Pinion angle question

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SSG_Karg

SSG_Karg

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Trying to track down the root of a vibration I've been having. Decided to verify pinion angle.
Car is 72 Duster with warmed up 318, 4 speed, 3.91 8 3/4, 002/003 S/S springs, 28" tire.
Checked angles with full weight of car on suspension at ride height. Currently transmission angle is 88* (or 2* down from level). Pinion reads 92.5* (or 2.5* up from level). I checked it with the Tremec app on my phone and it gave me the ok. Now, from what I've read here, this is about where I want the angles under load. So I'm thinking of adding 2* shims to lower the pinion angle to 90.5 (or .5* up) to get them closer to equal upon acceleration. Car is street car that is driven like a hot rod should be and gets half a dozen or so passes on the strip. Opinions on my pinion? Thanks.
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That sounds like a reasonable approach, the process of elimination. You can always go back. Your driveshaft could also be the cause of vibration. Not sure how you would check that.
 
The angles should be equal (parallel) when the pinion is under load, not when the car is sitting static. When you're accelerating the pinion will/should rise 2 to 3 degrees, if it is not aligned under a load it will vibrate.

Treblig
 
When are you getting the vibration?
What are the conditions?
Doubt it will make a significant difference but have someone about the same weight as the driver sit in drivers seat and re measure angles.
 
I'll be watching this thread as well. Just installed my new Dana 60 and I've got a vibration when I floor it. Extremely smooth under light throttle, only vibrates a little when smashing the throttle. I'm also thinking about buying a few different degree shims.
 
Forgot to mention. In service manual ( 1967 Dart Coronet Barracuda) it lists various rear pinion angle degrees and how to set it up.
 
  • Vibrations at relatively low speed (under ~30 MPH) are often due to mechanical issues such as:
    • Phasing
    • Alignment
    • Straightness, either due to a new shaft not being built straight or a used shaft being bent.
      • You would need a dial indicator to measure such radial run-out and that would probably best be done at a drive line shop, because after straightening, the shaft will likely need to be balanced as well.
      • Could also be due to a u-joint not being installed properly or a drive shaft flange not fitting properly causing the shaft to not line up with the output shaft or pinion gear.
      • And realize that drive shafts are typically straightened by use of heat and cold. The drive line shop will use a torch to heat one side of the shaft, expanding the steel on that side, while cooling the opposite side with a wet rag to shrink the steel there to pull a shaft back into straightness. That said, any application of sufficiently high heat can case shaft to lose straightness.
  • Vibrations at relatively high speeds are often due to balance problems.
    • These vibrations may come and go as speed increases as you move in and out of resonant frequencies of the drive shaft.
  • Vibrations that get worse when transitioning from acceleration to coasting to deceleration, like when you back off the gas over the top of a hill and before you go into full on engine braking, may be due to loose or worn parts, like loose flange bolts, worn or over-extended slip yoke, etc.
  • Vibrations that get worse say going uphill or accelerating at speed than when going the same speed on the flat or downhill, or vice versa, might be due to a slight alignment issue.
    • If worse uphill/accelerating, the lower u-joint angle may be moving too high as the axle and pinion tip up under load, if so, tip the static pinion angle down a little lower than it is now.
    • If worse downhill/decelerating, the lower u-joint angle may be moving too low as the axle and pinion tip down from the lessened load, if so, tip the static pinion angle up a little higher than it is now.
  • Vibrations at very high speeds may be due to approaching the drive shaft critical speed, which is essentially the resonant point where the shaft begins to whip and vibrate violently.
    • In this case, only a new driveshaft design will help, changing material, tubing diameter or wall thickness, etc.
    • These sorts of RPM limits are usually up in the 8000-10,000 RPM range, so typically only seen in race vehicles.
 
Vibration occurs at speed. Seems to increase with vehicle speed not engine rpm. At 100mph it is bad enough to shake the dust out of the headliner! I've already had tire balance checked, replaced drive shaft and u joints, rebuilt trans with all new bearings and tailshaft bushing. Wheel bearings are freshly greased and tight.
Haven't tested since doing all this work yet as its winter here and too much **** on the roads. I'm just trying to rule out any possible cause now while I have the time. Think I'm gonna put the 2* shims in anyhow to get a little closer to parallel under acceleration.
 
I have seen where drums or rotors were out of balance. Some shops have the ability to balance tires on the car.
 
Put the rear up on jack stands and run it up and feel the vibration then mark the drive shaft in 1/4s, add a hose clamp and see if the vibration is better or worse then turn the clamp 1/4 turn and try it again

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A couple things.
Pull shaft and mock up a couple test bars,2’ long to go in place of the u-joints. The bars can be a little small (1” drill rod) and weged in yoke eyes. This gives you 2 parallel bars to measure for square and check phasing.

Other, if you have a smart phone there is a pinion angle app by Tremec.
 
That has a +.5 pinion angle which is BAD!

I would roll it down so the angle finder is 0 to 1* down with at least a 3* shim. IMO, 2* is shim marginal at best to get angle in the right spot.
 
crackedback said:
That has a +.5 pinion angle which is BAD!

I would roll it down so the angle finder is 0 to 1* down with at least a 3* shim. IMO, 2* is shim marginal at best to get angle in the right spot.
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That’s what I was thinking as far as the angles go. .5* up static is no bueno. I’m thinking that the S/S springs and relatively low power will not create much more than a couple degrees of change under load, certainly not at cruise. So you’re thinking a 4* shim would be a little better than the 2*?
 
If you have a 2* try it and see if it helps.

I like at least 3* down or my stuff.
 
For whatever its worth my 1967 dart shop manual says that engine oil pan flange should be level ( shim the trans mount ) and the 8 3/4 pinion should also be level (shim the spring) this is for Dart 111" wheel base. there are other settings for other models.
 
Dana67Dart said:
For whatever its worth my 1967 dart shop manual says that engine oil pan flange should be level ( shim the trans mount ) and the 8 3/4 pinion should also be level (shim the spring) this is for Dart 111" wheel base. there are other settings for other models.
Click to expand...


I think you mis read that somehow................

Crackedback knows what he is talking about. The driveshaft speeds up and slows down every 1/4 turn. The two joint angles at the ends cancel this effect between the trans shaft and the pinion shaft. If they are unequal, or OUT OF TIME (as with a separate slip spline/ yoke) they will vibirate

The short story is that with the car loaded "as normal" on the tires, and under heavy acceleration, the trans shaft and the pinion shaft should be PARALLEL to each other

This is my favorite "go to video" for the subject

 
Yes, I understand the concept. But how much time does the car spend under heavy acceleration compared to part throttle cruising? The shaft in those videos certainly is not under any heavy acceleration. Right now I have a .5* up pinion angle which I don’t like. My plan is to add a 2* shim to lower pinion to 1.5* down compared to trans angle. Will test when weather permits. If the vibration decreases I know I’m on the right track and may try 4* shim to dial it in.
 
SSG_Karg said:
.View attachment 1715141928
Click to expand...

Your pinion is +.5* up in relation to the transmission. That is too high. You need to move the nose of the rear end down in relation to the transmission a degree or two. If you shim the nose down 2 degrees, it will be 1.5 degrees down in relation to the transmission centerline.

For me it's easier to put the car up on jack stands so that the transmission is level or do the math to get the transmission side of the equation equal to zero.
 
jbc426 said:
Your pinion is +.5* up in relation to the transmission. That is too high. You need to move the nose of the rear end down in relation to the transmission a degree or two. If you shim the nose down 2 degrees, it will be 1.5 degrees down in relation to the transmission centerline.

For me it's easier to put the car up on jack stands so that the transmission is level or do the math to get the transmission side of the equation equal to zero.
Click to expand...

I have been chasing a vibration issue that starts at 95-98 mph and up. My pinion angle is 1 degree down in relation to the transmission/engine centerline. I even swapped out my differential in the hope it will cure the vibration. I have yet to be able to get the car up to speed to verify the vibration has been eliminated.
 
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