02-08-2009, 01:57 PM
Hi, I'm bcbasine's dad. I have rebuilt numerous piston engines and even one rotary, but had never tackled an automatic transmission until now. We do have the Mitsubishi (http://www.3si.org/forum/#) shop manual on CD, which makes things easier. When my son first bought the car, it would sometimes suddenly "shift" itself into neutral, always while in 4th gear on the highway. My son would pull off to the side of the road, and then it would function normally. I noticed when he got the car that it was leaking transmission fluid, and after a couple of weeks I checked the level only to find that it was normal-which means that the person he bought it from overfilled it, thinking that this problem was caused by a low fluid level. Eventually the car stopped on the highway-for good. After having it towed home, I checked the fluid and found it to be dark with a burnt smell. The transmission was removed and disassembled. The end (overdrive) clutch and the front (direct) clutch were both badly worn, and in addition the piston in the front clutch was cockeyed! Yes, it was actually stuck at an angle. I reseated it with a pin punch, then removed the piston to examine it. I saw no warpage or other damage, so I reassembled the clutch, replaced the worn frictions and steels and reassembled the transmission. The car continued to have the same problem, and finally stranded my son for a second time. This time the end clutch frictions were okay, but the steels had gotten so hot that they were warped. The front clutch was okay, but the planetary gear assembly had burned up. I had disassembled the valve body the first time around to rid it of the burnt fluid, but hadn't disassembled any of the pistons-except for the front clutch. This time I took them all out and found-duh-that the outer o-ring of the end clutch piston was broken in two places. This explained the original problem, but why did the planetary melt down? I took a look at the oiling system. It looks like the fluid comes out of the torque converter through the center of the input shaft, then is taken off at the pump and routed to the cooler, then back to the rear half of the input shaft where it exits through various holes along its length. I could not find any blockage in the shaft, but I replaced it anyway since one of the journals was scored. I also blew compressed air through the cooler, and it did not appear to be blocked. I ordered a set of gaskets and seals, a set of bushings, and steels for the end clutch from bulkparts; a used input shaft, band, and filter kit from wit; and a used planetary assembly and shell from teal. The guy at teal had me count teeth and measure a couple of dimensions since not all f4a33 planetaries are the same. I put it all back together, but after 400 miles the planetary ate itself again. It is sitting on my bench in pieces. All the clutches survived, and although the fluid smelled burnt, it had a normal color and there were no particles in it.
What am I missing here? One thing I should probably point out is that the first two times I did not use the official Diamond SP fluid. I used Castrol multi-vehicle import instead. Many of you may think that that substitution caused the problem, but I am skeptical. All automatics have planetary gearsets that must be lubricated, and besides that I have a hard time believing that a large company like Castrol would expose itself to a lawsuit by listing Diamond SP-II and Diamond SP-III as compatible fluids on the back of the container if there was any chance of transmission damage. Incidentally, I did check the fluid level before I drained it. I could not, of course check it hot, but this dipstick has both a hot and cold mark on it. The level was over the cold mark slightly. I originally set the level with the transmission hot, 400 miles back.
It's difficult to tell for sure, but it looks like the problem starts at the interface between the sun gears. This time, for example, the two sun gears are fused together and will not come out. The last time they came out, but the thrust washer between them had melted into mush. There are signs that the entire planetary assembly has gotten very hot. In 4th gear the pinion carrier is driven and the larger sun gear is held. The smaller sun gear, though not connected to anything, spins slightly faster than the input shaft, so if there is a lack of lubrication this will burn up quickly. Interestingly, the inner bushing on the smaller sun gear on the end nearest the torque converter is not damaged at all.
Hopefully someone has either seen this problem or can suggest where to look. The original planetary gearset survived over 100,000 miles, but something has obviously changed.
02-10-2009, 11:16 AM
Just a swing in the dark here...you obviously know way more about Auto trannies than I, or possibly anyone else on this board, does.
The only thing I can offer up, how are the engine and tranny mounts in the car? I know that with the manual trannies worn mounts can cause if to pop out of gear becasue of the excessive movement...maybe if the same thing is happeneing here it's causing excessive wear on the trans? Maybe momentarily going into neutral or 2nd?
Again, just a shot in the dark, but it's all i can offer up with my limited knowledge.
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