Bad U-joint?

Any squeaks? Particularly backing up slowly? Any "clunk" starting in either direction. If so, suspect a "U" joint. If you have a bad one, change them all at once.

I'll second all of that.

Could be u-joints . Easy to check - put the parking brake on , gear shift in neutral . Might want to chock the wheels , I don't usually . Slide under the truck and rotate/shake the driveline . If you see movement in the joint it's shot .

It can be shot with no appreciable looseness. The joint can be tight instead of loose and still cause a shake. Generally these squeak, or "chirp"

From what you said I suspect it's wheel related. Out of balance tires often act up within certain speed 'bands'.

If wheel speed vibration frequency sounds right, look for loose lugs and missing wheel weights (there will usually be a dirt 'witness mark' on the rim where a lost weight was). Look at both sides, inside and out. Look over the wheels/tires for obvious things like ply separations, wads of stuck on spooge or whatnot.

A bad front wheel bearing/s can sometimes produce vibrations that vary with vehicle speed... and as they get worse can even induce an eerie low pitch 'humming' like sound into the vehicle. I haven't run into many of these, but the ones I have were more felt than heard, and sometimes seemingly originate from 'everywhere'.

If after all the driveshaft is suspected, go under shake/wiggle as mentioned above looking for joint slop. (RWD driveshafts rotate much faster than wheels, so if responsible, the frequency will be a good bit faster.)

If you can quickly (and safely) dash under the truck immediately after driving, feel for hot bearing cups. Use caution, a bad one might be quite hot.

If so equipped, look at the shaft center support & bearing... check it for mounting security and bearing slop.

Look over the shaft itself for stuck on spooge, foreign matter like rope, extension cord or the like wrapped around, missing bolts, physical damage etc.

Also, some vehicles have a fair sized weight bolted to the transmission output shaft housing to 'soak up' vibration. If you have one, be sure it's tight. While there, grab the output housing or front of the drive shaft, shake and check for a busted or sloppy rear engine mount.

Not a bad idea to look over all this stuff whenever your down there, vibration or not. Just look over every thing in general with an emphasis on delicate stuff, like brake hoses/lines, exposed wiring & connectors, CV boots and on and on.

Good luck, let us know how it turns out.

Erik

Your transmission is going out, not worth fixing, time to scrap it and find a new truck

Me three.

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Erik fired this volley in news:spam-984467.22445207102013 @news.dslextreme.com:

Really? Even when he said it ONLY happens when accelerating in that speed band, but not when coasting or decelerating?

Unless he's got a horrible tread separation, there's no "drive vs. coast" defect I'm aware of in tires that could cause that symptom.

Lloyd

Ignoramus3720 fired this volley in news:KpydnZDhG6ir9M7PnZ2dnUVZ snipped-for-privacy@giganews.com:

In addition to the suggestions about U-joints and trannies (but not tires), It could be a torque/speed problem related to the engine performance. It might be missing at a certain torque and speed AND vehicle speed range.

I lean more toward it's being a tranny problem.

When's the last time you completely drained, flushed, and re-filled the transmission?

Lloyd

I had a puzzling speed-related vibration problem that turned out to be a rusted-out upper shock mount in the front. It's out of sight behind a flange on the spring mount so I only found it when I bumped the shock and it moved. Other than a slight steering wheel shake at certain speeds the truck handled normally.

The factory manual says when replace the rivets holding such things to the frame with bolts, use Grade 8 one size larger.

jsw

A relatively minor tread separation CAN cause an under-load shake - but will usually also shake under moderate braking.

We are talking about the old horses vs zebras vs unicorns thing here again.

Check for horses first. For all it takes to pull a driveshaft, just pop it out and chech each joint for play/stiffness. Mabee half an hour's work on a bad day? And if the joints are bad, you have 1/4 of the work done already.

Can you generally tell by unbolting the flange and wiggling the u-joint by hand?

The few I've worked on were pretty obviously bad once freed from the tranny or differential. The OEM ones were "lubed for life", so their life ended when the lube ran out.

I've heard that sticky driveshaft slip joint splines can cause strange symptoms.

jsw

Since it's not a Ford, with their damnable 4sp OD tranny, I strongly doubt it. Mine felt like it was missing in 4th at 75 during heavy accelleration.

What kind of truck, age, mileage, engine size and all?

I've been thinking about this, last few hours. With the "worse on accel", it sounds familiar. One email friend of mine suggests it might be tune up and ignition related. Might be missing on one cylinder, which is worse on accel (timing advance).

. Christopher A. Young Learn about Jesus

Certainly a possibility.

In the could-also-be-in-addition-to-what's-been-mentioned department...

Depending on the pickup, if it has a 2-piece driveshaft with a carrier the carrier bearing could be shot, or just the rubber supporting he carrier could be shot. Usually midsize pickups are the biggest with this arrangement, so probably not relevant.

Could also be a worn out slider (where it fits into the trans with a 1-piece shaft), or just bad output bearings in the trans.

Dave

Can virtually always feel it when unbolted.

Looking for unicorns again, stormy. Or at least Zebras.

If you want to look for Zebras I've got another one for you. I started feeling a bit of a shake at 95Kph recently on my Ranger. Not consistant - and it went away when I backed out of the throttle or declutched. Dead smooth when declutched. Checked the tires last evening and guess what I found? One rear tire was about 10psi low - and the truck has posi. Aired up, and no more shake on accelleration.

Not a horse, but not a unicorn either. Mabee not a zebra - mabee a mule???