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Old 08-06-2004, 12:00 AM
Dep ME's Avatar
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Pinion Angle Mystery

I know this has probably been discussed about a gizillion times but after reading a dozen or so articles, I'm still confused. Hopefully someone can help out.

I have a IFS and 9" rearend installed on a 53 F100 frame. There is no body or cab installed. I am in the process of making motor mounts, to install the engine and transmission. That means I have a crankshaft centerline and the rear pinion flange to work with.

The pinion flange is 2 degrees positive (pinion stub above the horizontal plane).

I've read somewhere the motor should then be set 2 degrees negative (transmission stub below the horizontal plane) because of the positive pinion angle. Others have talked about adding an offset to take care of the spring wrap up. Someone else told me to set the crankshaft level and the pinion stub at 6 degress negative. One advised to set the engines at 3 degrees negative and the pinion 3 degrees positive. After all this, I'm past the confused point.

I realize that when everything is put together, I may have to make adjustments to the pinion but that's not the point. The point is...

All I want to do is mount the engine and transmission and still have the pinion angle issue, somewhere in the ballpark. Can someone tell what angle I should mount the crankshaft centerline at?

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Last edited by Dep ME; 08-06-2004 at 12:16 AM.
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Old 08-06-2004, 01:46 AM
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Here is some good reading.https://www.fleet.ford.com/truckbbas/non-html/Q14.PDF

But in short, the u-joints should be at the same angle in opposite direction so that they cancel each other.

Taken from another site:

The universal joints work as follows:

When the output shaft turns, the two caps of the front universal joint must turn around the center of the output shaft.

When we look at the opposite side of the universal joint the other two caps on the universal joint must turn about the center of the drive shaft.

Because the drive shaft is at some angle to the output shaft, the cross of the universal joint must wobble back and forth to allow the bearing caps to trace these circles out while rotating.

This causes the rotating speed of the drive shaft to fluctuate on every turn, at first speeding up slightly faster than the output shaft, then slowing to slightly below the output shaft speed. If this effect is not counteracted with a second universal joint, it will create vibrations.

At the other end of the driveshaft, there is a second universal joint. This joint is timed to the front universal joint in order to be exactly opposite to it. When the drive shaft speeds up from the action of the front universal joint, the action of the rear universal joint slows it down, and vice versa. This produces a constant shaft speed at the differential shaft.

Automotive drive shafts are not straight for the reasons explained above. The rear end moves up and down, so the drive shaft can never be perfectly straight.

Last edited by xtreme off-road; 08-06-2004 at 01:52 AM.
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Old 08-06-2004, 03:12 AM
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Although your explaination and the article was informative, I'm as befuddled as before.

The question still remains. What angle should I set the crankshaft centerline to?
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Old 08-06-2004, 04:23 AM
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The best info I've managed to come up with over the years is that with the rear end positioned at it's half way point in it's travel (1/2 total shock travel) you should have a straight line from the crankshaft plane to the pinion shaft plane. That assumes that the rear suspension at rest will sit at that point. I put a 351M /auto and 9" into my 1953 Ford sedan using this procedure and it seems to work just fine. Race cars and ultra high performance cars probably need more engineering but the average street machine is a lot more forgiving. Hope this helps..
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Old 08-06-2004, 04:37 AM
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The question still remains. What angle should I set the crankshaft centerline to?
Very simple. If carbureted, you set the engine in to allow the carb mounting pad to set level after all the suspension work is done, i.e. the pad must be level sitting in the chassis. The rear is then shimmed to the crank centerline. FI gives you a little more leeway.
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Old 08-06-2004, 04:41 AM
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For street/street & drag use the following.

Mount the engine so that the carb base on the intake manifold is level (front to rear as well as side to side). This will cause the crank centerline to be at 3-4 degrees down at the rear. The centerline of the rear pinion shaft should be up the same angle as the crank centerline. Any side offset of the pinion shaft to the crank centerline is not a consideration at this point.

On a drag only setup, the pinion shaft is set down to allow for spring wrapup in some rear suspensions. Coil over suspension, rear coil suspension and transverse spring suspension do not have spring wrapup and this down setting is not used. Also on drag only setups the crank centerline may be set so that it points up in some situations.
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Old 08-06-2004, 05:12 AM
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Frisco is right on but to put it in other words. Think of extending the tranny output shaft all the way back even with the rear end and extending the pinion shaft all the way forward to even with the tranny. These shafts would be parallel when the rear axle housing/ pinion angle is set properly, even though they be off set . The order you do your installation is set your frame level side to side and the desired ride height at the front and rear, build your motor mounts and tranny mount for the carb mounting base to sit level and the motor near the center of the frame with crank shaft parallel to the frame center line if clearances will allow. Now install your rear end and set the pinion angle to match.

Trees
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Old 08-06-2004, 01:06 PM
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Thank you all, ever so much !!
Dennis
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Old 08-06-2004, 01:48 PM
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Set car at ride height and pinion/output shaft angles should be equal and opposite.

http://www.carcraft.com/howto/91758/

The following picture courtesy of MADXJ
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Old 08-07-2004, 06:40 PM
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First I must say that some of my friends think I am anal about driveline angles. That said. You are only guessing if the body if off. When I do mine I load the car with sand bags and duplicate what I will be doing. If I am on a long trip I load for the trip and then only use a small axle wrap number and if I am going to the strip I change that a lot. ( I have a fully adjustable rear) For your case. I would look at shooting for equal angles between the trans and the pinion with about 1\2 inch center line difference. That is required for the universal to work. Then planning on having the pinion about 1\2 degree lower for a street rod that is not run too hard. Try and set the system so that you can adjust it later as you put the body and operational weights into the truck. It does make a difference and I really think most folks don't really understand what is required. If you work at it things will be smooooth.
Bob
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Old 08-11-2004, 12:56 PM
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Pinion Angle Mystery

FAIRLY SIMPLE !
Using the digram in the previous post, and with the chassis and suspension loaded as it will be at the curb, keep the angle of the driveshaft to pinion shaft and driveshaft to transmission output shaft at 3 degrees or less, with both being equal. Except under extreme conditions, i.e. pro drag racing, etc., most suspensions will maintain those angles, close enough to minimize vibration, throughout normal travel. THIS WORKS! With the digrams previously posted as reference, you should end up with a smooth driveline.
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Old 08-11-2004, 05:43 PM
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Drive Shaft Angle

Most answers were right on. But- Is your F-100 going to set level at the curb when you get through with it ? Are the tires/wheels going to be same size front & rear ? IF SO, then level the carb flange on intake manifold when motor/tranny is setting on all mounts, like the other reply said. Then find a flat/level place on the motor like where the distributor goes into the block. You will get a 3 to 3.5 degree down angle. Adjust the rear end housing to get the same pinion/yoke with angle pointing down towards the floor/ground. Why ? this is what causes the needle bearings inside the U-Joint caps to rotate. Otherwise the needles will get FLAT SPOTS on them. If you are using an un-cut drive shaft the phasing of u-joint crosses is a don't sweat it point. A drive shaft shop knows how to phase a shaft if you are putting in a chopped one. Which is criticle, vital, important, imperative.
Don Nicklason
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Old 08-11-2004, 06:02 PM
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Thank you. Looks like I'm headed in the right direction.
Right now, I'm 2 degrees down on the engine and 2 degrees up on the pinion. I suspect those angles will all change when I get the cab, bed and tires on but I'll be somewhere in the ballpark.
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Old 08-14-2004, 07:11 AM
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Wow, information overload...... I need some Tylenol.
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Old 08-15-2004, 04:56 PM
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Dep, I don't want to beat a dead horse since you have already set your 2 degree angle. I have only done this on seven rods(8 if you want to count my pickup the second time) and have set all of them with the body off. On each, I determined where I wanted my ride height, front and rear, set the motor and transmission mounts and welded in the rear suspension. I then adjusted the suspension to give me the ride height when every thing was done. Front end is easy when using a Mustang II because a parallel lower control arm sets the spindle center and the outside diameter of the selected tire then sets the ride height. In the rear, I use the selected distance from the top of the rear axle tube to the bottom of the frame to determine the ride height and put a block in that space, level the frame front to rear and then measure from axle centerline to determine the outside tire diameter. If you want to use same size wheel/tires front and rear, then you would vary the distance above to level the frame. You can then raise/lower the suspension when every thing is installed in the vehicle to give you the ride height. Just remember there are many ways to skin the cat and since you figured out how to do your pinion angle, the you can complete the rest of suspension challanges.

Trees
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