Hey guys,

My truck has had the same vibration issues as long as I've owned it (about 7 years now) but now that I've got a fairly stout engine under the hood and drag race it every once in a while, I think fixing that vibration needs to be my priority.

It seems to start around 40 mph and lessens significantly around 65 or so, but even then I can't really even see anything through the side mirrors due to the vibration. If I'm moving at a constant speed and take my foot off the accelerator, it goes away, but if I put it in neutral and slowly rev it from idle to 4,000+ rpm, it won't come back, so I'm almost positive it's not anywhere in the engine.

I don't know if this is normal or not, but there is about 3.5 inches between the tailshaft of the transmission (C6) and the flange where the u-joint is on the yoke (Is that about normal, or could the engine/trans somehow be sitting further forward than they should be after the engine swap? It's got aftermarket engine mounts for the swap, but still the factory trans mount.)

Also, I can crawl under the truck and wobble the driveshaft/yoke a noticeable amount (tough to measure, but maybe 1/8" total side to side movement at the u-joint?) I'm fairly certain that is not normal... Would the solution just be to find another yoke at a junkyard, or is there something else wrong that caused the yoke to wear out (driveshaft out of balance maybe?)

Thanks for the help guys!

 

This sizable amount of play is not normal and you have to determine where and why the play is there.
Is it the u-joint that is bad or is it the splined section of yoke?
If it is at the splines, I am confident that the movement is also up and down.
You will have to remove the slip yoke, and take a close look to determine where the problem is at.
If the slip yoke is worn, it has to be replaced, and a salvage yard piece might work, but the length of exposed slip yoke a concern.
Do you have a pic of this?

 

Well, when I move it by hand, I can see the yoke itself moving in the tailshaft, so I'd assume that's the issue. It just started pouring outside or I'd run out and take a pic right now. The next chance I get, I'll get a picture and take a close look at the tranny mount to see if it would allow it to slide forward. If not though, what else would cause that? Could the axle have moved backwards somehow?

 

The bushing in the tail of the tranny could have a lil slop, which may help with the shakes

 

If the trans mount goes south, the trans cant really move except for side to side, or up and down. Remember that the trans is still bolted to the engine, and the engine owuld have to move forward as well.
Perhaps the entire thing is too far forward, but that it not the issue, here. The slop has to be addressed.
Sure this other issue will present a future problem, but the wobble or slop in the slip yoke is a real problem.

 

Yeah, I understand what you're saying about the real issue being the slop. I'm just wondering if maybe when I installed the motor mounts for the engine swap, somehow they were too far forward, which would then obviously cause both the engine and the tranny to be too far forward. If that were the case, do you think that could have contributed to the yoke and/or the transmission bushing to wearing out?

And karjunkie, would I have to pull off the tailhousing of the transmission to replace that bushing?

 

Here's a pic of the slip yoke:


It's kind of tough to tell, but that's right at 3.5 inches from the flange of the yoke to the tailshaft. The rust towards the tranny side makes me think it used to be in there a bit further than it is now, no?

Edit: I tried to get a video clip showing the slop, but it's dark and wet outside and it didn't come out well

 

Well sir, you have a real problem there, and I am truly surprised that this slip yoke has not fallen out of the trans yet.

You can see (rusty area) where the slip yoke used to be inside of the tailshaft, and the is the major contributing factor is this. You can even see that the oil seal is falling out.

This being said, the engine mount has to be addressed, and you have to see whether or not you have the engine too far forward. Perhaps the engine mount is backwards, or some other issue here. With that amount of distance you mmight have had to modify the x-member to even get the mount to bolt up, but who knows.
Yes sir this is a problem and you have to fix this, and hope that the output shaft is not hammered.
The output shaft only comes out from the pump end, so lets hope the spline are still in decent shape.

 

Well, thanks for the help. I'll take a close look at the engine mounts when I get home from work today.

I guess I should consider myself lucky it's all in one piece after a few 100 mph runs at the drag strip? Haha!

 

Staybroken, yes, the tailhousing does have to come apart, good luck with everything!

 

Well, after looking at the engine and trans mounts, I can't see any way to move the engine and trans back at all without modifying both of the crossmembers... I briefly looked at the rear axle, and I can't see any evidence it's not where it was from the factory.

I'm wondering then if maybe it's had the incorrect length driveshaft the whole time?

 

If your engine and transmission are bolted up and every thing fits like it should I would just get a longer drive shaft. It would be easier than trying to shift every thing back. Has the transmission been replaced with one that might have a shorter tail?
-John

 

I'd been thinking the same thing... Just measure my driveshaft and get one made (or find one) that's a couple inches longer. Is there a guideline as to how much room for suspension travel there should be? Is an inch and a half enough?

I did actually replace the transmission a while back. It was several years ago at this point, and the old one is long gone, but I'm almost positive they were the same length.

Thanks for the help!

 

Take your old one in and they can use that one to make U a new one.. Much better than trying to find a used one.. Also make sure U use NEW U-Joints... May also want to change out that rear tanny seal.

WOW, are U lucky...

 

That makes sense. What kind of place would I go to to have that done though? A regular machine shop? After searching around on the internet, all I've been able to find are places that will make me one from scratch based on dimensions I would provide to them. If there are local shops that would do it, I sure don't know how to find them.