High speed drag.

So driving on the highway in 5th gear at or above 6000 rpms (speedo cable is broken at the moment) i get a rythmic vibration from the rear wheel. It feels like im driving over those tiney speed bumps. No real noise is made from what i can hear.

Im thinking this is either 1) not enough or no oil in the rear diff or 2) need to lube or replace the axle...

Ideas?

 

Could also be the tire isn't balanced.

 

na, this wasnt constant.... It would go on - off - on - off. probly at 1/2 second intervals. Between drags it would be smooth.

 

I have heard from more than one old timer that each rim size (ie 16, 17, 18, etc) has a harmonic at a specific high speed range. Can't remember what speed ranges he mentioned but my experience supports this theory. I'm not sure who I would ask to confirm this but it does make a smattering of sense.

 

correct, however it doesnt apply here because (or perhaps i failed to mention) this keeps on going past 6k rpms... its not like its just from 6000-6500.

 

Does it happen in all gears or just 5th? Could very well be something wearing out and getting sloppy back in your rear end or drive train. Not sure what kind of XJ you have but I have a maxim x and I know that it pulls pretty good up in the higher RPM. So if you have a similar bike, it may be when your axel, bearings or whatever may be wrong, is binding up thus producing the vibration. When she is planting her power. Just a suggestion, I'm no expert but sounds like something is sloppy. Or it could be something simple. Just my 2 cents . Good luck.

Mike

 

I still think Woot is right. A imbalance can be an oscillating event. It will start wobbleing then reach a frequency imbalance and subside. Then it starts all over again. It will also be unnoticable at slow speeds. Once you hit the higher speed it will start and should get worse as you increase speed. Doesn't take much to remove the tire and have it balanced. Most shops will do that while you wait.

 

Indeed. Imbalance appears at specific speeds and is lower in magnitude until it hits the right frequency.

But at highway speed a 1/2 second interval is more on the order of seam spacing of a concrete roadway.

 

Ok, the rythmic vibration was what I was going by. Don't think I really understand the 1/2 sec interval. I can interpret that 2 ways. A vibration that ebbs up then down or is instantly on then off. That could be a bearing or even the brake shoes trying to grab.

 

I'd check the factors first above ib your last post just to make sure then look for imbalences , my 2 bob too.

 

its not fading in and out. Its ON and OFF.

What i thought is maybe the gears are going.... In 5th gear at 6k rpm, perhaps the ring/pinion are rotating finally to fast. Maybe they are worn.

But i dont think thats the most likely of situations.

I need to drain the final gear oil and put new in first. If i remember its .2L. But how do i tell ? Will it just fill up the the fill hole?

After that im going to pull the axle and lube it.

 

Never mind on that how much to fill question... that was dumb.

 

I think as previously mentioned you are going to find a bearing problem when you lube that axle but dont expect it to be very noticeable because like was mentioned before (by MikeT), at 6k your pretty well loaded up.
Could still be a gear thing but my 1st guess is bearings.
Good Luck
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