I have had an upper shock mount come loose on my car........a 1940 Dodge, I relocated the upper shock mount a couple of yrs ago, it seemed to work o/k, however last week I noticed a noise from the passenger front side, cut short the drive & came straight home...........on inspection I noticed the upper shock mount had come loose, it was held onto the frame with three 5/16th UNC thread high tensile bolts threaded INTO 3/16th plates with nuts welded on their inside, this was inside the frame.......pic shows the two horizontal bolts and the spring and flat washer used UNDER each bolt head......there is one more 5/16th UNC bolt going vertically into a nut inside the frame as well........when I checked, the bolts,washers and nuts had vacated the premises and just the bracket was swinging in the breeze still attached to the shock absorber so I am unsure whether the bolts broke or came undone although there is some markings on the bolt holes in the bracket consistent with the bracket moving on the bolts and cutting small grooves into the hole side.........after noting that the bracket where the two horizontal bolts went thru was not quite hard against the frame I bent it and is now sitting perpendicular to the frames outer side............. ............MY QUESTION IS.......... .............which is the stronger method..........insertion of bolts into threaded plate and/or nuts on the inside of the frame..........OR...........weld two bolts onto a piece of flat plate and insert this inside the frame which will have the two bolts protruding thru the frame & bracket and allow flat & spring washers together with nuts and /or nylocs on the outside(the easier option also)..........Loctite of some sort will also be used this time..........Also whilst I think the 5/16th UNC High Tensile bolts were strong enough there is just sufficent room to drill the holes in the bracket for 3/8th UNC or UNF bolts if it felt is needed.............the main issue is that it is almost impossible to access the inside of the frame where the bracket fits so the threaded plate/welded nut was my original solution............I await any comments..........Andy Douglas
cant weld the bracket to the frame? did the bolts have any clear shank or threaded right up to under the bolt head,? do your shocks bottom out? and not that you asked but do you have a couple of free threads sticking out past the nyloc on the upper control arm?
Last first.........yep there are a couple of threads past the nyloc end, as for welding the bracket to the frame........that was one idea we, my mate & I, thought about when we did the shock relocation but neither of us were certain about the welding straight onto the frame , tho' I suppose the barcket could have been welded onto another wider plate and that then welded onto the frame.......the bolts were threaded up to the bolt head, which when now that you mention it was possibly not the best idea, they are/were 3/4" long ..........also the shocks whilst short did not appear to bottom out but it is close...............got me thinking about a couple of things now....lol..........tho' any comments on my original question re the direction of the bolts, ie, into or out of the frame........andyd
In my opinion that mount looks plenty stout enough. 5/16 bolts should be fine whether with plate or nuts. I also think your shack has bottomed, now that would break things! Do you have rubber stops that hit before the shock bottoms?
Starting with the hardware. It looks like the bolts are grade five. Thats good. Fine threads are stronger than coarse. At the bottom of the pic there is what appears to be another nyloc nut. Those are not graded for strength and would best be used to assemble a metal swing set for the kids. Get rid of those. Now, keep in mind that shocks work in both directions. That bracket is nice but is designed to take a load in one direction only. It would be under compression to the top of the frame one way and hinging or flexing out the other. Your shock could bottom out in either direction. Since the shock mount is not a perishable part, and would never need replacing, I would weld it up and forget about it
That is a nice looking bracket, but I would say off the top of my head that the 5/16” bolts are too small for that type of loading (dynamic shock) and broke off. On my Lexys LX450 (i.e. 80 Series Land Cruiser) I have 8 mm bolts connecting the sway bar link brackets to the frame which works fine, but they wouldn’t see the same type of loads. I think part of the problem is the bolt pattern/ placement. I can see the room you have is bery tight, but ideally the bolts should be placed outside the centreline of the shock axis to provide more resistance to any moments (torque) applied. The other issue is how well does the bracket surface fit against the frame. All bolted connections reply primarily on the friction created between the mating surfaces for their strength. If the bracket has any gaps or spaces between it and the frane, that could alsi be a reason for the failure. Hope this helps a bit.
Is the third, vertical bolt, at the top somewhere? Anyways...I doubt the problem is the way the nuts are installed. It has more to do with the bolt size. Think about the bracket as a lever, and the shock mounting point is where the load is applied to this lever. And the load is the weight of the car, or more. You're asking a lot of pair of 5/16" bolts (only the two outer bolts, of the three, are taking all the load, until they get loose, then the center one finally can take some of the load)
If you can get the bolts back in ? Tighten them up good , mark the heads in line top to bottom, take them out one at a time, drill small tie wire holes where you marked them reinstall and tie wire them !
@squirrel makes a good point. I should also mention the point I made about surface contact with the bracket would also apply to the plate inside the frame. My guess is that one or both did not have sufficient contact with the frame causing the loads to be transmitted directly to the bolts leading to their failure.
The OP mentioned something about using what sounded like both flat washers and split lock washers under the bolts. Might this be a case where you'd be better off using the split lock washers only? On the inside of the frame, if there's room, how about maybe a 3/8" thick plate drilled and tapped for the bolts?
I agree with ziggster and squirrel. Personally, I would never use a 5/16 on such a mount; 3/8 or even 7/16 would my choice, and I would space them out from the shock centerline. This subject has been covered many times at www.p15-d24.com and I recall seeing some photos of various designs that looked good.
How come you didn't use metric bolts ? Don't know how long ago you installed the bracket but a while back there was a problem with bolts being made overseas and foisted off as being higher quality than they actually were. That said, I would simply redrill and retap to 3/8 or a similar size metric and use Grade 8 bolts. You may be able to find some (Allen Head) that have a little plastic insert near the end to help lock them in place. You could also use some Blue Locktite. I would drill all the way thru the welded nuts inside and retap them all at the same time. If you look for a 2 flute tap, you will find them available in a longer length that should allow you to reach all the way thru the inside nuts. Use some WD 40 and clear the thread regularly as the last thing you want is a broken tap inside your frame. https://www.msdiscounttool.com/cata...WKJaUCitdv7FSkPlqm2J1DiXMz4-9RahoC24MQAvD_BwE
We can' see the bottom of the mount, but if it were mine I would like to have a horizontal piece,top and bottom that sort of captured the fhrearame and absorbed vertical loads. So, very little load on the bolts them selves. And, another probable source of your issue is the bolts being threaded all the way to the head. So, they don't really fit the hole all that well. I was working on my Mitsubishi box truck rear springs and mounts when I discovered the bolts that fasten the spring brackets to the frame are a pressed fit into the frame. Metric bolts with about 1/4" unthreaded and almost one with the frame. NO wiggle possible. Maybe you could make up similar bolts and drill/ream the holes to fit. A slightly undersized hole then reamed to size for a standard bolt would be about right. A high strength bolt and matching nut (maybe two, back to back) well oiled an pull into a pretty tight interference fit.
Thanks guys, its good to get some comments & opinions, all of which are making me consider a few options, the big problem as I've mentioned is that where the mount fits and has to be situated due to the shock clearance is that there is very little room to get anything inside the frame..........nuts or even a threaded plate are difficult to align.........admittedly I did it originally but I was a little bit more malleable, ie 2-3ys younger, when I did this which is why I'd like to weld the bolts to a plate and insert it with the 2 bolts pointing out..........the 3rd bolt will still insert vertically between the two shock plates...................and Metric??...........no chance..........I throw any metric bolts I find in the trash bin............lol.............at the end of my legs I have feet, not metrics............lol..............going to a club run today so will ask for opinions there too.............I appreciate all comments..........thanks........andyd
How about putting a lower lip on the bracket so it becomes c shaped , that way the bolts hold it in place , the structure bears the load ..
Jim, I agree the bolts are probably too small for the bracket, but I can't quite understand your statement about "the load is the weight of the car, or more". On compression the shocks compress fairly easily (depending on valving), so it's doubtful they see a load equal to the entire weight of the car. On rebound, they only deal with the weight of the suspension. Coilovers would be a different story as then the bracket would be supporting the weight of the car. Am I missing something?
The length up and outward of the bracket is a lever and where the bracket meets the top of the frame is a pivoting fulcrum n shock absorber compression...the distance from where the bracket meets the frame down to the bottom bolt is the short end of the lever....the eye of the shock ( long side of the lever) appears to have about a 3 or 4 to one motion ratio....probably stretching the bottom bolts....
I agree with Iton, Nylocs and split lock washers belong on children's toys. I stopped using split lock washers long ago when I saw how they dig into the surface and could raise a burr which can lead to stress cracks. Nylocs are not strength rated, and in a high temp application the plastic "lock" can melt. I have switched to using flat washers and Stover nuts on everything. Most threads will loosen at 75% of the make up torque, Stovers require an equal amount of torque to loosen them. A small amount of anti-seize on the threads, Tighten the Stover nut and forget about it, forever!
I am confused if the bolts broke or just came loose and left the vehicle. If they broke, such as fatigue cracking or overloaded due to suspension bottoming out, then there should be part of the bolt in the threaded nut. If there is no bolt at all, that indicates to me the bolt just loosened up. While I think 5/16 is a little on the small side, if they just loosened that indicates it was not a strength issue. A properly bolted joint does not really change the tension in the bolt, even with some bending load on the shock bracket. A tightened bolt is actually very slightly stretched, which provides the clamp load, sandwiching the bracket under the bolt head. The bracket should be very flat against the frame when it is tightened.
I'd bolt the bracket back on to hold it in place, then weld all around the bracket. Remove the paint, get good welds. I agree that the way the bracket is designed, it works well under compression, but will want to pull the top of the bracket away from the frame as the suspension drops. I suspect the continual movement of the bracket probably broke the bolts or stripped threads in either the nuts or the bolts, and will do so again unless you can somehow attach the top of the bracket to the frame. It does appear that the position of the upper shock mount on the bracket is the same height as the upper shock mount on the control arm. That would indicate to me that the shock is probably not reaching either end of its stroke. Its not hard to be be sure the shock has more travel then the amount of travel the suspension has., I would check that just to be sure, though its not unusual for shocks to be the limiting factor in the extremes of some suspension travel on some vehicles. Gene
The reference to metic bolts was because you are located in Australia and was kinda "tounge in cheek", but then sometimes a metric can get a thread size in between standard thread sizes when the next larger std thread would create a problem. Figured getting quality American standard bolts might not always be easy down under........
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