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FWD w/welded Diff

Posted by ElectroTech 
john vanlandingham
John Vanlandingham
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Re: FWD w/welded Diff
June 26, 2015 03:38PM
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DG_Rally
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ElectroTech
Hey man, with the loosening bolts I'd bet your inner and outer CVs are not "timed" together, meaning that if you had the boots off both ends the bearings should line up perfectly, otherwise they will work against each other a little tiny bit, this is really easy to see with u-joints since it's just 2 yokes needing to line up. Probably only off by one or 2 splines.

That's very possible. I'll check them out the next time I have them out. Thanks!

Din't say it at thwe time but that clocking or timing while legit on conventional U-joints, dun't think it has any bearing at all on Rzeppa joints...cause they run at a "constant velocity"..kinda why we callz 'em zat..

I never see-d nuthin' bout clocking CVs, they're symmetrical



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ElectroTech
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Re: FWD w/welded Diff
June 26, 2015 04:24PM
True story. The are called constant velocity but it's only within a certain range of angles.
This comes from the ATV world where you can have 12" of travel in an 18" shaft.
Another issue I've seen is mismatched angle machining inside the shaft, meaning 2 different manufacturers joints fit the same shaft but the race angle is machined differently.

I would suspect with the loosening bolts the mix of stiff suspension and high steering angles is pushing the design limits of the "CV" and a slight difference in phasing could be part of the issue.
http://i410.photobucket.com/albums/pp185/swcb20/1E5A4EB6-7531-4763-8940-862ED144DE45.jpg



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Pete
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Re: FWD w/welded Diff
June 26, 2015 07:30PM
Question though - does it really matter when the axle is moving along a mostly fixed plane at the inner, but is moving along that plane AND can also get 50-70 or so degrees of motion along a different axis from steering? In other words, that outer joint be floppin' and flippin' all over the place so what does "timing" have to do with anything?



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ElectroTech
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Re: FWD w/welded Diff
June 26, 2015 08:26PM
Yes, it is a unit 2 joints together to make a CV shaft, not simply 2 separate entities independent of each other, it is the same exact principle as 2 old school U-Joints. The 2 sets of races need to be in line with each other or binding will occur at the extreme end of the design. It's not nearly as pronounced as a U-Joint setup but it does happen.
Simple enough for Dave to be the guinea pig, he can check his, and verify if they are out.



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Re: FWD w/welded Diff
June 26, 2015 08:57PM
It's not the same principle, though, since the whole concept of clocking goes out the window when you factor in that the two ends of the shaft will not be in any kind of harmony.

Ever look at a steering shaft that has two U-joints in it? The U-joints are not clocked relative to *each other* like in a driveshaft, but rather they are clocked relative to *their natural angle* because the steering column and the rack input are on two completely different angles/planes.

Front axles are the same way, except one of the angles/planes is highly variable. So: Even if you're going to clock it, what are you going to clock it *TO*? Are you going to clock it so it makes sense poitned straight ahead? Or are you going to clock it so it makes sense when at full droop and turned outwards or full stuff and turned inwards, like you'd be at your most likely high inner CV angle? And if you do that, what steering angle are you going to choose?

Or do you say piss on it, it's not going to make enough of a difference to matter in the real world compared to a bunch of other factors?



Pete Remner
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Silence is golden, but duct tape is silver.



Edited 1 time(s). Last edit at 06/26/2015 08:58PM by Pete.
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ElectroTech
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Re: FWD w/welded Diff
June 26, 2015 09:38PM
This is real world experience I am talking about, have seen it in real life, have seen service bulletins from driveline engineers. The joint do work in harmony, since there is a steel shaft that doesn't twist between them. You simply clock it so that looking at it in a straight line the races line up perfectly not off by a couple of splines. I've literally had hundreds of CV shafts apart albeit in a far worse service environment. The inner joint moves when you steer, dependant on the pivot point of the outer (in relation to the ballpoint) it might move rearward or forward. At full droop and full steer if the joint isn't phased correctly there is a telltale click, not unlike a worn out CV. This was CV shaft 101 when I pulled wrenches on Polaris ATV/SXS for 3 full years, new guy would replace a CV boot and customer would return complaining of a clicking noise. How else do you explain the loosening bolts on Daves car, if the inner CV was unaffected by the outer and his shafts are of the correct length what force is loosening the bolts, it surely wouldn't occur in a rear single plane application.



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ElectroTech
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Re: FWD w/welded Diff
June 26, 2015 10:46PM
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Pete
It's not the same principle, though, since the whole concept of clocking goes out the window when you factor in that the two ends of the shaft will not be in any kind of harmony.

Ever look at a steering shaft that has two U-joints in it? The U-joints are not clocked relative to *each other* like in a driveshaft, but rather they are clocked relative to *their natural angle* because the steering column and the rack input are on two completely different angles/planes.

Front axles are the same way, except one of the angles/planes is highly variable. So: Even if you're going to clock it, what are you going to clock it *TO*? Are you going to clock it so it makes sense poitned straight ahead? Or are you going to clock it so it makes sense when at full droop and turned outwards or full stuff and turned inwards, like you'd be at your most likely high inner CV angle? And if you do that, what steering angle are you going to choose?

Or do you say piss on it, it's not going to make enough of a difference to matter in the real world compared to a bunch of other factors?


Perfect, you are validating what I am saying. The reason the steering shafts are purposely out of phase is to ensure the joints flip at the same point, the steering shaft angles never change therefore allowing you to optimize the timing.

Same issue in th ATV/UTV driveshaft between the transmission and the front diff, it runs alongside the engine and then angles over to the center, the joints are purposely welded 46° apart. Have to explain this to every farmer who buys one over the counter because they have been taught since the age of 5 to time them...........and back to what I was saying originally....

The reason you want a farm implement driveshaft and a FWD CV to be timed is the same, you time them equal because this is "neutral" meaning you can turn left, right or go up and down, each direction is worse than neutral. If you clock the splines on a FWD CV out of neutral the action is better in one hemisphere and worse in the other. We set it neutral because this is where the fastest speeds are and this is where the most heat would build if they were out.

Someone spent the time to make that chart I posted in the link and it certainly wasn't me.

Some guys put spacers in their racks to limit travel in the CV, the bearing surface doesn't change but we are nearing the point where the curve really ramps up and the velocity is no longer constant and a guy hits a bump where the engine cannot spin the wheel due to available traction and you drive the shaft right apart because of the difference in speed.



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Pete
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Re: FWD w/welded Diff
June 27, 2015 06:30AM
So what do you line up when the outer is an Rzeppa and the inner is a tripod?

I still don't see it. There can't be any speed oscillation in an Rzeppa because the balls are always the same radius from each other and the points of contact are the same relative distance to the shafts.

BTW - I had an OE axle come loose on a VW. Someone used the wrong bolts. VW used triple square bolts for a reason, you can get more torque on them than a similar sized Allen or external hex bolt. Or maybe VW put the axle together out of phase. Entirely possible given that the normal operating mode is with maye 1-2 degrees of bend at the inner joint.



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Re: FWD w/welded Diff
June 27, 2015 08:50AM
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Pete
So what do you line up when the outer is an Rzeppa and the inner is a tripod?

I still don't see it. There can't be any speed oscillation in an Rzeppa because the balls are always the same radius from each other and the points of contact are the same relative distance to the shafts.

BTW - I had an OE axle come loose on a VW. Someone used the wrong bolts. VW used triple square bolts for a reason, you can get more torque on them than a similar sized Allen or external hex bolt. Or maybe VW put the axle together out of phase. Entirely possible given that the normal operating mode is with maye 1-2 degrees of bend at the inner joint.

I never said it would be the inner joint causing the issue, it's nowhere near it's design limits. The outer at full lock/droop would be the likely culprit. Only talking a couple of percent which is the same reason VWMS and a slew of others shimmed the steering racks to limit full lock just slightly.

As far as torquing capability goes I find that amusing, I agree in larger sizes the triple square is stronger, but in these smaller sizes the bolt head will twist off or the threads will strip out of the aluminum flanges long before the ability to twist is taken away from holding power of the driver. I would venture to guess this is more of a Phillips vs Robertson or Metric vs Standard argument then anything else, same for the lug bolts, internal 27mm hex, internal 17mm hex, shifting patern and so many other things they did different for difference sake.

My comment was not drawn from thin air but real world experience with CV shafts, hundreds of them.
Driveline engineers spoke of this issue in their service bulletins and someone also took the time to make a fancy graph to illustrate their point (not mine).



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