealed, or do I have to go to the dealer to refill it? Answer: There is a 1/8" plug that is used with a special tool to refill it. Then post a link to the thread that has the refill details from the sticky.

Question: How does heat affect the longevity of my transmission?
Answer: Refer to the following chart:
Dead Link Removed

01 SPORT TRAC 75K, the 2-3- FLARE

Thanks Glacier for the 5r55e diary. The diary explained so much, parts and term definitions and suggested upgrades for the flare that my truck is experiancing. I now have some understanding as before the reading I did not even know that the tranny had a VB or what it did. Please don't laugh
As you can figure out now there is no way i would pull the VB out so my question is when i take the truck to the local Ford dealership for the so called diagnostic will they know what the problem is or should they know? Via the tranny tester for continuity and resistance. What questions should i ask? Or should i just post the results here to see if the diagnostic outcome is reasonable to the problem. I just don't want to be taken advantage of when i spend more money to fix the problem. Thanks again for this website

You might mention the TSB to them.

How do I know if the main control gasket is blown on my '95 4r55e? If it is, where is it, and how do I fix it? I was pulling my boat up a steep hill when the engine suddenly revved, and the tranny no longer does anything in any gear.

The only sure confirmation without hooking up a pressure gauage is to drop the pan and pull the valve body and check. A pressure gauge can also tell you more easily.

I doubt you have a blown gasket, they usually allow SOME pressure and some shifts. Your problem may be pump related. I'd have a pressure gauge put on it if it were me.

OK, here's a weird one for you.

1993 Explorer 4WD, A4LD, was working fine until about two months ago. Then it started showing a slight delayed engagement problem starting out in OD 1, followed by normal shifting from 1-2, 2-3, and 3-OD with normal lockup, worst when the transmission was totally cold and gradually improving as it warmed up. This whole problem got progressively worse until my first start in the morning was a series of brief "grabs" in 1 until it got up to about 20 mph, at which point it would engage normally and once again go through a completely normal series of shifts all the way to OD with normal TCC lockup. Reverse worked normally, always has, this issue only affects forward gears.

I dropped the pan and changed the filter, got back to more or less normal operation, but then the same thing started all over again, delayed engagement at first, then progressing to brief grabs when starting out cold, going back to normal when warm. Then it jumped out of the partial on-off engagement in 1 and completely freewheeled, at which point I could get going once by shifting down into 1 and running the engine at fairly high rpm until it engaged again, which got me to work one more day. The next day, it began freewheeling the moment I got out of the driveway and wouldn't go any further.

I did an engine-powered flush (thanks whoever it was that posted instructions for that) and changed the filter again, and the transmission worked perfectly for one road test trip of about 5 miles, then after being parked for a day, went right back to no forward gears at all. Reverse still worked fine.

After that, I checked the valve body (clean, a few slightly sticky valves but none the worse for wear), cooler (bit dirty but now clean), fluid (now clean enough to look like it just came out of the bottle), and governor (looks like an illustration out of an auto shop textbook, completely clean). There was no metal or burnt clutch/band odor in the fluid. Everything about this thing says hydraulic/control problem rather than mechanical/power flow problem, but does this pattern of symptoms sound familiar to anyone? I suppose it could be a blown seal in the forward clutch (cringe) but that doesn't explain the intermittent operation before it gave out .. could it be the pump, or a servo, or a blockage somewhere inside the case, or am I going to need to really get inside this thing?

By the way, Glacier, I can confirm that the governor in the 4WD A4LD *is* removable without removing the extension housing. It's not easy if you're not thrilled about the idea of dropping the bolts or the governor valve parts down into the extension housing and/or pan, but if you have small nimble fingers it's quite feasible.

Removing the transfer case without a lift is a brutally exhausting job and requires a pretty low profile transmission jack, but it's also doable ..

It sounds like it could be the valve body gaskets, or the modulator. Connect a pressure gauge, and take some readings in different gears. Do this when it is cold, since your symptoms happen when it is cold.

You're not the first to suggest the vacuum modulator, although I'm trying to figure out how it would cause this pattern of symptoms. I'll definitely check it, though, only takes a minute to pull the vacuum hose off and see if there's fluid in it. (Come to think of it, I seem to recall the fluid level going low at some point in this process without any noticeable signs of leakage. It might have just been filling the TC back up after the de-fluiding process, but I remember a couple of times thinking fluid was just disappearing somewhere. Might be a clue. Didn't seem to have an unusual appetite for fluid before this all started happening, but that may be neither here nor there at this point.)

I sure hope it isn't the VB or separator plate gaskets, the ones in there now are brand new and went in when the VB went back in. (And I tested after the VB went in, no change, same behavior.) The shop manual gave me a bit of a scare when it mentioned there might have been some check balls on top of the separator plate, but I don't recall any falling out when the separator plate came away from the case. The only unaccounted for bit I inadvertently dislodged was an L pin holding the "valve that shall not be removed" in the VB, I think it was the 1-2 accumulator, spool was still in place but was slack and wasn't holding the pin in very tight, put it back, no harm done as far as I can tell. The separator plate was definitely NOT stuck to the case when I removed it, though, which makes me think there may have been a little leakage on one or both sides of the plate, so it's possible you were partially right and maybe I fixed that in the process of checking all this stuff. ;-)

But still, the modulator .. hmm. How would a modulator failure cause complete loss of forward gears but normal operation in reverse? Is it that critical to the forward clutch circuit? (given that the forward clutch seems to be what controls the initial gear engagement in OD/D 1..)

And while this may sound like a really stupid question, does anyone have any pointers to VB/hydraulic schematics, operating charts (as in which bands/clutches/sprags are engaged for which gears in R, OD, D, 2, and 1, I've made a crude one but have nothing to check it against), where the pressure test port is, and what pressure values to expect in which gear selections, etc.? Basically, basic diagnostic specs I can work from?

(No, my manual isn't the FORD factory book, can get that one but it's surprisingly expensive and somewhat out of my budget for now. May have to bite the bullet, but if I can work around it for now and get back to where I can at least *drive*, I can save up for the FORD book and get it later on..)

This thread explains how to use a transmission pressure gauge: http://www.explorerforum.com/forums/showthread.php?t=117998. Read Glacier991's A4LD rebuild diary, and the valve body rebuild diary for more information.

Ah, that gives me an idea of where the port is on an A4LD, thanks ..

Finally had a chance to crawl under the Explorer again tonight, and pulled the vacuum line from the modulator. Good news (since it identifies a likely culprit that means I probably don't have to go in after the pump or forward clutch seals!), modulator is most definitely bad.

It still bugs me because it's kind of counterintuitive that the modulator failing would cause the forward clutch to not engage, not the behavior I'd expect just from first principles (which would sort of make me expect behavior like in 2 or D, staying in low gears and engaging/shifting hard). But it occurs to me that since the modulator is basically a spring pushing on a pressure regulator spool, with a diaphraghm working against it, and no vacuum input drives TV pressure offscale high, someone at Ford probably figured it would cause excessively hard forward clutch engagement which would be very hard on the OD and case sprags, maybe they actually designed in some limit behavior in the VB as a failsafe. Or the VB just characteristically responds that way to zero governor pressure and line pressure on the TV.

Or whatever. It's possible to go nuts analyzing this stuff too much, but the upshot is I'll probably be up and running in a week or less, and without spending a couple thousand bucks in parts/labor on a rebuilt transmission of uncertain history and saying goodbye to my known good mechanical components. Glacier991, if I haven't thanked you enough for posting the critical info it took to get me back on the road without going broke, thank you. BrooklynBay, you too. You don't know how much money and downtime you guys saved me!

You are right about the TV pressures... yet somehow it doesn't seem to make a huge problem when you lack the modulator working as it should, as you might expect. Keep us posted.

Bad news, wasn't the modulator. Modulator was definitely failed, fluid in the vacuum line was a clear indication of that, but it wasn't causing the failure to engage.

Which leaves the pump and the fluid seals in between the valve body and the clutch piston. Next step is getting hold of a pressure tester and doing the idle and fast idle pressure checks. The engagement in reverse does seem to be slow and kind of mushy, so maybe this is indeed a pump problem and the boost valve just happens to be kicking the pressure up to where reverse can engage but the other gears can't? I'm hoping the pressure checks give me some additional info ..

Your analysis of why you have reverse because of boost is accurate. You could have a major leak somewhere.. a check ball, a torn seal, a valve body gasket....or, a failing pump....you are on the right track.

Thinking it's most likely the pump, because of that slow mushy engagement in reverse, almost like it's taking its sweet time filling up the accumulator for the reverse-high clutch. Seems more and more like it's bleeding internally somewhere. Valve body has come out and gone back in, body, check balls, pressure relief valves, and accumulator pucks all looked OK.

By the way, thought I'd share a suggestion on the no-air-tools-on-transmissions rule. One thing that sped up putting my VB back in was a cordless drill with a torque clutch on it, set to the lowest possible torque, 2 or 3 I think. Spins the bolts in and snugs them a little over finger tight without any risk of damaging threads, and then I just go over the bolts with a socket and ratchet. Saved me a lot of time running in all those bolts! ;-) The clutch is *mandatory*, though, regular drills don't have one, it has to be a cordless. My trusty Black & Decker cordless is fantastic for this particular job ..

Well, now I'm completely stumped.

P, N, and forward gears come out about 70-75 psi, R gives me a wild needle vibration that covers about 90-160 but seems to center around 115-120. Couldn't quite get to R WOT with one foot (this was a quick and dirty check), but got about 250 at stall in reverse, which suggests that R WOT would top out around 280-300.

Obviously not a weak pump or bad seals. Blockage somewhere in the forward clutch circuit? Is that vibration with R boost significant?