250sx help!!! Rear diff issues

[toddsf150]

I have a '85 250sx, bone stock. Im having a couple of issues and one big concern. first, while riding, it felt like one of the tires was out of round. I replaced the front tire, as it was original. The problem persisted. I think I have narrowed it down to one our both bent rim(s) on the rear. It is definetly not a bent axle. The major concern I have is with the rear off the ground, I went through the gears, and in fifth gear there is a loud grinding noise coming from the rear diff. Its only in fifth gear. Could it be some thing wrong with that particular gear, or is it as simple as a rear diff flush. I have owned the trike a year, and I doubt the fluid has ever been changed. It also seems like its hard to turn the tires in neutral. My other atvs spin a lot more freely when off the ground. I can't great the noise when riding the trike, I can only hear it when the rear is elevated. Thanks. Any help is appreciated.

[Flyingw]

You can try flushing the diff but the correct way of handling it is to remove the diff and open it up. If you ignore the problem, you may wind up with a 365lb pet rock. If you decide to open it up, let me know and I'll lay out the issues and areas of concern otherwise its pretty simple to inspect it.

[dougspcs]

It took you more time to turn on your computer and start this thread than it would have to pull the plug and drop the oil and see what kind of trouble you were into..

Git out there boy..then come back and ask questions!!

[toddsf150]

I did check the rear diff fluid earlier. It appears to be red in color. I don't think it is low, but it probably is old. It seems to me that some thing is grinding/squealing when the rear end gets up to high speed. What is the procedure for opening up the rear end, and what am i looking for? I've never went into a rear diff before.

[dougspcs]

Chunks and bit of metal are the 1st clue. Use a small magnet and run it thru the fluid when you drain it.

However..likely the noise you are hearing is the u-joint.

Since with the rear lifted and no weight on it the angle will be pretty sharp one the u-joint on the driveshaft from the transmission down into the differential. If you have it spinning fast while raised it may be causing the joint to clatter..

Doesn't mean it's bad, just make sure the rubber boot between the rear of the transmission and downtube is good.

If your fluid drains out without chunks or milky colour that may indicate water intrustion you are likely good..don't worry about tearing into it. Change the diff fluid and change it often. Especially if you like to puddle jump..

Also make sure you remove the right rear wheel and clean and dry out your brakes regularly. They are of a bad design that don't seal well and it will keep your shoes from rotting and falling apart.

They are a rock solid, unkillable machine with a bit of regular TLC..have fun.

[tri again]

spooky.

trike off the ground and only in 5th spinning fast.?

Driveshaft angle exaggerated?

I've been putting neodymium magnets on all my drainplugs.
Snap 'em right to the bolt heads.

Red gear oil?

They want 80wt hypoid 3 POINT 3 ounces so change it, pleeeease.

and yes, brakes can get stupid over the years.

What doug said about the u joints makes sense
and flyingw has been into a few of those so he knows

[dougspcs]

spooky.

trike off the ground and only in 5th spinning fast.?

Driveshaft angle exaggerated?


Yeah I'd agree with 'tri again'..not a great plan!

Don't do that!!

[toddsf150]

I normally dont do that, I promise!! I was only doing that to figure out if my rims were bent. Now that you mention it, the driveshaft was at a steep angle. That may have something to do with it. I love the machine to death. The motor on it is very strong. Im just trying to look after it! I will drain the fluid tommorow and see what I get. How often should it be changed?

[dougspcs]

I normally dont do that, I promise!! I was only doing that to figure out if my rims were bent. Now that you mention it, the driveshaft was at a steep angle. That may have something to do with it. I love the machine to death. The motor on it is very strong. Im just trying to look after it! I will drain the fluid tommorow and see what I get. How often should it be changed?

I change mine every fall before storage..plus after every ride that involves rear end submersion.

Also make sure the little black rubber hose from the top of the differential to the air box is intact..it's the breather and if it's missing or broken will allow water to get in the differential.

[toddsf150]

Good advice. Ill check that too. I keep her out of water/mud. I did blow the build up out of the brakes front and rear recently. Lots and lots of brake dust. I will follow up once I change the fluid. If theres any debris in it, ill let you know.