Drive Shaft: Requirements for custom driveshaft design?

[garyash]

I'm getting ready to order a driveshaft for my Indy car project. I'd like to get some comments on universal joint angles from people who have needed to get custom driveshafts made. I have read that the ideal situation is that the axis of the front yoke is parallel to the axis of the yoke on the rear axle, even if they are not in the same plane, i.e. at the same height. Also, the u-joint angles should be 3 degrees or less. I can't get there.

The 1937 President straight 8 engine sits exactly horizontal, will generate 150-200 hp. There is a 1936 President 3-speed transmission without overdrive or freewheeling. The 1928 Commander GB-W rear axle (3.31 ratio) is currently tilted upwards at a 3 degree angle. The pinion yoke at the front takes the same u-joint as all Studebaker cars from about 1935 to 1966, a Spicer 1310 or SKF UJ369. The driveshaft I have from the 1928 car is an oddball thing with a 5" diameter mounting flange. The u-joint is encased in a sheet metal shell, but it has a cross-like forged donut with the 4 arms sticking out. It's probably something like a Spicer 1330 with 1.063 dia. caps and about 3-5/8" from end to end. The drive shaft was 2" diameter and has a slip-joint in the middle. My new driveshaft will be under 22" long.

I'll need a shaft about the same diameter with 2 different type ends. The front angle may be as high as 7.8 degrees and the rear angle should be about 4.8 degrees. This is more than I wanted to wind up with, but there don't seem to be many options. I really, really do not want to move the engine now! I can adjust the tilt of the rear axle a bit, as I currently have a set of 6 degree shims under it to get it to the 3 degree up position. At 60 mph, the engine and driveshaft should be turning about 2200 rpm. According to a table I found showing maximum u-joint angles versus rpm for about 3000 hour life, I think I'm mostly OK. Apparently, doubling the joint angle cuts the life expectancy in half. In my wildest dreams, I would like to run the car in some vintage racer events and get it above 100 mph, but we're talking about a few minutes above 3000-4000 rpm in 3rd gear. In the end, u-joints are pretty cheap to replace every few years.

I'd like to avoid doing anything grossly dangerous or generating horrible driveline vibrations. Do I need a double Cardan joint at the front to halve the front angles? Do I need to rotate the axle downward 3 degrees so that the flange points horizontally like the engine, even if it makes the height difference and joint angles worse? Anything else I should do to get the best result? Or, is this going to be OK as is?

Oh, and I can't get the #$%! rusted caps out of the u-joint. There are no wires or clips to hold them, only that domed cover held them in place for the last 88 years. The cross can't move sideways, so I can't push on the caps. What's the secret to getting them out?

[Jeffry Cassel]

Sounds like a really neat project! I would soak the U joint in acetone and ATF or Diesel fuel and oil for a long long time. Take it out every few days and tap it with a not-to-big hammer. If that fails try making a relieving cut with a small air cut off tool so you can tap on the exposed sides to loosen it. I would look for a good speed and custom shop and seek their counsel. They will need to fabricate a drive shaft any way. I think you are going to be OK with the angles. If it looks really good it will probably be good. There will be a lots things you will need to tweak once you get it together. My biggest problems with the drive line have come from following the shop manual!

[Dan Timberlake]

How are the angles when looking from above ?

[PackardV8]

Since the engine is horizontal, exactly what prevents the pinion from being shimmed to same?

Jack Vines

[jts359]

I've did business with this shop twice over the years but they have been in business forever Mr.Driveshaft Hurley pond Rd, Wall N.J. Maybe they can help, Ed

[52-fan]

On the bright side, when this is all over you will be the forum expert.

[jclary]

Regardless of the angles, my (under educated) opinion is that balance will be the most important aspect of successful performance of this shaft build. Getting the balance perfected should go a long way in overcoming other specs that might push the envelope of design limits.

Another source of information to study, would be to examine the design, performance, and specs of pto driven farm machinery. Talk about extreme angles, look at pto driven bush hoggs, post hole diggers, and other equipment that are not only operated at crazy angles, but often raised and lowered by feet, rather than inches, while in operation.

[DEEPNHOCK]

Gary,
I spent a lot of years in the business as a mfr rep and sold U-joints for C/R - Precision - Neapco, and a couple of others.
Had to train people on drivelin installation and operation, including phasing, sizing, angles, one/two/three piece drivelines.
OK.... Having said that.

The DANA driveline guide is very good. Their driveline balance equipment (the high speed stuff) is excellent.

Now, about angles. The reason they design some angle into the OE driveline is for u-joint oscillation.
This is important for u-joint life. If the alignment is perfect, then there will be no oscillation of the u-joint cap on the trunion.
The rollers will not rotate in the cap and on the trunion and they will 'brinnel' into the cap and trunion and fail prematurely.
So, some angle is added.
Whatever angle you put into the front, you take out of the back.
If you build in 2 degree's in the front, you take out 2 degree's at the back.
And remember, that does not mean it has to be vertical. It could be horizontal.
Engines are regularly moved to the right for steering box clearance.

Now... After hitting you over the head with that....
This is a low use race car.
If you just line it up straight and run the snot out of it, you will probably never notice premature wear, because your mileage will be way lower than a street use vehicle.

Feel free to contact me if you have any questions.

[garyash]

Jack, I can take out the 6 degree axle shims and put in 2.5 to 3 degree ones. This will rotate the pinion shaft down to the horizontal position so that the transmission output shaft and axle pinion shaft are parallel. However, in doing so, u-joint mounting plate and the location of the u-joint pivot also rotate downward by nearly 3/4 inch. The vertical height difference becomes 3.67". The horizontal spacing decreases about 0.2 inch. The front and rear u-joint angles will now be the same, but they will be 9.7 degrees, about 2 or 3 times as high as they should be. The alternative is to drop the back end of the engine about 1.6" to have it tilt down at 3 degrees like modern cars - not happening!

Dan, there is zero angle side-to-side. The transmission and axle are centered in the chassis.

Jeff, I'm not so concerned about wear as I am about creating a really annoying vibration while driving down the highway at 50-70 mph.

Also, I have to think about driving over bumps, etc. and the vertical travel of the axle. For the most part, it will move up and down with little front/back motion. I considered what happens when a bump forces the axle up 1" or 2". I also looked at what happens on the rebound when the axle moves down 1" or 2". The upward motion doesn't cause problems, it's the rebound, which can create u-joint angles of 12°-15°. See the table below. [My high school trigonometry teacher would be proud of me.] That may still be OK, since it won't happen often and hopefully not at high speed. I'm going to go visit the guy at my local driveshaft shop this week to see what he says, and let them take apart the old u-joints. Once the yoke plate is off the old driveshaft, I think a little simple machining on the plate will allow the installation of a modern 1310 u-joint with snap rings or clamps for cup retainers. All of the parts to build a new driveshaft with a slip joint are off-the-shelf and not very expensive. There are numerous shops that will machine a custom yoke flange from 4140 billet steel for not too much money.

Take a look at those rock-climbing off-road Jeeps or 4x4 trucks and think about how steep their driveshaft angles are. Some of those trucks must have bad vibrations when they drive down the highway and they may break u-joints fairly frequently.

As part of my driveshaft paranoia, I read about "critical speed' for a driveshaft. That happens when the shaft starts bending from it's own weight at high rpm and starts to look like a jump rope. I ran the calculations for a 2" o.d. steel tube with 21" length. It told me I should worry if engine revs got over 30,000 rpm in high gear! So, a lot of other things will blow up long before that old straight 8 pulls anything over 4500 rpm.