I have a 95 Explorer Limited, 4.0 pushrod, 4R55E transmission, 4x4 via a Borg-Warner 4405 (my selector says 2WD, 4WD AUTO, 4WD LO), Air Ride Control (loud compressor), 136K miles. I have a strange drivetrain problem: my vehicle clunks, jerks, bucks and thumps.

To be more specific, when shifting, the vehicle will either jerk forward, buck backward, or shift fairly normally (sometimes firm, sometimes soft). When the vehicle bucks or jerks, there's a loud "clunk" or "thump" sound from somewhere underneath the vehicle that sounds behind the driverseat, and the buck/jerk is fairly violent - that is, you feel it well. When it jerks forward, the front end actually lifts up and the rear lowers a bit - when it bucks backward, it feels as though the front brakes are pressed momentarily, and the front end lowers. The bucks and jerks seem more noticable when the vehicle is speeding up rather than slowing down, but it's noticable in either case.

The transmission has been rebuilt 3 times at a cost of about $5000 so far. There hasn't been 3000 miles put on since the original transmission failure. Apparently noone can rebuild it properly - I had a Good Deal Transmissions shop rebuild it the first two times, and AAMCO rebuilt it about a month ago. I informed AAMCO of these drivetrain problems about a week after it was worked on, and the local manager took it for a test drive. He said to wait and see if it gets better. A week after that I took it back and said the problem is getting worse - fix it. They kept the vehicle for 3 days and said they took out some tranny fluid because the level was high, and it was driving like a charm now. I picked it up to find the condition exactly the same, and the fluid level just as high as it was before. The AAMCO manager is telling me the shift points and everything are as they should be, and he mentioned something about my engine having a knock.

Anyway, so I've been doing my best to be a good citizen and believe AAMCO instead of burning down their shop in a fit of rage (or something to that effect :P) and I've been researching the internet and repair manuals on possible causes. I've replaced a number of things so far without an effect on the problem: new fuel filter, new EGR valve, new TPS, new spark plugs & wires, new alternator, new IAC, new u-joints on rear driveshaft, lubricated slip-yoke on rear driveshaft, new PCM, cleaned the MAF, I even removed the front driveshaft. So far I have a lighter wallet, less confidence, and some newfound knowledge of drivetrains.

I'm installing a new IAT tomorrow. I also got a copy of the ATSG 4R55E service manual, and it seems the only components left that could affect the internal operation of the transmission would be sensors on the transmission. I'm wondering if I have a vacuum leak somewhere. Are there any symptoms to indicate this? Even so, would this affect my transmission? I've seen posts about vacuum modulators and transmissions but I don't see anything about it in my service manual.

I stumbled across this thread about the 4405 transfer case https://www.ford-trucks.com/forums/s...smission+noise which seems something I should address but I'm not sure it's what is causing this problem, as the symptoms seem different.

I'm also wondering if my engine mounts could be bad, and if this could cause the drivetrain whiplash. I could use new suspension bushings all around - they look bad and squeak - but I can't imagine them causing this.

Any advice, suggestions, clues..?

 

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Replaced Intake Air Temperature sensor this morning, no effect. EEC IV still reports 111 - shouldn't the computer be aware of all the drivetrain thrashing?

 

Extra strain on the drivebelt may cause improper transmission shifting..

The 4R55E manual says an A/C clutch is engaged when the A/C compressor is engaged. This electro-magnetic clutch informs the PCM of extra strain on the drivebelt, in turn directing the PCM to adjust EPC pressure and TCC modulation.

My aged power steering pump makes alot of noise, even when the wheel isn't turned. Could the pump be straining the drivebelt, unbeknownst to the PCM? Could this be causing incorrect EPC pressure and TCC modulation (which i believe would cause my symptoms) ?

How can I determine if the power steering pump is straining the drivebelt? Is this a possible cause?

 

Isuspect you ran KOEO and KOER codes and then got 111, system pass. If so, and proven here, the PCM wont pick up everything. Especially once you get away from the engine controls systems, there are fewer PCM inputs and thus less potential codes you can get.

Not sure what kind of troubleshooting you've been doing. Have you pu it in nuetral or just let off the gas when it bucks to see if it goes away?

I'm actually thinking cat converter. When the honeycomb breaks up it can lodge sideways and not let gasses by. Poor little 4.0 is trying to pump air and once in a while a little gets through and you get a burst of power and then ugh, it chokes again.

I feel for you a bit at having changed all those system controls components and the PCM if you had no codes indicating an error. On troubleshooting computer controls system, one must think like a computer. All those things you changed are monitored by the PCM. If one were bad, it would tell you - not always the the right thing, but it would say something. Now that you have a problem that the PCM is not sensing, look for the things that don't tell the PCM anything. And your auto trans has several or more inputs to the PCM, so I'd rule out the trans.

One other thing that it might be, and I have had little experience with these all wheel drive systems, is that there should be some type of viscous coupling between the front and back. I don't know if this is internal or external to the transfer case. But obviously, it has to be after the transmission. If it is a drive line issue, I'd look into that.