720 rear end vibrations.......not good

[Pacific coast Datsun]

vehicle- 85 720 K/C

suspension- rear, lowered w/ 3 inch blocks & middle leaf removed. Carrier bearing raised 1 3/4 inches

front, cranked torsions.

Issue- I noticed alot of vibrations coming home last night on the freeway coming from the rear end. At any speed over 45 i can feel the truck vibrate pretty bad, enough so it makes the mirrors & seats shake. & the faster i go the worse it gets. If i let off the gas @ freeway speeds the vibration IMMEDIATELY goes away.

I got under the truck today & inspected the rubber surrounding the center bearing, a little dry but intact

checked the driveshaft for any weights that may have fallen off, all there

checked the lugs on the rear tires, all tight

checked the weights on the rims, all there

checked the driveshaft for excessive side to side play, moves maybe 1/2 inch both ways which may or may not be normal

My educated guess is either the center bearing & or the rear U joints went bad.

Anybody ever have a similar problem & if so what was the fix?

I dont want to / cant afford to replace a part if it is'nt bad so please help a brother out :rolleyes:

[Jersey]

Mark, just out of curiosity, when you let off the gas does the rear of the truck sway at all?

[datzenmike]

Only way to tell is get under there and inspect. Leave in neutral, block the tires so it won't move and jack at least one wheel off the ground so you can rotate the drive shaft. If the rubber is rotted the drive shaft will wobble around by hand easily. If it's firmly in place try the U joints next. Position yourself at 90 degrees to the drive shaft and grip both sides of the U joint by hand. Try to push with one hand while pushing with the other then switch. Do this in four 90 degree positions on the shaft. There should be NO looseness felt in the side to side direction. Now try twisting the two sides of the U joint in opposite directions... again there should be NO noticeable looseness felt. Now check the other two U joints.

 

A drive shaft is a heavy mass that is precision balanced and spins at high speed usually more than 3 times as fast as your tires. ANY looseness in a U joint will allow the drive shaft to move off center and the balance is lost and it wobbles causing severe vibration.

 

 

Wheel weights may have fallen off.

A piece of brake drum may have fallen off.

A tire may be damaged

[Pacific coast Datsun]

Jersey- no side to side movement when i let off the gas. But, today ill check all the shackle bolts just incase.

D-mike- Ill check all that you mentioned & get back..TY.

[Pacific coast Datsun]

Ok..got the tires off the ground, truck in neutral & i spun the drive & i notice a little play in the rear U joints. So naturally they will have to be replaced.

Whats the best way to safely remove the old U joints?

[Roadracer Al]

I've always just used a rubber mallet to remove the bearing cups after removing the spring clips. The cups may not push all the way out, but enough that you can grab on them with pliers. You *must* mark the orientation of the assembly or it won't be in balance later.

 

Assembling the new parts is a little tricky - first off, you have to ensure that the needles don't fall out. They should be factory greased, but it's good to check this before getting under the truck. You should be able to push the cups partway into the dogbones, and finish them with a C-Clamp -- don't beat on new U-joints with a hammer! I usually get one side started, push it in slightly too far, install the clip, then push it back out until it's seated on the clip.

[Pacific coast Datsun]

I've always just used a rubber mallet to remove the bearing cups after removing the spring clips. The cups may not push all the way out, but enough that you can grab on them with pliers. You *must* mark the orientation of the assembly or it won't be in balance later.

 

Assembling the new parts is a little tricky - first off, you have to ensure that the needles don't fall out. They should be factory greased, but it's good to check this before getting under the truck. You should be able to push the cups partway into the dogbones, and finish them with a C-Clamp -- don't beat on new U-joints with a hammer! I usually get one side started, push it in slightly too far, install the clip, then push it back out until it's seated on the clip.

Thanks Al. What i noticed on these U jonts is theres no spring clips.

Do i simply use a mallet /mini sledge to work the old ones out? I shot alot of wd-40 on them incase thats the procedure.

[Jersey]

Jersey- no side to side movement when i let off the gas. But, today ill check all the shackle bolts just incase.

D-mike- Ill check all that you mentioned & get back..TY.

yeah, I was kind of thinking maybe shackle bolts...back in the 80's, my buddies '73 620 had similar symptoms and that's what we found to be wrong. In your case it does sound like u-joints...which are no fun installing. The other thing I was going to ask you, are you good on the gear oil in the diff?

[]2eDeYe]

http://community.ratsun.net/topic/2329-u-joint-replacement/

 

:D

[datzenmike]

Thanks Al. What i noticed on these U jonts is theres no spring clips.

Do i simply use a mallet /mini sledge to work the old ones out? I shot alot of wd-40 on them incase thats the procedure.

 

2eDeYe' date='12 May 2010 - 02:58 PM' timestamp='1273701492' post='302499']

http://community.rat...nt-replacement/

 

:D

 

 

There should be snap rings on those U joints.

[Pacific coast Datsun]

Steve TY for the link,& a HUGE ty to D-mike for the writeup & pix. my confusion was regarding the C clips. My U joints dont have them on the outside. Im hoping i can do this repair without having to remove the rear shaft. I have a big C clamp i can use to press the new joints in place.

[moparvwfreak]

its a whole hell of a lot easier to do with the drive line out.

[sinner720st]

i have the same truck as you... im telling you from experience, you are going to want to pull the rear shaft out. just take with i think a 12mm and 13mm, kind of think you need two 12mm open end wrenches, your u joints most likely have little C-clips on the inside of the caps closest to the trunion.

[]2eDeYe]

X a billions...your not gonna want to do that laying on the ground. :mellow:

[Pacific coast Datsun]

Ill follow the advice & yank the rear shaft out to do it. Started removing the 14mm bolts @ the axle & 2 are stuck... :blink: Grinder time !

[Pacific coast Datsun]

SERENITY NOW!!!!!!!!!!!!!!!!

i got the old, bad, worked,out of round U joint out with the assistance of my grinder & a cut off wheel.What was left of the needle bearings fell out as i cut it off. Bought new U joint, install on the driveshaft side piece of cake, i go to install teh C clips on the yoke side....................2 hours later i gave the FUCK up !!!!!!!! Yes im doing this w/ the shaft on the truck because the 4 12mm bolts by the center bearing were stripping / cant barely get a wrench on them & 2 of the 14mm bolts on the axle were stripped [had to cut them off].

So now i suppose ill have to remove the entire driveshaft & try & get a better angle on it or say fuck it & have a shop install the POS F-ing C clips so i can make it to work!!!!!!!

If i had the money/good credit id be driving a 2010 Frontier !!!!!!!!!!!

[Buzzbomb]

SERENITY NOW!!!!!!!!!!!!!!!!

i got the old, bad, worked,out of round U joint out with the assistance of my grinder & a cut off wheel.What was left of the needle bearings fell out as i cut it off. Bought new U joint, install on the driveshaft side piece of cake, i go to install teh C clips on the yoke side....................2 hours later i gave the FUCK up !!!!!!!! Yes im doing this w/ the shaft on the truck because the 4 12mm bolts by the center bearing were stripping / cant barely get a wrench on them & 2 of the 14mm bolts on the axle were stripped [had to cut them off].

So now i suppose ill have to remove the entire driveshaft & try & get a better angle on it or say fuck it & have a shop install the POS F-ing C clips so i can make it to work!!!!!!!

If i had the money/good credit id be driving a 2010 Frontier !!!!!!!!!!!

 

I had a vibration and a "clicking" sound coming from the rear of my 720 shortbed. I did the twist test, and my U-joints had way to much play. I know this is Ratsun and things are done as cheap as possible, BUT..I tried for an hour to loosen my U-joints (driveshaft out) so I could swap them out. I just couldn't get them to budge. Long story short, instead of beating my head against the wall, I spent 5 minutes on the phone and found a shop that would remove and install the U-joints for $40- for both sides. I paid them, vibration and clicking gone, best $40 spend in a long time. They installed everything right as I marked the drive shaft, and ALL the clips. I had a clip missing on one end, and I think it was causing a vibration around 50 MPH.

[irsa76]

vehicle- 85 720 K/C

suspension- rear, lowered w/ 3 inch blocks & middle leaf removed. Carrier bearing raised 1 3/4 inches

front, cranked torsions.

 

Wait, you've got blocks and pulled a leaf from the pack? That would mean you've only got 2 leafs left right? I'd have a look at the rear suspension for possible vibrations. I know a few people who've had issues with loose blocks.

[ronnny]

I also would check for loose bolts with the blocks in the rear. I do more 4x4 stuff on chevies but that is a big common problem in lifted trucks. If you do a google search you will find a detail picture write up of changing ujoints. a little search and i found a write up on waterpump change on a 4.0 jeep. I thought both my 81 kc and 84 rc niether had a carrier bearing. With a vice or a press it is a very easy job to do. With a few beers and the truck in my yard would do it for just the fun. But i am in georgia. Good luck.

[Pacific coast Datsun]

Thanx guys. The shackle bolts are all tight. My issue was a bad U joint. Ill get a pic of the carnage in a few days. The actual install of the new part was easy. I sandwiched the yoke between 2 16mm sockets in the vise, tightened slowly till they pressed in. Was able to do the same for the other 2 cups from under the truck. My frustration is the remaining 2 C clips.

[Pacific coast Datsun]

Ok finally success! I ended up pressing the 2 cups in a but farther in & the C clips slid right in. Test driven & no vibrations, i should be good for another 130.000 miles :rolleyes: Pics of the old U joint soon!

[Pacific coast Datsun]

Here you see the carnage....i had to cut off 2 of the cups then drive out the remains with a socket extension & mini sledge..........

are'nt these supposed to be round ?? :unsure:

Im glad this repair is over.