I have a 96 Dakota w/3.9 and 42RE transmission. During the past couple of years, the truck (which gets light use) has developed a persistent whine (or buzz) when the vehicle goes more than 30 mph. The noise is pretty loud, and obviously not normal.

I have changed the trans fluid and filter with no improvement. I didn't notice any unusual debris in the pan. There is no leakage, and the level is normal. (the fluid is the correct type)

The noise seems to be related to load, and if the trans is shifted into neutral while moving, the noise goes away. This indicates to me the problem is probably fluid pressure...

In researching this, I am not sure which is the more likely culprit - the pump (cavitating under load); or, if there is some other blockage preventing trans fluid from getting to the pump. I read that the O/D solenoid and pressure switches have a screen which might get blocked, but was unclear whether this would block flow to the pump, or simply cause them to throw codes.

I do most of my own work - but, I have not ventured inside a transmission before. If it si a pump, is that replaceable without taking all the guts out of the transmission? Or, is it terminal? I am at a standstill as to what the next step is to diagnose the noise. Any assistance that you might be able to offer is appreciated.

Thanks!

 

There is a transmission diagnostic chart in the FAQ(just a few posts above this one). Without hearing the sound in person it is hard to tell what it is. What I can suggest is to take it to a transmission shop, most will do test drives for free, and find out what they think of it. Take it to several places. Good luck.

 

Having good line pressure inside a transmission is a critical thing. I rebuilt a 700-R4 once out of my old Camaro and thought it would be smarter to not open up the pump itself. Boy was I wrong! The pump was bad in the first place which is what caused the transmission to fail originally, and what caused it to immediately destroy the brand new clutch packs.

On a side note, I also thought I was having transmission issues in my Grand Prix because the car started making noise. I checked the transmission fluid level and it was low so I added some. Nothing changed. I later ended up checking the power steering fluid which turned out to be low, and also turned out to be the culprit of the noise.

What I learned from that, (and what I'm trying to pass on to you) is to verify is isn't the cheap stuff before you condemn the expensive stuff!!!

 

Thanks to both. I am certain that the noise is in the transmission - and not power steering (I wish...). I read the FAQ, and am curious why the transmission cable would cause a noise if it was in contact with the bell housing? It is probably not my issue; but, I will be checking it anyway... You would think that used transmissions would be plentiful considering the number of Dodge and Jeep vehicles that used them - but they must be gold based on availability and price for them! I am not really looking to double the value of my truck here - but, it is definitely worth fixing for a reasonable price.

 

Quick update, and questions...

A few weeks ago, I put the truck up on a lift and ran the truck in drive. Noise was deafening underneath! I have been resigning myself to needing a new transmission since this really sounds more like a hard part failure in the trans.

Last night, on a whim, I shut off the O/D on the transmission traveling around 35-40 mph (prime noise speed) and the noise went away. Today, I drove it to the highway with O/D off, then clicked it on when I got on the highway - noise came back. It is much less noticeable when driving 60+ mph, so I left O/D on til I got off the highway.

I have seen that the O/D unit appears to be removable from the transmission - possibly without even dropping the transmission out of the truck. I am not able to find any troubleshooting that addresses the conditions that I stated above. I am suddenly hopeful that I would be able to replace the O/D unit only, and this might resolve my problem. Are there any troubleshooting steps for my symptoms that anyone is aware of that I can reference? Any other items I need to consider here - such as whether the O/D switch is actually doing something inside the transmission case - and not just the O/D unit?

Finally, I also came across some posts on the internet that say you should not leave the O/D switch on all the time. I do not use the truck to haul anything other than my *** to work - never tow (no hitch), seldom put anything in the bed (other than 240lbs of weight in snowy weather).

I am having no shifting issues, the truck runs good, and I have been getting 19.5 mpg on mostly highway driving. Its really just the noise I hear that is concerning me - and I don't want to have a catastrophic failure all of a sudden!

Thanks!