U-joint Question

[Old Geezer Richard]

I have a spare u-joint with low mileage under 30,000 I came across and as I was checking the play in the joint I noticed a flat spot while flexing the joint back to the straight position .... Is this flat spot a normal thing with a used u-joint ?? because I was thinking about replacing my existing u-joint on my bike with this used one , reason being my Old Fat Lady is almost at 100,000 miles and I woild not like have any surprises while on the road  .....  Another question ,  when I do check out  the u-joint on my bike what will I be looking for as far as wear ??  How is the u-joint suppose to act when I check the play in the U-joint ( loose or stiff ) ,  and will a u-joint make any kind of noise to let me know ahead of time that its rewady to crap out ?? ...  Thanks the Geezer

[Chrisj CMA]

You cannot tell much about a U-joint just handling it by hand.  What I do is clamp one end down (like in a vise) and grip the other end with a vise-grip plier to use as a handle.  Then try to twist it back and forth in the same action it will undergo force in use.  If there is no play then its probably good for a few more miles.  If you feel play while trying twist it then its not going to last a long time

[gordonv]

Had a fellow rider's joint go from making noise for the first time, to driving it 20 miles to a shop for inspection, and diagnosed as a failure. That was during the drought on u-joints. I think he had 30-40K miles on the bike.

I see nothing wrong with inspection when you have the rear off, but I don't think it is a frequent failure point at any specific mileage and yours could go a lot longer before failure if it ever does.

Doesn't mean I don't have a spare, and will consider taking it with my to Inzane, to avoid an extended stay somewhere while on the road.

[Old Geezer Richard]

 Hey Chrisj CMA , when you say twist with the vice grips , you literaly mean twist from right to left to see if there is any play , right ?? I'll try that tomorrow .... But what about that flat spot I feel when I flex the joint up or down or side to side , is that normal ?? Thanks the Geezer 

[Skinhead]

Hey Chrisj CMA , when you say twist with the vice grips , you literaly mean twist from right to left to see if there is any play , right ?? I'll try that tomorrow .... But what about that flat spot I feel when I flex the joint up or down or side to side , is that normal ?? Thanks the Geezer 

Twist as in try to rotate it, Clockwise counter-clockwise.

[Louis Durocher]

You should not have a flat spot. The joint is supposed to be a little stiff with no spot

[Chrisj CMA]

Hey Chrisj CMA , when you say twist with the vice grips , you literaly mean twist from right to left to see if there is any play , right ?? I'll try that tomorrow .... But what about that flat spot I feel when I flex the joint up or down or side to side , is that normal ?? Thanks the Geezer 

Yes, rotational play is the real bad sign that there is wear.  Im not really sure what you mean about a flat spot, but if the joint is good and tight, no play when twisted Id run it

[da prez]

  The U-joint has four sets of roller bearings(think rolling pin as in baking) that swivel on a shaft. A U-joint has to have movement up and down or side to side or it is useless. If it stays in a straight line , the bearing will hammer a groove in the cross.(shaft). With the joint out , flex it the full range of motion in both dirrections to feel for any lumps or stiff spots. The joint should move smooth. Causing a twist with it in a vise is also recomended , but may not always show a bad spot. If in doubt , change it. The ammount of flex in a U-joint in degrees determines the size of the roller (needle) bearings. I have changed hundreds over the years as a heavy truck mechanic , but the principal is the same. If you have no flex or movement , you do not need a U-joint.

                                da prez

[Ricky-D]

A flat spot would indicate indexed bearings.  The U-joint is toast.

***

[John Lane]

My other hobby (curse!) is rockcrawling jeeps. If you shock the drivetrain u-joints and such will fail. I try not to have spinning tires meet lots of traction, some folks like to do burn-offs and hole shots by revving her up and dropping the clutch. Parts are not long for this world if you routinely do that.

[RainMaker]

There should not be a flat spot in any rotational aspect of a u-joint.  If it's all you have for an emergency, it may work but I'd get a new one before making a long trip.

I've been packing a new spare U-Joint and alternator in my saddlebag for years.  It's the surest way not to have a failure of either on a trip.  The alternator in the bag today is the 3rd one since 2 have been used by other riders on long trips and it's the second u-joint for the same reason.  I also carry an extra kickstand spring and screw, throttle and clutch cables and mushroom patches with rubber cement.  All these parts in the bag have kept me from having any issues with the bike on long trips.  It's just karma, I think.

[Cracker Jack]

There should not be a flat spot in any rotational aspect of a u-joint.  If it's all you have for an emergency, it may work but I'd get a new one before making a long trip.

I've been packing a new spare U-Joint and alternator in my saddlebag for years.  It's the surest way not to have a failure of either on a trip.  The alternator in the bag today is the 3rd one since 2 have been used by other riders on long trips and it's the second u-joint for the same reason.  I also carry an extra kickstand spring and screw, throttle and clutch cables and mushroom patches with rubber cement.  All these parts in the bag have kept me from having any issues with the bike on long trips.  It's just karma, I think.

Where do you get your clutch cables? I haven't been able to find one.

[RainMaker]

There should not be a flat spot in any rotational aspect of a u-joint.  If it's all you have for an emergency, it may work but I'd get a new one before making a long trip.

I've been packing a new spare U-Joint and alternator in my saddlebag for years.  It's the surest way not to have a failure of either on a trip.  The alternator in the bag today is the 3rd one since 2 have been used by other riders on long trips and it's the second u-joint for the same reason.  I also carry an extra kickstand spring and screw, throttle and clutch cables and mushroom patches with rubber cement.  All these parts in the bag have kept me from having any issues with the bike on long trips.  It's just karma, I think.

Where do you get your clutch cables? I haven't been able to find one.

Duh - sorry.  Both throttle cables, upper and lower.  That will teach me to post at this time of night.