Hot Rods Pinion Angle...Issue or not?

'30 Model A...Not sure what frame is under it but it's not FoMoCo...
I've had it a couple of years now and it rides great...while peeking forward from under the rear end today was the first time I ever noticed that the pinion angle looks wrong. Took some quickie measurements with the angle finder and the pinion face is 2 degrees downward, where the transmission (measured at the Y block valve cover) is 4 degrees downward.
I took the trans mount bolts out and jacked it up and am planning to shim the rear of the trans about 1/4"...which looks like about 2 degrees at the valve cover...so a total of 4 degrees.
It also has a 4 link setup in the back, so maybe I can swing the pinion a couple degrees upward?

On the other hand, LOOKING at the driveshaft to pinion connection it looks straight...is this even a problem? Like I said, 2 years that I have had it and it rides great...except that I think I need to remove a leaf or two in the back to soften it up.

 

no rumbling vibrations at speed?

 

What squirrel said... with a further thought that if it rides and runs fine and has done so for a while probably nothing to worry about. Is there a perfect way? Yes. Are all the hot rods out there perfect? no. Mine's not perfectly parallel either.

 

None that I have ever noticed but the car is loud at speed, so I probably wouldn’t hear much.
Maybe I will stick these shims in and be more mindful next time I take it up the highway.

Thanks gents.

 

If it doesn't make any noise, and you don't feel vibration, I'd leave it alone.

 

Looks like ladder bars to me. Clevises at the diff end?

 

Pete and Jake's ladder bars.

 

It is within acceptable range. Leave the angle alone.

 

With the ladder bar suspension it is a moot point . The rear universal never changes angle, and the front universal constantly changes angle with different ride heights

 

With ladder bar rear control arms the pinion changes angles as the suspension cycles , with a parallel 4 link , the angle is constant .

 

I wrote "Universal Angle" Not Pinion Angle

 

I'm not sure how when you change the pinion angle you keep from changing the universal joint angle that is attached to it ( the pinion ) ? But hey , whatever works !

 

I absolutely agree ... with someone ... I think

maybe

 

I see what @Kerrynzl is saying. The pinion angle doesn’t change, but yet the u-joint angle will.
Ie a tri-4 bar. If the rearend is going up and down and the transmission is not, the u-joint angle changes, but the rear doesn’t.
Well, at least in my mind!

 

Good deal Kerry, hey, I drink cheap beer

 

Ok.....type...
Delete......type........delete....man, if it doesn't vibrate and you know enough to ask the question then run it until it becomes an issue. Then replace the u-joint. Otherwise enjoy ....

 

Well, I wasn't able to fit my half-assed shims under the rear of the tranny anyway, so it will stay as it is.

Thanks!

 

If the pinion rises and lowers during spring compression, the universal joint angle has to change. The front yoke is in the trans, and trans doesn't move, so the driveline has to rise and fall as the rear axle moves. No way this happens if the rear universal doesn't have movement and changes angles with driveline changes.

 

Funny...I have another thread now about how the rear spring (9 leaf spring pack) doesn't really allow any movement because it's so stiff. I guess I'll focus on the spring pack and not worry so much about the pinion angle.

 

The normal action of a leaf spring set up is to rotate the pinion upward as torque is applied. So many people put the pinion angle less than the transmission angle so that when it rises it will be complimentary to the trans angle. Worst thing is if the pinion angle rotates so much that it exceeds transmission angle.
With the ladder bar set up you prevent that rotation when torque is applied but the rear end still travels up and down as the suspension travels over irregularities in the road.
If you are just worried about that difference because it looks wrong but has proven to work OK, then I wouldn't change anything. If you wish to lower the car or soften the suspension......then the only way to know the final result is to test it by trying it.

 

He has long ladder bars that pivot up by the front yoke. pic post #1.

 

Long or short there's movement ,the amount varies but there is movement !

 

No.
Assuming the front mountings are in line with the front universal joint, when using ladder bars or truck arms the rear uni joint will always operate at the same constant angle (apart from miniscule change due to component flex). The front uni will be the only one that is constantly changing the angle it runs at, but this will be no more than it would do with a 4 link rear end setup. In fact, because the ladder bars will be longer, the front uni angle change will be less.

Effectively, when using ladder bars or truck arms, the whole shebang is a solid unit that only arcs vertically around the front mount pivot point.

 

The ladder bar is a pivot point up front with the rear end rotating in an arc about that point. Yes there will be some very minor change in the angle of the pinion as it moves up and down, but not like the immediate rotation and change of several degrees when torque is applied to a leaf spring suspension with no ladder bar.

 

That's a HUGE assumption ( that the pivot point of the ladder bars is at the same point of the front universal ) ????? Ladder bars are only similar to truck arms ,dependent on bushing flex ,there can be quite a bit of difference from a solid unit .

 

If the drive shaft moves up and down in relation to the frame or floorboard reference then the U joint operating angles are changing too.

 

Yes, but the pinion stays on essentially the same angle when located by a ladder bar. while the u-joints change.

 

Any thing that travels in an arc , the angle is changing in relation to the earth ( level) I wasn't aware we were talking about closed drive lines ?
I'm done
Hope the OP is enjoying his ride !

 

No yeah buts about it.
Perhaps a definition of terms :
Pinion angels is referenced off the ground, level ground makes it easier to measure.
The engine angle is the same reference level ground.
The Ujoint working angle is the difference between the drive shaft and the yokes or centerline of out put shaft and CL of pinion.

The differential’s orientation to the ladder bars will not change because it should be welded. There’s adjustments but once it’s set it doesn’t change between the ladder bar and the pinion.

That differential assembly with the ladder bars swings in the vehicle. As it swings the pinion angle that’s referenced from the ground changes too. The pinion angle changes.

The joint working angles come off the drive shaft angle. The drive shaft angle is also referenced off of level ground. It’s the difference in elevation from transmission to pinion.
The springs change, the frame gets closer or further from the ground, then the differential/ladder bar assembly is swinging on the pivot and the pinion moves the pinion angle changes , the drive shaft moves and the ujoint working angles change.

Those changes are not huge, and getting everything into a mid range is usually enough for everything to work without calling attention to itself.

Setting up the perfect driveline angles, chassis level, engine down to the rear, and pinion parallel all gets thrown in the trash with a rubber rake and even worse if you’re lowering it a bunch. On the lowering aspect you get engine down to the rear, driveshaft up to the rear and pinion down to the rear. Bad juju

 

Generally it is about 15 degrees.