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Rust-O-Matic 09-05-2017 12:33 AM

Correct clock/phasing/orientation of yokes on '66 C20 2 piece driveshaft
Does anyone have a picture of a correctly assembled 2 piece driveshaft for a '66 C20? Or any input on the somewhat long story below? It has a th400 and HO52, just fyi.

I'm chasing a vibration, and the brand new set of Cokers i just put on didn't fix it... or the shop didnt balance them correctly. So, I decided to replace all the u joints and center bearing on my driveshaft to rule it out. When I put it back together I realized I hadn't marked the position of the yoke that bolts in front of the center bearing, and now the two shaft halves (which I did mark) didn't line up like they used to. Which is weird, because it felt like the yoke in question would only fit on the splines one way.

Afterward, I took the whole assembly to a shop in KC to be balanced, and the guy told me I had the center yoke clocked wrong, because it's supposed to be aligned with the one at the other end. Ok, makes sense. So he doubles the damn price and says he will rotate it for me. He also told me in the same breath that the splines are such that it can only be installed one way. (If that's the case, how could I have got it on wrong!?)

So I pick it up the next day and the center yoke is still crooked, but the guy insists he took it off and turned it. He says "apparently this one was designed to be a spline off". Original weights have not been touched, and I have no real proof he did anything. He said the way I had the yoke, it vibrated, but once he allegedly turned it, he ran it up to 3k rpm and it was balanced fine. No idea, this is just what he told me.

The point is, I'm trying to verify if anything he said is true, because the rear end still vibrates a little (jacked up with wheels removed) and I can't make any sense of my manual ('63 service manual). Specifications table on 15-5 lists correct phasing, but I can't figure out which applies to me. I'll attach a pic. Looks like some yokes are supposed to be aligned, some are supposed to be "x" number of splines out of plane.

My hope is that I can verify 100% the driveshaft is assembled correctly, and the yahoo at the shop was telling the truth, so that I can take it back to the tire shop and tell them definitively which tires to check/redo.

I know there's a rear tire issue because I jacked each one up this evening and run it to about 25 mph and they shake (one side worse than the other). In the process I pulled each wheel off and ran it with just the bare hubs/drums, which is when I noticed it still has a vibration, although not nearly as strong.

Sorry for the long winded post. Any help and or pics would be much appreciated.

Rust-O-Matic 09-05-2017 12:36 AM

Re: Correct clock/phasing/orientation of yokes on '66 C20 2 piece driveshaft
2 Attachment(s)
Here's what the manual says...

Rust-O-Matic 09-06-2017 11:52 AM

Re: Correct clock/phasing/orientation of yokes on '66 C20 2 piece driveshaft
Nobody has ever worked on their 2 piece driveshaft? Or has a C20 they could snap a pic of the shaft on?

Maybe my post was too long... All I really need to see is the yoke at each end of the front half, so I can tell if they are aligned or turned a little.


jayoldschool 09-06-2017 01:06 PM

Re: Correct clock/phasing/orientation of yokes on '66 C20 2 piece driveshaft
Some shots when I rebuilt mine:

Rust-O-Matic 09-06-2017 02:47 PM

Re: Correct clock/phasing/orientation of yokes on '66 C20 2 piece driveshaft
My hero! Ha! Thank you very much for the pics, that's exactly what I need to see.

The yokes at each end of your front shaft are installed 90 degrees out from each other. Mine are more like one spline out from each other, nowhere near 90 degrees. I think the driveshaft shop screwed me. :devil:

Do you have any idea if yours' had ever been taken apart before you rebuilt it? Looks pretty original to me.

AussieinNC 09-06-2017 05:03 PM

Re: Correct clock/phasing/orientation of yokes on '66 C20 2 piece driveshaft
Cross style universal joints must be clocked at exactly 90 degrees thru transitions or they will vibrate...

Have never, in 40 years, ever heard of one designed to be one spline off...

What I have seen is a yoke swapped out and not be indexed correctly...

Remove the center yoke u-joint, undo the bolt in the front shaft rear yoke u-joint yoke and move it one spline...

Re-assemble it and make sure the extreme ends of the assembled shaft will have the shaft yokes both in the same plane.


jayoldschool 09-06-2017 06:09 PM

Re: Correct clock/phasing/orientation of yokes on '66 C20 2 piece driveshaft
Wow, I've never been someone's hero, lol

Glad to help! Have fun, everything will work out. Don't be afraid to do stuff yourself if a shop can't/won't do it right for you...

Rust-O-Matic 09-06-2017 06:54 PM

Re: Correct clock/phasing/orientation of yokes on '66 C20 2 piece driveshaft
Thanks guys, for confirming what I suspected. I think Aussie hit the nail on the head.

I replaced all the u-joints and center bearing myself, because I literally don't trust any local shop to do it correctly. Then I took it to have the balance checked because I wasn't certain I got the center yoke back in the correct orientation. That's when things went south. If I could have balanced it myself too, I sure would have.

Since the idiot at the shop smeared black paint all over everything (which I'm still pissed about) once he got done "balancing" it, none of my original marks still exist. So even if I take it back apart and rotate the center yoke to be 90 degrees out like Jay's pics show, the two shaft halves could still be installed 180 degrees out, and the whole shaft be out of balance. I guess if that's the case it will vibrate and I'll just have to take it back out and press them apart again, and turn it.

Good grief, why is the easy stuff always the hardest part? This started out as a simple u-joint switch-a-roo to make sure that wasn't part of my vibration issue...

AussieinNC 09-06-2017 07:02 PM

Re: Correct clock/phasing/orientation of yokes on '66 C20 2 piece driveshaft
You can trial balance yourself using of all things...a radiator hose clamp...

Use a screw type clamp ...unscrew the clamp, place it around the end near the rear gear and tighten...

Test...if it vibrates, loosen the clamp and rotate it 180 degrees...retest...

You will be surprised with the results...

Also, on your wheel vibrating...I will almost guarantee the wheel is buckled a bit...or egg shaped...try another wheel on that axle...


Rust-O-Matic 09-06-2017 11:34 PM

Re: Correct clock/phasing/orientation of yokes on '66 C20 2 piece driveshaft
3 Attachment(s)
Been a busy night. I pulled that driveshaft back out after work, broke it down, turned the yoke and put it all back together. The "it only goes on one way" BS the driveline shop gave me is nonsense. I had to press the damn thing off because it was stuck, but it could clearly be installed in several different directions, albeit incorrectly. Once I lined it up 90 degrees out from the front one, it dropped right down the splines, like they were made for each other. I attached some crappy pics.

I'll slap it back in the truck tomorrow night and see what happens. I'll probably lift one side of the axle, remove the wheel, and run it up to speed to test for vibration. If it shakes I'll try the hose clamp trick. I feel like it's pretty much got to be in the factory orientation now, or 180 degrees off. I'll let you guys know if it's a huge success or I burn it down haha.

Then I can move onto the wheel balance issue. I had the shop static balance them on the inside face only, and I wonder if that's part of the issue. They're old and could well be out of round or something, but I drove the truck they came off of for years and never had any balance issues with it. One problem at a time I guess.

Thanks again for the help fellas.

Rust-O-Matic 09-09-2017 04:39 PM

Re: Correct clock/phasing/orientation of yokes on '66 C20 2 piece driveshaft
Here's an update. I got the shaft back in, pulled one wheel off the rear, and ran the bare drum/axle/driveshaft slowly from 0 to about 65 mph. Still have a vibration. I could see the driveshaft slightly (very slightly, not violently) shaking within the center carrier rubber, so I knocked the center u joint out, and flipped the rear shaft 180 degrees in relationship to the front shaft, and put it back together.

Fired it back up and ran the same test. Driveshaft seems to be smoother, but my eyeball isn't exactly a high precision dial indicator. Regardless, I STILL have a shake with no wheel mounted. So I soaked the brake drum with degreaser and pressure washed the ever loving snot out of it, and scraped some rust buildup out of the inside of the back edge of it. (Keep in mind this is an HO52, not a typical 10/12 bolt that the drum just slides off of).

Fired it up, same test, same shake. After staring at it a while I can clearly see the drum/axle housing/trailing arm vibrating up and down once it's up to speed. I took a short video but I'm not exactly sure how to share it with you guys.

I got disgusted and gave up for the day, and decided to put my new $130 (ridiculous) copper heater core into the freshly restored and painted housing, only to find the copper lines are off just a little bit and it doesn't freaking fit. I tried to flex them ever so slightly to allow the housing to go around them, and one of them broke right of in my gorilla hands. What a crappy finish to a crappy week.

Enough whining though, does anyone have any idea what would cause my drum/axle to vibrate as I explained above? Do they balance those things? Are replacements available? I can't seem to find any exactly like mine, and the couple I have seen cost as much as a good used 14 bolt, which I'd kinda like to swap out anyway for the higher gears. My current 4.56s suck. Just fyi, I had the drums off a while back to rebuild the brakes, and at the time the bearings inside appeared to be in good clean shape, with no signs of gouges, grooves, or galling that I could find.

AussieinNC 09-09-2017 05:46 PM

Re: Correct clock/phasing/orientation of yokes on '66 C20 2 piece driveshaft
Time for the radiator hose clamp on the rear half of the driveshaft...

If there are any balance weights on the shaft now, place the screw clamp head opposite the weight position. Tighten the clamp and retest.

As you test, move the clamp head around at 45 degree will find the sweet spot...

All shafts and rear axles have a certain amount of vibration...that's why the center carrier has a rubber damper in its design.

If you are still concerned that the vibration is too bad it may be time for a totally different driveshaft...but don't be surprised if the new one vibrates just as bad.

BTW...some large brake drums do have balance weights welded on them...maybe one has been lost...look for areas on the outer surface where a weight may have been welded on at some time.

Re: Heater core tubes...not the first time I have heard of this...are you sure it was the correct heater core? The holes thru the outer case are usually much larger than the core please...

Try the hose clamp works...


Rust-O-Matic 09-09-2017 06:59 PM

Re: Correct clock/phasing/orientation of yokes on '66 C20 2 piece driveshaft
I'm not totally sure the vibration is related to the driveshaft. I'm sorta thinking out loud here, not being argumentative. I appreciate the input. I don't see any vibration in the center of the shaft anymore, and what I do see seems to be coming from the drum end of the axle. I could actually see the drum and the trailing arm (which was supported on a jack stand) hopping up and down about 1/4" at certain speeds. I realize it's all connected and vibration could be trasfered througout the whole system, but the drum hops like a tire out of balance, although not as violently. Does this still sound driveshaft related?

I started a separate thread about the heater core. I just took some pics I'm about to post. I'm absolutely positive it's the correct core. Outlets just aren't quite in the right locations. Here's a link :

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