I'm replacing the rear-end in my '53 F100 with a 9. My quandary is should I center the pumpkin or the pinion. Esthetically, the pumpkin centered is preferable; however, is the drive-shaft offset a detriment or does it matter? My inclination is to center the pinion for functionality. I don't think the additional weight on the long side will make any difference. How did you install your rear-end and any comments on the two options? Thanks for your insight.
An off-center pumpkin is of no consequence as far as u-joints are concerned. Even adding the typical rearward slope of the driveshaft, the u-joint ""sees" only a single angle from the combined 'down and to one side' driveshaft. As long as rear axle pinion and engine/trans centerlines are parallel, and the u-joint is not at an extreme angle, all is good.
The only time the offset pinion makes a difference is when a driveshaft tunnel is involved (and it isnt in your case), as it may hit the tunnel.
You might consider is the pumpkin exposed to the world where everyone following you down the road will see it as being kattywompus and offset or is the vehicle set up so that those following you or standing behind it don't see the pumpkin. As the others said, the drive shaft and U joints aren't affected enough to write home about no matter what some self styled experts say.
We have narrowed qiute afew rear ends and i always keep the factory offset & never had a problem with function. Seen one that was centered, the car had bad vibration under hard acceleration. & high speed cruise. The guy ended up narrowing another 9 inch & kept the factory offset & it cured all the problems. I always keep the factory offset. I figure every auto manufacturer does it so tbere must be a reason why. But to each his own. I just know i have never had any vibration problems even up to 140 mph.
If your not going to change the rear end width, always center the wheels under the fender or if not fendered, off the body sides . Jack
Many engine/drive trains are offset to the right passenger side and is one reason pinions are also offset. The actual 9" pinion offset is about 15/16", so with a centered engine and pumpkin, the horizontal U-joint working angle is about 1 degree or less in a normal wheel base car/truck and probably won't cause any problems in most setups. However, this angle has to be (or should be) included with any vertical working angle, as this now becomes a compound angle. If the vertical angle is near or exceeding 3 degrees, the added horizontal angle could be the cause of vibration with common single cardan U-joints. This subject comes up often, and is probably best to do some research to better understand it. The link below is one of many that should help. http://www2.dana.com/pdf/J3311-1-DSSP.pdf
V8 Bob, I always read your posts when I come across them and find them well written and knowledgeable. So it with respect that I seek a better understanding of your comment above 're "compound" angle. When I posted on this subject that phrase came to my mind as well, but I discarded it as possibly not applicable to this situation. Here is my reasoning. If, for example, one takes a centered pinion, but with the driveshaft having a downward angle of 3*, that scenario could be rotated 90*, 180* or at any angle throughout the 360* rotation...and the u-joint operating angle is exactly the same, no matter how it is "clocked". For example, if the pinion was level with trans output shaft, but 3* to the passenger side, it would be exactly the same as a centered pinion 3* below the trans shaft. So, as my reasoning goes, it is only a difference in the 'clock' position that occurs when the pinion is not centered, and that does not significantly change the actual operating angle of the u-joint. I fail to see that there are two or more angles present that would justify calling this situation a compound angle. I would think a compound angle might exist in the case of a two (or more) piece driveshaft in which the center joint is not in a direct line with the end joints. In those cases on OEM vehicles I believe is where carden style CV joints are found. What am I missing here?
Hnstray, Open the link below and scroll down to figure # 5. What I call horizontal and vertical angles are referred to as top and side view operating angles. When you have the pinion offset from the transmission center line, you have created a compound U-joint operating angle. The text with figure # 5, along with much of the other info found in this link, will explain compound angles, and the need to calculate "true operating angles" better than I can. http://www2.dana.com/pdf/J3311-1-DSSP.pdf
Bob, Before I replied above, I did exactly that......but didn't see anything the first time that altered my view. I will view it again and look for my oversights, if any. Thank you for your response. Edit: the main points included in Dana's guide (linked above) is that; a) ideally, operating angles should a minimum of 1* but not exceed 3*, b) angles on either end of the shaft should be within 1* of the other (in light duty applications...within 1/2* in heavier/commercial apps). I did not see any definition of, or reference to, compound angles. I remain of the opinion that with a single piece, 2 u-joint driveshaft, the u-joints "see" a single angle, regardless if the pinion is centered or offset. That should be the case, unless the pinion angle is not parallel with the trans output shaft. The only caution is that the resulting angle not exceed 3*. It may be possible that the total angle could exceed 3* if the offset, for some reason, where outside the common amount of offset seen in production vehicles or, of course, the verticle spacing of the trans and pinion centerlines, combined with the driveshaft length, produced an angle greater than 3* Regards, Ray
I remain of the opinion that with a single piece, 2 u-joint driveshaft, the u-joints "see" a single angle, regardless if the pinion is centered or offset. Regards, Ray[/QUOTE] Winner Winner.....Chicken Dinner!!!!! Frank
most center section offset is for aesthetic purposes giving the driver room and the drive shaft u joints see one angle
I used a 8" from a Mustang or Maverick in the yellow rdstr in the avatar but it can be seen from the rear so I used two short side axles, which as someone mentioned narrowed it 15/16" which is not exactly centered, but close enough. That was back in the late 80's and I've never had any vibration or U-joint failure.
Ray, If you scroll down to figure #5 (and 6, 7) you will clearly see the top and side angles that create a compound working angle. Honest! fab32, Facts trump opinions, and if you also view the above link, you'll see there are more than one angle with an offset pinion. Really!
Hum, to me it says there is one angle (True operating angle/Compound Angle) that must be computed off of the offsets on the vertical and horizontal axis using the formula in the article. Am I reading it wrong? I'm glad you posted the link, I setting up a new rearend for my Anglia right now. I've never run into a problem on a street driven car or a drag car running a centered pumpkin, but the driveshaft on the Anglia is gonna be about a foot long so it needs all the help it can get. I'm going to center the pumpkin on it and offset the engine and transmission 1" to the right. That's the way it's been run since the 60's (with an Olds rearend that also has the pinion offset about an inch like the Ford). Any car that is sprung and has a ladderbar type suspension is going to have the pinion angle change anytime the ride height of the car changes also. Not much but some, so perfection is kinda out the window.
The pdf posted has a formula to calculate the single working angle from the compound angles. It's all the same thing, just a mater of what perspective you're using. Top and side view, or working plane.
Right. See page 9 fig 5 for the angles, See pager 10 for the formula for calculating the true operating angle.
Ok Bob, My error in reading "pages 5 thru 7", versus "Figures 5 thru 7" and beyond, and not going through the bulletin far enough to get to what you were referencing. I totally missed the info on the pages further in. I see what you (and Dana) are saying. However, in the end, after the calculations are said and done, it appears to me there is one angle remaining. It may differ from the single angle (side view), after the second angle (top view) is added to the calculation (therefore a compound angle), but the calculation produces a single angle......does it not? It appears to me that the question at that point is whether or not that product (angle) is within the recommended limitations of the u-joint operating angle range.
Yeah u have 2 angles to take into account. 1 is basically for simplisity pinion angle, the second is piniion offset left to right. The drive shaft is never at a straight line from trans to rear end no matter what angle the drive shaft is veiwed from. This is said to prevent whip, vibration, and allow the joints to absorb more load smoothly. I have always set them up with several degrees of angle both vertical & horizonal. I figure going thru all the work & expense of narrowing a rearend for a customer its 1 less what if that i dont have to worry about. Customers usually only wanna pay once for a job. Like i stated to each their own, i just do what i feel gives the customer the best "& most trouble free job.
Correct. My main point is any top-view offset angle has to be addressed, not disregarded, as the resulting true operating angle could exceed the U-joint limitations.
Well now, I'm glad we had this little discussion Thank you........I feel a little better edicated.............
The amount of knowledge contained within the skulls of HAMBers just amazes me. Thanks to all for the excellent input.
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