BMR Suspension's New S550 Rear Upper SHOCK MOUNTS: SM760 - Design Finalized!

[Brian@BMVK]

I cannot give you an accurate spring rate answer due to it being variable. Spring rate will change due to it being constantly changed. The effective area, volume, and pressure are continuously changing when driving since there are bumps, cracks, etc in the road. After talking to the manufacturer, they cannot give an accurate response to spring rate even at a given pressure.
Hub center to wheel opening driving: 13.5"
Hub center to wheel opening parked: 10.25"
Shock body and Shock mount gap driving: varies due to spring rate ever changing but stationary its about 5"
Damper setting: 22 clicks. (1 click softest/30 clicks hardest)

That is very low, far lower than most lowering springs. It's about a 1.5" drop from stock. For the spring rates I expect the bags to be in the range of, I think you're also running the shocks too firm. @strengthrehab has the Pedders, which should be very, very similar and runs between 18-22 clicks with 1300# rear springs for a handling application. I'm struggling to see how you have 5" between the shock and the mount at that ride height. Have you confirmed that?

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[2015DIBGT]

That is very low, far lower than most lowering springs. It's about a 1.5" drop from stock. For the spring rates I expect the bags to be in the range of, I think you're also running the shocks too firm. @strengthrehab has the Pedders, which should be very, very similar and runs between 18-22 clicks with 1300# rear springs for a handling application. I'm struggling to see how you have 5" between the shock and the mount at that ride height. Have you confirmed that?

I will do what I can to get a verification on the measurement.
I am also not positive as to what each "click" does or what the range of difference is that the BC shocks have.

 

[Brian@BMVK]

I will do what I can to get a verification on the measurement.
I am also not positive as to what each "click" does or what the range of difference is that the BC shocks have.

Best way to do that is to get the car up, take wheels off, and put jack stands under the knuckles/spindles. It won't be at exactly the same height, but it will be close enough. In reality, you'll have a little less clearance than whatever you measure doing that.

On the adjustment range, my point was that I think you're several clicks too high, not just one or two. I don't think the air springs will approach anything near 1300 lb/in, so you'd probably see better ride with the adjustment near the middle of the range.

 

[aleccolin]

Looking more and more like a stiff damper can impart enough force to rip a rigid mount out of the sheet metal, without an impact force from bottoming on the jounce bumper or shock body.

Ford screwed the pooch on this one, but the design of the OE shock mount makes me think they realized that before production. Or maybe they were going for low NVH and just got lucky, something makes me think they’ll never admit to anything either way.

 

[Brian@BMVK]

Looking more and more like a stiff damper can impart enough force to rip a rigid mount out of the sheet metal, without an impact force from bottoming on the jounce bumper or shock body.

Ford screwed the pooch on this one, but the design of the OE shock mount makes me think they realized that before production. Or maybe they were going for low NVH and just got lucky, something makes me think they’ll never admit to anything either way.

And yet we don't see people with MCS, Cortex coilovers who also street drive ripping them off (with both very high damper rates and spring rates). It doesn't take much bottoming metal-on-metal to induce cracks, and once that's started, the slightest thing could cause a catastrophic failure.

There is a spring rate and ride height piece of this, along with proper bump absorption. I beat the crap out of my car all last year and into this spring with the very first set of BMR mounts, and there isn't a single shred of damage there.

 

[aleccolin]

In a traditional setup (non-coil over) the spring isn't acting on the shock mount, only the damper is, correct? I don't see what spring rate has to do with it aside from the increased dampening force required to counteract oscillations with an increase spring rate.

Ride height of course factors, but only in a bottoming scenario. The Viking shocks are ripping out without bottoming (ostensibly). It's a mystery, but just because there are examples of others NOT failing doesn't mean that super stiff dampers aren't a commonality among those that ARE.

 

[shogun32]

Looking more and more like a stiff damper can impart enough force to rip a rigid mount out of the sheet metal, without an impact force from bottoming on the jounce bumper or shock body.

you got more data? Any damper that stiff might as well be rigid.

 

[Brian@BMVK]

In a traditional setup (non-coil over) the spring isn't acting on the shock mount, only the damper is, correct? I don't see what spring rate has to do with it aside from the increased dampening force required to counteract oscillations with an increase spring rate.

Ride height of course factors, but only in a bottoming scenario. The Viking shocks are ripping out without bottoming (ostensibly). It's a mystery, but just because there are examples of others NOT failing doesn't mean that super stiff dampers aren't a commonality among those that ARE.

The coilovers mentioned are true coilover, so they would impart far higher total loads under compression than a divorced (stock style) setup would.

The Viking shocks are ripping out without bottoming

I've not seen substantial proof that this is true.

 

[Crowd Hunter]

Looking more and more like a stiff damper can impart enough force to rip a rigid mount out of the sheet metal, without an impact force from bottoming on the jounce bumper or shock body.

Ford screwed the pooch on this one, but the design of the OE shock mount makes me think they realized that before production. Or maybe they were going for low NVH and just got lucky, something makes me think they’ll never admit to anything either way.

That area is weak and not made to withstand much more forces than the stock setup. I would be leery about stressing that area any more than it is from the factory, but fortunately, that should be an easy area to beef up.

 

[2015DIBGT]

Best way to do that is to get the car up, take wheels off, and put jack stands under the knuckles/spindles. It won't be at exactly the same height, but it will be close enough. In reality, you'll have a little less clearance than whatever you measure doing that.

On the adjustment range, my point was that I think you're several clicks too high, not just one or two. I don't think the air springs will approach anything near 1300 lb/in, so you'd probably see better ride with the adjustment near the middle of the range.

Got some info regarding ride height shock spacing. Between the shock body and under side of the upper mount I have 4” (+/- 1/8”) of shaft showing.

 

[strengthrehab]

Welp...my car is basically broken. I can't say it is due to the BMR shock mounts as I've been running them for a while... but I've never bottomed out, not super stiff, divorced coilover design.

Moving to another design soon. I contacted BMR, but haven't heard back.

Not happy.

 

[aleccolin]

Fuck man, that sucks. Someone handy with a TIG torch (and with a lot of patience) can chase and weld those up, just a matter of making sure you get all the cracks cleaned out really well. Still going to get some trash in the puddle.

By divorced coilover, do you mean a spring with an adjustable height seat in the stock location, and a damper in the stock location (with BMR upper mount)? Just want to be sure.

NVM just looked up the Pedders Extreme XA coilovers, looks like that's the case. The shock body is adjustable in length, is it set shorter than OE, longer, or same?

 

[strengthrehab]

Fuck man, that sucks. Someone handy with a TIG torch (and with a lot of patience) can chase and weld those up, just a matter of making sure you get all the cracks cleaned out really well. Still going to get some trash in the puddle.

By divorced coilover, do you mean a spring with an adjustable height seat in the stock location, and a damper in the stock location (with BMR upper mount)? Just want to be sure.

NVM just looked up the Pedders Extreme XA coilovers, looks like that's the case. The shock body is adjustable in length, is it set shorter than OE, longer, or same?

Same length as OE.

Have a guy coming to MIG it on Saturday I think (as long as my garage breaker can handle it)...if not, I have to farm it out. Luckily there is a place that works on 4x4 stuff about 3 miles from my house.

 

[aleccolin]

I've got a working theory that the alloy used for the sheet metal - while good for a deep draw - becomes very brittle when welded and what you're seeing is failure of the metal in the heat-affected zone. Could be the sheet steel was produced out of spec, or the engineers just didn't account for the HAV changing the temper on the parent material. Or maybe the stresses induced during stamping just don't play well with the welded area.

Does anyone know of an instance of this occurring with the OE mounts?

 

[Brian@BMVK]

I've got a working theory that the alloy used for the sheet metal - while good for a deep draw - becomes very brittle when welded and what you're seeing is failure of the metal in the heat-affected zone. Could be the sheet steel was produced out of spec, or the engineers just didn't account for the HAV changing the temper on the parent material. Or maybe the stresses induced during stamping just don't play well with the welded area.

Does anyone know of an instance of this occurring with the OE mounts?

I think you've got a good thought there on the material used vs draw depth. I don't know what type of weld nut they use...which can drastically change the type & size of HAV.

I'm not aware of any failures with them. Usually the OE mount fails before anything else.

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