Need Some Help Diagnosing A Problem.

[snagged in outlet 3]

I haven't been able to figure this out so any help would be great. When I get to 40 mph and the transmission shifts into overdrive (4th gear) I get a vibration in the gas pedal. If I accelerate right through 40 to past 50 mph it doesn't do it. It gets really bad if I have to keep my speed anywhere in the 40's. It feels like when you drive over the warning strips on the side of the interstate only not quite as severe. I only feel it in the gas pedal, not the steering wheel.

V8, 180K, Automatic. Other than that it runs fine. I won't mention what I've checked so far so as not to influence your thoughts. Unless you guys think I should.

Thanks in advance, SIO3

[FishinCricket]

Ever had the transmission replaced or repaired?

Have you checked your U-Joints?

[jjtroutbum]

u joints? drive-shaft? tires balanced properly or a broken belt in one. Just guesses really hope you find it before having to chuck cash at possible solutions that always sucks.

2wd or 4wd? stock suspension and wheels and tires?

[eric1978]

My guess would be a tire balance problem and not the transmission. Have the tire guys throw the front tires on the balancer. You may have thrown a weight or something. Not sure that would make your gas pedal vibrate though, but that's the first thing I think of when there's any shaking involved.

[snagged in outlet 3]

Thanks guys. 4WD and it had bilstein shocks that I replaced with sensitrac miles before this showed up.. Stock wheels and tires.

Already did the tires, rotated and balanced, they were cupped but it's not that. Had the planetary gear replaced 3 years ago. Checked the heat shield on the exhaust system and the cat converter.

Is there a way to check the u-joints on my own in my garage?

SIO3

[jjtroutbum]

Thanks guys. 4WD and it had bilstein shocks that I replaced with sensitrac miles before this showed up.. Stock wheels and tires.

Already did the tires, rotated and balanced, they were cupped but it's not that. Had the planetary gear replaced 3 years ago. Checked the heat shield on the exhaust system and the cat converter.

Is there a way to check the u-joints on my own in my garage?

SIO3

Have to get the axle up and supported and rotate the drive shaft by hand. If there is any play in the drive shaft u loint is bad. I am one of those guys who get the shop to show me such things while the vehicle is up. Since my garage has been neglected for several years.

Its been awhile since I had any similar issues so I got a refresher here.

DIY: Replacing Universal Joints

[Thom]

If you have a positraction rear end it can cause problems simuliar to what are describing. I had it happen with a truck rear end once. The good news is that there is an additive that is supposed to be used at 60000 + miles. solved the problelm in about 25 to 30 highway miles after adding.to rear end..

[snagged in outlet 3]

Thanks everyone. I also think u-joint at this point in time. But what is the name of the additive you used Thom?

Thanks again, I'll let you know what transpires.

SIO3

[fishinwrench]

Does your tach or voltmeter flutter while the vibration is being noticed ?

If you are driving in 3rd (not overdrive) does it still happen ? 40mph in overdrive would be like "coasting", so it could be falling in and out of OD.

No fault codes have been set ? no "service engine" light ?

Also make sure you aren't running in Auto 4wd. (I've done it myself, so don't feel bad if that's the case )

[snagged in outlet 3]

Wrench

Tach doesn't flutter

Does not do it in 3rd, it starts the instant it shifts into OD but not if I'm accelerating pretty hard.

Yes I am coasting but accelerating enough to keep it in OD and 40 to 50mph after 50 or so it stops.

It's not going in and out of 4th. The vibration is too rapid.

No codes or lights

Not in auto 4wd. Unlike my wife who drove it around in 4wd low until it cracked the planetary gear . She said "Honey when I turn sharp in the parking lot it was doing something wierd."

SIO3