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carlvon
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Joined: January 09, 2015
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Location: San Antonio, TX
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 Posted: Mon Mar 02, 2015 8:42 am Post subject: PSA - Nord-Lock your drive shaft (CV) bolts |
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 Don't let this happen to you
I had my drive shaft come off on the way home last week.
I was under the bus just the day before fixing my heater flaps. When I finished that, I checked that the bolts were tight.
At work, I normally do not park in the parking garage, but the ground lot was full. I like to see my bus from my office, so I parked on top of the parking garage.
Between the up/down/turns in the parking garage and the stop and go drive home, my drive shaft bolts worked loose. I stopped at a light, and when tried to go, I heard a thwack-thwack-thwack. It sheared one bolt, twisted another, and stripped all of them.
When it came off, the bearing took a good beating.
This was on a new assembly installed in January. I don't remember the brand, but I bought it from BAP, so I assume it's EMPI. The OG side I repacked and reused hardware on was still tight. Maybe the new bolts stretched, who knows.
On advice from Bala and TCash, I purchased a package of Nord-Lock washers from Fastenal and installed them last night.
Because a picture is worth a thousand words, check out the video below to see why Nord-Lock washers are better than the lock washer normally used to attach the drive shafts.
Link
The washers were on sale - 25 washer pairs for only $11 is cheap insurance if you ask me. I'm going to pick up a new boot and hardware set today, and finish installing the drive shaft. My torque wrench will be in the bus for the next two weeks, and I am going to test the bolts before each drive. Might be overkill, but I'm really curious to see how well the Nord-Lock washers work.
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Carl
1978 Champagne Edition II 2L FI |
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Bala
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Joined: December 04, 2003
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| Posted: Mon Mar 02, 2015 9:12 am Post subject: |
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Dang, your bolts took a beating!
I've driven a little over 100 miles with my Nord-Lock washers installed. I'll check them soon and report back.
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SGKent 
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Location: Citrus Heights CA (Near Sacramento)
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| Posted: Mon Mar 02, 2015 9:15 am Post subject: |
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show us what kind of washers were under the heads of the bolts when they loosened. Factory washers are similar to your new washers. Also - looking at the threads on those bolts that failed, they never should have been used again. They look over-tightened. What torque setting did you use?
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin |
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carlvon
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Joined: January 09, 2015
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Location: San Antonio, TX
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| Posted: Mon Mar 02, 2015 9:32 am Post subject: |
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| SGKent wrote: |
| show us what kind of washers were under the heads of the bolts when they loosened. Factory washers are similar to your new washers. Also - looking at the threads on those bolts that failed, they never should have been used again. They look over-tightened. What torque setting did you use? |
I didn't take a picture of the original washer, but they looked like this.
They are similar, but the Nord-Lock uses a pair of Belleville washer with one side that's serrated and the other side that has a cam. The cams go together and keep tension on the joint.
The bolts that failed were new bolts included with the drive shaft assembly I bought from BAP and were not reused. They were tightened to 25 lb/ft. The wear on them is from the vibration they encountered when the bearing came off.
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Carl
1978 Champagne Edition II 2L FI |
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airschooled
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| Posted: Mon Mar 02, 2015 9:39 am Post subject: |
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I'm with SGKent- those bolts look over tightened. But I tighten mine to 30 ft.lbs regularly, and they never look like that. How much did you pay for the bolts? Most hardware stores have a cheaper and softer version of our proper bolts. They're not correct. The real VW ones, or good 6-point replacements, should be at least $1.25 per bolt. More with the washers.
Robbie
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Wildthings
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| Posted: Mon Mar 02, 2015 9:45 am Post subject: |
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| carlvon wrote: |
| They were tightened to 25 lb/ft. The wear on them is from the vibration they encountered when the bearing came off. |
VW upped the spec on the identical hardware on the Vanagon to 33 ft*lbs. This is the spec I have been using for decades on all my VW's. At 24 ft*lbs the outer race of the joint will work back and forth against the flange loosening and weakening the bolts.
I think your fancy washers may be part of your problem as well. If you don't tighten them to just the right point where they click over the next serration then the ramp action of the washers will cause the bolts to back off to the previous serration.
Last edited by Wildthings on Mon Mar 02, 2015 10:01 am; edited 1 time in total |
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carlvon
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Joined: January 09, 2015
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Location: San Antonio, TX
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| Posted: Mon Mar 02, 2015 9:50 am Post subject: |
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| asiab3 wrote: |
I'm with SGKent- those bolts look over tightened. But I tighten mine to 30 ft.lbs regularly, and they never look like that. How much did you pay for the bolts? Most hardware stores have a cheaper and softer version of our proper bolts. They're not correct. The real VW ones, or good 6-point replacements, should be at least $1.25 per bolt. More with the washers.
Robbie |
The bolts came with the drive shaft assembly from BAP.
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Carl
1978 Champagne Edition II 2L FI |
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carlvon
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Joined: January 09, 2015
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Location: San Antonio, TX
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| Posted: Mon Mar 02, 2015 9:54 am Post subject: |
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| Wildthings wrote: |
| carlvon wrote: |
| They were tightened to 25 lb/ft. The wear on them is from the vibration they encountered when the bearing came off. |
VW upped the spec on the identical hardware on the Vanagon to 33 ft*lbs. This is the spec I have been using for decades on all my VW's. At 24 ft*lbs the outer race of the joint will work back and forth against the flange loosening and weakening the bolts. |
That's exactly where they wore. If you notice the thread that would stick in the spindle is fine.
| Wildthings wrote: |
I think your fancy washers may be part of your problem as well. If you don't tighten them to just the right point where they click over the next serration then the ramp action of the washers will cause the bolts to back off to the previous serration. |
I didn't have the Nord-Lock washers installed when the drive shaft came off, but looking at the physics of their marketing, it doesn't matter where the cam is - so long as the angle of the cam is greater than the angle of the thread pitch.
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Carl
1978 Champagne Edition II 2L FI |
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PITApan
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| Posted: Mon Mar 02, 2015 10:07 am Post subject: |
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| carlvon wrote: |
| SGKent wrote: |
| show us what kind of washers were under the heads of the bolts when they loosened. Factory washers are similar to your new washers. Also - looking at the threads on those bolts that failed, they never should have been used again. They look over-tightened. What torque setting did you use? |
I didn't take a picture of the original washer, but they looked like this.
They are similar, but the Nord-Lock uses a pair of Belleville washer with one side that's serrated and the other side that has a cam. The cams go together and keep tension on the joint.
The bolts that failed were new bolts included with the drive shaft assembly I bought from BAP and were not reused. They were tightened to 25 lb/ft. The wear on them is from the vibration they encountered when the bearing came off. |
Left the pics in for reference.
The washer still depends on the friction of the serrations against the bolt head and the flange. The little cams look fancy, but to get it apart, those serrations have to slip. For the cams to exert any force the bolt has to turn without the serrations slipping. One force is being balanced against another---bad idea in general.
For them apples, you can use a serrated washer. But hardened bolts make these solutions tricky. The serrations don't dig in.
If you want live tension on the bolt head you use warpy washers, possibly several of them. These are actual springs that push upward on the bolt generating a lot of friction in the threads. The other classical solution is use-once stretching bolts. I know of some universal joint to flange applications that use stretching bolts (although people reuse them with lock tight to save $2.50) |
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Randy in Maine
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| Posted: Mon Mar 02, 2015 10:16 am Post subject: |
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I always just use the new bolts that come with my CV joint Repack kits and use new belleville washers that don't come with the kit.
If you do not use the torque spreader bars, the harder washers will dig into the softer steel in the boot flange. You hav eto have them.
I also re-torque my bolts after about the first 100 miles. I re-check the torque every once in a while after tha,t but they never move any. |
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PITApan
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| Posted: Mon Mar 02, 2015 10:37 am Post subject: |
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| Randy in Maine wrote: |
I always just use the new bolts that come with my CV joint Repack kits and use new belleville washers that don't come with the kit.
If you do not use the torque spreader bars, the harder washers will dig into the softer steel in the boot flange. You hav eto have them.
I also re-torque my bolts after about the first 100 miles. I re-check the torque every once in a while after tha,t but they never move any. |
There are also Schnorr Washers, which are a Bellevilles serrated on both sides. But I suspect fresh bolts and the higher torque spec. getting more stretch on them is key. |
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Randy in Maine
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| Posted: Mon Mar 02, 2015 10:40 am Post subject: |
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| I was thinking that Schnoor and Belleville washers are the same. Mine are serrated on both sides and are sort of "cone shaped". I think I bought them at McMaster Carr or someplace like that. |
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PITApan
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| Posted: Mon Mar 02, 2015 10:56 am Post subject: |
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| Randy in Maine wrote: |
| I was thinking that Schnoor and Belleville washers are the same. Mine are serrated on both sides and are sort of "cone shaped". I think I bought them at McMaster Carr or someplace like that. |
Schnoor, which are a species of Belleville, that is, a conical spring washer. |
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Brian
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Randy in Maine
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carlvon
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Joined: January 09, 2015
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Location: San Antonio, TX
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| Posted: Mon Mar 02, 2015 12:40 pm Post subject: |
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| PITApan wrote: |
| The washer still depends on the friction of the serrations against the bolt head and the flange. The little cams look fancy, but to get it apart, those serrations have to slip. For the cams to exert any force the bolt has to turn without the serrations slipping. One force is being balanced against another---bad idea in general. |
Think of the bolt and the cam as inclined planes. The static friction is greater on the serrated faces and bolt threading than that of the cam faces. As the joint vibrates (jost effect), the cam slips before the serrated faces slip. As the cam slips, it applies more tension to the serrated faces because the cam incline slope is greater than the bolt thread incline slope. The net result is the clamping load remains nearly constant. There is a bit of clamping load loss when the cam first starts to slip, but it is only a fraction of the total clamping force.
| PITApan wrote: |
| If you want live tension on the bolt head you use warpy washers, possibly several of them. These are actual springs that push upward on the bolt generating a lot of friction in the threads. The other classical solution is use-once stretching bolts. I know of some universal joint to flange applications that use stretching bolts (although people reuse them with lock tight to save $2.50) |
Wavy washers are worse than true Belleville washers, but the principle of them are the same. Spring washers are highly susceptible to fatigue and have a maximum life. Under dynamic loading, they fatigue quickly when deflecting > 75% of their cone height. I'm not sure of the pitch on the CV bolts, but assuming it's 1mm, you'd need to find one, or stack them in parallel, to a cone height of at least 1.25mm. The cam on the Nord-Locks don't fatigue, so it's one less thing to worry about.
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Carl
1978 Champagne Edition II 2L FI |
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carlvon
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| Posted: Mon Mar 02, 2015 12:46 pm Post subject: |
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That's pretty much what came in the the assembly kit. The problem with that washer is it doesn't specify if it meets DIN 2092, but it does meet the cone height requirement of > 1.25 mm. I'm not saying there's something wrong with belleville washers, I just like the physics of the nord-lock better.
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Carl
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PITApan
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| Posted: Mon Mar 02, 2015 1:40 pm Post subject: |
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| carlvon wrote: |
| PITApan wrote: |
| The washer still depends on the friction of the serrations against the bolt head and the flange. The little cams look fancy, but to get it apart, those serrations have to slip. For the cams to exert any force the bolt has to turn without the serrations slipping. One force is being balanced against another---bad idea in general. |
Think of the bolt and the cam as inclined planes. The static friction is greater on the serrated faces and bolt threading than that of the cam faces. As the joint vibrates (jost effect), the cam slips before the serrated faces slip. As the cam slips, it applies more tension to the serrated faces because the cam incline slope is greater than the bolt thread incline slope. The net result is the clamping load remains nearly constant. There is a bit of clamping load loss when the cam first starts to slip, but it is only a fraction of the total clamping force.
| PITApan wrote: |
| If you want live tension on the bolt head you use warpy washers, possibly several of them. These are actual springs that push upward on the bolt generating a lot of friction in the threads. The other classical solution is use-once stretching bolts. I know of some universal joint to flange applications that use stretching bolts (although people reuse them with lock tight to save $2.50) |
Wavy washers are worse than true Belleville washers, but the principle of them are the same. Spring washers are highly susceptible to fatigue and have a maximum life. Under dynamic loading, they fatigue quickly when deflecting > 75% of their cone height. I'm not sure of the pitch on the CV bolts, but assuming it's 1mm, you'd need to find one, or stack them in parallel, to a cone height of at least 1.25mm. The cam on the Nord-Locks don't fatigue, so it's one less thing to worry about. |
methinks you missed my point. Nothing climbs a cam unless the serrations don't slip. if the serrations aren't going to slip, you can skip the cam. if they are going to slip, the cam is useless. Balance of forces problem.
It would appear the cams can exert force on the serrations to keep them from slipping---but only if the serrations aren't slipping in the first place.
Belleville washers are statically loaded, not dynamically loaded. So when you bring up the dynamic case it's moot.
Last edited by PITApan on Mon Mar 02, 2015 1:46 pm; edited 1 time in total |
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cmonSTART
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| Posted: Mon Mar 02, 2015 1:45 pm Post subject: |
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Excuse the noob while he goes and checks something...
Thanks for sharing.
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carlvon
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| Posted: Mon Mar 02, 2015 2:20 pm Post subject: |
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| PITApan wrote: |
methinks you missed my point. Nothing climbs a cam unless the serrations don't slip. if the serrations aren't going to slip, you can skip the cam. if they are going to slip, the cam is useless. Balance of forces problem.
It would appear the cams can exert force on the serrations to keep them from slipping---but only if the serrations aren't slipping in the first place. |
I didn't miss it, but my physics explanation might have been too technical. I think I understand what you are trying to say, that the cam can't slip unless the serrated side moves, but that's not how it works. There is no balance of force because the amount of force required to slip is different for the serrated face vs the cam face.
Basically, there is more static friction at the serrations than there is at the cam, so the serrations don't slip, the cams do. It takes more force to slip the serrated face than it takes to slip the cam face. The bolt head stays at the same place on the top serrated washer, and the joint face stays at the same place on the bottom serrated washer. The angle of the cam is greater that the pitch of the bolt thread, so when it slips, it tightens up on the tensile load of the join by driving a wedge into the joint.
You can't do away with the cam because the cam acts like the spring in the belleville washer keeping tension on the join. As the cam slips, the tension increases which prevents the screw from self loosing.
| PITApan wrote: |
| Belleville washers are statically loaded, not dynamically loaded. So when you bring up the dynamic case it's moot. |
All washers are statically loaded - that's the preload placed on them when torquing the bolt. The torque applied to the bolt is not the same as the clamping load (preload) of the joint. This is due to the friction coefficient of all of the surfaces. If you torque the bolt to 25 lb/ft, the clamping load might only be 20 lb/ft. This is why it's recommended to lubricate bolts when torquing a joint.
Nearly all joints are also dynamically loaded. Joints experience dynamic loads due to vibrations and other environmental/mechanical factors.
The loading of the belleville washer changes as it acts like a spring. The greater the deflection, the greater the dynamic load.
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Carl
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