Drive Shaft: Drive Line Angles

[wdills]

So I am on to the next topic of investigation regarding the vibration in my Hawk that occurs around 73 mph. Tonight I measured the angles of all the drive line components. Engine / Transmission is about 6 degrees down. Drive shaft is flat, 0 degrees. Differential pinion is about 6 degrees down.

From what I have read, to get the ideal setup I would need a 12 degree wedge to rotate my differential around to 6 degrees up. This seems like a lot of wedge. Would I be better off putting a shim under the rear engine mount to flatten out the down angle of the engine / transmission a little and then picking a wedge for the differential?

[64studeavanti]

I think 6 degrees is a bit much. IIRC, the target is around 3. Which transmission do you have? If manual, do you have the spacers under the rear mount?

[wdills]

I do have a manual transmission (3spd / OD). No I don't have any spacer under the rear engine mount. Car didn't have any when I got it, and I never thought to look if any belonged there. Looking at the parts book, it appears that I need spacer P/N: 1548406. I have checked the major online vendors and nobody lists them. Anyone know how thick they are supposed to be? I saw an old post that suggested 1/2" but the poster did not seem sure this was the correct measurement.

[WCP]

Wayne, I believe the general rule is for engine to be 3.5 degrees down toward the rear, a 0 driveshaft, and 4-5 degrees down toward the front for the axle. That may translate to something like 7, 3.5 & -0.5-(-1), or 8, 4.5 & 0, engine, driveshaft, axle, depending upon engine to frame angle.

[DEEPNHOCK]

??
Whatever you put in at the front, you take out at the back.
If the crank centerline is down, then the pinion should be up.
Maybe remove a degree or two for spring wrap...
There are numerous spring and driveline shops that can help you out...

[wdills]

I apparently have several things to deal with. First priority is new rear springs. I know mine are week and letting the back of the car sit lower than it should. Changing the height of the rear of the car will impact all the other angles so I need to take care of this first. Plan to get a new set of HD springs. Once they are installed and the correct ride height is restored, then I will get back to drive line angles.

Second, I need to level out the engine a little. I will have to check how much clearance I have in various places to determine the best way to change the angle. SI has thinner front mounts and I can add a spacer at the rear mount. Objective is to end up around 3 degrees down on the engine / trans while still maintaining fan to shroud clearance as well as all the other things that could hit when you start changing the mounting position of things.

Once the engine is at a better angle I will determine the correct wedge to change the pinion angle. I am hoping for 3 degrees down on engine and 3 degrees up on pinion. Fingers crossed.

[Hawkowner]

Max angle between shaft and center line of the yokes should be 6 degree. The yokes should be parallel.which yours seem to be.
Hawkowner

Hawks have a critical wheel and tire vib at The 70 mph range. Are you sure it is drive line tires and wheels have a vib in the ten Hertz range.ls the vib a bounce or a drumming noise.
Hawkownhner

[Treblig]

https://video.search.yahoo.com/yhs/search?fr=yhs-mozilla-004&hsimp=yhs-004&hspart=mozilla&p=how+to+set+drive+shaft+angle#id=6&vid=15a88240b99e4a78e9df9cc64042896d&action=view

And many more examples.

Treblig

[alpayed]

Hawks run a brokenback arrangement. Transmission is down, shaft horizontal and the pinion points down. If you raise the rear transmission mounts to get 4.5deg to 5 deg down and leave the diff down 6deg it should solve the problem. They need to be equal within 1.5 deg. Not necessarily equal and opposite but equal.
What is happening is as the speed increases the diff angle changes (winds up) and your transmission is still 6 down but the diff has wound up to 2deg down.
You then get a large difference (4deg) which causes the vibration.
The angles will always change and on a broken back arrangement you need to have a happy medium so that under all driving conditions the angles remain not too far out.
On a more conventional arrangement the angles cancel when the suspension moves up and down because the transmission and pinion are parallel. However the diff will still wind up so the 1-1.5degperload should be there. This arrangement will not work on a hawk unless you alter the transmission tunnel at the rear. It is not deep enough to allow the driveshaft to be high at the diff.
Hope this helps.
Allan

[wdills]

Hawkowner, I have heard about the 70mph Hawk vibration. I just don't understand where it comes from. Wheel and tire doesn't make sense for me because I have aftermarket wheels and new radial tires. They were spin balanced so I don't see them causing the vibration. Bad drive line angles are the most reasonable thing I have run across so far.

Allan, I am concerned that I won't be able to get the ideal equal and opposite 3 degree angles due to clearance restrictions. I hope to at least achieve a broke back arrangement with 3 degrees on both ends. From what I have read the angle of a U-joint should never be more than 3 degrees.

[64studeavanti]

Try the easy stuff first. My 4spd Avanti had vibration problems when it did not have the spacers installed under the rear mount
Adding them cured the problem. IIRC, they were about 1/2". You could use a stack of washers and vary the number to suit.

[wittsend]

Please read post #9 - again. As alpayed has stated you have a 'broke back' configuration where the transmission AND the pinion shaft point downward. Some have mentioned the configuration for a standard set up (both parallel) but the driveshaft would probably have to pass through the shaft tunnel to achieve it. On my '64 Daytona I don't think I could get any less that 6 down at the trans. I don't recall what the pinion was at but I know it didn't match. I'll look tomorrow and see if I can find what it was. Remember you are comparing angles to each other and not necessarily that the shaft is at 0. In theory you could figure it out on a sloped driveway.

[bensherb]

Allan, I am concerned that I won't be able to get the ideal equal and opposite 3 degree angles due to clearance restrictions. I hope to at least achieve a broke back arrangement with 3 degrees on both ends. From what I have read the angle of a U-joint should never be more than 3 degrees.

After setting ride height with new springs, tires , etc... When parked on a flat level surface, I would put my angle finder on the carb flange of the intake and raise or lower the engine/trans at the trans mount until it's level. Then, measure the trans output shaft angle and adjust the rear axle pinion angle so it is paralell. This is how I've done it many, many times and have never had any problems. I had no problem acheiving the correct arangement in my dads '53 coupe. It has a GM TH350 trans, a Ford 8" rear axle, a one piece drive shaft and sits and looks factory stock. Actually I set it up twice; I replaced the Dana 27 with a Dana 44, then later replaced the 44 with the 8".

Ideally, the operating angles at each end of the driveshaft should be within 1 degree of each other and at least 1/2 a degree of operating angle; not inline.

As for a max drive shaft angle; 3 degrees is incorrect. Perhaps you read 30 degrees. Take a look at the front drive shaft on a 4wd truck sometime. The more extreme the angle the more likely you'll bind the U joint and twist the driveshaft into a knot with the application of the needed power, plus, the U joints won't last long. U joint life decreases as the angle goes up and it is forced to work harder.

The max normal operating angle for a driveshaft that is expected to turn at 5000 rpm is 3.25 degrees. As the expected driveshaft rpm drops the max normal operating angle can increase, for example at 1500 rpm a 11.5 degree angle could be considered normal.

[5brown1]

How do you set the angle with the two piece drive shafts?

[wdills]

bensherb, I didn't mean a max drive shaft angle of 3 degrees. We have plenty of 4wd trucks around here with drive shafts that look to be 30 degrees or more. I was referring to the operating angle of the u-joint. According to the Spicer / Dana website the operating angle of their u-joints should be no more than 3 degrees.

Based on feedback received, I am just hoping to get my u-joint angles less than three degrees even if I can't get away from the broke back configuration that Studebaker designed.