vibration question

[hinkv10]

My truck has been laid up for almost a month and I've been dying to driver her. I pulled the inner fenders and was going to replace them when I found a small amount of rust forming so it turned into a project and I used por on everthing. Long story short I go to drive it and now I'm noticing more of a vibration thru the whole truck at highway speeds. I rarely drive it on the highway as its so much fun driving it on the back roads.

Its an 87 but its a carbed engine from 84, np205 and a th350 so nothing is original there. The rear driveshaft clunks when you put it into gear and it always has. The rear driveshaft is hard as a rock, no play whatsoever and I can't move it a millimeter.

The front driveshaft can be turned freely because it is in rwd and moved side to side making a clunking noise pretty effortlessly. I've always had more of a vibration with the hubs locked in 2wd. Now my questions.... I'll go take a pic in a minute of the rear driveshaft showing the rear ujoint.

1. The rear ujoint looks to be too small for the part that mates to the rear diff. It doesn't go all the way thru the yoke? Should I replace the ujoints for that reason. What else could cause the clunking when putting into D or R?

2. I'm assuming I need to rebuild the front driveshaft. Right? No clunking noises or side to side motion is normal? Money is tight and now I have a second money pit, 72 Dart that needs a rear axle bearing and then a whole rear upgrade so it looks like I'll be in the poor house for awhile. Thanks in advance

 

[hinkv10]

Pic of rear driveshaft

 

[hinkv10]

Take 2

 

[bucket]

Yeah that doesn't look right. Need to take that apart and investigate. See if the cups have the clips to properly center the u-joint in the yoke.

 

[hinkv10]

its not wide enough. The other side is in almost as much, little less but it looks wrong to me. I've only been driving it around like this for a year and a half. This is the same truck that came with bolts in the motor mounts but no nuts so the guy I bought it from was a hack.

 

[MadOgre]

its not wide enough. The other side is in almost as much, little less but it looks wrong to me. I've only been driving it around like this for a year and a half. This is the same truck that came with bolts in the motor mounts but no nuts so the guy I bought it from was a hack.

That actually looks pretty normal as to where the cups are sitting in the yoke. Like Andy said though make sure there are clips on the inside of the cups centering it properly. If there are no clips make sure the little stops on the yoke are there and that the cups are sitting up against them with no play, they are little stops that keep the cups from moving outward in the yoke. Sometimes they get worn off. If that is the case then you must use clips on the U Joint cup itself on the inside to do the same thing-prevent the cup from walking out in the yoke.

But the angle of the driveshaft to the yoke/differential looks way off, maybe its just the way you took the picture ?

 

[MadOgre]

Yep so I just ate some cake LOL Andy is right that doesn't look right. If the other side is about the same then you have the wrong U joint. The out side of your cup should sit in from the out side of the yoke barely an 1/8 inch more like 3/32

I went and looked at mine

 

[bucket]

Yep so I just ate some cake LOL Andy is right that doesn't look right. If the other side is about the same then you have the wrong U joint. The out side of your cup should sit in from the out side of the yoke barely an 1/8 inch more like 3/32

I went and looked at mine

Is it just me or does it also look like the straps don't hold the cups snug in the yoke?

 

[hinkv10]

Is it just me or does it also look like the straps don't hold the cups snug in the yoke?

I'm going to take it out tomorrow morning as well as the front driveshaft. I haven't received any responses on the front driveshaft but I have to assume that if you can take the driveshaft in your hand and "shake it" and it makes a clunking type noise then it has too much play. I already replaced the ujoints in the front axles so this is the only thing left.... I always had a vibration when driving at higher speeds with the hubs locked but in 2wd. Now it is doing it when the hubs are unlocked. The only thing i didn't check was the bearings but i will and don't expect there to be any play.

I'll bring the rear driveshaft to my machine shop and see what they think. The rear driveshaft has absolutely no play or movement by hand but makes a loud clunk when put into gear. I'll also measure that yolk and see what they think about that. Any chance it is the wrong one for the truck? too big?

 

[MadOgre]

No there is supposed to be a space in the middle of the strap. There all like that.

 

[MadOgre]

Cant see the yoke being the wrong one but u joints can share the same cup diameter while the cross measurements are different. If im not mistaken you can use inner clip u joints on any set up but the outer clips are application specific. ? It looks like maybe its sitting in further because it is the outer clip style. Im not sure. I don't see how it fits the driveshaft and not the yoke, if it is the wrong u joint.

Your front driveshaft sounds like a good candidate to be rebuilt. Is there any play at the transfercase ? Both front or back drive shafts ?

My bolts on the front drive shaft to transfer case flange came loose last winter and I put about 15-30 km on it like that and now im looking for a transfercase rebuild kit ! With bearings !

Could be the splined slip yoke needs replacing ?

 

[bucket]

A sloppy front slip shaft is common, just normal wear and tear. If it get's too bad, it can actually bind up and cause a lot of damage. It won't cause vibration in 2wd with the hubs unlocked, unless you have a hub that is stuck locked even if the knob is turned to 'unlock'.

No there is supposed to be a space in the middle of the strap. There all like that.

Right, but it looks like the cup might not be fully seated in the yoke.

 

[MadOgre]

Well I don't know. He says the other side is pretty much the same.

 

[Greybeard]

FWIW- Sometimes a clunk when changing gears is a sticky slip in the rear driveshaft. That slip joint needs actual lube, not dirt and water inside. To correctly lube the slip joint depends on the type of slip you have. If the zerk is close to the yoke then you have to reach a finger into and between the cross and the end of the driveshaft and cover the weep hole there while pumping grease into the slip until it comes out from under the wiper seal (dust cap) at the other end (I always removed the dust cap first, it simply unscrews). If the zerk is at the driveshaft end near the dust cap then pump grease in until it comes out of the weep hole in the yoke. If it comes out of the wiper seal first then it's best to remove the shaft and pull the slip apart and clean and re-lubricate. And get a new dust seal before putting it back together.

What happens when the slip doesn't slide easy is that it binds the rear suspension after coming to a stop or when it's put into gear. This isn't too common with a stick, more so with an automatic. However, any bind will cause some vibration since the rear axle has to fight to move the slip joint. This will cause a momentary u-joint out-of-phase alignment (similar to wheel hop) from one end to the other which can cause associated vibrations.

With that said, my guess is that it isn't this problem and it is what everyone else suspects it is. The loose front driveshaft slip may cause some vibration but to me it's doubtful that you would feel it. That shaft does not have the weight to create enough vibration to feel unless it's seriously ready to fail or the shocks are way past worn out. But this is just my opinion. YMMV.

 

[hinkv10]

I dropped off the front drive shaft on Friday to be rebuilt. I think I had too "small" of a ujoint in the rear of the rear driveshaft. I'll be installing both on Monday evening and then I'll report what I found. Thanks for the info