AW4 and flexplate

Im a noob here and have read many posts on the AW4. I recently purchased a 92 XJ for 200 bucks. What a score. Drove it home with it making a noise like what has been described as a broken flexplate. Read it here before taking it apart. There was only 1 bolt holding the engine and tranny together! Broken flexplate was what I found. I ordered a new one and put it in along with a new converter just in case. No shavings in tranny pan but not taking chances. Unfortunately the thing shakes like crazy by the time you get to 3000 rpms. My question is is the 4.0 internally or externally balanced or did I get a junk flexplate? It has Made In Mexico stamped on it. Thanks for all the help.

Had that happen - ended up replacing the transmission, because there was a half-inch of daylight around that one screw. The first planetary set was "tilted" in the case, and would not turn. Problem!

The torque converter was fine - but the flexplate was shot, and I needed a Sawzall to tear down the transmission. Fortunately, if you can still turn the input shaft, you don't have that problem - but, being me, I'd probably drop the valve body (which you can do without tearing the thing apart and replace easily) and look for wear marks around the planetary shells (you'll know them if you see them.) The AW4 is the "pump shotgun" of transmissions - it does like abuse, but even it has its limits.

The use of LocTite #242 (or equivalent) on the engine-to-transmission screws is recommended. Not by the FSM, but certainly by me!

was it shaking before the repairs as well? I'd lean toward a bent flexplate if it started after the repairs, but I would also double check torque of all the attaching bolts (flexplate) and nuts (torque converter) and verify the concerter is fully seated in the front pump.

Didnt notice a shake when I drove it home. It gets noticable by 2000 and just gets worse from there. I felt the shake after putting it back together and unbolted the converter from the flexplate to isolate the problem and pushed it back so it didnt rub while the engine was running. All you have to do to make the vibration is rev it up past 2000 rpms. That tells me its on the motor side not the tranny. Vehicle drives and shifts fine. Like I said, the flexplate and converter are new. Converter was definately seated when I put tranny back in. I also got a set of service manuals with the XJ so I found out the depth setting before bolting it up to the engine. Locktite on the bolts I hadnt thought about so I will have to
do that when I get to that point again. Im wondering if maybe having the motor and tranny at different angles when I bought it wiped out the rear main. I'll have to drop the pan to see whats up there. Would have thought the oil pressure would have dropped if that was the case. Im fresh out of ideas so any more that I can look for? And thanks for the help.

The rear main isn't a "pressure" seal, it's a "wipe" seal. It's just there to make sure oil doesn't leave the block, but it doesn't hold a good deal of pressure (despite sealing against the rear main bearing.)

However, it's worth checking a couple of things - do you have (or have access to) a dial indicator? Two things I'd check - and both require splitting the engine from the transmission:

1) Crankshaft runout at rear main. Read off of the edge of the flange, and turn the crankshaft. I believe spec is not more than .001" of runout at the crank, but that would have to be verified. This checks for a bent crank (which is possible)

2) Crankshaft endplay at rear main. Without turning the crank, just pry it up and down and see if there is more than .001" of endplay at the crank. This checks for rear main bearing wear.

Both tests would indicate a component that wants replacing - #1 tells you if you need a new crankshaft & bearings, while #2 tells you if you just need new bearings. Do both, just to make sure.