Strange Revving, not engine

[mlmpetert]

I have a 97 explorer, with a rebuilt 4.0l SOHC engine aboutt 4k miles ago and rebuilt trans about 20k miles ago.

3 times now after driving for 20+ minutes and going over 50 mph I have gotten a hi pitched revving noise and my engine drops to 1000 rpm (about idle). The noise allmost sounds like crotch rocket bike.

All 3 times i have been on the highway and pulled over immediately, however my ex will run fine and idel fine, and when i get back in to drive it drives fine. No check engine or transmission light. Also all 3 times the AC has been on. Also I replaced my vehicle speed sensor about 3k miles ago.

Any ideas?

Thanks

 

[mlmpetert]

Im thinking it might have somthing to do with the torque converter?

 

[sportr4c]

does sound like a tranny problem. not sure why if it was just rebuilt though. could be overdrive, but sounds like it's doing just the opposite if the revs are dropping. could it be upshifting for some reason?

 

[gijoecam]

Is it doing it on deceleration (i.e. coasting against the engine) or when cruising steady-state?

-Joe

 

[mlmpetert]

All three times its done it while I was cruising, with my foot lightly on the gas.


The engine was just rebuilt but the transmission is actually used

 

[mlmpetert]

Well I took my girlfriend to the airport today and its doing it. It seems like I have to drive for 25 plus minutes before it will do it

gijoecam:
It happend 3 times today on the way back from the airport, all three times it was when I was decelerating. When I went to get on a exit and lifted off the gas and it did it.

After the first time it happend I turned off my ac and radio and listend the whole way home. I got to hear it twice more and both times it sounded like it was coming from right under me. Think it is a transmisssion problem.

Anyone got any ideas?

 

[gijoecam]

You probably don't want to hear my diagnosis.... I hate to sound like an alarmist, but....

Transfer case. It will sound like a buzzing/whizzing noise, like two gears whirling against each other, right? There's a not-so-uncommon issue with the transfer case shift rail bores that can cause that type of noise. Over time, the shift rail bores get worn out (they go from round to oblong) and the that prevents the shift rail from holding the low range gear set in place. Due to the helical cut on the gears, when driving forward, the gears are forced into place. However, when coasting or reversing, the gears are forced the opposite direction, and rub against (something they're not supposed to). Eventually the problem will get so bad that you lose the ability to use reverse at all, if the gears don't grenade themselves sooner.

Run a search over in the transmission and transfer case forum and you'll find plenty of info. Omega Machine sells re-machined case halves with an insert in the shift rail bore, as well as a revised shift fork that has a better set of fingers to hold that gearset in place.

That's my best guess without hearing it...

-Joe

 

[mlmpetert]

gijoescam, it sounds like it might be the transfer case from what you discribed.

I took my car to the shop and left it for the weekend. They couldnt find anything wrong with it. Right now i only have the problem when im driving for at least 20-30 mins. on the highway, and it didnt sound like they were willing to drive it that long on the highway.

I have my current transmission under a life time warrenty so im hoping that its not the transfer case, but well see.

I got to go on a trip this coming weekend so i will post with any problems