Universal(s)

[Toploader]

How can one tell if the U-joint(s) have issues?

I have to determine if I have a U-Joint problem, or a rear brake drum problem.

Many times I hear a dull thud sound when in reverse, or drive.

Guess I have to pull the drums?

[johnunit]

they're not exactly a major fail point, but they do wear out. Get the car up in the air, and basically hold the side of the u-joint going to the axle and rotate the driveshaft back and forth, feeling for play. Repeat on the transmission u-joint. There will be play after several degrees of rotation from inside the axle and transmission, but the u-joint play will be different from that.

Of course, a lot of people (myself included) just spend the 20 bucks on name-brand u-joints as part of the general rebuilding of an old/high mileage car.

[gadget73]

pull the driveshaft and roll both yokes through their full range of motion. If the joints don't move smoothly in all directions, they're done. A clunk noise you may be able to find by rocking the driveshaft. If some of the men are dead, it will flop around like that. When they're dry, it just won't rotate smoothly.

[85crownHPP]

Yep, if they are real bad, you will feel slop when you push/pull/yank/wiggle/turn the shaft by hand. You may have to try many different directions of force to find the play. If you are hearing the "CLUNK", it should be bad enough to show this way.
Also, if they are that bad, usually the grease/grease seal is long gone, and one or more of them will look like they have rust oozing out of them, while the good ones might have a nice film of dust-covered grease dampness around them (or be clean). Bad bad ones will even have the 'cups/caps' start you break and chip away on the inner lip from the bare nub smashing into them.

When mine went bad in the 85, I heard/felt a grindy/growly sound when I let off the gas on the highway. I just looked up a pic, and they weren't even that bad... I've replaced much worse!

[Toploader]

Another thing I am thinking is a motor mount??

[gadget73]

the way the motor mounts work in these, they can't really let go. They sag, but they are designed in such a way that they won't let the motor rock all that much. There is a big metal plate that goes over the top of the mount, so the inner piece is basically sandwiched between the top and bottom plates. It can rock about an inch, but thats it. Its not like one of those crappy Cheesler mounts that will damn near let the engine come through the hood. The trans mount being gummy or the trans crossmember being rotted out will do it though.

[85crownHPP]

It's pretty easy to check them - you have to try to yourself or have a friend watch the engine while you power brake it with little blips of the throttle in drive and reverse. The worse they are, the more the engine will twist and buck when you do it. You typically should only hear a clunk when normally going into gear if they are REAL bad.
In some cars, if they are bad enough, it will literally look like the engine tries to jump out from under the hood, and you can sometimes feel the engine getting tossed around anytime you accelerate with any gusto...!

[Toploader]

I will try to get lift time at my buds shop soon!
Tanks to all for the ideas

[sly]

the passenger side motor mount on my 88 is pretty much gone... the fan still doesn't tough the fan shroud. Trans mount is ok... so nothing actually contacts for clunkage in my clunker. Last time I replaced the trans mount though, the tail of the trans was banging the crossmember every shift and sometimes vibrating on it when stopped.