# Not sure if it's transmission or something else.....



## madhatter256 (Feb 2, 2010)

I have 1996 Sentra GXE w/ automatic transmission. I'll do my best to describe the problem.... 

Short story: I think my transmission is failing to stay on the 4th gear when cruising at a constant speed (not accelerating). I really can't tell as my car doesn't have the tachometer to show the RPMs, which can be really helpful in diagnosing my problem. I can only go by the noise... normally it makes a humming sound, but during sometimes the humming noise level drops a bit and goes back to normal and then back down. It does it for a little bit unless I step on the gas and the noise is normal. This has happened to me when driving between 60-70mph and 40-50mph. I changed the transmission fluid shortly after it did this and it has done this a lot less frequently than before...

If it was a transmission problem, would the problem be more consistent and apparent? 

Long story:
Two weeks ago I was cruising on the freeway doing 65mph to 70mph. All of a sudden the car makes this noise what sounded like the RPMs were dropping. I put some of that lucas transmission 'anti-slip' fluid and it helped for a little bit. When the weekend came I drained the transmission fluid and I will admit that I've been meaning to that for a month but never got around to it. It drained a good 5.5quarts about, as it took that much to refill it to get my dipstic back to normal fluid levels. The old fluid was darker than the new one but not that much. I also replaced the VSS unit because I have that computer code error that's common with this vehicle. Replacing that did improve my speedometer/odometer functions.

One thing I noticed when I was driving with the bad VSS is that it wouldn't kick in after driving for a long while and going at high speeds (60mph+). When the VSS kicked in I could hear the noise coming from the engine getting lower (thinking the RPMs are dropping, thus thinking it's going into OverDrive). Just recently though I decided to drive without overdrive turned on and the car's tranny/engine was much more noiser than ever, so now I'm thinking the gear isn't slipping and that it might be something else.

either way, the car seems to be on its last legs. I mean it runs great other than this current problem. AC blows ice cold and all power windows work. Cruise Control doesn't work but that's not a big deal. 

If it does turn out to be the transmission, then it's time to get a newer car... I just hope this car can last me a few more months!


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## jdg (Aug 27, 2009)

In this setup, the 4th gear torque converter lockup is controlled by the computer which needs a VSS input to tell it when to lockup. So, if you had a bad VSS, the tranny wasn't going into lockup which would keep the revs high, and worse, the heat high.
It's probably kicking in and out of "lockup" while in 4th gear.
For help in troubleshooting, maybe go out and buy you a cheap tach from somewhere. Doesn't have to be accurate, but would help to let you know if the engine is revving up and down while cruising at a steady speed, and therefore if your tranny is actually slipping.
In my '97, in 4th gear lockup, at 60MPH, the engine spins about 2,450 rpm (roughly 40.5 RPM per MPH). If it spins much faster than that, it's either not in lockup, still in 3rd gear, or could actually be slipping.


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## madhatter256 (Feb 2, 2010)

Well because I drove on 3rd gear yesterday, the car was definitely louder when I was driving it at speeds of 60mph. SO, when I'm driving with over drive ON, the car is much quieter. 

I believe now that it's not really slipping back down to third gear, but what you just explained.

I will mess with the electrical connections on my gauge cluster and see if it can allow the VSS a clearer signal path to the ECU because of the way they wired this.


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## jdg (Aug 27, 2009)

Get out on a road somewhere and accelerate the car normally from a dead stop up to about 60MPH. You should feel 4 shifts, 1->2, 2->3, 3->4, and shortly after that you'll feel the torque converter lock up. If you're into the throttle hardly at all, it won't lock up the torque converter and you'll be able to back out of the throttle very slowly and feel that 4th "shift" (which is actually the torque converter locking up).
If you had a tachometer, you'd easily be able to see this, because if you're going down the highway, say at 60MPH, on a level road (ya know, cruising, hardly into the throttle at all), and press the brake pedal just enough to make the lights light up but not enough to initiate any braking action, the torque converter will unlock and you'd see a jump of about 200-300 RPMs on the tach. Take the foot off the brake and a couple seconds later the torque converter will lock up and the rpm's will go down another couple hundred or so.


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## madhatter256 (Feb 2, 2010)

Well it hasn't done this at all today on the way home from work and this morning going to work.

This weekend I'll work on it, but I'll keep an eye on it and see if it does it again... so far it hasn't...


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## madhatter256 (Feb 2, 2010)

Well it's an on againg off again type of problem. Had a lot going on this weekend to not be able to check my gauge cluster. 

The problem started back up again, this time a bit worse than before, the car lunged forward a bit while doing 65mph as if it was punched in the stomach.

Might have to install a tachometer. Seeing instructions on how to install one on youtube...


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## skeeter123 (Apr 30, 2010)

It could be that your cruise control problem and transmission problem are related. As JDG said, when you touch the brake the computer will unlock the torque converter. It will also turn off the cruise control. You should check your brake switches (under the driver's dash, placed so that they are switched open/closed by hitting the brake pedal). There may be two separate switches, one for brake lights and one for cruise control. On my 98Sentra, there were black plastic disks that were glued on to the brake pedal, which served as the impact point for the switches. After 11 years one of them just fell off, disabling the cruise system. I scrounged another piece of plastic and just glued it to the brake pedal; problem solved. On my Chevy truck, the contacts on the brake switch got dirty and wouldn't make contact, so brake lights wouldn't come on and it was hard to move the gear selector out of park (you have to press the brake pedal before you can get it out of park). If the switch is not adjusted properly, it may be making contact intermittently (like when you go over a bump), and kicking the trans out of OD.
Hope this helps.


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## jdg (Aug 27, 2009)

When was the last time you gave the thing a really good tune up? A complete and full tune up and checked everything else...timing, idle speeds, etc.?

My thinking is that your engine might be working too hard at highway speeds and requires a bit too much throttle (due to possibly needing said tuneup) to maintain speeds in 4th/lockup and needs to downshift into 3rd/non-lockup to maintain speed....hence the 'punch in the stomach' feel, which is actually only the downshift.

I don't know about you, but it isn't brain surgery to figure out if the thing is downshifting or not, or for that matter, to figure out what gear it's in currently by just using your butt in the seat and feeling for the upshifts and downshifts.


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## madhatter256 (Feb 2, 2010)

The "punch in the stomach" feel the car did today was when shifting from 1 to 2nd gear.

I know for sure it's the torque converter not locking as I rode with just the 3rd gear and felt a big difference in noise level and the engine simply worked harder.

List of things done to the car:

New plugs
New wires
new upper timing chain tensioner
new valve cover & gasket
Regular oil and filters replacement, recently replaced fuel filter
new speed sensor

That's all i can think of at the moment.

I know of the following things I need to take care of but I don't have the space nor tools:

oil leak through crankshaft pulley
oil leak near the distributor rotor.

I guess the condition isnt great, but I live in a dense apartment complex where working on your car is suicidal from the traffic with no vacant areas to work on my car. Only place I can work on it is at my parents, but that's 60 miles away. So I'm doing the best I can when I can.

Reading through the service manual, I have to check a lot more areas than just the transmission.


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## jdg (Aug 27, 2009)

madhatter256 said:


> oil leak through crankshaft pulley
> oil leak near the distributor rotor.


See the "stickies" for how to change out the front seal for the oil leak on the crank pulley. In some ways, that job is a lot easier than changing the upper tensioner, and shouldn't take you more than an hour.

The oil leak near the dist. rotor is also easy. Mark the distributor, scribe a line on the distributor itself and the head. Pull the distributor, pull out the old o-ring, put in the new o-ring, put the distributor back in, line up the scribe marks, tighten everything down...done.

And shouldn't cost more than a couple bucks for the crank seal and the o-ring.


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