Transmission slippage???

[evildrbug]

I have a strange problem that doesn't seem to quite match up to anything I've found searching here or elsewhere on the web. I have a 95 Explorer XLT with automatic and 4.0L, over 200 k miles. Fluid level is good, but it's probably due for change.

The problem is that occasionally, when i've driven at highway speeds for an hour or more nonstop, the engine will intermittently speed up by 300 - 500 RPM, and then return to "Normal" speed, getting more frequent if I continue at speed. The vehicle doesn't speed up, or slow down, the only way you would notice is by seeing the tach jump and hearing the engine speed up. If I get off the highway and shut it off for 5 - 10 minutes, it will stop, some times for 15 - 20 minutes, some times for good. It doesn't do it at all at lower speeds. Taking it out of OD at highway speed causes the engine to speed up by 800 - 1k RPM, so it doesn't seem to be intermittently downshifting.

Any idea what the problem could be, and what would be involved in fixing it, or getting it fixed? TIA.

Bill

 

[BrooklynBay]

It sounds like the torque converter is locking & unlocking or it might be a shift flare if it does it only in certain gears.

 

[dogfriend]

It sounds like the torque converter unlocking (and relocking). Does it occur when the road is slightly uneven? I have noticed that mine will unlock on a very slight uphill grade at certain speeds.

 

[evildrbug]

That was kind of my first guess. It seemed to be more frequent going up hill, and I think I tried popping it out of OD while it was running faster, and it sped up by the normal 1k or so for downshifting to 3rd, and then dropped back down a few hundred RPMs in 3rd as well. There's no noticeable slippage when it shifts.

So if this is it, would I need to replace the converter, or could it be an electronic/controller issue (telling it to unlock when it shouldn't, or somehow getting a signal that makes it think it should unlock), and if so, how would I tell?

Thanks!

 

[BrooklynBay]

Your transmission uses a modulated TCC solenoid, so you shouldn't feel a harsh lock/unlock like the older A4LD. It's possible that the solenoid isn't so good anymore. Considering that you have high mileage, you might want to either rebuild the valve body or replace it.