Does anyone know what would happen or symptom if a '99 4r70w was have to have dextron 3 put in it other than the required mercon 5.
I just bought this truck and have reason to believe that this may have been done to this transmission.
It seems a little sluggish at times, but in all it works pretty good.
Any advice or thoughts on this would be great.

 

Hello ricor,

All you can really do at this point is put the correct fluid in it. Look on the dip-stick and it will say either "Mercon" or "Mercon V". Have the tranny flushed and replace the filter. If you take it somewhere other than a Ford dealer be sure to tell them what type of fluid to use. I took my truck to a shop and there computer said all late model F-150's use Mercon V and I know my 4R100 didn't, good luck.

 

Mercon V is a transmission fluid that was designed to stop the "shudder" and sloppy shifts with the newer transmissions. Mercon V is a must in these tranmissions. Ford Motor Company will not warranty any transmission if they detect the wrong fluid has been used.

I just spoke with my dealer and he assured me that Ford would do a fluid analysis and if they detected any hint of Dextron 3 being used, they would revoke warranty.

I had a 96' Tbird that had dextron 3 in it for a while. The car developed a vibration or "shudder" if you will, between shifts. This shudder was the transmission slipping. At that time, Ford was in their transition period of changing up to mercon V, so the fluid was changed and the tranmission was flushed under warranty. Dextron 3, when the fluid is new, will work fine......until there is a few miles on the oil and it starts to break down. Then the problems start.

I would do as rkjerue suggests. Get it flushed and drop the pan and filter while your at it. Better safe than sorry....especially if you have any warranty left!

 

The shudder is the mechanical lockup of the torque converter slipping. It occurs when the Mercon breaks down from heat. I had the problem with my 95 Lincoln Mark VIII after the thermostat stuck closed and the engine overheated a little. I switched it to Mercon V but Mercon would have done just fine I am sure. Mercon V is semi-synthetic and will take a little more heat before it breaks down. If it is a 98, the recommended fluid is Mercon V and that is what I would use.

 

Thank You all for all the info--so far the tranny seems to be ok, but also seems to a little sluggish on rare occasions, especially when its really hot. I've been told also that "lubeguard" will convert dextron3 to mercon with approx. 1oz per quart. Therefore making a tranny service alot cheaper. I went one step further and emailed lubeguard. They claim that they will stand behinf their product 100%, and that warranty would be given if their product caused a tranny to fail.
Has anyone ever tried it with dextron3 or is this just a snake oil that one should stay away from?

Ricor

 

Roadie is right about the torque converter slipping.

I would avoid the additive. Maybe it works.....maybe it doesn't. All I know is that I was told to stay away from these "magical" additives that make the oils equivalent. They say that it works, but who knows?

I'd rather spend the extra money for the Mercon V and not have to worry about proving/disproving someone elses' claims. It's not that much more money anyways.

If it calls for Mercon V, just put it in. Transmisson services don't happen that often.....