So I’ve just installed my new transmission and I’m ready to install the driveshaft. I checked the pinion angles, front and rear, with my digital angle finder and I’m scratching my head a bit. The transmission output is pointing downward at 2.3°, which seems to be nominal from what I read. However, my input to the rear end is pointed downward at 3°. I expected it to be pointed upward around 2° and parallel to the tranny output. I replaced the rubber snubber for the differential, but I really can’t see how I’d swing the input angle from -3° to +2°. I’m wondering if this might be the reason the car has had a consistent 55mph vibration since I bought it. Any thoughts on how to correct the rear angle? It seems like I’d need less meat on the lower rubber cushion. 🤔

 

You need to describe what modifications have been made to your drivetrain. If none I would be skeptical of your measurements and would want to verify with folks here with pictures. There is a driveshaft setup called the w arrangement which it seems to be what you have measured, but to get there takes some doing. The difference of 0.7 degrees doesn't seem all that bad a misalignment for that configuration. Also, you know I assume that the motor is offset in the chassis so measuring angles is kind of a two dimensional effort.

I faced somewhat the dilemma you have but my angles were way out of whack. Forum helped me a lot to figure out what to do. Here is my thread on the subject, suggest you look it over and see if anything there helps you

https://www.corvetteforum.com/forums...aft-angle.html

 

Thanks Ignatz!

I’ve been doing an awful lot of reading on the topic tonight. I like the premise of the “w” arrangement as it’s very nearly attainable for me. Swinging the rear differential up 5° to get it parallel with the tranny output is a daunting task. The car has a 383 with a Tremec TKX 5-speed. It was previous an L48/TH400 car.

 

Well, I removed the cushion and swung the dif up as high as it can physically go. I’m still at 1.6° down. There is zero chance of aligning these angles in the “Z” configuration recommended by most driveshaft references.



So I trimmed the lower cushion down until the dif angle matched the transmission angle at 2.3° down and I guess I’ll see if the “W” configuration is truly a thing. 🤔

 

Are trying to do this with the leaf spring end bolts and nuts tightened in place?

 

Just a quick spit ball shot but Driveshafts are not supposed to be a straight line there should be some angle in them even in a fixed points application, if I remember my drive line class a million years ago you need 1/2-3/4° minimum to maintain U joint lubrication and are not to exceed 12° maybe 15° to avoid over angle flexing/Imbalances.

Your vibration I would give a good look at the U joints, my two door Tahoe had a Nasty vibration that would only show up 68 MPH and go away at 82 MPH.
0 to 68 smooth all the time, but that Highway vibration had to go and seemed like a exhaust Vibration so while chasing the exhaust with same tools in hand needed to pull driveshaft I did and found 1 pivot Frozen

 

Yes you must check all the u-joints for smooth operation!

Even brand new driveshafts, and half-shafts, with brand new u-joints sometimes just don't go together correctly, and there can be some binding.
You need to be able to flex the u-joint all around, with your bare hand, and not feel any differences as the joint fully flexes. One side unhooked of course.

I found 3 sticky but brand new stainless full roller rockers during my engine build this way. They could have bent a pushrod, or much worse. Half-shaft u-joints are even more sensitive to mis-installation, especially the outer h/s ones, because that bolt on flange is very thin and bends very easily during u-joint installation. A bent flange or yoke will cause a vibration, because the joints are no longer centered correctly. A driveshaft spins faster so it typically causes more vibration issues than a half-shaft. Half-shafts do not even have to be balanced, they do not spin fast enough, just not bent.

Excellent video below. You can "hear" the problem. It is hard to explain, so go listen. When the 2 angles are exactly equal, the issue at the 1:31" mark goes away. With either the Z or W arrangement. Just like noise cancelling headphones, the vibrations cancel each other out.
https://www.facebook.com/watch/?v=544158829753902
Ok it's on facebook and will not post here.

Search for "Driveline angles explained." by "Street FX Motorsport USA"

It's worth it!

 

Are you measuring with the car's full weight on the tires and suspension settled?
This might be a stupid question as I've never measured angles of these components so don't know how the settled weight may change the component angles.

 

In your car ( C3) your drive shaft between the Differential and Transmission doesn't change any tangible amount you're Differential is solid bolted (Not Moving) Transmission for most part Solid bolted. So lifted or on ground same.

You're 1/2 shafts Now that charges to the point that some of that stuff in the video could be a factor but doubtful and that would only be while suspended because I'm sure they got it right by the time you're car was made

 

You will be fine. That is the way to do it. The two angles must match. It is a vibration resonance thing. The speed oscillation has a specific frequency and wavelength. When the two angles are exactly the same, one shaft speed oscillation is exactly 180* out from the other, at the same wavelength, and they cancel each other out. Exactly how noise cancelling headphones work.

Making the degrees smaller, lessens the amplitude (or volume) of the oscillations in the first place. So that is a good thing. But the degrees matching is much more important.

The cancelling out effect works in either the W or the Z arrangement, it makes no difference. Most cars are setup for the Z arrangement, especially leaf spring cars, hence the common Z arrangement recommendation. C3s are set up for a W setup, for space constraints. Some have forced the diff into a Z arrangement, but it is not necessary. In leafs you have to allow for a little pinion angle rotation under power. Not required in a solid mounted diff in a C3.