stub shaft end play-How much?
When I put my 66 on the lift and grab the rear tires at the 6 and 12 o'clock position I can move them in and out a lot. How much if any end play should the stub shafts have?
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Re: stub shaft end play-How much?
Russ,
Not sure you are talking about play in the differential housing yokes or play in the wheel bearing from the description of 6 and 12 o'clock. Check out where the movement is and how much. It could be ok or it could need attention.
Differential housing yokes clearance should be in and out. The wheel bearings shouldn't be sloppy enough to move wheel in a cocking motion. -
Re: stub shaft end play-How much?
Russ -
You'll have to differentiate between axial play in the rear spindle in its bearings and axial play in the differential side yoke; the best way to do that is to disconnect the half-shaft so you can check each component without any influence from the other one and report what you measure.Comment
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Re: stub shaft end play-How much?
Presuming it's the differential yokes- AFAIK there is no factory spec for maximum clearance. How much is 'allowable' is a different matter. Some beleive that there's a direct theoretical relationship with car handling characteristics and end play- others with practical experience have deliberately or inadvertently driven for decades with essentially unrestrained yokes. I tend to side with the latter group.
If the wear is due to loss of case hardening on the tip of the yokes, eventually this will need to be addressed as the diff case it self can become damaged as the yoke dust shield wear into it.Comment
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Re: stub shaft end play-How much?
There is no play in the spindle bearings. When I grab the wheel at 12 and 6 o"clock and pull/push in and out the whole assembly including the trailing arm moves in and out. When I do this the rear end yoke is what moves in and out allowing the wheel and trailing arm to move.Comment
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Re: stub shaft end play-How much?
Russ,
But how much movement? A 1/16"......an 1/8"? Anything less than a 1/16"--say a 1/32"--and I don't imagine you'd be asking. Let's get some numbers.
WAG
1966 Bowtie coupeComment
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Re: stub shaft end play-How much?
Michael,
So.........you are saying that the racers run unrestrained yokes........doesn't that mean the only thing holding the wheel vertical (or as close as practical with all the camber change) when cornering is the trailing arm? I thought the half shafts were the upper component and the strut rod the lower in order to adequately support the wheel when side loads were encountered.....i. e., cornering. Let's get to the bottom of this. And I thought the yoke clips inside the diff were intended to control in and out movement of the yoke???
WAG
1966 Bowtie coupeComment
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Re: stub shaft end play-How much?
Russ,
To my way of thinking your yoke play is reason for (serious) concern. But then that's just my opinion. Let's see what people have to say about my two comments on the clips and the necessity of a finite maximum to the yoke movement in order to support the wheel in the vertical plane. Also what others have to say about your 1/4 to 3/8 inch.
WAG
1966 Bowtie coupeComment
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Re: stub shaft end play-How much?
At the completion of a C3 frame off in the late '90s, I became aware of similar end play in the differential yokes and presumed that this was a serious and unacceptable problem. A local shop that specializes in diff overhauls challenged my beliefs and the owner showed me his own car which was deliberately built with no NO c-clips to retain the yokes. His contention was that there is always inward pressure on the half shafts and yokes and only when the wheels were off the ground would the load reduce to zero or below.
Not quite believing what he said, I took a bunch of measurements and had a proper 3D analysis done at work by a colleague. Turns out the shop owner was 99% correct. While driving in a straight line, there is approx. 300 lbs of inward force on each yoke. As the car rounds a corner, the tendency for the outside tire to 'tuck under' is counter acted upon by the increased weight on that corner of the car (due to body roll) acting through the suspension to ALMOST negate a reduction in compressive load on the yoke. This diagram can help visualize why:
Note that the lower strut rod outer pivot point is well inwards of the wheel/tire centre point. The location of this pivot point is critical is determining the inward load of the yokes. My original crude analysis indicated that a lateral load of well over 1G would be required, something impossible for a stock C2 or C3 to achieve with sliding sideways into a curb or similar. An acquaintance managed to dig up an engineering paper issued by GM for the newly introduced 1963 discussing this very subject.
where it is stated that the inwards load is not positive under all conditions but reduced to a minimum of 19% under maximum lateral load (hard cornering).
The following video then surfaced which shows the interaction in 'real life'. Note that this is a modified C3, using much wider and stickier tires than stock and also inwardly offset rims, all of which decrease any inwards load on the yokes:
Not also that the car is being used in an autocross event, far exceeding what would be seen under normal street driving. Watch carefully at 1:24, 1:44 where the drivers side yoke can be seen to momentarily be pulled outwards. The owner of the car later discovered that the yoke c-clip was no longer in place.
Is this an issue for street driven cars? I'd bet that the majority of C2s and C3s on the street have excess play on the diff yokes for all sorts of reasons- yet the owners are unware until they go poking around underneath like the OP has. I beleive it is more a commercial issue that something related to 'safety'. My 2 cents.Comment
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Re: stub shaft end play-How much?
Michael,
Thanks a whole bunch for taking the time to delve into this and get the answers. And I even understand (scary?) most of what you and the GM engineers are saying. Another read through and I may have full comprehension (real scary). As an information source this forum is by itself worth the price of membership. My applause, could it be heard, is deafening, Michael. It is too bad, as has been said elsewhere, that more members do not use this site to enhance their knowledge.
WAG
1966 Bowtie coupeComment
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Re: stub shaft end play-How much?
That "engineering paper" about the 1963 is included inthe library material I just got from SAE thanks to Duke's suggestion in another thread on this board.
Bill I echo your comments about the value of this baord.TerryComment
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Re: stub shaft end play-How much?
Michael, WOW!!!! That is really a lot of info! Talk about getting ones question answered!! Many thanks for going to all that trouble to answer my question so well. RussComment
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Re: stub shaft end play-How much?
All------
One thing to keep in mind: the yoke axles are case hardened. The differential center pin which limits the inward travel of the yoke axles is hardened to a greater Rockwell hardness than the yoke axles. So, the center pin always "wins" and the ends of the yoke axles wear. Once the wear is through the case hardening, wear accelerates dramatically. When the yoke axles have 1/4" of end play, a lot of wear has occurred. Notwithstanding other problems that may be created by such wear, guess where all of the ground-off steel particles go?In Appreciation of John HinckleyComment
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Re: stub shaft end play-How much?
This is a common question on all the forums and has been for years. Mike states the axles are forced inward and this is correct as the axles are forced in they hit the posi cross shaft which is about 55-60 Rc. Over time the real concern is the axle will hit the diff housing where there is a 1/8" boss at the seal. If no repair is made at this time the axle(s) will start to grind into the boss then the seal and then you may end up loosing the diff or face some machine work to correct it. At that point the endplay will be in excess of 3/16" travel. As Joe mentioned the grindings end up in the gear oil and become a fine lapping compound so to speak which isn't good for bearings or gears. Now there are plenty of guys who did nothing more then drop the diff and install rebuilt or new (usually imported) axles and still had 020,030,040" or more endplay.
The axles were hardened up until '74 or so then they were pretty soft. I don't know why this happened but it has been a problem since 75 for the 75-79 axles. I'm not sure about the service replacements from that period but this lead to the opening of the rebuilt axle market using hardened tips pressed into the faced and bore ends of worn out axles. If you look at a rebuilt axle you will see the seam at the snap ring groove. The QC on these does vary from very good to poor but that is more of an in-house problem then a design issue. I have used a lot of the rebuilt axles and they hold up fine.
When I blueprint a posi I set the spider lash to near -0- and do not use the plates or springs. Anyone can see this procedure on you tube under Tom's eaton posi tuning. It's the only way I ever built them as well and this will usually require fitting rebuilt axles because, if done correctly, will leave no room to install a snap ring and it will pop off. I set the endplay to 005-010" on vette 10 & vette 12 bolt posi's I built. There was never a published spec that I found but that is what works for me.
Excessive endplay is from :
1- worn axle faces
2- worn or sloppy posi setup
3- worn cross shaft hole(s) in the posi case
All of these can be corrected.Comment
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