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RPM

Engine, Driveshaft and 3rd Member Angles

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I'm starting my own thread as I've hijacked bigmal's enough.  A bit of history on my 69 Mach One equipped with a 351W stroked to 393, AOD, 9 inch with 3.70 Ford gears and traction lok, triangulated 4 bar coil over rear suspension. 

I lowered the motor one inch to fit the shaker air cleaner to the hood. The car sits maybe 3-4 inches lower than stock. I didn't really lower the car per se, I built the suspension to the height I wanted. My bad memory says the bottom of the rockers are 5-6 inches above the road. 

Since I've had the car on the road, it's had a very slight cyclical vibration once it gets up to 55 mph or so. I can feel the vibration in the steering wheel and on the seat. The steering wheel doesn't visibly vibrate and parts don't rattle. But it bothers me, as I know it shouldn't vibrate. 

While setting up the drive train, the only angles I ever checked were the crankshaft and 3rd member. I never checked the driveshaft. Until now. 

These are the angles of my drive train obtained by a digital level:
 
Engine,  3° down on the back side. 
Drive shaft, .3° down on the back side. 
3rd member,  2.75° up on the front. 
 
If my math is right, the drive shaft to 3rd member angle is ass backwards. This angle has the U joint above a centerline drawn thru the ds and pinion. Not good. 
 
Do y'all think I can fix this by putting the pinion angle at <1° up in front and raising the trans mount to match the 3rd member? Or is my thinking out to lunch?
 
With the rear U joint that far out of spec, how did it not shake all the parts off my car?

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Ideally the driveshaft should be at a steeper uphill angle then the diff. For example if the pinion is level and the driveshaft is 1 degree down this is the opposite of ideal although it will not necessarily cause a problem. The problem is when the amount of angle is not the same at the engine or trans as i mentioned in my other post. I posted photos and videos on driveshaft angles on here a while back but i can't find it now. Its much easier to understand by looking at those. Even though you have a fixed diff the faster you go the higher the front of the car gets and the lower the rear gets and this changes the angle of the driveshaft relative to both the trans and diff 

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Here is one of the photos i posted before. Look carefully at the bottom image as it might be hard to see what it is depicting. If one has driveshaft angles like this, i will definitely cause a vibration. This is the last example in my post above that I was trying to explain. The driveshaft must always be downhill more than the trans AND uphill more than the diff, or vise versa.

 

 

drive-shaft-angles-1024x.jpg

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This does not apply to your car because you have a link suspension, but maybe it will still help. It shows how the pinion angle can change drastically on some vehicles which is not ideal but it won't necessarily cause a noticeable vibration providing the driveshaft angles are within the proper range once the vehicle is moving at a steady speed.

 

 

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Ya, I watched that clicker video a couple of times yesterday before posting this thread. This is a drawing of my angles which I thought I posted last night. Because I didn't see the  same direction of my angles in the pics of the drive shafts, I thought I'd have a problem. 

1288316243_MyDrivelineangles.thumb.jpg.25a381dfd78594097ff2d1abbf7eb320.jpg

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Is your sketch correct or am I not reading it correct?  It looks like the pinion centerline is above the engine -trans centerline.  I'm no expert on this topic by any means so I'm not saying you cannot sort through it.  You probably recognize by now all the things that added up to the issue, lowering the motor 1", lowering the car 4", installing a longer than original trans.

Maybe I'm getting too old, at some point in my mind I think all the mods aren't worth the troubles they sometimes cause.

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2 hours ago, 1969_Mach1 said:

Is your sketch correct or am I not reading it correct?  It looks like the pinion centerline is above the engine -trans centerline. 

Yes, it is, and you are correct. (My driveshaft does travel downhill to the pinion yoke, if that even matters) And I didn't see that type of set up in the images online of the driveshaft showing the right and wrong way of setting them up. That is when I became concerned. Then this morning I viewed the video above again and noticed he showed his demonstration as I have mine as being ok. 

I'm no expert on this topic by any means so I'm not saying you cannot sort through it.  You probably recognize by now all the things that added up to the issue, lowering the motor 1", lowering the car 4", installing a longer than original trans.

Ain't that the damn truth! As my dad would say, it seemed like a good idea at the time. Btw, my FMX  and AOD are identical in length and mounting points. 

Maybe I'm getting too old, at some point in my mind I think all the mods aren't worth the troubles they sometimes cause.

We are dead nuts on in agreement with this thinking. 

 

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Bob i think you meant my drive shaft travels up hill to the pinion yoke or at least thats the way u have it drawn. It does not take very much lowering on these cars to get the results on your drawing.  My suspension is bone stock and with it sitting on tires the drive shaft is very close to being parallel with the car. Only a slight downhill to the pinon.  

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1 hour ago, det0326 said:

Bob i think you meant my drive shaft travels up hill to the pinion yoke...

Na, the drawing is tilted a bit in the photo. Everything tilts down front to back. 

•The back of the trans is lower than the front of the engine and sitting at 3°.

•The back of the driveshaft is lower the the front and sitting at .3°.

•The pinion yoke is lower than the back end of the driveshaft, and tilted up at 2.75°.

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Based on your photo, there is a .25 difference in angle between the trans and the pinion. If it were me, since your diff links are adjustable, I would just start trying different pinion angles, starting with rotating the pinion up .20 degrees. If there is no noticeable change try 1 degree up from that new position (3.95) and if that doesn't help maybe even try 1.2 degrees down from the current position (1.75), which should make it worse.

 

 

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Yes Terry, your drawing is correct. Thank you. 

Thanks Mike, I'll put that on my current to do list while I have it up in the air. 

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Did you check if the drive shaft is out of round? Or unbalanced?

Try checking if the yoks are welded on center to the shaft and each other. That will cause a harmonic vibration as well.

Just a thought.

 

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Ya, both drive shafts I've used are in phase. The aluminum one currently in the car is used from an Explorer. I visually checked it for damage, then checked it for run out with a dial indicator. The other one is a new steel DS is steel to oem spec from Dead Nuts On in Fresno. 

I plan on checking the rear axle flanges for radial and axiel run out here soon. 

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As I will also be lowering my engine and going with an aftermarket transmission, I have a feeling that I will be dealing with this too. Bob, anyway we could pull exerts from this and put it in the "How To" section?    

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Damn RPM we have the same set up.

I used lowering motor mounts as well so I could run a Vic Jr. Intake.

If you look at my car from the side the rear end appears to sit higher than my trans output shaft does.

My engine and trans are pointed down, Driveshaft actually runs slightly UP hill to my rear diff if I recall.

But from what I have read and the videos I have seen it should not matter as long as angles are equal but opposite which means if my trans was 2 degrees down my rear end should be pointing up 2 degrees to cancel out, and I have tried shimmying the rear up more and down more and nothing has really helped.

I'll climb under my beater tonight and take measurements of everything and report back.

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2 hours ago, MikeStang said:

Damn RPM we have the same set up.

I'll climb under my beater tonight and take measurements of everything and report back.

Thanks Mike.

"My beater" Really? You can stay, but the BS had got to go. 

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Decided to try something different for a change and dropped the car down off the stands and sat it on all 4 wheels at ride height, then popped the carb off and set the digital indicator on the carb mounting Pad and came up with 4.6 degrees down angle...is it just me or does that seem rather steep? The manifold is a Vic Jr. And I have drop motor mounts.

 

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4 hours ago, RPM said:

I always thought the carb plate was supposed to be horizontal. 

Yeah me to bud.

However from what I have been reading this is not always the case and a lot of the time it is based on the intake manifold design.

I dont have my Vic Jr. Off the car or I would measure it and see exactly how much of an angle it had cut into it.

Anyone running a Vic Jr. That can put an angle finder on carb mount surface and tell me what kinda degree fall you have?

At least I came up dead nutz left to right tho ..hahahah

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the dual planes will typically have a slight angle built into them like ~3 degrees carb pad to cylinder head.  the Victor jr does not (0 degrees).  measuring the carb pad without a reference only gives a partial answer.

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