- Home
- About Us
- Join/Renew
- Member Benefits
- Member Pages
- Log In
- Help
- Museum Store
The U-bolts clamping the front axle to the springs on my 845 have single nuts – see picture. I assume this is how it was originally, but since the rear axle uses double nuts and Packard used double length nuts, I wanted to double check. I don’t think this was messed with by previous owners, but don’t know for sure. Thanks, Jim
Some owners have placed plastic or soft metal spacers between each leaf to prevent wear and squeaks. This demands new longer ‘U’ bolts to be made and used. The original factory method used grease slathered between the leaves and then leather boots or metal covers placed over them.
Upon searching for a reasonable process for restoring 100 year old
springs, the painting of, re-arching(sp.), and lubricating, caused more
headaches than other questions that had to be answered. Everybody had
a different conclusion. The only thing they agreed on was that a
different outcome would occur if a different approach was followed.
They mostly agreed that grease or rust would eventually blemish the
highly visible light colored paint. One of the things they shared with
me is that the springs needed friction to do their job. They couldn’t
provide me with a path to get the right amount. Do you paint the spring
totally before assembly? Is reaching each spring necessary? Do you use
graphite? If you look at early car pictures, you don’t see springs
being a focal point for ugliness. Later Pierces were covered and not
easily viewed. What did they do at the factory? What about in 1912?
As usual, my restorer listened to my very clear instructions and did
what he pleased.
It is good to double check on double nuts or in your case, the octuple lack thereof.
If the single nut arrangement is consistent throughout the eight locations on your front springs, then it is likely correct, or the idiot who last greased the springs 40-years ago messed up front to rear (although in a consistent fashion).
However, if it will set your mind at ease, correct or otherwise, there seems to be ample thread showing on your U-Bolts to accommodate another nut.
Personally, I would just leave them as they are unless the single nut and locker do not appear to do the job. If that was the case, I would just replace the single nut and washer. Otherwise, they are likely fine.
I will also tell you that I do not have the constitution / disposition /personality to be the owner of a concours anything.
Have fun with the car and have a laugh at Tony Costa’s humor! There is wisdom in that boy.
And by the way, did you ask ANYTHING about greasing the springs, or did that line of discussion just appear? 
I love the topic of greasing leaf springs (although I realize that wasn’t the original question), it brings out so many opinions.
If the contact surfaces between each leaf were perfectly frictionless, then the car better have darn good shock absorbers. One function of leaf springs is to dampen movement, and the amount of damping is directly related to friction between each leaf. Of course, springs can’t be rusted together either, or there’s no inter-leaf movement and thus no “spring”.
My personal opinion is that most cars have the best ride when leaf springs are cleaned/smoothed separated (bead or sandblasted), painted with an epoxy primer, and assembled dry. There are many who believe the opposite, that there should be oodles of grease between each leaf……and I’m not sure there’s a right or wrong answer…..
well, I think Tony brought up the question of how to lubricate the springs in the middle of earlier dissertations on spring breakage. In the midst of my research of ancient engineering scrolls I came across a statement that the role of friction to provide damping in leaf springs was greatly exaggerated and not assumed in suspension design – unfortunately I can’t find it at the moment. I think the main reason for greasing the springs is to prevent squeaks and wear.
I also do drivers, not concours cars, you can tell from previous pictures I am committing the heresy of not doing a “frame-off” restoration. A car should be judged from the drivers seat doing 60. I am reusing the original metal covers which means I couldn’t tolerate the increased thickness of adding plastic interleaf pads. I cleaned and painted each leaf to prevent more corrosion, “slathered” the springs in grease when assembling, and after the above picture was taken wrapped them in canvas and replaced the metal covers as was done originally. My metal covers all have odd rectangular holes in them which I can only guess were some ones attempt to grease the springs by poking holes through the covers with a screwdriver. I decided it was a bit silly to do body work on spring covers , so the holes are still there on freshly painted spring covers, mute testimony to who knows what! It makes my restoration a willy-nilly combination of Smithsonian style preservation of original parts where functional and replacement where necessary for function (Smithsonian restored airplanes are never flown again).
At any rate Tony, I think the answer is that the leaves on your older exposed springs were probably greased between the leaves and wiped down to keep them looking sharp. It takes so little grease to coat the surfaces that you might be able to re-grease by putting the grease on the edges and ends and drive it around for a bit to work it in and then wipe the excess off- I imagine it is a ripe topic in AACA.
Jim
In relation to the original question about the single nuts securing the spring U bolts, no matter what you decide to do I would replace the lock washers at the very least.
I have seen many old lock washers just fall apart when the nut is removed thus the lock washer was providing no ‘locking’ ability at all.
Craig is correct, old lock washers tend to be junk!
New stainless rules.
Split lock washers are another debate, with perhaps a consensus in the engineering world that when torqued properly the lock ring is useless, being crushed flat without any ability for the angled edge to “bite” into the nut as intended until the nut has backed off so far that the preload is lost anyway. They are there basically for show on a restoration. The following link will download a NASA fastener manual which may be of interest on the subject: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19900009424_1990009424.pdf
I don’t think certified aircraft ever use split washers.
Double “jam” nuts as used on the rear axle are also apparently problematic, not being very effective and being difficult to torque to properly preload the bolt. Whether it seems to make sense now or not, I have a theory for why the front would be single and the rear would be doubles. The springs are mounted above the front axle, meaning the weight of the car bears directly on the bottom spring leaf rather than via the U-bolt. This was done I think to accommodate the front brake torsion bar going through the middle of the axle and below the king pins. The rear springs go under the axle and this means the weight of the car is hanging on the u-bolts. The clamp-up pre-loads should render the difference meaningless, but might explain what was going through their heads. Packard used cables to the front brakes, the springs are under the front axle, and used double length nuts. This little exercise has led me to fuss over whether I might have over-torqued the front U-bolt nuts, I think I will re-do them.
Sorry, for the “Cliff Claven” impression, I am a designer by nature and I find this stuff interesting, and somewhat more grounded than the speculations of “ancient astronaut theorists”
Jim
I don’t believe that split ring lock washers are supposed to “bite” into the nut, but merely exert tension against the nut so that the threads of the nut exert pressure against the threads of the stud / bolt. That is what keeps things locked. Old split ring washers loose their spring and thus their ability to exert tension against the nut.
If you want washers that “bite” you need STAR washers, most commonly used to insure good electrical contact.
Why split ring lock washers would not be used on aircraft is the CONSTANT vibration and its related stress. The vibration itself would cause nuts and bolts to come undone which is why aircraft bodies are riveted and not bolted. Heck, the vibration of an aircraft causes the metal to rupture. You do not see that on an automobile.
Your other nutty explanation seems reasonable, Cliff. 
Pete, the tension supplied by the split washer falls out of the equation once the torque is sufficient to flatten the washer, the torque determines how much the pre-stress is on the bolt, pretty much independent of the washers underneath (except for surface finish and lubrication of the surfaces). In other words, once flattened, the tension supplied by the split is not additive to the total bolt tension. Note that splits are never used on cylinder head bolts, they stay put by virtue of the tightness and stretching of the bolt, which the engineering sources cite as the prime method for joint tightness. Loctite has been shown to be much more effective. Aircraft often use permanent thread deformation which requires tossing the nuts/bolts when removed. Jim
Jim, Read the NASA piece on locking mechanisms. Interesting, however curious that the tension caused by a locker would disappear when flat. One would think that there is memory in the metal otherwise the locker would remain flat when the nut comes off. I will need to discuss this with my 3rd-year Mechanical Engineering student Son (He knows EVERYTHING – ).
I also understand the concept behind stretching threads as the locking mechanism, I just thought that the lockers enhanced that otherwise, flat washers would do just as well.
Need to meditate on this one.
Peter, its not that the tension disappears, it just goes to a constant value once fully compressed, and just becomes equivalent to a flat washer. If you put a coil spring on a bolt, the spring will provide increasing tension as the nut is tightened until you reach the point where the spring is fully compressed. Then it becomes a solid thick washer, and further turning of the nut will increase the tension on the bolt and the spring will act as a solid washer, without any difference in the stress level than if it were a solid washer. One of the odd calculations your son may have done in machine design is that the tension on an adequately torqued preloaded bolt such as a connecting rod is nearly constant despite extreme variations in load on the rod, its the reason such a highly stressed bolt being pushed and pulled with such heavy loads can be torqued up to ~75% of its ultimate stress and not fail from fatigue. Another Mr. Know-it-All! I have actually done a little bit of bolt stress analysis on aircraft structures but we never use splits in aircraft, so never dealt with them beyond throwing them in on car and home projects. I had vaguely understood split washers weren’t supposed to be re-used, they clearly provide a resistance to backing out once they are loosened, but I had always had my doubts about their effectiveness in the first place when fully torqued. I didn’t go looking it up until this thread. Jim
I can’t remember any connecting rod bolts or nuts using lock washers, or main bearing bolts or head bolts. I do see lock washers on manifold nuts and other low torque and flexing applications. A high torque nut by design has to be pretty hard, so a lock washer would not be able to ‘dig in’ anyway.
I once spoke with a guy who used to work on old locomotive engines, he mentioned that they used a sledge hammer on a special wrench to tighten the connection rod bolts.. I asked how could they tell when they were properly tightened ?? He said they measure the amount the bolt stretched. Each bolt had a value for how much it needed to stretch to have the correct tension for the connecting rod.
The torque we use for a bolt is really just a way of measuring how much we are stretching the bolt, and therefore how much tension we are putting on the head, the main bearing cap or the connecting rod.
In high performance Diesel truck applications, the higher the expected turbo boost pressure, and therefore the the greater combustion camber pressures, the stronger the head bolts or studs needed. There are special high tension studs and nuts available on the aftermarket. If stronger bolts or studs and nuts are not used, then head bolts stretch, and the head gasket blows out.
So a lock washer is really only useful in an application where there is expansion and contraction and the fasteners cannot be too tight or rigid or the parts will break when they expand. and the fasteners must be made from softer metal than a lock washer.
Most connecting rod nuts have a built in ring that is distorted with a punch into a slot in the rod cap. locking the nut in place. Or the nut is safety-wired.
Greg L
The recommendation of high load bolt manufacturers is that every time you undo your conrod bolts you throw them away & fit NEW ones.
Cheers from the Land of OZ
Another bit of trivia – as Greg says, the stretch of the bolt is actually the preferred measure of torqueing for extremely critical bolts, a torque wrench ft-lbs value having a fair amount of inconsistency depending on lubrication, surface finish etc. The WWII Rolls Royce Merlin head/cylinders were done by “feel” by craftsmen with years of experience. When Packard took on the task of building them they tried to adopt US auto practice of setting definite torque values but had lots of failures with such a high performance engine designed at the margins for minimum weight. They had to measure strain to get a consistent enough build to stop the failures. Fortunately, our old auto engines aren’t that finicky! Jim