Help - transmission slipping

[smwmustang]

When leaving the stop sign it rev'd up and slammed into gear...my kids literally thought we had been rear ended. I may drive it around the block just to see what happens as I have not moved it since I got home.

I will call one of our two decent indy shops today just to get a cost on tear down to check it out.

I will also reveiw some more threads to see if I can locate one that is similar to my situation. Since I only drove it another mile when it happened, I really don't have much info to give or to go on.

Shawn

[bcredliner]

That's different than I understood. Make sure the indy can read any codes the computer is showing. Strongly suggest two opinions before approving any work. I would post the diagnosis for owners that have a similar problems to chime in. Also search- Summary of Transmission problems- for a description of various transmission problems. FYI-many of the owners with transmission problems have had work done that did not fix the problem that is the reason to be cautious.

[RRPhil]

One possibility....

By far the most common problem with the 5HP24 (now that the F-clutch piston & A-clutch drum stiffness issues have been addressed by ZF) is the failure of the axial needle roller bearing between the B-clutch hub and the C-clutch drum. This allows the input shaft to move rearwards a few millimetres inside the B clutch drum uncovering an O-ring seal which subsequently splits :







The result is that the A-clutch, which is used in 1st, 2nd, 3rd & 4th gears, loses pressure & slips. This would normally cause the control system to engage limp-home mode but, because this would be 4th gear (which needs the A-clutch), the system has no choice but to engage 5th gear - and it often comes in with a bang.

The 5HP24 was originally designed for an input torque of 420Nm and your 4.6is produces 480Nm so ZF presumably increased the system pressure so that the clutches could withstand the higher torques (though ZF did add an extra friction plate to the D-clutch). It’s possible I suppose that the higher pressures would be more likely to cause the bearing to fail sooner on a 4.6is than a 4.4i.

Transmissions suffering from this problem often drive perfectly when cold because the oil pump can keep up with the leakage from the split seal (and therefore maintain hydraulic pressure on the A-clutch) when the fluid is cold and much more viscous. After around 10-20 minutes of driving, though, the fluid thins to the extent that the leakage reaches the point where the pump can no longer maintain the clutch pressure and the clutch slips.

Phil

[BigBlack48is]

Originally Posted by RRPhil

One possibility....

By far the most common problem with the 5HP24 (now that the F-clutch piston & A-clutch drum stiffness issues have been addressed by ZF) is the failure of the axial needle roller bearing between the B-clutch hub and the C-clutch drum. This allows the input shaft to move rearwards a few millimetres inside the B clutch drum uncovering an O-ring seal which subsequently splits :







The result is that the A-clutch, which is used in 1st, 2nd, 3rd & 4th gears, loses pressure & slips. This would normally cause the control system to engage limp-home mode but, because this would be 4th gear (which needs the A-clutch), the system has no choice but to engage 5th gear - and it often comes in with a bang.

The 5HP24 was originally designed for an input torque of 420Nm and your 4.6is produces 480Nm so ZF presumably increased the system pressure so that the clutches could withstand the higher torques (though ZF did add an extra friction plate to the D-clutch). It’s possible I suppose that the higher pressures would be more likely to cause the bearing to fail sooner on a 4.6is than a 4.4i.

Transmissions suffering from this problem often drive perfectly when cold because the oil pump can keep up with the leakage from the split seal (and therefore maintain hydraulic pressure on the A-clutch) when the fluid is cold and much more viscous. After around 10-20 minutes of driving, though, the fluid thins to the extent that the leakage reaches the point where the pump can no longer maintain the clutch pressure and the clutch slips.

Phil

Phil,

Awesome writeup!!! You are truly a wealth of knowledge

Keep up the good work and I will absolutely be contacting you if my 6hp26 goes kaa-boom in the future!

[smwmustang]

Ok, sorry for the delay in posting an update but with vacations and all I have not had time.

I did drive the car a few days and here is what I found out for more detail.

1. If I don't drive the car like I stole it then it all seems to run fine 99% of the time.

2. Occasionally when making a left or right turn, just as the car downshifts to probably 2nd gear in the turn, and I hit the gas it will slip a little and then go into gear pretty easily. If I let off just as I feel the RPM's going up it will shift and run fine.

Now I know it is not good to drive it this way and I only did it a couple of days to see how it would drive. One of those days nothing ever happened. My tags expired while I was out of town and I did not realize it so it is parked until the renewal comes in.

Based on this additional information can anyone with similar issues give me their thoughts. I would like to narrow it down before taking it to a shop an dhaving them tear the whole thing apart if it is an apparent issue.

Thanks,

Shawn

[bcredliner]

Have you tried shifting manually to see if the problem is also in manual mode?

I suggest you get the trans diagnosed at two Indy shops and get estimates of cost to repair from both.

[upallnight]

Truck doesn't move when you step on the gas but slams into drive when you raise the RPM? Sounds like the Forward Drum is cracked! Go to a trans shop that knows how to connect a pressure gauge to the trans and know something about pressure readings.

[smwmustang]

bcredliner...I have been driving the truck all day in manual and it seems to be working fine. the only issue is when I come to a stop, it is only shifting down to 3rd on its own and not all the way to 1st. I have to manually go to 2nd and then 1st.

If I remember correctly since I hardly ever drive it in manual, it should automatically downshift based on speed.

Thoughts?

[bcredliner]

I you are moving the shifter to shift, and don't downshift it to 1st. before you start off it will go to 3rd gear to get going. If you have it in manual but it is shifting on its own it should drop to first when you stop.