Rhythmic Vibration

[Micheal Nadeau]

I know I have searched on here, but can't really find an answer. I honestly can't remember if I have already asked the question here already, so here goes.....

Between 65-80 mph I have a rhythmic vibration that I can feel in the shifter and slightly hear. I have replaced the tail shaft bushing, the drive shaft (reused yoke as the one I received had a different spline count). Brand new Moog U-joints. The tires have been balanced, did it myself at work. No pinion noise. 60 and below it rides smooth, aside from the rumble felt from the exhaust. I don't see any run out in the harmonic balancer. I don't feel a warped fly wheel. I can rev the motor to 5K in neutral and feel nothing but the exhaust. After 80, it feels like it goes away. I have popped the pumpkin open and check carrier bearings. Axle bearings are good as well. Only thing I didn't like was the amount of play in the spider gears relative to the center pin. Its not very snug, you can see the vertical spider gears move around quite a bit on the pin. Does anyone have any idea what this issue could be? Because right now, this damn car is making me feel like the dumbest master tech I know.

 

[Micheal Nadeau]

and I noticed that 3 bolts on the drivers side header and 1 on the passenger side header were missing. When I replaced them and tightened everything up, almost felt like the rhythmic vibration got worse. In the air, with the control arms on jack stands and the rear axle on stands, the vibration is really noticeable in the exhaust.

 

[Boosted92LX]

I went through the exact same thing. I thought it was incorrect pinion angle doing it, but double adjustable uppers and corrected angle didn't fix it. Swapped stock drive shafts twice, along with stock yokes and u joints. What cured it? Aluminum Ford Racing balanced drive shaft. For some reason stock driveshafts on these cars just suck. Sometimes they sling balance weights, sometimes they don't even have to do that to buzz the whole car. It's an expensive upgrade, but the FRPP driveshaft makes mine smooth as butter all the way to 130 mph. Should have bought it a long time ago.

 

[jrichker]

Simple first step: make sure the yellow paint marks on the rear driveshaft flange line up with the paint marks on the rear axle flange.

You local automotive machine shop should be able to balance the driveshaft for you. That is the single best and least expensive option.

If you want to be adventurous, take 2 hose clamps and place them on the rear part of the driveshaft with the screw part of the clamps 180 degrees apart. This theoretically cancels out the imbalance caused by the clamps. Move only 1 clamp in 10 degree increments and observe to see if the vibration increases or decreases. At some point this should cancel out the imbalance in the driveshaft. This is all theory, and I have not personally tested it.

 

[Micheal Nadeau]

I had the previous driveshaft balanced twice, with no luck. Replaced the driveshaft with one from an SN95. No change. This morning I noticed it seemed to only be noticeable in 5th gear. I got up over 80 in 4th (with 4.10 gears........) and I didn't notice it. Could be rpm/speed based. I'm usually turning 2700-2800 around between 75-80. I'm am beginning to wonder if my yoke can be causing this, as I was forced to reuse it on the new driveshaft.

 

[Boosted92LX]

It doesn't make sense why it didn't work, but I did the same thing.... swapping shafts I mean. I used good straight driveshafts missing no balance weights. That didn't work, the aluminum Ford Racing unit fixed it. I didn't buy it either at first until I had five or six people here agree that's what I needed to do. It was hard to spend the 300 bucks, but it did the job. There are several threads here on the subject if you search for them. I agree you SHOULD be able to balance a driveshaft and have it work, but everyone who told me to bite the bullet and spend the money was right.

 

[Boosted92LX]

Whatever you decide, I hope you get it.

 

[Micheal Nadeau]

As of now, I have a motor to rebuild. Though I heard a main or rod bearing on the way home. Throttle hung so I had to shut it down. Wouldn't start back. Think it locked up.

 

[hoopty5.0]

yikes. no good on the motor.

If it helps, I had the same exact issues you were describing up until Friday night. I installed the FRPP driveshaft and now my car is smooth as glass. I was doing 90 this weekend and it felt like 30. No joke.

The rattle in the shifter was driving me nuts - that's gone as is a whine coming from the rear end.

 

[Micheal Nadeau]

The motor wasn't locked up, starter bit the dust. Number 5 rod bearing was almost gone. Pulled it apart, checked everything out, and replaced with all new bearings. Can hear a knock at idle after it gets up to temp. And its got an annoying miss now that I can't pinpoint. I swapped distributors, no change. The plugs and wires aren't 3 months old yet. Cap and button look perfectly fine. Also found that my pick up tube gasket was partially blocking the oil pump inlet. Replaced it and now I have (according to dash) just over 100 psi cold and around 60 psi at temp. Once I get up to temp though, when I come to alight my oil pressure reads 0 psi, until I tap the gas.

 

[A5literMan]

Piston knock? Notice it burning any oil? Ie rings? Did you check the mains when you had it apart? I also suspect something's going on with the oil pump/pick up. Also you mentioned some vibrations. Did you check the balancer? Has it started to come apart?

 

[A5literMan]

The motor wasn't locked up, starter bit the dust. Number 5 rod bearing was almost gone. Pulled it apart, checked everything out, and replaced with all new bearings. Can hear a knock at idle after it gets up to temp. And its got an annoying miss now that I can't pinpoint. I swapped distributors, no change. The plugs and wires aren't 3 months old yet. Cap and button look perfectly fine. Also found that my pick up tube gasket was partially blocking the oil pump inlet. Replaced it and now I have (according to dash) just over 100 psi cold and around 60 psi at temp. Once I get up to temp though, when I come to alight my oil pressure reads 0 psi, until I tap the gas.

Also 100psi cold is pretty high. Must have some tight tolerances on the bearings. Mine were on the tight side when I redid mine a few years ago(don't remember the exact measurables) and my pressure runs around 75-80 cold/with a load. About 40 at idle when hot.

 

[Micheal Nadeau]

I looked at two of the mains, but was running out of time so I didn't check them all. Which could be my own damn fault, but I went on a wing and a prayer. The balancer looks fine. The rubber doesn't appear to be coming apart. I haven't noticed any oil burn. The misfire was coming form the #4 boot having a split in it. Never saw it until I pulled the wires to get ready to pull the plugs, then the boot started coming apart. AM is sending me another set. Their customer service is pretty bad ass!!. Both of the junkyards here in Savannah are having a 50% off sale this weekend, so I am grabbing a long block from a 99-00 exploder. Anyone need GT40 heads and explorer upper/lower??

 

[Micheal Nadeau]

Once I am hot, I am running around 50ish psi. My gauge doesn't gradually fall to zero, it will be reading 50ish, then drop to zero. I need to get a mechanical gauge before the sending unit to watch it. I think the sending unit has debris on the screen.

 

[A5literMan]

Good idea on the explorer long block. Do you already have some descent heads? If not (you prob already know) keep the gt40's with the upgrades/cam etc. what wires are you running? FMS are notorious for this(if that's the brand)

 

[Micheal Nadeau]

Yea I have a set of reworked GT40P's now with comp double sprung valve springs good to .600 lift. Also have the explorer intake that has been gasket matched.

Ironically enough, they are FMS wires. You would think they would design them to work with the FMS headers.