New strange vibration

[CruiserMax]

I have a 76 FJ55 with Toyota power steering pushing 33/12.50's. I recently did two long road trips without any problems. All of a sudden I noticed that I am getting a slight but annoying vibration. Its hard to tell where it is coming from. More noticeable when I am in third or fourth. Its there when I have my foot on the throttle. I thought tire pressure may be the cause. My right front is off by 6 PSI. But I get the vibration with my foot on the throttle and it goes away when I lift my foot, so I am guessing the tire pressure is not the culprit. I checked and tightened all lug nuts on all four tires. Any clue as to a check-list to figure this out?

Thanks!

Max

 

[largenfirm]

Check your harmonic balancer. Check your u-joints.

Also, are you missing any of your wheel weights?

Kirk

 

[65swb45]

If your only variable is acceleration, then that would limit the source of vibration to those things that respond to acceleration. That would be

engine

clutch

transmission

transfer case

driveshaft

differential


That limits things a bit!

Quickest test is to block the tires, release the parking brake, put trans in neutral, and try pushing up on both ends of the rear driveshaft in the same direction as the crosses of the
u-joint to check for joint play. Also grab the two halves of the shaft and try rotating them in opposite directions.

 

[hammerhead]

That's a U-Joint my friend. I just changed my rear U-Joint in my rear shaft last week. It had those exact symptoms.

 

[CruiserMax]

Thanks guys. I at first jumped to the conclusion that it must be tire or wheel related. But the symptom is mainly noticeable under acceleration: slight but constant rumbling vibration. Definitely noticeable in 3rd and 4th gears. If I am cruising steadily in 3rd the vibration is there. It goes away as soon as I take my foot off the gas. I'm guessing the vibration is hidden by slow speed in 1st and second. In any event I think you guys are on the right track. I'll check the u-joint.

Max

 

[skyshark186]

Had the same problems on my 73. U-joints were bad and had some nasty nuckle slop on the front end. New u-joints and a knuckle rebulid from CCOT and it drives like a caddy.

 

[CruiserMax]

What do new u-joints cost? Any good sources?

Thanks,

Max

 

[CruiserMax]

I checked the rear drive shaft and yup, you guys are spot on: the rear u-bolt feels really loose. It moves back and forth. The front one seems tight though. I'll replace both...

Thanks again,
Max

 

[Pin_Head]

Don't use NEAPCO aftermarket U joints; they don't fit even though they are supposed to.