Tranny vibration?

[chadhargis]

I've got a strange issue that hopefully is nothing serious. I have a 98 Sport OHV auto with 89,000 miles on it. It runs and shifts beautifully, but I find that when it gets into overdrive and I'm going up a hill, when I give it some gas, it vibrates like I'm driving over a ridged section in the road (like when you come up to a toll booth or hit the rumble strip on the side of the freeway). If I mash the pedal to the floor, it kicks down just fine. Upshifts and downshifts are smooth and not "clunky". I considered getting the transmission fluid flushed since I bought the vehicle used with 87,000 miles and I don't know the history but I don't want to do that if the tranny is about to fall out.

I'm also experiencing a shimmy at about 70mph that feels like my wheels are out of balance. I know they aren't because I balanced them. They are dead on perfect. But at 70mph the truck shakes like crazy. Very strange. 80mph...smooth as silk...same with 60mph....but right at 70mph (the posted speed limit in my area) it shakes like a wet dog.

Any suggestions on what I can check? I really don't want to take it to the shop. They will find SOMETHING wrong even if it's only a minor adjustment.

 

[Runnin'OnEmpty]

Chad, that could be the infamous Ford torque converter "shudder". It's caused from the ATF fluid shearing in the TC. If that's indeed what it is, new fluid will cure it for a while. I would change the fluid and filter, and see if that helps. (Be sure to put Mercon V back in it.)

As to the shimmy, you might try checking the toe-in alignment. The specs are + .12 degrees, + or - .25 degrees. You can do a rough check by running a string from the back tires to the front, and eyeballing the string.

 

[chadhargis]

I'll run over to Jiffy Lube and have the tranny flushed out. Hopefully that will stop the shudder.

Thanks for the tip!

 

[guitar814]

mine was doing the same thing. I changed the fluid and put some additive in it and now it is perfect.

Good luck

 

[Cyclepsycho]

Chad, let us know if that solves it. I have a similar problem.

 

[chadhargis]

Just returned from Jiffy Lube.

Good news...the tranny seems to be doing MUCH better, and the shimmy at 70mph is gone too!

The tech at Jiffy Lube is a former Ex owner and he said the torque converter is bad about getting gummed up due to Ford equipping the tranny with a low volume trans fluid pump. He said most cars only take 15 minutes or so to flush...some fords take up to an hour and a half. Mine took about an hour to complete.

I haven't driven it much, but it seems to be much smoother and I didn't feel any shudder on the way back from Jiffy Lube. The old fluid was so dark that you couldn't see through it. It cost me $100 to have them do it, but it's worth it not to have to mess with it.

My guess is that the fluid hadn't been changed in 89,000 miles.

 

[chadhargis]

I'm going to recant my previous testimony regarding the 70mph vibration. The tranny does shift much better and the shudder is gone. Still worth the money.