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I am thoroughly confused. The patient is a 2000 F-150 XLT, 5.4L V8, 4WD, 4R70W transmission, 255K miles. I put about 140K of those miles and they were mostly highway miles. The problem starting out: when the fluid was cold, going up a hill, when it shifted from OD down to third it would lose all torque: the engine RPMs would shoot up to 4000 or so and the truck would slow from 70 MPH down to about 50. It didn't do this all the time, just every now and again. About six weeks ago I lost all of my transmission fluid while going down the freeway due to a ruptured cooler line. Once I fixed the leak and filled her back up I couldn't get into third or overdrive. I could accelerate to about 30, the transmission would try to shift into third, and it would essentially go into neutral, no load on the engine and zero torque to the wheels. I managed to get it home by manually putting it into second. I ordered a rebuild kit, ATP's LMS12, which includes all of the gaskets, seals, and friction/steel clutch discs. I took the transmission apart and found the direct clutch had basically been incinerated: the steel drum was discolored blue from heat, covered in carbonized transmission fluid, the lip seals on the piston were disintegrated, all of the friction material had been worn from the discs and the steel plates were deeply grooved. All of the hard parts like the planetary/sun gears were pristine and looked pretty much new, no real signs of wear at all, same for the aluminum case. So at this point I ordered a new direct drum, along with some other things that weren't included in the rebuild kit like the EPC solenoid, sun gear and planetary bushings, accumulator pistons, and overdrive servo piston. I also bought a new torque converter. I meticulously cleaned everything with solvent and compressed air and reassembled everything with transmission assembly lube. All new clutch packs and bushings, new EPC, all bolts torqued to spec, all clearances measured and checked against the clearances in the service manual. I put the transmission back on the truck and test drove it about three miles and I'm having the same problem: going past 30, the transmission tries to shift into third and just goes into neutral. What the hell? I thought about it and read through the service manual and thought it might help to change the shift solenoids, since a stuck solenoid can cause problems like this. No luck, I install the new shift solenoids and it's doing exactly the same thing. At this point I take the transmission back off and take it apart and when I get to the direct drum it looks just like the first one, friction discs worn completely away, drum discolored from overheating, and the pan and new fluid is full of metal and grit from the shredded clutch discs. This is after two test drives that totaled less than six miles. So I think about it some more and try to figure out what could cause this to happen again. The options I came up with are that I screwed up when I rebuilt the direct clutch somehow, like maybe a torn lip seal or improper clutch pack thickness, or there's a leak somewhere in the valve body that's either causing the direct clutch to engage when it shouldn't or not providing enough fluid to the direct clutch. I also noted that the snap ring on the first direct drum was a little loose in its groove after I rebuilt it. At this point I buy a brand new "loaded" direct drum, with new psiton, all of the lip seals, clutch discs, etc.. already assembled and a remanufactured valve body with the shift kit installed. I clean everything, assemble it, once again, check all of the clearances, torque all of the bolts down to spec, everything looks great. I put it back on the truck, fill it with clean fluid, test drive it and... it's still doing the exact same thing. What. In. The gently caress. I am completely out of ideas. I have replaced nearly every single part in this transmission: every gasket, every seal, every check ball, every clutch disc, the entire valve body, the torque converter, all of the solenoids, the overdrive band and servo piston, both accumulator pistons, various snap rings. How could the same problem keep recurring after such a thorough rebuild? I haven't taken it back off yet, I want to measure the fluid pressure at the LINE and DIRECT test points to report here before I do, but I'm sure when I take it apart I'm going to see signs of an overheating direct clutch. Any ideas would be greatly appreciated. Revenna Fox fucked around with this message at 02:57 on Mar 19, 2022 |
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Mar 19, 2022 02:45
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| # ? Apr 29, 2024 15:56 |
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Have you taken it to the dealer to have them look at it? I had a 98 explorer with (I think?) the same transmission which had something funky happen to the programming. I was partially stuck in the snow and the ABS/TC flipped out and it started shifting very hard into 1st from too high a speed when slowing down and would activate the ABS if I tried to slow down very gently but not if I was slowing at a moderate pace. Indy shop couldn't figure it out, but dealer reprogrammed the ECU/TCU and it fixed it immediately. Worst case scenario you are out 100 bux for a diag fee and have to listen to a service advisor's preventative maintenance package sales pitch
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Mar 20, 2022 06:27
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Programming isn't going to absolutely wreck a transmission within a few miles. The 4R70/75 is a fickle rear end in a top hat. My only guess is OP hasn't replaced the transmission cooler - the cooler and hoses will hold a lot of transmission-destroying poo poo after a transmission shits, though I would think it would last more than a few miles. My stepdad went through this on his 01 F-150 (also a 5.4), but it made it about 50 miles before making GBS threads the bed.. 3 times in a row. New transmission cooler and not-Aamco got it back on the road for a few thousand miles before it started slipping again, but he had all gears every time (the first 3 times it'd lose 3rd and 4th again pretty quickly). He got rid of it instead of fixing it a 5th time. I know there's a couple of springs and accumulators related to 3rd and 4th, and my own 4R75W is showing signs of a broken spring on one (4-3 downshift revs way up then slams into gear if I don't slowly roll into it). Have the accumulators and springs been replaced with upgraded components? Have you replaced the torque converter + cooler and flushed the lines to get all the debris out? Are you running the correct OEM Motorcraft filter and Mercon V fluid, or aftermarket? Are you soaking the clutches and steels in ATF for a day before installation? Beyond that I got nothin, this is mostly stuff I've learned from Precision Transmission's Youtube channel.
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Mar 20, 2022 07:47
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Did you replace the pump? If not, have pics of the gerotor? Find your direct and line pressure at idle, half, full throttle in your foward gears. It seems to me that the pcm isn't commanding enough line pressure(failing transducer) for the direct clutch to hold in gears 3/4 or the pump isn't able to generate the pressures required.
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Mar 20, 2022 15:39
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In answer to posed questions: all new Mercon V fluid (three times), new filters (after both rebuilds), and new torque converter. Cooler was flushed with solvent and compressed air, and the lines are new. I did not replace any of the accumulator springs, since none were broken and they were still good and springy. The replacement valve body does have new springs. I forgot to mention it, but the ECM never threw any transmission related codes before or after the rebuild. I got a pressure tester in the mail today and I have some info Note: Engine idles at 900 RPM At the LINE tap at idle I'm getting 65 PSI in P, N, and D 100 PSI in R 60 PSI in 2 55 PSI in 1 190 PSI in N at wide open throttle The pump is original, when I took it apart during the rebuild, nothing really looked worn or scratched in it, and these pressures are in the reference ranges in the service manual At the EPC tap, at idle I'm getting 0 PSI in D, R, 1, and 2 <-what the hell? 5 PSI in N and P 80 PSI in N at WOT I found this spec sheet that gives the normal EPC pressure at idle as 20-50 PSI. I replaced the EPC with a new Borg-Warner D76431 as part of the rebuild, along with the plastic wiring harness, so I do not know what's going on here. I tried test driving it again with the gauge attached to the DIRECT tap, the pressure was 0 PSI in P, R, N, 1 and 2, which is what it should be, peaked at 180 when it shifted into third at WOT, which seems too high, then tailed off to zero again, I don't know if it just quit or if this was when I let off the gas. You'd never know it, but it's pretty drat hard trying to drive while looking at a gauge taped to the floor. I guess you're supposed to do some kind of a "stall" test where you hold the brake and the accelerator but the thought of doing that freaks me out a little. I saw a condition chart (can't find the link right now) that shows the state of the bands, solenoids, and clutches in different gears and noticed that the intermediate one-way clutch is overrunning in 3 and 4. I just now realized that I didn't check to see that the one way clutch was turning freely when I had it apart. Revenna Fox fucked around with this message at 01:23 on Mar 22, 2022 |
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Mar 22, 2022 01:08
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| # ? Apr 29, 2024 15:56 |
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Yeah don't drive it with the EPC pressure that low. Pump pressure is good. Next thing, grab a multimeter and probe EPC solenoid voltages at the transmission electrical connector while its running. Seems to me there's a chafe leading to open circuit/short in the harness, or the driver IC for this solenoid died causing your original transmission and subsequent rebuilds to fail. E: stall test tests the converter's stall speed and it'll also test the holding power of the engaged clutches. I'd advise against doing this with such low EPC pressure. cursedshitbox fucked around with this message at 01:52 on Mar 22, 2022 |
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Mar 22, 2022 01:49
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