Trans Goes Into Neutral While Driving

You have this right! It is quite obvious that your Montero has a rebuilt tranny installed. It is also obvious that the former owner really didn’t know how to keep the transmission in good shape because of the overfill.

Most of your current problem — your transmission is slipping badly — is related to the overfill. Because of the added pressure, the transmission fluid likely was flowing through the transmission at a higher-than-normal rate of speed, stressing the parts to the breaking point. It is quite likely that the clutches and bands have gone. It is also possible that not only are the clutches and bands bad but also that the gears may be gone as well (your vehicle has several sets of planetary gears installed each of which, or in combination with other sets, represents a specific gear).

Given the immediate problems, you are looking at replacing the transmission again, unless you can find the shop where the older transmission was so obviously replaced. If you can then you may ask them if their work was warrantied, despite the change in ownership of the vehicle. If it was warrantied then you may be able to have the shop eat most, if not all, of the cost. Or, you may get a split with them. All you can do is try and ask, if you can find the information.

If you cannot find the shop where the work was done and you have to replace the transmission then you are looking at a $3,000 cost.

It’s not necessarily true that if the clutches are just starting to go that you will lose the gear altogether. Let’s assume that the clutch pack is just starting to go. What are the symptoms? The most common ones are going into and out of gear; staying in gear for awhile and then slipping out; using manual shifting to engage the clutch pack involved and then shifting up to the next gear.

It is probably only a matter of time — there is actually no predicting when; it could run like this for hours, days or weeks — before the clutch wears out altogether and the transmission hangs up.

You added something interesting to your list of symptoms. I noticed just now that you said your Montero will “accelerate under moderate throttle and it will go into neutral at around 1,200 rpms, too early to be going into 2nd.” That also shows that the problem is a lot bigger than you think it is.

When a transmission starts to have problems holding the right rpm and not shifting at the right spot, it also says there is slippage going on. Now, you might be right that it is not totally the fault of the clutch pack, but, the suspicion certainly points in that direction. And, yes, it could be bad solenoid pack on the transmission control solenoids (your minivan has two) that could be causing a problem with your gearing. It could easily account for the variance in the shift rpm and it can cause your Montero to perform just as you describe it. And, yes, you will have to check out this possibility, but, the money is still on clutch pack or clutch pack/band damage.

Let’s go back to your original question when you described the problem. You said the tranny was badly overfilled. It certainly was at two quarts over the fill mark. This is a situation that your transmission cannot tolerate for long. It involves the way the tranmission works and since you have done some diagnostic work already on the device, it is likely that you know exactly how the transmission work, however, a little basic refreshing never hurts.

In operation, the automatic begins by spinning up the torque converter spins up and starts the flow of transmission fluid through the turbine blades and into all parts of the transmission (this is a simplification). This is essentially still on the outside of the transmission as the fluid the torque converter has started to move has not yet had a substantial impact on the internals of the transmission. From this point, though, things happen fairly quickly as the now moving fluid is redirected to the proper path to engage reverse, assuming you are backing out of a parking space. In this redirection, the fluid is sent through the route that sets up reverse. It first encounters the proper solenoid that activates reverse. The fluid then, using second gear, sets up the proper planetary gear alignment (involving second gear and others at the same time) so that your transmission goes into reverse. At this point, the transmission activates the reverse clutch pack and band so that the transmission is linked through the pressure plate to the driveshaft and, through the U-joint, the rear wheels so that your Montero backs up.

Now, moving the selector to D (first), the transmission fluid is redirected from the reverse path to the forward path and a flow is set up that is activated by the control module solenoid (its proper firing is the key to the proper operation of your transimission). When the solenoid is energized, the path that is chosen is first gear and the proper planetary gearing is set up for first. Let’s assume everything is fine to this point, but the clutch pack is beginning to go. At this point, the solenoid fires, setting the gearing to first and the fluid has been routed not only past to the first gear but it also has activated it. The only step that remains after this point (in broad terms) is that the clutch pack and band must engage and your vehicle should move out.

Do you see what could be happening here and why it may be that the clutch pack is on the way out? If the clutch pack is breaking down, it is slipping and not sending the fluid to the pressure plate so your Monetero is not going to move forward. If it is only starting to go bad, it can easily re-engage or, it can be put into gear manually, and work correctly. The only thing is that you don’t know how long it will be until failure happens and you are stuck in traffic with horns blaring away. It’s best not to take chances, so have this device fixed.

Yes, it does look like something else at this point — having the TCM solenoid checked is always a good idea — but it’s most likely the clutch pack that is shot. The damage occurred when the transmission was overfilled.

Normally, a transmission is meant to operate at a specific pressure. The pressure is related to a properly filled transmission (up to the mark and no more). When it is at the proper pressure, everything “plays together” nicely. When you begin to experience severe overpressure parts are damaged. Clutch packs are forced to slam into action and bands tighten with too much force. Even check valves in the valve body slam home with too much force, potentially damaging them. It is not a nice environment. It is not something that should be left unattended for long. You never did say how long the transmission ran overfilled, but a good guess is a long while. The time that it was overfilled led the problem you are havig now.