hi, i have a '98 F-150 4x4 with the 4R70W aute trans. when i checked my atf today with it idleing in park i noticed that there were bubbles on the dipstick. i wiped off and put it back in and checked it again and found the same thing (i did this about 5 times) i then walked over to my dad's 97 with the 4R70W and checked his (while it was idleing) and did not see any bubbles or anything. my question is.....is this normal and should i be concerned about it???

thanks in advance

Jake

 

I have heard that this can happen for two reasons: 1) overfilling the transmission makes it churn in the fluid, creating bubbles (so you might need to take out a bit if it is overfull); 2) some additives have been reported to cause bubbles, so if you have added anything other than transmission fluid, that could be the cause.
Hope that helps.
Frank.

 

I did notice that it was a bit overfull......i got it with about 128,000 mi and the tranny was rebuilt at about 132,000 mi. it now has 141,000 on it. thanks for the info and im glad that its nothing too serious

 

Well there are a couple other things that might cause bubbles. You might have a valve body that is loose or the filter is not snugged up properly. Either condition could cause the tranny to suck air and make bubbles. You would need to drop the pan to check this.

I would expect a rebuilder to be careful about thses things so it is less likely to be a problem in your case.

I would just remove some of the fluid and check to see if the bubbles go away. A few bubbles is not unusual. Wild guess is say 5 -10 bubbles is OK. If the dipstick is covered with bubbles, you have a air leak or foaming fluid.

According to some shops and depending on your driving style, it is almost time anyway for a fluid change. If none of the easy fixes work, I would drop the pan snug things up and change the fluid. The filter can be a bit tricky to properly install on some trannies. Often there is an O ring that needs to be removed and a new one properly seated. Then you plug the filter into that. Often plugging the filter into the O ring is a beach. Most that I have changed, kind of "snapped" into place after getting them lined up and pushing with firm pressure. While you are at it check the torque spec for the valve body and snug up all the bolts you see on the body, I have occasionally found a few loose ones this way.

Good Luck,

Jim Henderson