OT: 1990 F150 vibration at 65-70 mph under load
 

Totally stock '90 F150. It vibes pretty good between 65 and 70 mph, then, above 70 mph, it's gone. I turned off the AOD, but same vibration. If I let off the throttle (between 65 and 70 mph) the vibration goes away. So, it only vibes when under throttle and between 65 and 70 mph.

Tires are almost new. Shocks are old.

I can only think of 3 things:

Unbalanced driveshaft
U-joints
Something in the rear



Tough to tell where the vibes are starting from, but I do NOT feel it in the steering at all.

Any ideas?

thanks,

Mark

my first guess would be driveshaft unbalanced or joints also does that truck have the long shaft with the carrier bearing they were famous for vibrating when they started to go

I'd bet u-joints, unless you have a whine which would indicate a rear diff problem.

Ditto on the carrier bearing if it's a 2WD with 2 piece driveshaft.

It's a 4x4.

What's that rubber bellows on the driveshaft? I think it was located at the front end of the driveshaft, near the front u-joint.

That seals the slip joint-that is another possibility for a vibe. Is the truck lifted ??

might be worth taking the shaft out and checking it over. i use A1 driveshaft they are in baltimore great guys not much more than doing it yourself and the will check balance as well. if you find a bad joint put in a good one i wont use anything but dana spicer i learned the hard way!!

I had an 89 F-350,4x4 with the same problem. I had the tires balanced, drive shaft balanced and it still vibed. It was the tranny tailshaft bushing. Check it out.

Kurt.

What's a tailshaft bushing? This is my first 4x4.

The truck is bone stock.

I had a simular problem. There would be a vibration under load and only at certain speeds. Replacing the U-joints solved the problem.

Don't forget that you have a handful of U-joints in the front axel of that thing too!

Kook,

Tailshaft bearing is the last bearing going out the tranny. You didn't say if it was manual or automatic tranny. If the tailstock bushing was that shot, I think you would have a pretty good leaker going. Got any?

There are a lot of things that could cause your problem. My experience has alway been it's either the suspension or tires. Try rotating the tires back to front and see if the vib moves to the steering wheel. My monies on a balancing weight fell off.

Get your boat back yet? April is next week you know!! Glad to see you went American with the tow vehicle.

BT :cool:

if the rear shaft has a slip shaft it should have a fixed yoke. just out of curiousity are you running around with the hubs locked in? do you have manual locking hubs or automatic ones? does your rear driveshaft unbolt at both ends or just rear and slide out of transfer case??can you see if the u joints have grease fittings in them or not?? by the way what size tire is on this truck??

Blue Thunder:

Everything is dry underneath. I will try rotating the tires - that's the easiest thing to do, for starters. Any idea why an out of balance tire would only cause a vibration when under load???

No, boat is not back yet. I plan on being out by the end of April. How's your's coming along?

mxz800:

No, hubs are not locked....... but what would happen if I did run around with them locked, but still only in 2WD mode? The hubs are manual. I'll have to take a look and see about the driveshaft, and where it unbolts - I thought both front and back, but not sure. As I recall, there were no grease fittings on the u-joints. The tires are stock 235/75/15 size.

ok lets see riding with hubs locked in is not all that bad but if a joint in the front axle was goin bad this would help pinpoint the problem. u joints not having grease fittings is almost always a sign of a stock or bargain joint. just wanted to make sure you didnt have like 35 inch tires on this truck with stock gears. i have had a few fords both lifted and stock and found the driveshafts in the fords are not that tuff to twist so when you take the shaft out check this or better yet get in balanced. keep us posted

Kook,

I was thinking that it was more speed related than load related. When you let off the gas, your speed drops out of it's resonance range. What happens when you get over seventy? If you go to 75 then let off, does it vibrate from 70 to 65?

Boat is coming right along. Been having major troubles with my apparent bastard bravos, but mbam is trying to help me out. I think I have it now. All I have left to do is finish wiring in some switches on my new dash, install the upholstrey, tune the engine I just re-installed and imron both drives. One good weekend and I am ready!!b Keep it touch.

BT :cool:

If you can remove the driveshaft and carrier ,if its a extended cad .Mark the shaft at yoke so u know where to put it back on at check all the joints to see if they feel tight or are binding . A ujoint will be really bound tight before it gets loose. Also look for rust dust around the caps of ujoint. check trans mount to. are your tires cupped out or smooth ? good luck on your search!!!!

Blue Thunder:

As I recall (the truck is not tag'd yet, so I am not driving it around on a regular basis), the vibes totally go away over 70 mph.... If I got up to 75 or so and let off the gas and slow down to 65, I do not go through the vibration.

Convincor 251:

Std cab. No carrier bearing. Just a shaft connected at both ends by u-joints...... with the rubber bellows type thing not far behind the front u-joint.

I'd still remove the shaft just to make sure . It sounds like a bad joint or slide yoak specially if it only does it on excelleration, because thats when the drive line is under a load. Do you hear any noise when it's vibrating?

No noise - at least none that I can hear (other than the vibration). 3 day weekend, I'll start wrenching. Appreciate all the feedback.

-Mark

Kook,
Iwouldn't do too much until you can drive it everyday. You'll soon find out how big a problem you have. You'll also be able to methodically recognize what the result is from things you try like rotating the tires. Like someone said earilier, make sure you have it full out of 4wd. I had that exact problem one time on an old powerwagon. Vibrated like hell 55-60mph. It was that it wasn't coming out of 4wd even though I tought it was. Stupid me. Took blowing the front rear to figure it out.

BT :cool:

and the winning answer is.............
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u-joints. The one at the differential was pretty FUBAR - nddle bearings ground into a rusty powder. :eek:

That would do it. You should have a great tow truck now.

BT

glad to hear it was such an easy fix!!!!!!!!!!

:D good job on your repair !!!!!!!