| [GMCnet] Output shaft bolt size [message #224857] |
Tue, 08 October 2013 08:22  |
Jp Benson
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I'm about to install my CV axles and recall some threads on GMCnet describing how the bolts holding the axle to the output shaft can loosen while driving. The bolts are 3/8" but the bolt holes on the inner CV flange are large enough for a 7/16 bolt with a little wiggle room left. Has anyone ever drilled and tapped the holes on the output shaft and used 7/16 bolts?
Thanks,
JP
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| Re: [GMCnet] Output shaft bolt size [message #224862 is a reply to message #224857] |
Tue, 08 October 2013 11:01  |
Jim Miller
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On Oct 8, 2013, at 9:22 AM, Jp Benson wrote:
> I'm about to install my CV axles and recall some threads on GMCnet describing how the bolts holding the axle to the output shaft can loosen while driving. The bolts are 3/8" but the bolt holes on the inner CV flange are large enough for a 7/16 bolt with a little wiggle room left. Has anyone ever drilled and tapped the holes on the output shaft and used 7/16 bolts?
Personally I think the reason they loosen while driving is that they were not installed to the proper torque and/or someone ignored the admonition to always use new bolts when re-assembling. GM certainly knew how to calculate the torque delivered across this assembly and what sort of clamping force would be required to keep it together.
When you get can a pack of 25 of these bolts from McMaster-Carr for $11.40 (part# 91271A644) and a pack of 100 washers (91104A03) for $5, why mess around by second guessing the engineers that designed it?
Good info at: http://gmcmotorhome.info/front.html
--Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Output shaft bolt size [message #224863 is a reply to message #224860] |
Tue, 08 October 2013 11:06 |
Jim Miller
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On Oct 8, 2013, at 11:56 AM, Dan Gregg wrote:
> I have the drivers side drilled and wired. Could not keep them tight. Passenger side never comes loose.
IMO this could have been caused by someone driving the vehicle for some amount of time with loose bolts. With a sloppy assembly the constant torque/counter-torque between the axle and drive flange would tend to beat out the threads to the point where the bolts cannot maintain their installed torque and, consequently, the clamping force between the flange faces is much less than required to do the job.
--Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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Hamilton, OH
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| Re: [GMCnet] Output shaft bolt size [message #224876 is a reply to message #224857] |
Tue, 08 October 2013 13:11 |
Ken Burton
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Just replace them with new bolts and lock washers from McMaster-Carr and torque them properly. If it still bothers you then use thread locker on the threads or drill and safety wire them. I personally like the safety wire idea but have never needed it.
Be aware when drilling them that those bolts are very hard.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Output shaft bolt size [message #224882 is a reply to message #224878] |
Tue, 08 October 2013 14:09 |
Jim Miller
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On Oct 8, 2013, at 2:31 PM, Jp Benson wrote:
> It seems weird that GM engineered a 7/16 hole on the CV joint flange for a 3/8 bolt. So far it looks like nobody has gone to a larger bolt.
The hole being slightly oversize does not matter as the bolts are not in shear. They are in tension only - it is the friction between the clamping faces of the two flanges that transfers torque from one flange to the other.
I think it is absurd to safety wire them. We aren't talking about an aircraft where a bolt working its way out of a hole is a life-safety issue. Safety wire does nothing at all to help keep them tight. If a bolt in our CV works ever so slightly loose then it is immediately contributing absolutely ZERO to the integrity of the assembly. If enough of them loosen up then you are destroying the threaded flange after which time no amount of torque, thread locker or safety wire will keep them tight.
If enough bolts come loose then you should hear clunking as you transition from forward to reverse and vice versa; this will happen LONG before the bolts come out of the holes. That clunking noise should be a prime reason to investigate immediately.
--Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Output shaft bolt size [message #224884 is a reply to message #224882] |
Tue, 08 October 2013 15:29 |
Ken Burton
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Jim,
Over the years I have gone out on two different Black List calls where people have lost all of the bolts on the driver's side. Both were just driving down the highway and all of a sudden they thought they lost the transmission. One of them had less an 200 miles on the the bolts since someone worked on it and did not tighten them to spec.
I have no idea if they heard any clunking. They definitely were not driving backward and forward on the Interstate. Safety wire is simple if you have drilled bolt heads. Thread locker is even easier.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Output shaft bolt size [message #224894 is a reply to message #224884] |
Tue, 08 October 2013 17:29 |
Jim Miller
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On Oct 8, 2013, at 4:29 PM, Ken Burton wrote:
> Over the years I have gone out on two different Black List calls where people have lost all of the bolts on the driver's side. Both were just driving down the highway and all of a sudden they thought they lost the transmission. One of them had less an 200 miles on the the bolts since someone worked on it and did not tighten them to spec.
Ken,
I think we can agree that there was a problem in how their CVs had been connected to the driving flanges especially in the 200 mile case.
I think we should also be able to agree that safety wire has no contribution toward maintaining the original torque on the fasteners it is wired through; its only function is to retain those fasteners should they become loose. In the case of aircraft the hope is that the loose fasteners will be found during an annual or hourly-interval inspection and the problem corrected at that time.
Now, in the two cases you describe safety wire would have indeed retained the bolts - all of which would have eventually become loose. As an increasing number of the bolts loosened up the clamping force between the flange faces would have decreased to the point where differential motion would start to occur between them. Once the differential motion starts to occur between the faces you have wear and of course the more wear occurs the more the motion will increase.
Had there been safety wire in place on the two cases you mentioned the owners would have not learned about the loose interface between the flanges early on. They would have blissfully driven their coach while the two faces slopped back and forth, damaging not only the mating faces but also the threads in the driven flange and the clearance holes in the CV's flange. There could also be brinnelling of machined surfaces inside the CV joint itself as well as between gears in the final drive due to the shock load those surfaces would absorb when the slack was taken up during acceleration/deceleration transitions and also forward/reverse transitions.
I argue that it would have been better to have not had safety wire in place so as to learn about the assembly problem ASAP rather than drive several hundred or thousand miles while the sloppy CV-to-flange-assembly was causing irreparable damage to multiple items in the driveline.
> They definitely were not driving backward and forward on the Interstate.
Certainly not. What they were doing was making numerous transitions between engine propulsion and engine braking - transitions that were made each time the accelerator pedal was pressed and released. Each one of these transitions would have resulted in differential motion and consequent wear across the CV-to-drive-flange assembly.
> Safety wire is simple if you have drilled bolt heads.
"IF" being the key word there - as drilling 180,000 psi alloy-steel bolts is not trivial.
> Thread locker is even easier.
I would agree with that. Is thread locker recommended in the GM procedures?
--Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Output shaft bolt size [message #224897 is a reply to message #224896] |
Tue, 08 October 2013 18:05 |
Jim Miller
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On Oct 8, 2013, at 6:39 PM, David H. Jarvis wrote:
> How far can a bolt loosen that has been safety wired?
> If done properly, not more than 1/4 turn?
In this particular application the face of the CV is clamped incredibly tightly against the face of the final drive's flange due to the ~80 lb-ft of torque on each of six bolts. The design is such that the entire propulsive force of the vehicle is transmitted through the friction interface of those two faces - it is NOT transmitted through the bolts in a shearing manner.
If the bolts loosen by ANY amount then the clamping force begins to be compromised. If enough of them loosen then there is no longer a friction interface between the faces and you start to have differential motion and wear between the two - and at that point it is just a matter of time until something gets destroyed.
Safety wire doesn't help keep them tight. It just keeps them from getting away if they become loose - but in this application they cannot be allowed to become loose therefore (in my opinion at least) safety wire doesn't buy much. I carry a spare set in the coach so if mine manage to get away I'll just put more in to get me to a safe place to effect a proper repair.
--Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Output shaft bolt size [message #224905 is a reply to message #224903] |
Tue, 08 October 2013 19:51 |
GMC_LES
Messages: 569
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Location: Montreal
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Jim i have to both agree and disagree regarding your comments.
First, if safety wire is done correctly, the fastener should not be able to loosen more than a degree or so unless there is a very long run of wire (stretch).
The image linked to in the previous post is not a good example of how to safety wire. Proper safety wire should always pull each fastener in a tightening direction should the opposing fastener try to come loose.
Second, and this is where i agree, "safety wire" is intended exactly as you implied. It provides a safety margin should the fastener come loose. It was never intended to serve as a method of fastening.
Regarding the CV bolts. Due to their specs, i doubt that they exibit much stretch, so the degrees of rotation to acheive the full torque of 80 ft lbs. is probably much less than a 1/4 turn, but certainly more than a few degrees. Proper safety wire techniques should keep the bolt from loosening to a "full loose state". Would a set of partially loosened bolts still provide enough clamping to prevent a CVJ from moving? It would certainly depend on numerous conditions, but from many peoples experiences here, it appears to work in most cases.
Just my personal opinion based on over 30 years wrenching on aircraft and jet engines.
Les Burt
Montreal
1975 Eleganza 26ft
A work in Progress
On Oct 8, 2013, at 8:15 PM, A. <markbb1@netzero.com> wrote:
>
>
> Jim Miller wrote on Tue, 08 October 2013 18:05
>> ...
>> Safety wire doesn't help keep them tight. ...
> Wired like this, how much can it loosen?
>
>
> http://www.gmcmhphotos.com/photos/data/1/safetywired.jpg
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> UA (Upper Alabama)
> CanyonLands most likely for a parts coach. Sequoia being restored to service.
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A work in Progress
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| Re: [GMCnet] Output shaft bolt size [message #224907 is a reply to message #224903] |
Tue, 08 October 2013 19:56 |
Jim Miller
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On Oct 8, 2013, at 8:15 PM, A. wrote:
> Wired like this, how much can it loosen?
> http://www.gmcmhphotos.com/photos/data/1/safetywired.jpg
I did some quick research and found that the axial clamping force of a 180000 psi 3/8"-24 fastener at 70 lb-ft of torque is right around 10,000 lbs. This pressure is borne on the interface surface between the CV flange's bolt-hole perimeter and the surface under the head of the bolt. If for whatever reason that tremendous amount of friction cannot keep the bolt from loosening then I do not think a piece of 0.030 safety wire is going to stop it either - at least not for long.
--Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Output shaft bolt size [message #224910 is a reply to message #224905] |
Tue, 08 October 2013 20:19 |
Jim Miller
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On Oct 8, 2013, at 8:51 PM, Les Burt wrote:
> Would a set of partially loosened bolts still provide enough clamping to prevent a CVJ from moving
Hi Les,
Thanks for your comments. This thread originally started with an observation that the clearance holes in the CV joint were approx. 7/16" while the fastener's major diameter was 3/8". The question at the time was about moving up to 7/16" fasteners to eliminate the 1/32" of clearance on any side of the bolt and to prevent loosening.
Regardless of whether moving up to 7/16" by drilling/tapping the final drive flange is a good idea or not, the observation points out that if the flanges are not clamped together tightly enough to prevent ALL motion between them then there are a few degrees that they will rotate through. Even with only 1/32" of room around each bolt the constant changes in torque direction as the vehicle is accelerated and decelerated will result in the bolts experiencing shearing forces as well as the clamp faces being slid across each other which will produce increasing wear and decreasing friction between them over time.
I don't know what the crossover point between "enough" clamping force and "not enough" is but I'm going to do what GM said to do and call it good. If people want to use safety wire then by all means do so but personally I don't see it being worth the effort to try and drill those glass-hard fasteners. If on the other hand I had an EDM machine sitting around then it might be a different situation. <smile>
--Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Output shaft bolt size [message #224914 is a reply to message #224907] |
Tue, 08 October 2013 20:50 |
GMC_LES
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The big question is "why do the bolts come loose in the first place?"
The main reasons would normally be one or more of the following.
1) insufficient torque during installation.
2) fatigued bolt that has loosesp it's elasticity and relaxes its torque over a period of time.
3) dirty or damaged CVJ mating flanges.
4) worn, damaged or dirty fhreads on either the bolt or the output flange, creating a false torque reading.
My previous comments on safety wire were based on having healthy and clean parts.
Regarding the ability of safety wire to prevent rotation of a bolt. It actually doesn't require much force to stop a bolt from turning loose on its own. The question is will the wire be able to prevent the bolt from rotating enough to loose its clamping ability.
In my career, i have rarely seen safety wire that broke due to bolt rotation, but I have seen many loose bolts with intact safety wire. The loss of bolt clamping in most of those instances was due to other component failures and not the fastener itself.
To end this off. I agree that new fasteners and use of locktite is a very good approach for the CVJ flanges.
On my own coach i will be using new bolts and some nord-lock washers. These washers actually increase clamping forces on the fastener should it start to rotate loose. I've used them for years on some of my VWs & AUDIs to prevent the inner CVJ bolts from coming loose and they work as advertised.
http://www.nord-lock.com
Les Burt
Montreal
1975 Eleganza 26ft
A work in Progress
On Oct 8, 2013, at 8:56 PM, Jim Miller <gmcnet@jcmco.com> wrote:
>> On Oct 8, 2013, at 8:15 PM, A. wrote:
>>
>> Wired like this, how much can it loosen?
>> http://www.gmcmhphotos.com/photos/data/1/safetywired.jpg
>
> I did some quick research and found that the axial clamping force of a 180000 psi 3/8"-24 fastener at 70 lb-ft of torque is right around 10,000 lbs. This pressure is borne on the interface surface between the CV flange's bolt-hole perimeter and the surface under the head of the bolt. If for whatever reason that tremendous amount of friction cannot keep the bolt from loosening then I do not think a piece of 0.030 safety wire is going to stop it either - at least not for long.
>
> --Jim Miller
> 1977 Eleganza II
> 1977 Royale
> Hamilton, OH
>
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| Re: [GMCnet] Output shaft bolt size [message #224915 is a reply to message #224907] |
Tue, 08 October 2013 20:52 |
Jp Benson
Messages: 649
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Guess I'll use red loctite. It's probably no coincidence that the loose bolts are always on the driver side. I recall from my pump jockey days in the 60's that some of the older cars had left hand thread wheel lugs on one side to keep the wheels from coming off. Don't remember which cars or which side though.
Drilling the bolt heads sounds pretty difficult. Even with my best HF Cobalt drill bits. Pre-drilling in the correct position for wiring as shown in the diagram is pretty darn clever. I'll keep the old bolts stashed in the event of an emergency.
JP
On Tuesday, October 8, 2013 8:56 PM, Jim Miller <gmcnet@jcmco.com> wrote:
On Oct 8, 2013, at 8:15 PM, A. wrote:
>
>> Wired like this, how much can it loosen?
>> http://www.gmcmhphotos.com/photos/data/1/safetywired.jpg
>
>I did some quick research and found that the axial clamping force of a 180000 psi 3/8"-24 fastener at 70 lb-ft of torque is right around 10,000 lbs. This pressure is borne on the interface surface between the CV flange's bolt-hole perimeter and the surface under the head of the bolt. If for whatever reason that tremendous amount of friction cannot keep the bolt from loosening then I do not think a piece of 0.030 safety wire is going to stop it either - at least not for long.
>
>--Jim Miller
>1977 Eleganza II
>1977 Royale
>Hamilton, OH
>
>
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