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!

I wrote that.

Last version I saw was in the S/T truck service manual.

I do not have a copy of it electronically.

K

Straight line is ideal - for a little while.

The problem becomes that the needles brinnel themselves into the bearing caps because the caps are not rotating, causing a disturbance over time.

As a result a "small" angle (ie, 1 to 3 degrees), equal and opposite in direction, is best in real life.

The reality is that it is not going to stay straight, anyways, because of suspension movement and rear axle windup.

K

Good information Keith. Do you have anything to add re leaf spring axle wrap? If my engine is down 3* and the pinion moves upwards 4-5 degrees, pointing it down in it's static position by 2* should get me somewhere between 3-4* up opposing the output shaft I would assume?

I want to revisit this a bit. I do have a set of 2* pinion shims that I am going to get installed next week. However, I keep coming back to the fact that this new issue cropped up due to a change in transmission, not a change in the rear axle. The car sits the same, the axle wasn't moved in any way etc.

I don't have angle measurements of the previous engine, but I'm fairly certain it was at a shallower angle, simply because I lost ground clearance at the header collector, which is noticeable now that I scrape that coming on and off my lift, where before I didn't.

I know the engine is down slightly over 3* and the driveshaft is up 2.5*. My understanding is that because these are opposing angles, instead of similar angles, I would add those together to get the working angle at the slip joint. That gives me a working angle of 5.6* as the car sits. That is before the pinion climbs the ring gear which would exacerbate that angle further.

I am thinking now, that this may be an "and" solution. Not only do I need to point the pinion down a couple degrees (which will reduce the angle at the slip yoke slightly) but I believe I also need to bring the tailshaft up slightly, further reducing that angle.

I plan on doing the pinion shims first and seeing where I land, but as I think about this more, it may be necessary to make changes to the transmission mount as well.

You need the rearend angle?

The engine down 3º and driveshaft should be down (from front to rear is direction used) 2.5º ?

Is the new tranny longer than the stock tranny?

:confused:

The car is lowered significantly. About 2" in the front and 3" in the rear. The rear drop alone accounts for much of the wonky driveshaft angle. As the car lowers in the rear, the pinion rises in relation to the transmission output shaft.

The new transmission is longer than the factory TH400 that the car was born with. It's shorter however than the long tail TH400 that was in the car when I purchased it and was just replaced.

So yes, trans output shaft/engine is down 3.1*. The driveshaft is up 2.5*. Because the angles oppose, my research indicates the slip yoke operating angle would be 5.6* at static. As the pinion climbs the ring gear, that angle would actually worsen if I'm thinking about this properly. I'd be well outside the 1-3* operating angle recommended for the slip yoke.

Making an assumption that on the leaf spring rear, the pinion would rise 5*, that would also put that angle out of whack as it would oppose the driveshaft angle under load.

Which it's not a wonder I'm getting a shudder in the configuration.

That's why I think ultimately I'll need both. Get the pinion down a couple degrees to help that joint and the tail shaft up maybe a degree to degree and a half to help that joint.

Your driveshaft goes up to the rear pinion from the tranny?


:confused:

Yup, it sure does. Consequences of how low I have the car. As the rear comes down, the pinion moves upward in relation to the transmission, causing the driveshaft to travel upwards.

I have some things working in my favor to fix the issues though. I don't run a carburetor, so my engine inclination doesn't need to care about float levels. I also run electric fans, so I don't need to worry about the fan coming in contact with a shroud. Between moving the pinion down a couple degrees and moving the output shaft up a degree or two, I should be able to get the driveshaft in a more favorable orientation, primarily to the slip yoke. I believe that will return the car to shudder free orientation. I may have to play with it a bit though.

I can't really measure it well with the new crossmember in the car, but I suspect the tail shaft sits 1/4 to 1/2" lower in it's current configuration. The factory TH400 crossmember appears to sit higher than the g-force crossmember and there was an added 1/2" bar stock on top of that to extend out the trans mount to support the long tail TH400.

I will PM you with some questions about this

A quick update on this. I have installed a 2* pinion shim in both directions. This moved the pinion down about 1.5* and up about 2.5, not quite a full 2* in each direction. No change in vibration was noted with either direction.

I would actually say the vibration is getting worse and it has changed where it occurs from slightly off idle, to a now rpm dependent range of around 2800-3800 rpm before it then clears up.

Of note, because the engine angle is steeper, my header collectors have been scraping pretty badly getting the car on and off the lift. This has created a number of exhaust leaks in the system and moved things in such a manner that there are witness marks on the passenger side pipe from hitting the cross-member, as well as the passenger side collector flange which is now hitting the transmission pan. I know that exhaust hitting floorboard and such can cause some weird vibrations, but this is extremely noticeable in the car.

I have a new set of headers going on the car next week that should fit better than what's on there. They'll re-align the exhaust as well and get it off of the cross-member. I guess we'll see if that has any effect.

I have also ordered some transmission mount shims to try and raise that angle slightly as well. I know its working angle is still beyond what is considered "good."

I raised the transmission output by a 1/4" tonight which brought the engine to 2.8* down and the driveshaft to 1.4* up. A much better working angle at 4.2*, but still a bit outside of spec.

I haven't test driven the car yet as it's got a nasty exhaust leak that will be corrected later this week. Hopeful that the change here along with getting the exhaust in a better location will cure this vibration.

Have you taken the driveshaft out and measured the transmission angle and then the pinion angle? The angle of the driveshaft isn't relevant.

If your trans is down 3 degrees you want your pinion to be up 3 degrees to have a net zero driveline angle. If you have 4 degrees up rotation of your pinion from axle wrap then you would want to set your pinion 1 degree down to get to a zero driveline angle while driving. If you want a different angle than zero you can adjust as necessary. I run Caltracs with split mono leafs on my race car and Caltrac suggested a 2 degree pinion adjustment since there isn't alot of axle wrap with their set-up and I have zero vibration even at 134 mph.

I'm using the harmonic balancer to get the engine/trans angle and I'm easily able to get the pinion angle with a straight edge on the pinion flange.

Right now with the engine down about 2.8* and the pinion up at about 1.5*, that should give me a pretty even 2.8/2.5 equal but opposing spread under load. With the driveshaft up towards the pinion, the working angles are bigger than I'd want, but they are now better at around 4* at the u-joints.

Well, the search for this mystery vibration continues. The vibration is present with the pinion at it's factory setting, up and down 2* and I have additionally added another 1/4" of spacer to raise the output shaft on the trans.

I just got the car back from the exhaust shop and that is no longer hitting anywhere on the car, so that is also not the culprit.

I guess my next areas to look at are probably the torque converter and possibly the transmission itself.

That's one of the things I'm going to check.

However, I took the car out for a bit this afternoon and found some new information. This appears to be RPM dependent, not speed dependent. Putting the trans in low gears I can replicate the vibration at low and moderate loads starting at about 3000rpm. I then checked the car sitting still with the transmission in park. Although it isn't as bad, you can feel the vibration start at that same rpm and continue with increasing rpm. It is at its worse between 3000-3500 rpm and does get better as rpm increases, but doesn't go away above that rpm.

This vibration was not there previous to the transmission swap. Looking first at what changed, I need to check the torque converter and the transmission itself.

I'm going to be pretty upset if this 1000 torque converter is somehow out of balance. The TSP unit I had in my TH400 was perfect.

I dont think there is a high chance this is your problem given the tests you have done, but to give everyone food for thought. Im fighting a similar issue with vibration. I read a review the other day for the M/T drag radials that I have on my car that says "They balance poorly and rattle your teeth out"

Then it occurred to me that I have only had those drag radials on the back since I started messing with my pinion angle. Before I lowered the car I mostly had the Rally II wheels with generic street tires on it. So Im going to swap back to street tires on the rear and see if it changes or eliminates my shake. Maybe my 60 MPH shake has been tire balance the whole time.

Good information for sure. I have actually heard this about drag radials in general.

I can create my vibration sitting on the driveway in park, so it's definitely not the tires.

Happens to the best of us.

I chased a vibration for about half a season; had my new Hoosiers balanced at least twice.

Turns out I had flat spotted the front tires at some point. New front tires fixed it.

K

This is good. Divide and conquer is what it is all about.

If you can separate "RPM dependent" from "Vehicle speed dependent" from "Load dependent" then it creates a whole long list of things you don't have to worry about.

K

It's definitely rpm dependent, but load effects the severity. In park you can feel the vibration grow between 2800-3000 rpm and it's at its worst from 3000-3500rpm. It is still there, but subsides after 3500 rpm.

While driving the car, the vibration is worse during moderate acceleration. At full throttle the vibration is present but not as severe.

Motor mounts perhaps? Those have been in the car since I purchased it in 98.

I would say to check the converter to flexplate mounting.
If this is a new converter (to you?) it could be bolted up crooked.
Unbolt converter from flexplate and push converter away from flexplate.
Start engine and see if it still vibrates?

Check the flexplate while under there to see if there is any noticeable problems. (bent/crooked, holes wallowed out, etc)

When bolting back up, make sure the converter is pulled against flexplate evenly and tighten bolts without cocking the converter as it is rotated.

:confused:

This is definitely on my agenda to check. The flexplate was a new SFI unit that was installed about a year and a half ago. Doesn't necessarily mean anything however.

The converter is a new TSP unit. One of their billet faced triple clutch deals.

One thing I just realized is that the vibration range tends to be in the range where the converter starts to couple. It flashes to about 3100 rpm under load.

Update on this. I spent some time diagnosing over the past couple days and weekend. There's no visible wobbles or shakes coming from the flex plate or torque converter. All the bolts are tight etc.

On a hunch and some extended reading, I changed out the transmission mount from the poly mount that was installed with the trans, back to a rubber mount. To my surprise this almost entirely get rid of the vibration. I would say a reduction of over 95% in fact. I can still very faintly feel a vibration, but it's almost imperceptible now.

I still need to track down what exactly is creating the vibration to begin with.

how worn is the slip yoke and output shaft of trans?
Also check the bushing in tailshaft

Sounds like a NVH problem which can be hard to deal with.

It also might suggest a phase problem with the 2 u-joints on the shaft.
If they are a little out of phase can be a problem that is hard to trace.

Or the factory spends ton on NVH so maybe the rubber (durometer?) is the correct reduction for the vibration?

:confused:

The transmission mount that was on previously was terribly worn. It was probably 50% as soft as the stock rubber replacement I just put in. I would gather there may have always been some sort of latent vibration, that was soaked up by the fact that the trans was sitting on a sponge.

I've got the engine out of the car for unrelated issues now. It has factory type motor mounts, but they appear to be in decent condition. I may decide to change those out while I have the engine out. Whether or not that will help, I'm not sure.

There's a lot of solid mounting in this car, between the delrin suspension bushings and delrin/aluminum subframe mounts. Some amount of NVH transfer has to be considered acceptable.

Final update on this.

After getting the engine back in the car for it's unrelated issue, I did decide to replace the motor mounts with a set of mighty mounts. Upon further inspection you could see the rubber starting to tear and delaminate from the steel casing.

Nothing changed with the vibration moving to new motor mounts.

After doing further testing to isolate the vibration, I did narrow it down to engine side with the torque converter dismounted from the flex plate. This week I replaced the unknown age, but seemingly in decent condition factory type balancer with a BHJ from Nitemare performance. I'm happy to say that the vibration is now gone with exception of a very slight buzz near the very top of the rpm band. Based on the drill marks present in the factory type balancer, I believe whoever did the rotating assembly on this engine back around 97-98 likely tried to neutral balance the stock balancer and there may be a slight imbalance in the rotating assembly itself. All of this likely masked by the poor and soft mounting the car had.

As I've replaced bushings, engine and trans mounts and gone to more rigid mounting of the subframe and suspension components, that slight imbalance is there. I've been beating on this thing for many years and I assume I'll be able to continue to do that. But, I'm socking away money for a rebuild at this time.