Pinion and driveshaft clearance questions

[County]

Finally put the bed back on after refreshing suspension, brakes, etc. 5" drop springs on back and CPP crossmember with the trailing arm mount points at the top instead of the bottom. Other relevant thing might be I put in new poly trans mount bushing.

'72 C10, th350 trans. 3 things on my punch list after getting full bed weight on and full weight on suspension were Panhard adjust, pinion check, and DS clearance check.

Panhard was good, moved diff over 1/4" or so, seems pretty good to go.

Pinion is giving me fits. I've read the threads, watched the vids, etc. I can't seem to get decent readings without pulling driveshaft again, but averaged a few measures that were close.

Couldn't get good tailshaft angle, so used straight edge on harmonic balancer.

This is what I came up with.



Do I need to get these numbers down to 3 degrees? The vibe chart says operating angles should be okay up to 4krpm before they become a concern, but I'm new to this.

What is the easy fix? Please be specific like I'm a child. I'm old and tired...

Secondly, I have plenty of up/down room through the crossmember, but with the truck pinion being offset, I have about 3/4" on the drivers side through the loop, but only 1/4" or so on the passenger side. Is this a concern?



Not a good pic, but taken from rear facing forward, using the side edge of ruler to show smaller gap.

Any advice for me friends?

[County]

Forgot to add, Truck probably not level, ramps in front and jackstands in back. I zeroed gauge using the top bed sill rail.

I don't believe this will change anything, just trying to give all info.

[HO455]

It doesn't matter if the truck is level just that the rear axle is at ride height. The front on ramps isn't a problem. Jack stands way back by the transmission crossmember will cause the frame to sag and the engine angle will be lower in the front than it normally sits.

The side to side offset is normal. You may be able to get more clearance by loosening the transmission mounting bolts and pushing the rear end over. Slotting the mount holes is also a possibility to gain clearance. Also try loosening the new crossmember and prying it to the side to may help too.

If you have an adjustable panhard bar I would adjust it so both wheels have the same dimension from the fender well lip to the edge of the tire. Then recheck the dimensions in the drive shaft loop at full droop and full drop. The rear end will move side to side as it traverses through the full range of movement. The shorter the panhard bar the more pronounced the side to side movement is. Go to post 513 in the link below for how I set up my track rod (panhard bar )

https://www.67-72chevytrucks.com/vbo...698377&page=21

When measuring off the harmonic balancer I would check it in several spots (Rotate the engine) to make sure it gives you consistent repeatable readings. It's pretty common for balancers to wobble and that would cause an erroneous reading.

Since both your U-joint angles are close to the same it may not be worth the time to get the angles lower as you may not have any noticeable vibration. At this point personally i would leave it until I had done some road testing.

The link goes to how I measured the angles on my Burban post 348.

https://mail.67-72chevytrucks.com/vb...698377&page=14

Good luck and post how it comes out.

[pjmoreland]

If you end up having vibrations and you want to get your u-joint angles below 3°, then you'd need to raise the rear of your transmission somewhere in the ballpark of 1.25", and you'd need to tip the front of your rear end down approximately 0.5° from where it is now. This is assuming you're working with a shortbed truck. You would need to experiment with your exact setup to confirm these numbers.

[mr48chev]

Originally Posted by HO455

It doesn't matter if the truck is level just that the rear axle is at ride height. The front on ramps isn't a problem. Jack stands way back by the transmission crossmember will cause the frame to sag and the engine angle will be lower in the front than it normally sits.

Good luck and post how it comes out.

There is the correct answer "as it normally sits running down the road most of the time.

For a 1 piece driveshaft the angle of the output shaft and pinion should be parallel to be "perfect"

I found this discussion on Grassroots motor sports that the poster Volvheroic seems to have found the workable info on https://grassrootsmotorsports.com/fo.../256268/page1/




I'm finding a lot of conflicting info on two piece driveshafts and the only thing that makes sense is that you want all three U joint angles within 1 degree of each other. The thing that often causes vibrations and messes things up is that the angles don't match or come close enough to matching.

This first drawing came off some group on the net and the front half of the two piece driveshaft being and extension of the crank/output shaft line isn't going to fly 90% the time.

The second one is off the Spicer how to use our driveshaft angle gauge but their page may need an engineering degree to follow https://spicerparts.com/anglemaster/measuring-angles Still it shows what most of us have with our two piece driveshafts.

[County]

Thank you for the replies so far, lots of good info to digest. Not sure why I'm having so much trouble wrapping my head around this.

One piece DS, btw.

Raising the tailshaft 1.25" seems to be A LOT. Not sure if I have that kind of room to work with, especially with my already tight shaft clearance.

I'm at @ 6 degrees now at both ends, so if I bring the trans tailshaft height up to where I'm in the 3 degree ballpark, wouldn't I need 3 degree shims for the diff? I don't think I'm understanding why the tailshaft correction would be so large, but the diff would only need a .5 degree adjust? Just trying to make it work in my head.

I'll review all the thread links as well. Part of my problem may have been I read way too much and I'm sure some bad info as well.

That's a good idea using a socket on the yoke cap, I'll try that as well.

Thank you again.

[pjmoreland]

Originally Posted by County

Thank you for the replies so far, lots of good info to digest. Not sure why I'm having so much trouble wrapping my head around this.

One piece DS, btw.

Raising the tailshaft 1.25" seems to be A LOT. Not sure if I have that kind of room to work with, especially with my already tight shaft clearance.

I'm at @ 6 degrees now at both ends, so if I bring the trans tailshaft height up to where I'm in the 3 degree ballpark, wouldn't I need 3 degree shims for the diff? I don't think I'm understanding why the tailshaft correction would be so large, but the diff would only need a .5 degree adjust? Just trying to make it work in my head.

I'll review all the thread links as well. Part of my problem may have been I read way too much and I'm sure some bad info as well.

That's a good idea using a socket on the yoke cap, I'll try that as well.

Thank you again.

When you raise the transmission tailshaft, there is very little angular change to the transmission since it is pivoting about the engine mounts that are a significant distance forward from the transmission mount. That is why there is very little angular change needed for the rear end to keep it parallel with the transmission output. My truck is very similar to yours. I have the CPP trailing arm attachment crossmember and I have 6" lowering springs in the rear. I had to raise my transmission significantly to eliminate a vibration issue. My driveshaft is quite high in the opening through the crossmember.

[pjmoreland]

You could experiment with the effects of raising the transmission tailshaft by removing the transmission mount bolts followed by jacking the the transmission up. You could then measure the resulting u-joint angles. Your exhaust system, shifter linkage, and fan shroud clearance might not cooperate. Personally, I would only mess with this after confirming you have a driveshaft vibration.

[Joyridin]

I could not get the tailshaft raised enough, so I changed the angle of the rear axle. Technically, my driveshaft now runs uphill instead of downhill. Both angles are at 2 degrees. It has been this way for years without any issues.

You have enough drop in the rear this might be an option for you. You can buy shims that go between the rear swing arms and axle. It was easier for me to just remove the mounts and weld in new ones.

[HO455]

Originally Posted by County

Thank you for the replies so far, lots of good info to digest. Not sure why I'm having so much trouble wrapping my head around this.

One piece DS, btw.

Raising the tailshaft 1.25" seems to be A LOT. Not sure if I have that kind of room to work with, especially with my already tight shaft clearance.
Thank you again.

On my Burban I was only able to raise the transmission 5/8" and still maintain clearance with the floor board. On different project I changed from aftermarket motor mounts to factory style mounts and got the angle to decrease.

As a side note 4x4 folks with lifted trucks would love to have to angles you have. Many of them struggle to get their angles in the 10-12 degree range and live with replacing U-joints every 20k miles.

[County]

Thats interesting on the up angles, never heard of that before.

And also true with 4x4s, I didn't think of that either. Especially on short wheelbase jeep, operating angles must be crazy.

[SCOTI]

Originally Posted by Joyridin

I could not get the tailshaft raised enough, so I changed the angle of the rear axle. Technically, my driveshaft now runs uphill instead of downhill. Both angles are at 2 degrees. It has been this way for years without any issues.

You have enough drop in the rear this might be an option for you. You can buy shims that go between the rear swing arms and axle. It was easier for me to just remove the mounts and weld in new ones.

Originally Posted by County

Thats interesting on the up angles, never heard of that before.

And also true with 4x4s, I didn't think of that either. Especially on short wheelbase jeep, operating angles must be crazy.

Extreme drops (>6") can fall into the same realm as lifted 4x4's.

The old adage that if the motor/trans is tilted/pointing down @ X°, then the rear pinion needs to be pointing-up @ x° is not correct IF the pinion is equal to or above the trans output.