e38 740iL transmission (5HP24 / A5S440Z) slippage

[mattgray]

Outside temperature for all of this is between 70 and 80 degrees F.

While getting onto the freeway my engine revved out as the transmission slipped. The transmission will no longer drive in forward or reverse except for the occasional engagement for 10-15 feet under its own momentum without me engaging the gas pedal. Sometimes, if I idle in park and then slowly go into R or D, then I get temporary engagement and can drive 10 or 15 feet before slippage.

No Fail Safe indicated on the dash cluster, no locking into any gear for limp mode.

Transmission has 206,000 miles, with service every 50,000 miles. Not a bad run.

Pulled the old transmission and installed a newer torque converter which had worked fine up to the point when taken out of service. No go, same slippage problem.

Obtained a newer transmission at a recycler/dismantler with 115,000 miles that had driven all the way to that vehicle's collision. Dropped the pan, found dirty oil and modest metal silt on the magnets.

Filled the (newer) trans. with clean oil, cycled the gears 2 minutes each with e-brake set, flushed the dirty oil, and filled it with clean oil. Installed the 'newer' transmission with my old torque converter. Again cycled the gears, 2 minutes each with e-brake set to get out air bubbles, rechecked and filled oil. Car was cambered forward about 2 degrees for fill. Then attempt at soft drive for 5 minutes...

No go. Still the same slippage on the newer trans. with older torque converter. Sometimes forward thrust for about 10 feet. Reverse works for a little while, about 20 feet with some acceleration, but then slips and the engine revs.

SO WE HAVE old trans. with newer torque converter, and newer trans. with older torque converter, and all of them exhibit the same symptom: slippage in forward and reverse, temporary engagement.

Only when I rev up the engine and don't let off, causing slight engagement of the transmission, will it say "Fail Safe" in the message area beneath the instrument cluster, but then that goes again when I let off the gas.

I'm getting tired of removing and reinstalling transmissions only to have the same problem. The only thing I haven't tried is installing the newer transmission and the newer torque converter (that's next). Before buying a NEW (rebuilt) torque converter, I'm wondering if I'm missing something obvious, such as a reprogram of the transmission ECU or something.

Help?

[JTL]

My car just stopped moving forward. I put the gear selector in drive but the car doesn't move. After a short while the trans failsafe message appears and the car starts moving forward in 4th gear. Reverse works ok still. I also have the 5hp24 trans.

I researched this issue on the web and discussed with a mechanic. The common point of failure for these symptoms is a failed 'A' drum. Apparently over time the pressure regulator fails partially allowing excessive fluid pressures into the gears which 'blow out' the top part of the drum. Fix is to replace the 'A' drum and pressure regulator and possible the lower valve body piece if cracks have developed in it.
If problems develop going in reverse the problem is likely to be the 'F' clutch.

I didn't see anything mentioned about the torque converter issues. Is it possible you have 2 bad transmissions? Holy crap - I wouldn't want to do this job multiple times?! Btw, I wouldn't mess around with rebuilt stuff too much.

My plan is to remove the exhaust and trans and replace the parts I described above. I'll probably end up getting a rebuild kit from Eriksson and replace a number seals and bearings etc. Gary Ferraro have a couple of really good 5hp24 videos on youtube.

Good Luck!