Another Caster Question...

[nvrstuk]

You've been making great progress. I can't remember if you have some type of solid anti-wrap setup on the rear yet. Typically we always want the pinion angle 1 1/2 to 2deg below the DS angles since you always get axle wrap w/o 4 link type setup.

Once it gets under it's own power put a GoPro underneath and focused on the pinion and watch it clock up! I really didn't believe there could be so much spring wrap on a "normal" acceleration till I saw it posted up on B-Fix about 25+ yrs back... convinced me then.

 

[Torkman66]

I did install traction bars on both sid leaf packs.

Looking at the Tom Woods Geometry article, here is a graphic.

I understand the need for having the 1 or 2 degree of angle but apparently with the Cardan at the transfer case, if you start at zero degrees, it nicely absorbs any angle changes up or down but really pays off when cruising because the DS is spinning in a line with the pinon. Smoother operation and no real wear on the u-joint.

 

[nvrstuk]

Interesting because I have also posted pics from their website regarding this exact scenario and they recommended in their pics on their site a 1 1/2 to 2 deg difference in the rear yoke and DS. Wonder why the change (edit: a few yrs ago) ? Also, every pinion rotates up with every application of the pedal unless you are 4 linked so if starting off with the yoke and DS angles identical you can instantly rotate past the safe point before you can blink.

The other point that T. Woods made back in the day was that at slightly offset angles the needle bearings in the caps are allowed to rotate slightly therefore not developing a wear position from inadequate movement. All needle brgs are designed to actually "roll or rotate" some.

Wonder what the new tech is that the new recommendations are based on?

 

[nvrstuk]

So my curiosity got the best of me and I went to TW and to HiAngle Drivelines sites and they are different although TW used to recommend what Jesse still does.

Below is from Hi Angle Driveline's site

ANGLES ON REAR SHAFTS W/ CV'S- On rear driveline's with a c/v conversion we like the pinion to be rolled to be 2 degree's down first then measure .

ANGLES ********If you can get angles this helps- We will first get the t-case angle usually off the trans pan and or engine pan-or valve cover-

(if not available put the angle finder on the face of the flange or yoke (WHEN STRAIGHT UP AND DOWN) and subtract from 90- ) then moch up the driveline angle with a

piece of string or a straight stick-from center of nut to center of nut the angle the shaft will be -put the angle finder on the that-.

on street-able applications in general we like to see the operating angle (the t-case and driveline angle together) at or under 22 degree's​

Jesse at HiAngle Driveline also states that having the yoke and DS exactly the same doesn't allow the needles in the caps to rotate therefore causing premature wear.

Anyway, looks like the guys that do this everyday have (edit) differing opinions.

I saw your post from TW and it's the first time I remember seeing a shop recommending the rear yoke and DS to be identical... since I'm sitting here taking a break having an afternoon cup of java and supposed to be researching fire alarm and camera systems I tooked at HiAngle's site and others.


Lost the source when copying ... "No, in a double cardan drive shaft, you do not want the yoke and the drive shaft to be operating at exactly the same angle; instead, the design is intended to function optimally when there is a slight angle difference between the two, allowing the double cardan joint to effectively compensate for angular changes during vehicle movement, especially when encountering uneven terrain. "

 

[DirtDonk]

I couldn’t convince a local jeep shop of that to save my life. He’s been doing 4-link suspensions for so many years, he knew what he knew and wasn’t gonna be told otherwise, even when it came to leaf-over-axle setups.
So yes, a linked suspension can be 0° offset from the driveshaft. But I agree with the others here, that it’s not optimal either.
That slight offset that the others are speaking of does help in the bearing longevity inside the joints. It’s a known commodity and has been discussed in depth and meticulous engineering detail for decades. Mainly in the off-road magazines back in the day.
And probably a lot farther back, in engineering journals.
A little bit of movement in the bearings is better than no movement and also better than too much.

I also would like to see a GoPro video of your setup, because of the missing leaves and added traction bars.
Be another set of data points.
We’ve done it with just different leaf spring setups, and we’ve done it with Wrap Traps. And probably Torque Tamers too.
But I don’t remember doing it with fewer leaves, or with this type of traction bar.
Maybe I just forgot. But even if so, it’d be nice to see it again.

 

[Torkman66]

So I also have now poked around the web and found lots of different opinions. About 50% of the articles/threads I read from across the truck world say zero angle between pinon and DS with Cardan at TC. Some say ensure you point pinon directly at the TC (that seems the same as in line with DS). The other 50% say to drop pinon angle 1 or 2* for pinon rise during acceleration

Here is a quote from a Motor Trend article. I think this is likely the best explination. The first part of this says 0* but then suggests putting pinon down a degree or two on spring-over axles.

"On rear axles with a double cardan-style ’shaft, the pinion and driveshaft should ideally be at a 0-degree operating angle at ride height. It is important to allow the double cardan joint at the transfer case to take up the difference in slope between T-case output and the driveshaft. Now with that said, there are some exceptions in the real world. On a vehicle with soft springs or springs that are susceptible to axlewrap (such as on a spring-over), it is acceptable to keep the pinion down a degree or two to make sure the angles are correct on acceleration. Again, every vehicle is different and this should be discussed with your driveline builder."

This is from Tom Woods Geometry article:

What about the 3rd joint [the pinon single u-joint] in the double cardan shaft? With this type of driveline it is important to rotate the differential upward so that you have minimal joint operating angle at the differential end of the driveshaft. Any substantial joint angle would cause the pinion to try to speed up & slow down two times per revolution. Causing what is known as a torsional vibration.

They do not reference anything about needle bearings, just that there should be "minimal operating angle." But if you use their angle calculator which tells you what size shim to use and you put in 18* DS and 18* pinon they call for -2* shim. If you put in 18* DS and 16* pinon, they call for no shim. So, that seems to suggest that by "minimal operating angle" they mean around 2* However I could be misinterpreting what they mean when they say "minimal joint operating angle." Rather than just go by the internet and various searches, I'll give them a call tomorrow and discuss further. Might be removing the 4* and putting in 2*...

 

[Torkman66]

Found this from Tom Woods himself from a 2015 post. This is the same graphic as on their store page in the geometry article.

 

[DirtDonk]

So that last one simply mimics what we’ve been saying for years here.
Not based on engineering or official documents or any manufacturers recommendations. Simply based on our own observations of hundreds of members here, who have experienced the good, the bad, and the ugly issues encountered when modifying our suspensions from stock.
Almost to 100%, anyone running a rear pinion angle of more than 2° below the centerline of the driveshaft, will typically experience a vibration under deceleration.
Anyone running a 0° angle, or any minimal angle above the centerline of the driveshaft, will experience vibration under acceleration.
This is how we, the members here (and broncofix, norcalbroncos, coloradoclassics and others), came up with the one to 2° down angle of the pinion. No calculations, no mathematics, just real world experience.

This ONLY for Early Broncos with “generally standard” leaf spring setups.
As mentioned, the Bronco suspension design (relatively short, narrow leaf springs mounted on top of an axle with a design like the 9-inch), promotes a fairly serious amount of axle-wrap.
Just basic driving around puts the rear pinion through some wildly wide angular changes.

 

[Broncobowsher]

I had a Ranger and did a V8 swap. Prior to taking everything apart I did some layout of what was in there. Took a brand new roll of dental floss I got from the dentist (found a use for that stuff afterall). Strung it from the center of the pinion to the center of the harmonic balancer. Was going to make reference marks to help put the V8 in. Found the U-joints had a built in lateral angle. The tail of the transmission was offset to the passenger side several inches. Even with zero pinion angle, the U-joints always have a side angle. Not much, but always there. Step back and look at it and you could see it, but you had to know what you were looking for to see it.

I also know of a car that had IRS and a perfectly straight driveline. The needle bearings would brenell, dent the races and flatten out, from the continous forces and lack of rotation.

 

[.94 OR]

Had a similar experience with a PTO shaft for tractor mounted tiller.
I would offset the tiller to provide roughly 2° at both ends with no problem.
The manager was a straight shaft guy and would adjust it back if I wasn't around. He couldn't figure out why I had to keep changing out u-joints.

 

[Torkman66]

@DirtDonk i agree completely. Sometimes the best info comes from real-life experience over the years. You and others are always a rich source of that and we all sure appreciate it!
I called Tom Woods and asked about their diagram and language in the geometry article. Gent said key is to have angle close to piñon with a 1 or 2 degree angle below. So exactly what you all are suggesting. He said if there is no vibration on acceleration or deceleration to just leave it. However he also mentioned the needle bearings require slight angle to turn.

So, summary and conclusion:
Yes, alighn piñon angle with DS angle minus 1 or 2 degrees.

I’ll bet if I reinstall the bottom leaf back into stack it gives me 1 degree…I’m getting pretty good at taking the leaves apart

 

[nvrstuk]

Remember that fully loaded your DS angles will change as your frame & tcase are now lower to the ground (& lessen the DS angle) throwing those angles off even farther & messing things up again!

This is why so many rear yokes are grenaded when guys are bottoming out the rear suspension under throttle suddenly hear loud clunking noises. Everything factors into maxxing out the pinion angle from axle housing rotation to DS being lower to the grd now and it grenades. Quite common.

 

[Torkman66]

@nvrstuk thanks! I’ll try to get piñon angle to 2°. I don’t have a GoPro to film but know what the axle wrap bump feels like under hard acceleration. It’s almost as if rear tires bump and skid slightly. I’ll go out and check that on a drive. I’m hoping the traction bars I installed keep axle wrap to minimum. Since I have removed 3 leaves to get ride level I might find axle wrap is still an issue. Could always add the Hellwig 2002 system to front of leaf if needed. They sure seem to get great reviews and most folks suggest they completely eliminated axle wrap.

 

[ntsqd]

I believe that the 2° advice is based on leaf spring rear suspensions. When those are put under load the pinion will rotate up to something close to 0° I do not think that this advice was adjusted for, or ever considered to possibly need revision when linkage rear suspensions became more common. At least not in the DIY field, but I suspect that some have done so and that is where the 0° suggestion comes from.

When the racing engine shop that I worked for built their engine dyno the local drive-shaft guys were pretty insistent on there being an offset in the centerlines between the engines and the load brake. They explained to me that the needles needed to rotate or they would brinnell and fail. We had two drive-shafts built and rotated them in use. They got a work-out, but they also got greased with every new engine test. Eventually they were on a 6 month rotation where regardless they got new U-J's every 6 months. We never had one fail, so we were doing and did something right.

Those experiences leave me with the opinion that 2° at the pinion is a good idea, regardless of rear suspension type. It won't hurt and it should help.

 

[Broncobowsher]

Those dyno U-joints never had to time on them to brinnell. If they dyno was running a durability test and running the engine for over 100k worth of mileage, then I would have expected to start seeing issues. The failure issues are not short term. The no angle brinnell issues are higher mileage durability issue.

 

[ntsqd]

The dyno was for development and proof of HP delivery. One day it could have a low CR 460 on it and the next day a highly modified ~2.3L for one of the local Pony Stock racers. The day after that might be when the twin-turbo'd 550+ci DRCE out of the local tractor-puller came in for some development work. I distinctly remember one 355 Sprint Car engine, it was mechanical music! They also offered a break-in service on it. Could opt to have your new engine broken-in on the dyno.

In the time that I was working there we never had any sort of failure of the drive-shafts, but we also were very proactive about not having a failure. Losing the drive-shaft could easily cost the owner his or her engine. Not something we wanted to have happen. I did the trig at the time, but don't recall the dims. For the length of the drive-shaft the engine mounts were off-set whatever it was that resulted in 2° operating angle for both U-J's.

[HIJACK]
One of the engines developed on it is responsible for cleaning up nearly every medium to large fuel tank leak resulting contaminated soil in the whole country. They ended up building several hundred clones of that engine & rebuilding about half of those after they had 100's of continuous operation hours on them. At one time they exhausted the nation's supply of cast pistons for that application. A couple were even shipped to the UK to clean up a WWII airport in-ground fuel tank leak there. Every one of those engines shipped ready to run. Long term durability testing was done by the customer in that case. The company considered 100 hours operation to be a minimum (some site conditions were extremely hard on the engines, in spite of some very elaborate filtering) and EoSL was 500 hours regardless of how well the engine was running.
The engine that we all wished we had been able to put on the dyno was an Olds 350 diesel block based 440ci gasser for a "Mom's Grocery-Getter" station wagon. Owner picked it up literally a week before the dyno was ready.[/HIJACDK]