would anybody know how to change the driveshaft u joints? there is a u joint in the rear driveshaft towards the front that is making noises. it is right before the transfer case. i tested it earlier and there is play in it. also if i am going in revers then i put it in drive there is a loud ping noise. to add to that when i reach about 50 mph the truck vibrates. any help is appreciated.thanks

hello? can anyone read what i wrote? does anyone know how to change a u joint?

I don't know what year you're dealing with, but try this:

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/18/c2/f6/0900823d8018c2f6.jsp

Also, searching the Blazer forum will provide a wealth of info. You'll need a propane torch if they're originals.

I know this is an older thread but I'll toss in my 0.02cents from just changing my ujoints today, all exact numbers are from my 1998 GMC Jimmy:

-Jack up the passenger rear tire to make room under the truck. It's easiest to access the rear driveshaft from the passenger side. Make sure to chock the front wheels to ensure it won't roll away.

-Put the tranny in neutral so you can turn the driveshaft. Turn it by hand so the first 2 bolts holding the driveshaft to the rear differential are on the bottom. Either jam it somehow or put the truck back into park and remove the two bolts. They will be 7\16ths in size. Put the tranny back into neutral and spin the DS again so the other 2 bolts are now visible and unbolt those. Don't loose the bolts and brackets!

-The driveshaft should be connected to the transfer case via a slip yoke. Depending on how seized in the ujoint is to the rear differential it should just push forward towards the front of the truck and pop out. Mine didn't and I had to get a crowbar in there to break it loose. Make sure you mark the top (or bottom) of the driveshaft and install it the same way it was removed to preserve it's balance. I used spraypaint.

-The transfer case end will now just slide out (pull it straight to avoid damaging the seal) of the tail cone. Some ATF will leak out. Catch it with a rag or use a bag or something to plug the hole to minimize fluid loss. ALWAYS re-add fluid that has dripped out if it is significant. You don't want to toast the xfer case.

-Now you have the driveshaft out of the truck. Wrap a clean rag around the end that came out of the transfer case and tape it with some electrical tape or something to ensure it stays on, you don't want to damage it.

-IF the ujoints have been replaced since it was originally assembled there will be a copper or similar locking ring inside holding the joint cap in place (the replacements you have bought will also have these if you need a visible example). Pop that ring out with a screw driver and proceed to the next step.

--->IF the ujoint are ORIGINAL from the factory they will be sealed in with a nylon locking ring that was poured in and CANNOT be removed. Get a propane or MAP gas torch. Heat each cap with the torch and if you heat it hot enough you'll see the nylon squeeze out a hole on either side of the yoke like toothpaste. There's a lot in there so keep heating it until no more comes out. Repeat this for EVERY ujoint cap on BOTH ends of the driveshaft.

-Now for the real work. Pounding the ujoints out. Take a socket that is smaller (just a bit smaller, not tiny) than the cap of the ujoint. Place it over the cap and support the opposite yoke on something SOLID, concrete edges are best. Make sure the bottom is NOT on the ground so the opposite cap will pop out when you POUND on the top. This takes some real gusto. HAMMER the socket into the cap until it pushed the cap on the bottom out. Once the bottom one pops out you can flip the driveshaft over and push the one you were just hitting back into it's spot and out the bottom. So now you should have 2 caps popped out and the "cross" is free. Remove the cross and toss it, unless it's the transfer case end, then bang out the other 2 caps completely freeing both yokes. Be very careful to support the driveshaft as you can damage it if you let the "tube" of the shaft take the brunt of the pounding.

-Once you have all the ujoints out it's time to install the new ones. Make sure if your new ujoints are "greasable" (they have a zerk fitting) that you remove all 4 caps and pump grease into the joint until the clear packing grease comes out and is replaced by nice green bearing grease. Place the cross into the yoke and put a ujoint cap on the top and bottom. Make certain the cross remains centered and slowly hammer the top cap in with the bottom cap on a hard surface (cement floor). Keep moving the joint while you hammer this in so it stays centered. Make sure both caps ended up flush on either side and install the locking clips on the grooves located "inside" of the yoke. My locking clips were too thick and I had to file them down with a hand file.

-One end of the driveshaft (the transfer case end) has all four trunions on the ujoints taken up, the other end (differential side) only has 2 taken up. The other two get held in by the bolts and brackets we took off earlier. MAKE SURE THOSE TWO FREE CAPS HAVE THEIR LOCKING CLIPS INSTALLED AS WELL. Making sure the driveshaft is oriented right (bottom marking is on the bottom) carefully slide the transfer case end back into the transfer case, make sure to remove anything you used to plug the end, if you did. Then make sure the two "free" caps on the rear ujoint are pushed all the way into the joint and push the driveshaft into the rear differential yoke. It should line up with the same amount of space on the top and bottom cap from the edge of the yoke. Spin it around and make sure it looks even. Then put the bracket back over one cap and start the bolts in. Tighten them up until the bracket contacts the ujoint cap but don't torque them yet. Rotate the shaft and tighten them so they touch as well. Does it look even? If not adjust it, if so then begin tightening them down. Tighten each side a few turns at a time so the brackets go down evenly.

If all goes well when you have them tightened down good the shaft will spin easily and won't bind up or grind within the joints themselves. Don't forget to grease them (if they are greasable) next time you do an oil change, grease it was makes them last. hth

Nice write up. I just want to point out that using a torch to remove the lock ring can distort the drive shaft and cause a vibration and/or premature wear. The same is true for using a hammer to beat out the u-joints. This can be prevented and the job made easier by using a U-joint press. If you don't have one, most auto part stores have them in their loan a tool programs (sometimes listed as a ball joint press).

Nice write up. I just want to point out that using a torch to remove the lock ring can distort the drive shaft and cause a vibration and/or premature wear. The same is true for using a hammer to beat out the u-joints. This can be prevented and the job made easier by using a U-joint press. If you don't have one, most auto part stores have them in their loan a tool programs (sometimes listed as a ball joint press).

Good point, that's why I went with propane to melt the nylon, I've seen shops use acetelyne and that can remove the temper of the metal and cause warpage. If the metal is heated and allowed to cool slowly it should be fine, the nylon is easily removeable without cherry'ing up the yoke and most of the heat is applied to the (soon to be tossed) cap. The presses are nice to have, personally I've had problems with them, broke a few of them and just overall found that hammering them out tends to break the "rust weld" that usually forms inside. Definitely give one a shot if you have access to one though :)