Rear shock mount

Tiny
TMCINTOSH11
  • MEMBER
  • 2002 FORD F-150
  • 5.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 285,233 MILES
Hello, I've had a small issue with my truck for about a year, my old leaf spring shackle mount rusted apart and when I fixed it I noticed my shock and mount was busted off the frame, I've not had any issues driving it like that except noise, but I just went ahead and removed the shock from it's mount on the axle so I could get a better ideal on how it could be fixed. The shocks are out anyway but I can't replace them until I can get this first. I included a few pictures of the mount and the frame were it once was, I've had mixed results from different shops and mechanics that weld, some won't even do it period, so I was going to ask you guys what my best bet was on this. One guy said as long as I don't do any heavy hauling I could go without shocks in the back since the leaf springs support the weight of the rear end anyway, the main problem I have currently with the other shock still in place is that it leans slightly, so what do you guys think? Can it be welded or mounted or a new plate? Thanks!
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Monday, April 8th, 2019 AT 1:17 PM

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Tiny
CARADIODOC
  • EXPERT
The truck is not leaning because of the missing shock absorber unless the other one has a helper spring on it. Shock absorbers never hold up a vehicle. Some people become confused when they see a gas-charged shock extend on its own, but that gas is just to reduce foaming of the oil inside. You can still push them back together by hand, so you know they aren't capable of holding up much weight. Shock absorbers only stop the continued bouncing of the springs.

When the upper mounts are on the cross member, the first thing I would look at is if that cross member is riveted to the frame rails. If it can be removed by grinding the rivet heads off, then pounding them out, look down south for one from a salvage yard. It can be bolted on instead of riveted.

It looks like your upper mounts are right on the frame rails. If that is what tore out you'll need to fashion a piece to go in there, but if the metal is that thin, it's going to be real hard to weld to without burning through it. The patch will have to reach to clean, rust-free metal on both ends. My limited experience has been with helping a friend repair smashed Dodge trucks in his body shop. The frame metal on those is just under 1/4" thick, so that provides a lot to weld to.

I suspect the reason no one wants to tackle this is for liability reasons. We have to think about over-strengthening a part that defeats a crush zone, and once someone starts welding on it, Ford is absolved of all liability involving safety issues, and the mechanic takes that on. They're also worried that if this part rusted out so quickly, what is going to happen when another section rusts away and breaks? I have visions of one side of the rear axle sliding rearward, then the drive shaft drops out and gouges into the road. I've seen that twice. The first one was on a Chevy station wagon. The car was almost at a 45 degree angle to the ground when the rear shot up. This would be less of an issue with a uni-body car. You'd have the floor to hold the car together. With a full frame, only the six box bolts will be holding everything together That might get you home, but it won't hold up to hard braking.
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Monday, April 8th, 2019 AT 10:33 PM
Tiny
TMCINTOSH11
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I did some digging around and found out how the mount I was holding in my hand in the picture goes on. It appears that there is a small tab like piece that broke off the frame that was yes riveted on one side of the mount and the other side of the top of the mount was bolted on to what use to be the EVAP emissions canister bracket, which rusted away completely (my truck has a lot of rust issues under the bed). So that's how it was up before, the other shock is held in place differently and isn't in any danger of breaking off. I have been driving it like this for over a year and I never had any bounce, in fact the ride is real smooth. What you described with the Chevrolet wagon sounds scary. I only mentioned going without shocks in the back because a couple of mechanics told me it's okay as long as I don't haul a heavy load or tow. One guy said bigger trucks don't even have shocks in the back because the springs is what holds up the weight of the truck, the lean might be from my tires I'm not sure yet, but yeah it looks like a bracket and a part of the frame was holding the mount in place.
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Tuesday, April 9th, 2019 AT 5:21 AM
Tiny
CARADIODOC
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You need a new mechanic. Even large semi trucks have shock absorbers. They're more important when hauling a load because the higher weight is going to want to bounce more. With a lightly-loaded truck, you'll bounce once over a bump in the road, and keep on going with no more bouncing. Think of a clock pendulum with the spring wound down. If it's a little stick with no mass and you give it a shove, it will stop moving right away. If it's that heavy weight on the end of a pendulum for a grandfather's clock, with one push, it will keep on swinging back and forth for a long time.

Remember too, as I mentioned, it is only the springs that hold any vehicle up, even railroad cars. Shock absorbers only resist movement up and down of the axle on those springs. If you have clearance for tools, and access to the mounting hardware, shock absorbers can be totally removed from any vehicle while it's sitting on the tires, and it will not drop in height one bit. Some people will argue that's not true, then they'll pull out a shock absorber with a helper spring around it. That again is a spring that helps the weak original spring. The shock absorber itself still does only shock absorber stuff. The helper spring assists the main spring and has nothing to do with damping bouncing.

To get technical for a moment, when shock absorbers aren't needed is a factor of the weight of what can bounce, and how fast it is rotating. Every wheel / tire combination has a "resonant frequency" at which it will bounce freely. That's affected by weight and location of that weight. Thinking again of the grandfather's clock pendulum, it has one frequency it wants to swing at. The spring adds a little energy to it to make up for what is lost as it drives the bunch of gears. If you come along and try to push the pendulum to swing faster or slower, you have to put a real lot of energy into it. To keep it swinging at its resonant frequency, all you have to do is tickle it a little up near the top. Railroad car wheels are so extremely heavy, it takes a real lot of energy to get one to bounce. We'll never get close to its resonant frequency, so that is one application where a shock absorber won't do anything of value.

It's common to find a one-ounce wheel weight on the lip of a wheel to balance the assembly. Take that weight off, and you'll feel the bouncing best at around 50 - 60 mph. Larger diameter wheels bounce at a different speed than a smaller-diameter wheel and tire. You'll also find balancing weights welded to the outside of most brake drums. Those can often be four to eight ounce weights. They travel in a smaller circle so they have less effect on balancing. If you ever see eight ounces of weight on a wheel, there is definitely something else wrong that must be corrected.

That resonant frequency is also why we often feel an out-of-balance tire at one speed, but not so much at a higher speed. It takes less energy to keep it bouncing at its resonant frequency, so what energy is put in has more effect, hence, stronger bouncing.

Another way to look at this is the spring's only function is to hold the frame and axle apart. How much is critical, and there are books in every shop that shows where to take those measurements on every car and truck model, and what they should be. If ride height is sagged, we replace the springs, or adjust them if they're torsion bars.

Shock absorbers resist the frame and axle moving closer together or further apart, but they don't care where they end up. It is only the movement they resist. That has two functions. It keeps the truck body from continually bouncing up and down, making us seasick, and it keeps the tire from bouncing off the road surface. The energy of a bouncing tire is transmitted through the springs and shock absorbers into the body where we can feel it. That energy has to be absorbed somewhere, and the shock absorber slows that down to spread it out over time so it isn't so abrupt when we feel it. Shock absorbers work hardest when vehicle speed matches the tire's resonant frequency.
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Tuesday, April 9th, 2019 AT 6:09 PM
Tiny
TMCINTOSH11
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How would I begin reinstalling the strut mount? I can cut all the old rusted broken brackets off the mount and clean it to smooth surface but does it have to be welded on or is there a way to use bolts and possibly clamps? I know the idea doesn't sound like it would last long but there's already holes in the frame from when it was built that I thought maybe I could use to put it back on. I thought about maybe getting a thick metal plate and fitting it to that area and bolting the mount to that, or maybe getting a mount like the other side from the junkyard and welding it to a fitted plate at the same angle, what do you think? Thanks for all your feedback on this I really appreciate it!
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Wednesday, April 10th, 2019 AT 5:40 PM
Tiny
CARADIODOC
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Welding on a plate gives you all kinds of possibilities. Then you can do whatever works best or is easiest for your skill level. One more thing you might consider is looking at how rear shocks were attached on older GM cars from the '70s. They had a fat bolt pressed through a rubber bushing, and that bushing was captive inside a round metal eye. When discarding the old shock absorber, that bolt went with it. This photo shows the replacement bolt that came with the new shock absorber. The end with the fatter threaded area is bolted to a plate, the shock is slid over the smooth part, then it is held on with a washer and nut on the smaller threaded area on the right.

Back in the day when I worked at a Sears Auto Center, replacing these was a daily job, and often the cars came in with the replacement bolts already installed previously, so we just saved the new ones. A lot of older mechanics have these laying around to be used for all kinds of projects.

Your rear shock absorber uses the exact same lower mounting method although I don't know if the sizes are the same. Looking at the threaded shaft up on top, you might consider welding on a piece of right angle instead of a flat piece. That would give you a place to drill a hole for that shaft. Getting the angle right would be a concern, but that would probably outlast anything original you could find to stick in there.

If you get an original shock absorber to work, one common mistake people make is they tighten the top nut as tight as they can get it. That will lead to rapid deterioration of the rubber bushings since they can't flex properly. The correct tightness for that nut is when the bushings have been expanded to the exact same diameter as the washers around them.
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Thursday, April 11th, 2019 AT 7:12 PM

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