I posted this by mistake in the transmissions forum. I'll try to delete it if I can.
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I've got a semi rythmic vibration I can't get rid of.

This is a 1993 f-150 extended cab 4.9 liter inline 6. 5-speed manual jap transmission.

I've had this vibration since I've owned this truck, and it's getting worse
I suspect the truck has been rolled sometime in its lifetime from a
dent in the roof, a few body parts have been replaced and a few other
things that indicate the truck has been apart at some time.

Most of the vibration is when it's going over 60 mph.
The vibration isn't rythmic like a tire going around. at 60mph and
higher it feels like the drive shaft or something kind of bounces with
various levels of amplitude.
Don't really feel it in the shifter much and don't really feel it in
the steering wheel.
Doesn't seem to change if the truck is coasting or under power or when
the brakes are applied.
The tires don't seem to be wearing bad or uneven.
So this is what I've done so far.

Things I've done:
Balanced all the tires with no effect. The guy at the tire shop said
that one of my rims seem to be bent.
Changed out all the rims. Exact same problem.
I noticed that there was some runout in the tires while they were
balancing them.

Talked the tire shop into exchanging the tires expecting that maybe
there was a belt separation or something causing the problem. Still the
same problem.

Got under the truck and checked the runout in the drive shaft and
noticed the rear shaft had probably a 0.2 inch runout. seemed like the
rear shaft was bent. The front appeared straight.
Took in the whole drive shaft and they said the front shaft was bent
but the rear was straight. They repaired it and replaced the three
u-joints.
He also indicated the front yoke was scored and thought this could be
the source of some vibration since the bushing where it mounted in the
tail of the standard 5-speed tranny was probably worn also.

I put the new balanced and straighten drive shaft in and @#%&^%, still
the same @#$$#$@#$ vibration.

I took a measurement of the front yoke and bushing and I don't think the bushing is bad, after further investigation. I has about 0.010 of play which according to one place I called is acceptable. I adjusted the center bearing and was able to get the yoke into the shaft another 1/2 inch. This made no difference in the way it acts.
The tranny mount seems good and tight, I tried to move the tail shaft
of the transmission around with no success.
The carrier bearing has not been replaced. It looks intact and theres
no breaks in the rubber. The shop that did the balancing of the
driveshaft didn't think that it was in need of replacement.

I'm totally out of ideas except change out the transmission and rear end. Theyre the only things left.

Any suggestions here?

Thanks

Dave

 

My first thought was carrier bearing. It may LOOK good, but there could be scoring or rough spots inside the bearing.

The next thought is pinion bearings??? or wheel bearings.

I recall a mention of a front driveshaft. So, 4x4....lockout hubs or auto locking? When was the last time they were serviced? What about the front axles, any extra play around there?

When was the last service of the transfer case and differentials?

Sorry I am not able to point to any one item to resolve your issue?

 

Thanks for the reply.
I should have mentioned the truck is 2WD, it has the split drive shaft. That is where the front came from.

Me too, about the carrier bearing, but it is quiet as a mouse.
Maybe a bent axle, but I put a dial indicator on it while it was up on jacks and the runout was minimal.

I'm going to try to find a dyno where I can get it up to speed and hopefully find out where the bouncing comes from.


Cheers

Dave