Seriously bummed with this drivetrain setup right now :(

[TotalyHucked]

So did it make it worse or no change?

 

[SquareRoot]

No change.

 

[SquareRoot]

I need to figure driveshaft speed at 60 mph. Going back to driveshaft shop and gonna check balance and phasing. I'd like to watch it be balanced at the speed it's vibrating.

 

[TotalyHucked]

Hmm. Just went back and re-looked at your pictures and saw the double washers/weights on the shaft. Maybe you'll get lucky and a rebalance will fix it, that's a fair amount of weight in that one spot

 

[QBuff02]

I'm curious.. I've crawled around a fair amount of these trucks and have never seen a cardan joint on a rear driveshaft.. i've seen two piece driveshafts and some odditites but never a setup like that. All the time on front driveshafts but never the rear. Was it year specific or application specific? I'd be curious about the phasing of the driveshaft and balance as well. Is there any noticeable play in that joint if you try to move it up and down or side to side? Having an extra joint just seems like a place to cause problems. I'd think i'd have that removed and a proper length driveshaft made. Or explain it to me, because i'd like to understand the reason or the need. i'm genuinely curious!

 

[nvrenuf]

I'm curious.. I've crawled around a fair amount of these trucks and have never seen a cardan joint on a rear driveshaft.. i've seen two piece driveshafts and some odditites but never a setup like that. All the time on front driveshafts but never the rear. Was it year specific or application specific? I'd be curious about the phasing of the driveshaft and balance as well. Is there any noticeable play in that joint if you try to move it up and down or side to side? Having an extra joint just seems like a place to cause problems. I'd think i'd have that removed and a proper length driveshaft made. Or explain it to me, because i'd like to understand the reason or the need. i'm genuinely curious!

The double cardan on the rear shaft is a modification, not factory stuff. It's a common upgrade for trucks to combat driveline vibration created by the new operating angles after being lifted, they're mostly used on Blazers because of the really short driveshaft.

 

[SquareRoot]

I'm curious.. I've crawled around a fair amount of these trucks and have never seen a cardan joint on a rear driveshaft.. i've seen two piece driveshafts and some odditites but never a setup like that. All the time on front driveshafts but never the rear. Was it year specific or application specific? I'd be curious about the phasing of the driveshaft and balance as well. Is there any noticeable play in that joint if you try to move it up and down or side to side? Having an extra joint just seems like a place to cause problems. I'd think i'd have that removed and a proper length driveshaft made. Or explain it to me, because i'd like to understand the reason or the need. i'm genuinely curious!

It's common on lifted trucks. I believe dodge used them in the past as well on non-lifted trucks. I could be wrong, that's what I was told. The benefit is that it runs smoother because the two joints cancel each other out. This also adds greatly to the life of the joints. In my case it's probably overkill and not needed. Since I was starting from scratch it wasn't much more $$$ to use a carden. For instance, I paid $550 for the entire shaft. The other "perceived" benefit is it's length doesn't count towards the shaft length. Since my setup (NV4500/205) is relatively short for a long wheelbase truck that was also a "perceived" benefit. To your point, yes, I can feel a minute amount of play in the joint and that's what caused me to notice the excessive endplay in the output shaft. However, I now believe the play in the output is normal and acceptable for this t-case. But, I think combined with this driveline it's a bad combination. Most lifted trucks that NEED this probably don't spend time on the highway at 70mph. For mall crawlers and offoad, you would never notice it. In my case with 4:56 gears that driveline is seriously humming on the freeway. I'm sure any imbalance will make itself known. Or--I'm completely full of S**T and grasping for straws.

 

[QBuff02]

The double cardan on the rear shaft is a modification, not factory stuff. It's a common upgrade for trucks to combat driveline vibration created by the new operating angles after being lifted, they're mostly used on Blazers because of the really short driveshaft.

now that you mention it, duh! on my part. Lol Many lifted blazers and broncos I have seen that setup, but stands to reason why i'd never seen them on most full size trucks. I do know as a kid growing up there were some seriously bad ass trucks around my parts when 42" swampers and then the 39.5 Bogger on monster wheels was all the rage. But i'm talking I was a teenager through that era. And to that point I do know a few guys that always were pissed about breaking u-joints and throwing driveshafts with that or similar setups. Maybe that was why? I remember a guy from our town had a '79 Bronco with 44" (I believe or maybe they were 42s as well) Gumbo monster mudders on it and it was so tall and so short coupled that he'd break a driveshaft quite regularly down at the sand bar and I know that one had Cardan joints in it for sure because I carried pieces to him more than once as a kid. My young mind always said it was the power that did it! Lol

 

[SquareRoot]

Hmmm...I wonder if I just solved the mystery?
Exceeding the Critical Speed DESPITE being balanced will cause vibration according to Spicer Website. My vibration starts at 60 mph and I can feel it thru the clutch pedal at that speed. Starting to make sense.

Funny, I had a thread about a one piece vs two piece given the length I was dealing with and somebody Flamed me. I guess if the shaft is 5+ inches in diameter it would work? @Keith Seymore

 

[QBuff02]

It's common on lifted trucks. I believe dodge used them in the past as well on non-lifted trucks. I could be wrong, that's what I was told. The benefit is that it runs smoother because the two joints cancel each other out. This also adds greatly to the life of the joints. In my case it's probably overkill and not needed. Since I was starting from scratch it wasn't much more $$$ to use a carden. For instance, I paid $550 for the entire shaft. The other "perceived" benefit is it's length doesn't count towards the shaft length. Since my setup (NV4500/205) is relatively short for a long wheelbase truck that was also a "perceived" benefit. To your point, yes, I can feel a minute amount of play in the joint and that's what caused me to notice the excessive endplay in the output shaft. However, I now believe the play in the output is normal and acceptable for this t-case. But, I think combined with this driveline it's a bad combination. Most lifted trucks that NEED this probably don't spend time on the highway at 70mph. For mall crawlers and offoad, you would never notice it. In my case with 4:56 gears that driveline is seriously humming on the freeway. I'm sure any imbalance will make itself known. Or--I'm completely full of S**T and grasping for straws.

My thinking though would still be that in a normal or somewhat normal application, it almost seems "excessive" to install one and it would just give another place to cause issue. By looking at the pictures your driveline angles appear relatively "normal" ~actually somewhat flat. You've got an interesting combo for sure and coupled with the low gears i'd tend to agree that any little thing could show its ugly head. Makes me interested to know what the driveshaft shop will have to say.

 

[nvrenuf]

I get the critical speed thing but 4.56's and a 31"ish tire was a factory combo, I doubt GM would have built this combination if it was problematic.

 

[TotalyHucked]

I get the critical speed thing but 4.56's and a 31"ish tire was a factory combo, I doubt GM would have built this combination if it was problematic.

But what size was the driveshaft in those rigs so equipped? Srs question cuz I have not worked on one.

I can tell you when I told the driveshaft shop my combo, they built me a big ole MF'r. Pretty sure mine is a 5" shaft cuz I can't go as low as my other buddies with 3" shaft thanks to the crossmember behind the cab

 

[SquareRoot]

I get the critical speed thing but 4.56's and a 31"ish tire was a factory combo, I doubt GM would have built this combination if it was problematic.

I'm not sure they did. With an auto trans, the driveshaft would be 11 inches shorter. With a 465 manual trans, I'm guessing they used the two-piece shaft, at least in the longbed? How many people would drive 60+ with that combo in 4th gear with the engine screaming at 3200 rpm? Remember, I have a 4500 w/OD.

 

[nvrenuf]

I know GM used a 4" dia shaft in some 2 door 3/4 ton applications because I've seen a couple but I'm not sure what the complete usage was.

As far as speed, while I agree that the average user of a 3/4 or 1 ton truck with 4.56's probably wasn't traveling with it GM certainly had a to build the trucks to be able to run the national speed limit.

4spd + 4.56 trucks were available, both 6 cyl (292) and V8. I'll admit all of the examples that come to mind were 4 doors but I really doubt GM wouldn't have offered the combo in a 2 door, I'd have to see proof (brochure / GM Heritage, etc) this combo wasn't available to believe that.

 

[TotalyHucked]

Don't forget, the national speed limit for the majority of the squarebody years was 55mph.

All of the 4.56 + 4-speed combos I've seen have either been regular cab tow trucks, CC ramp trucks, box trucks or camper special CC dooleys.