First Gen Pinion Angles
 

Does anyone have any information on suggested pinion angles for the first gen's? I know that with leaf springs, some accounting for pinion rise can be taken into account.

I'm trying to diagnose a low speed shutter on acceleration only that my 69 bird exhibits after swapping in a 4l80e.

Using Tremec's toolbox app, I measured the engine down at just past 3*, the driveshaft up at 2.5* and the pinion up at .2*. The app calculates a working angle of .1*

Just trying to cross this one off the list that could be causing the shudder. It occurs at moderate acceleration between 15-30 mph then tends to go away. It doesn't shutter during cruise up to 65 mph. I haven't had the car any faster than that yet, since the trans install.

What are your thoughts? Anywhere else to look? The driveshaft is a new aluminum unit from a trusted shop in town. Trans was rebuilt from a core over the winter, standard fare. TSP lockup converter. Attached to a Summit SFI flywheel that is a year old and has about 2000 miles on it.

..... just curious why the auto not a stick in there?

Aren't pinion angles listed in the assembly manual?

Mostly because the car is originally an auto car.

They may be. I don't unfortunately have an assembly manual.

It's easiest to measure without the driveshaft in. Measure the trans angle off the back and measure the pinion on the face of the yoke and add the angles for your pinion angle. Your measured angles of trans 2.5 degrees up and pinion 0.2 degrees up is a pinion angle of 2.7 degrees up without pinion rotation considered. Depending on the state of your leaf springs, the pinion can rotate 2-4 degrees up. I have Caltracs with split mono-leafs on my race car and Calvert said to set the pinion angle at 2 degrees down and it's perfect. It sounds like you need to get your pinion down to about 4.5 degrees so with 2 degrees rotation you will be at 0 degrees under load.

I use hotchkis leaf springs which are a multi leaf with all of the leafs captured/bundled.

That should help slightly with axle wrap.

I’ll have to see what option I have for pinion shims.

I use hotchkis leaf springs which are a multi leaf with all of the leafs captured/bundled.

That should help slightly with axle wrap.

I’ll have to see what option I have for pinion shims.

I can tell you that after I lowered my 67 I struggled mightily with it. At first it was low speed, like 35 MPH really bad. I did some shimming using the same tremec app you are and now its cool until about 65-80 mph then it has a medium shake. Just enough to be super irritating. I want to put a 1350 yoke on the rear end, and the corresponding end unit on the DS. I will get it rebalanced when the new end is put on. Im hoping my current issue is DS balance related. The internet seems to think that angle shudder usually occurs at lower speeds.

I agree with the above that it is hard to do it with the DS installed. Its also hard to be sure I have the car level on jackstands. Ive told myself if the driveshaft rebalance doesnt work Im just going to take it to a shop and let them do it on a 4 post so we know its level. I feel like everytime I loosen the rear end I am screwing up my front end alignment and need to have it re-done. Big waste of money.

I took the measurements with the car on my 4 post which is verified level.

My car is very low. Prior to the swap it did not have a shudder with the th400, at least not at low speed. I did have a droning type vibration at the big end of the quarter mile so about 100-105 mph that I noticed. That could be related.

Doesn't sound like your issue is necessarily incorrect pinion angle. A different than optimum pinion angle will primarily stress the U-joint and maybe cause a vibration. What is your current pinion angle and what suspension do you have?

I don't remember the angles. I did it almost a year ago. At first it was 100% pinion angle when it was shaking at like 30 MPH because when I adjusted the pinion after it made a notable difference. I do believe I got them within a degree of one another after adjustment. And I am hoping you are right and its just the shaft balance now. I think maybe it had a little shake when it was stock height that was just a little higher up in the range. Like 80 mph so I didn't feel it often.

Letting off the gas when its in shake will also briefly make it worse until it drops a few MPH. Which again, according to the internet points to a dynamic vibration rather than angle related.

I have ride tech lowering 1.5" springs in the front and 1" blocks in the back. Other than that its factory style. I do have a clamp on the leafs in the back on each side. Oh and subframe connectors.

I don't want to thread jack. I mostly chimed in to say that it was hard without the driveshaft out. And if this one is vexxing you there is maybe no shame in letting a shop do it. Especially one that can align the front end after. Mine is even more difficult at the front because there is a driveshaft loop in the way.

GM made an entire manual on vibrations
My manuals are somewhere else,
I ll ask for someone to look for it. Keep in mind this was written for engineers not backyard mechanics.

I think most here are on the right track. This new trans is shorter than the long tail 400 that was in the car and the mount I believe has the engine at a steeper angle down. I never measured the trans angle previously, but I would guess it was probably about 2 degrees down based on how the trans was installed.

I may try 2 degree wedges in the axle and see if that makes a difference. I want this smooth while cruising which is what the car does most of the time.

IIRC you want some angle that matches on each end one up one down same amount but less than 3 deg.
Ive heard it said that a straight line is best but I think thats in error.

Detroit speed has a discussion about pinion angle. They talk about their quadralink and leaf spring cars. https://www.youtube.com/watch?v=Vg1vo1tMqaI

Here's another video that briefly goes into drive line phasing if you haven't already considered this: https://www.youtube.com/watch?v=gmV4qwLfOMY&t=94s

I have verified that the u-joints are in phase. They both measure at the same angle from the caps. The shaft was built by Northern Colorado Driveline. Not that mistakes can't be made, but these guys have a stellar reputation in the rocky mountains.

I'm still fairly certain the pinion needs to come down a couple degrees. I spoke with Eric and NCD this week and he agrees with my assessment. I'm probably going to have to play with it a bit considering how low my car is. I'll start with 2* shims and make adjustments from there as I can.

In the DSE video they're describing the rear pinion recommended around 3 to 4 for leaf spring set up. Your trans/engine angle is spot on with what they're recommending.

2* for 2.5" leafs? If so, please DM me your price. Thanks!