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Old 02-06-2005, 10:07 AM
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short driveshaft high angle ujoints

We have a 34 ford in the shop with some vibration issues. heres the specs: 351w hooked to a C6 with a Gear Vendors OD mounted to that. That left room for a driveshaft that is 19" long,(ujoint to ujoint) to hook to a 9"rear end. The car is not slammed excessively but the motor is set at 6 degrees. (TCI frame, thank you) The ujoint operating angles as I measured them are as follows: ride height :12 degrees, suspension bottomed: 18 degrees We're suspecting the driveshaft is the origin of these vibes because of the short length and the resultant high operating angles.( We also know that these angles will lead to very early ujoint failure) I have set the pinion angle to be 1 degree lower than the trans angle as this chassis has urethane bushed 4 bars. We know something has to change. Obviously we'd like to start with the least expensive option which is the driveshaft. Would a shaft with double cardan type u joints at each end help? Is there such a thing as CV type joints for driveshafts of this type? also I saw in the knowledge base here that in extreme cases you can make the pinion/trans angles the same angle, only opposite, (I'm assuming you factor your pinion preload angle to this) and this would help to get the ujoint operating angles down some. I've heard the lifted up truck guys do this. Is this an option that works for things where vibration is undesirable? We can't move the trans very far with out too much work. if we have to move the tranny we'll get an AOD built for it instead to get the length down. Not our most favorite choice. I'm going to talk to the driveshaft shop on monday but I thought I'd post here too and maybe get some alternative views. Thanks for reading this, Mike S.
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Old 02-06-2005, 10:24 AM
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I know double cardan on each end is possable but I wouldn't do it. I would start out with a double cardan CV at the trans and then rotate the pinion up to point at the trans output.

I have had good luck on my lifted K5 with a double cardan CV from http://www.highangledriveline.com/ He really knows his stuff and sells to all over the place. Just give him a call...his website sucks.
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Old 02-07-2005, 10:18 AM
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You didn't mention checking the phasing of the u-joints. They should be 90degrees out of phase to allow for proper rotation without binding. This is especially important on a short shaft.
Here is a site with design tips.
http://www.clubfte.com/users/jniolon...nephasing.html
Here is a site with troubleshooting tips.
http://www.drivetrain.com/driveline_...eshooting.html
Mark

Last edited by astroracer; 02-07-2005 at 10:33 AM.
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Old 02-07-2005, 11:49 AM
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Quote:
Originally posted by astroracer
They should be 90degrees out of phase to allow for proper rotation without binding.
I don't know where you got this information. It is not correct. Even the links you gave don't say that. Did you mis-type?
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Old 02-07-2005, 12:00 PM
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The info is correct... The first link I provided has an illustration of it at the end of the article.... The out of phase joints prevent binding as the u-joints rotate...
Mark
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Old 02-07-2005, 01:08 PM
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Quote:
Originally posted by astroracer
The info is correct... The first link I provided has an illustration of it at the end of the article.... The out of phase joints prevent binding as the u-joints rotate...
Mark
Unless I am interpreting the article incorrectly; the u-joints are supposed to be in phase. Below is a quote from the article taken just above the illustration you posted.

" The position of the u-joint yokes on each end of the driveshaft can help smooth out this to some degree. The yokes should be positioned so that their center lines are on the same plane.

If you're using a factory shaft, all this has been taken care of. If you're building one or having one shortened or lengthened, the yokes should be positioned so that their center lines are on the same axis. The action of the opposite yokes tends to cancel out the speed variations of each other."

The emphasis is mine.
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Old 02-07-2005, 01:34 PM
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driveline

Who built this drive shaft?
Is it straight?
Has it been balanced?
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Old 02-07-2005, 04:29 PM
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Frisco,
Check out this site... Go to sections 9.2 and 9.3.
http://www1.mn.man.de/manted/aufbaur...l#Anchor-21683

You will see that a phased driveshaft only works when the input and output shafts are planer.
Both joints have the same deflection angle.
The two inner joint forks must be in the same plane.
The input and output shafts must also be in the same plane.

An unphased driveshaft is a requirement in any situation where the input and output shafts are not planer. The requirement seems to escalate when you throw movement into the mix. Steering shafts are one good example where the universals are unphased to keep binding or "hard spots' to a minimum.
The given example has the engine and trans sitting at 6 degrees from horizontal. It is not reported what the pinion angle is. Any deflection in the pinion angle during suspension travel can cause binding in a phased driveshaft. Especially one this short. A longer shaft may not have the same issues but this one is very short and it seems to have a high rate of deflection in the joints so I would question the phasing...
I am by no means an expert here but this is some of the stuff I have found while researching my Astro van build.
Mark
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Old 02-07-2005, 04:59 PM
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Quote:
Originally posted by astroracer
Steering shafts are one good example where the universals are unphased to keep binding or "hard spots' to a minimum.
I went to the link above. With all due respect Mark I still have to disagree with your findings. Even the links that you have given show the exact opposite of what you are saying (with one exception). Check your link and Figures 21, 22, 24, and 25. They all show the u-joints in phase. The exception that is shown is under 9.3 Figure 23. This is an unusual circumstance and not usually found.

As to your statement concerning steering shafts; once again you are incorrect. The link below is from the Borgeson site and clearly states as well as showing a drawing that the steering u-joints must be in phase to eliminate binding and premature wear.

Borgeson

I am not attempting to DIS you; but rather attempting to get you to re-read your own links. You might also take a look at any rear wheel drive car or truck with an open driveshaft. You will see that they all have the u-joints in phase. This is not done by mistake.

Peace!
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Old 02-07-2005, 05:39 PM
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Boy is my face red!
Frisco, you are exactly right! Looking at it in another light has shown me how I had misinterpreted all of that data. I had it in my head that the u-joints HAD to be out of phase to work correctly and that is NOT the way it is. I can't believe this! I KNEW I was right but, as soon as I started "reading" what was written, I saw I had taken the data and turned it around backwards... Sheesh!
I want to apologize to everyone who has read this thread and been misinformed by my ramblings. Especially Mike, who started the thread...
And even though I was wrong in my interpretation, phasing is still a viable issue.
Thanks for setting me straight Frisco. I appreciate your candor and you ARE 'da man!

Mark, red faced in Mi.
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Old 02-07-2005, 09:57 PM
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drive shaft

Wow that was quite the ride. I do know that rotating u joints about 25 (not 90)degrees to eliminate a hard spot works ONLY on steering shafts that have BINDING issues that can't be resolved in any other fashion. and it does not eliminate the hard spot , it only reduces the hard spot. Thats what the borgeson tech guy told me . And I know it works, I did it on a 27 t with a nailhead buick. Those solutions don't apply to shafts that spin at a somewhat higher rpm.(it was fun to watch ya'll duke it out tho) The shaft in question was balanced and is in proper phase. the operating angles are too high. the pinion is 1 degree lower (5*)than the trans shaft(6*) this is standard for 4-bar setups. The problem is it vibrates. it doesnt bind. I was trying to figure out a way to fill the space between the trans and pinion with something that would operate vibration free at a higher angle than the traditional single ujoint type driveshaft. Or move the things that I can to try to smooth things out. The drive shaft shop told me this morning that a double cardan can operate up to 10 degrees without vibration. If we get the shorter output shaft & tail case for the OD unit from gear vendors ( which takes 10" off the trans and we can make the driveshaft longer), we can get the op angles down to 9 degrees, which is outside of the rattle zone. That solution will cost about 2G not including the output shaft swap at the tranny shop. I guess I was looking for a little less expensive fix. thanks everyone for trying though, and man that german truck engineering link was cool.I'm gonna ponder that one for a while. thanks Mike S
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Old 02-07-2005, 11:49 PM
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I still stick with the double cardan at the trans only. I think you arn't seeing the what turning the pinion will do for you. Rear axles are about 12" from axle centerline to yoke centerline. When you turn the pinion it will reduce the angles on the driveshaft. It will be even more noticable with a short driveshaft. Try taking some measurements and drawing it out to scale.

Just given the #'s you put in your posts I did a quick solidworks sketch and got that if you rotated the pinion to point at the trans (which would be down in your case?) that you would end up with 7.5deg at the double cardan (at the trans) at ride height.

One more thing.
Is the output a fixed (with slip driveshaft) or slip yoke? It has been my experiance that fixed yokes vibrate less. They are also shorter to help with driveshaft length some.

Last edited by Triaged; 02-07-2005 at 11:48 PM.
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Old 02-08-2005, 03:59 AM
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Re: short driveshaft high angle ujoints

Quote:
Originally posted by powerrodsmike
We have a 34 ford in the shop with some vibration issues. heres the specs: 351w hooked to a C6 with a Gear Vendors OD mounted to that. That left room for a driveshaft that is 19" long,(ujoint to ujoint) to hook to a 9"rear end. The car is not slammed excessively but the motor is set at 6 degrees. (TCI frame, thank you) The ujoint operating angles as I measured them are as follows: ride height :12 degrees, suspension bottomed: 18 degrees We're suspecting the driveshaft is the origin of these vibes because of the short length and the resultant high operating angles.( We also know that these angles will lead to very early ujoint failure) I have set the pinion angle to be 1 degree lower than the trans angle as this chassis has urethane bushed 4 bars. Thanks for reading this, Mike S.
I am curious as to why the engine / trans is set at 6 degrees (I assume down in the rear). When setting the engine / trans in the frame the angle is determined by leveling the engine front to rear and side to side from the carb mounting area of the intake manifold. Most engines will cause the down angle to be 3 degrees.

Setting the rear pinion shaft down is correct for a drag suspension due to the constant load which in turn will rotate the rear housing up. On a street vehicle the rear pinion shaft should be set in an up direction the same number of degrees that the engine is set down. EXAMPLE: engine trans down 3 degrees. Rear pinion set up 3 degrees. The centerlines of the crank and pinion shaft should be parallel.

The other consideration is the installed height of the engine. Since the ideal situation wants the centerline of the crankshaft to be parallel to the centerline of the pinion shaft (Looking from the side in this example); If the engine is mounted too low or too high, even with the centerlines being parallel, the operating angles of the u-joints with a short driveshaft will be excessive.

I may be mistaken but I don't recall anything about setting the pinion angle in the down position just because you have a parallel 4-bar. I had parallel 4-bar with a modified Model 'A' rear spring in my '28 Ford Closed Cab Pickup. Rear pinion angle was set at 3 degrees up. I also have parallel 4-bar with coil-overs on my present project which is a '30 Ford Coupe and this is also set at 3 degrees up.

To Astroracer: The object is to continue to learn something new every day. I try to do that. Thank you for the good discussion.
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Old 02-08-2005, 09:31 AM
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triaged- yes we will definately run a fixed yoke on the new driveshaft and I also plotted out the angles on my big table and found the angle reduction. as I said in my original post I wondered about rotating the pinion down to point at the trans(same as the lifted truck guys, but upside down). I just need to know that this will work in a street car where vibrations are much more noticable. It worked on your blazer. it makes sense that it would work .Will a guy who makes driveshafts for a living say this is the case for our 34 ford. I suggested this to the first driveshaft shop we went to and he said shorten the trans if we could (we can)and to set everything up in the conventional fashion with the doub cardan/ fixed yoke at the trans. He said it's better this way. His knowledge seemed to be up to date but he didn't really want to go outside the box. I'm going to call the place that you recommended plus 1 or 2 more and maybe get some more input. Thanks for reading.

to frisco - The 6 degree motor angle was given as a reference angle. with the car on the floor it measures out to be 4 degrees. the relationship between components was what I was trying to illustrate. It is standard to add some angle to the pinion to compensate for rear end wrap in all cars, not just drag cars. Thats what I've seen and read. if there were no losses from friction and wind resistance or moving weighted objects from one point to another we would have a perfect machine. (we wouldn't need engines to move things either, they'd just slide wherever we pushed them, but that goes in the physics forum) We have these losses so I would say that 1 degree difference in trans/yoke angles to compensate for this is not at all excessive. I know that by just putting weight on the suspension can change pinion angle by 1 -2 degrees. where is the movement ? in the bushings. By design, urethane bushings move and give. if I were setting up a car with heim type rod ends I would probably set everything up as you say, with all angles being equal. Thanks for reading, Mike S
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Old 02-08-2005, 10:12 AM
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Quote:
Originally posted by powerrodsmike

to frisco - It is standard to add some angle to the pinion to compensate for rear end wrap in all cars, not just drag cars. Mike S
This is true with parallel rear springs. With parallel 4-bars there is no wrap up. The rear housing will move up / down in a slight arc, but will not be able to rotate because of the 4-bar.
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