Rear end slipping?

I have an 82 XJ750 maxim and I have a very strange thing happening. If I am on the highway and rev near 7K rpm I feel some sort of slipping in the rear of the bike. I will be full throttle and when the RPMs rise near 7K I get an awful vibration under my butt that if I didn't know better feels like the tire is slipping. I know that's not it because this bike doesn't have that much power. I don't think its the clutch because its not just the engine spinning up, there is something breaking loose and causing vibration. As soon as I let off the throttle it goes away and the bike drives normal.

Any ideas?

 

How many miles are on the bike?

It probably is the clutch, if you're getting a rise in RPM (unless your rear tire is completely bald.) Might want to have a peek in case something in there is coming apart. It wouldn't be the first time.

 

Need more info, like how many miles on the bike, how long have you owned it, how many miles have you put on it, how old are the tires, have you ever taken anything apart at the back end?
Info like this can help narrow down the problem.
Could be one thing or several.

Cheers, Graham

 

Bike has 24K miles
I have owned it for the last 5 years and I got it with 18K miles. Overall the bike is in good shape. The rear tire is fairly new and has good tread. Just passed PA safety inspection. I have never had the rear end or clutch apart. I change the oil regularly with yamalube and have changed the rear gear oil once

If it is the clutch would I feel a hard vibration under the seat? Honestly I can't say that the RPM's rise as it happens too quickly to notice. It kinda scares me since it feels like the bike is coming apart. Normally I don't push the bike this hard so it doesn't happen very often. The clutch seems to grab hard during shifts like it should. A better way to explain it would be if you have ever experienced wheel hop in a car, but instead at 7K rpm's on the highway

 

What oil are you running? I find that runing 20 w 50 GTX in cold weather causes my clutch to slip under heavy throttle when the revs hit... about 7 grand. I now run 40 weight in the spring and fall.

 

I run 20w50 yamalube in the bike since our riding season is mainly warm. Today was 70 degrees when it happened

 

You shouldn't be running GTX any more. It's CAR oil, and it now has "friction modifiers" too; to meet the new specs. Even Castrol themselves admit you shouldn't run it in bikes any more. My Norton was heartbroken after a 37-year relationship. Run Castrol 4T motorcycle oil; and if the clutch still slips, see below. You probably need to rebuild it anyway.

spdy0001 you should definitely pull the cover and inspect. The symptoms ARE those of clutch slip; but it shouldn't produce a "shuddering." You could also have a problem developing with the driveshaft or u-joints.

That one would be "out of my pay grade" but the clutch is also a very good possibility.

Everyone needs to understand two things about these clutches:

1- They're as simple as simple can be, even the 550s; but you HAVE TO PAY ATTENTION.

2- Thirty years old simply doesn't cut it. Just because you can't see it doesn't mean it doesn't need to be attended to, JUST LIKE BRAKES.

Ignore it, and put the bike back in service and guess what? It's gonna act up. (Just like brakes.)

Cheap and easy to fix then you're good for another 25K. What's not to love? (NOT just like brakes; those are neither cheap nor easy, just vital.)

 

So I had someone else look at the bike and the verdict is that the rear tire out of balance at high speeds. Since I never experience this at lower speeds Im not worried about it

 

Since they're tubeless tires you might want to investigate a bit further.

 

Just make sure that the tyre is not rubbing on anything.