1995 F-250 reg cab, long bed, 2wd, 5.8 auto, 249xxx miles. No carrier bearing.

Hello,

This truck has developed a very nasty vibe when under load, like going uphill, or going over 50mph. It is driven easily, doesn't tow anymore (but used to tow and haul heavy loads routinely.

Truck belonged to my FiL, and we bought it last year for my daughter to drive. The vibes started after my daughter says she ran over a rough RR crossing. They continued to get worse until we took it OOS.

I have replaced the U joints, as they were gnarley and might have been factory original.

Replaced a broken trans mount and tightened the pinion nut (about a half-turn). Pinion spins smooth and free. Tires spin opposite just fine when off the ground.

I am starting to beleive it's the rear end. The pinion yoke can be wiggled some. Sitting in neutral and reving will not duplicate the vibe. Plugs, distributor, and wires are a year old, with separators.

Any idea what might be causing this? I intend to open the differential tomorrow to have a look.

 

I was chasing a vibration, tightened the pinion nut maybe 1/4 turn. Soon after the pinion bearings failed. I think you're on the right track, pull the cover and have a look. If the pinion is/was loose, I'd bet the bearings are plain worn out.

 

I agree, start by investigating the rear...a half turn on the pinion nut is a lot

 

Pinion yoke should not have any wiggle what so ever. If you turned the pinion nut a half turn fairly easy you definitely have something wrong in the rearend, I too would be pulling cover to check things out. Gotta believe your gonna find metal shavings and maybe a few small pieces in there.

 

Ok. Pulled the diff cover and everything looks good. No metal, no chipped teeth or visible cracks. Everything spins buttery smooth. I was rotating the tire back and forth, and there is a little slop, but I don't k ow how much is normal. I watched some YouTube videos with similar slack and they didn't make special note of it.

When I say the pinion would move, I didn't mean up/down or side to side. I meant it would twist a bit. Also, after climbing back under, I think I tighted the pinion nut more like a quarter turn, not a half.

Anyone know how to post a video, without using YouTube?

 

It might also be worth noting that I recently replaced the brake booster. These issues popped up not long afterwards.

Put everything back together today and went for a drive. It may be my mind playing tricks, but when I turn overdrive off, the vibes seem to lessen. WTF?

 

Is it possible that you knocked a vacume line off while changing the booster? That can case a misfire and shaking. I'd look at the main vacume line to the booster first and work back to the engine. Good luck.

 

Is this more of a shudder? Misfires cause shuddering when mated to autos, particularly the e4od....low rpm misfires tend to worsen the shudder effect, and higher rpm eases the pain. You should perform all of your free and easy diagnostics before going any further - plugs, wires, cap, rotor, coil, vac lines, etc. With the info in your last post, I think it's likely you find your problem in a misfire.

 

most shudders under load I've experienced have been misfires. I'd change the plugs n wires if they haven't been done in a while then if that doesn't work move on to ignition/fuel system.

 

Found it. A plug wire had come loose from the plug, and I didn't notice since it was still snug to a tug, and didn't look disco'd. Truck runs like it should now, except a high idle.

​​​​​So, on to the next thing...tracking down a vacuum leak.

Thanks all.

 

Great news. Thanks for coming back and letting us know.