Camber plate install?

[Suprgnat]

Originally Posted by fe1rx

The offending feature is a spring. My guess is so that the strut prevents a variety of springs from getting loose at full droop.

It's probably a topping out spring or whatever the technical term is, and prevents the strut from crashing on full extension much like the bump stop does for compression.

[fe1rx]

Originally Posted by Ginger_Extract

How much fluid leaked out? Or was this strut dead before you cut it up?

The strut was full of fluid but had lost all pressure. The shaft stayed down when pushed. The housing was bent slightly at the knuckle. That is actually what started my investigation. I noticed a mismatch in my camber plate pointers when aligning the front. The pressure is there to prevent cavitation of the fluid so the strut still worked, just not optimally during high shaft speeds.



Another interesting factoid that surprised me - on the OE suspension the 135i runs on the rear runs on its bump rubbers even at static ride height. With the dust cover on you can't see this. Obviously the effective spring rate is very progressive, despite the fact that the spring is linear.

[Ginger_Extract]

I'm curious how much of an effect the bump rubbers have on dampening control. I noted the the front ones are actually pretty stiff. On my Mazda for example, the front and rears were very soft.

[fe1rx]

For what it is worth, the initial stiffness of the bump rubber is very soft, so one could argue its contact is incidental.

Milliken and Milliken say this (in "Race Car Vehicle Dynamics") about bump rubbers:

"While these have nothing to do with the damping performance as such, ... The 'rising rate' (nonlinear spring) provided by the bump stop is often critical to overall race car performance, especially on rough surfaces."

Of course the 135i is not a race car, but conventional wisdom seems to be that the car rides on its springs on normal surfaces and only engages its bump rubbers on rough ones. It would be interesting to know if the M cars also ride on their bump rubbers.

[fe1rx]

Originally Posted by Suprgnat

It's probably a topping out spring or whatever the technical term is, and prevents the strut from crashing on full extension much like the bump stop does for compression.

Actually a working strut can't crash on full extension because it is hydraulically damped.

Here is what I have found as an explanation of internal rebound springs. This from SAE:

"These shock absorbers with anti-roll springs are used normally in front suspension (McPherson Struts) as an auxiliary to reduce vehicle roll and, in some cases, it may replace the stabilizer bar. Vehicles with low center of gravity and low weight may allow the elimination of the stabilizer bar and the anti-roll function will be replaced by an internal rebound spring in the shock absorber. This alternative brings to the client significant cost savings and mass reduction."

[Suprgnat]

Originally Posted by fe1rx

Actually a working strut can't crash on full extension because it is hydraulically damped.

Here is what I have found as an explanation of internal rebound springs. This from SAE:

"These shock absorbers with anti-roll springs are used normally in front suspension (McPherson Struts) as an auxiliary to reduce vehicle roll and, in some cases, it may replace the stabilizer bar. Vehicles with low center of gravity and low weight may allow the elimination of the stabilizer bar and the anti-roll function will be replaced by an internal rebound spring in the shock absorber. This alternative brings to the client significant cost savings and mass reduction."

Interesting. In a motorcycle fork they have them to prevent the piston from crashing on extension.

I still don't understand how an automotive shock "can't crash on full extension because it is hydraulically damped". Is there some mechanism that closes off the hydraulic fluid orifice just before it reaches maximum stroke? Going to see if I can find some diagrams.

[Ginger_Extract]

Originally Posted by Suprgnat

Interesting. In a motorcycle fork they have them to prevent the piston from crashing on extension.

I still don't understand how an automotive shock "can't crash on full extension because it is hydraulically damped". Is there some mechanism that closes off the hydraulic fluid orifice just before it reaches maximum stroke? Going to see if I can find some diagrams.

It makes sense to me. The damper's resistance to compression and rate of rebound ramp up under deeper stroke, to prevent the internal piston from smacking the strut base and risking damage. The spring acts in the same way as a return spring would, it's a mechanical stop. There is a difference between the strut hitting the bump stops (usable travel), and hitting absolute bottom (absolute travel).

This is all part of the witchcraft and wizardry that is shock design. I'm curious Felix, when you had the damper apart, could you spot any shims or other internal damper design cues? As I understand it, it's all a matter of fluid control inside of the damper.

This thread is proving to be an excellent learning tool!

[Suprgnat]

Originally Posted by Ginger_Extract

It makes sense to me. The damper's resistance to compression and rate of rebound ramp up under deeper stroke, to prevent the internal piston from smacking the strut base and risking damage. The spring acts in the same way as a return spring would, it's a mechanical stop. There is a difference between the strut hitting the bump stops (usable travel), and hitting absolute bottom (absolute travel).

This is all part of the witchcraft and wizardry that is shock design. I'm curious Felix, when you had the damper apart, could you spot any shims or other internal damper design cues? As I understand it, it's all a matter of fluid control inside of the damper.

This thread is proving to be an excellent learning tool!

I suppose the range of suspension motion itself would also limit the likelihood of "topping out".

[fe1rx]

Originally Posted by Ginger_Extract

I'm curious Felix, when you had the damper apart, could you spot any shims or other internal damper design cues? As I understand it, it's all a matter of fluid control inside of the damper.

I had tossed it in my scrap metal bin, but since you ask, I have disassembled the piston for educational purposes. This damper is really unsophisticated.



Under compression the fluid flows past a single shim through the outer slots in the piston and also out past a shim (up in next photo) through the foot valve (to compensate for the volume lost to the piston rod).



Under rebound, the fluid flows through the inner holes in the piston and fairly freely in through the lightly sprung foot valve (up in next photo). Rebound flow through the main piston is controlled by a small spring-loaded piston under set-on-assembly spring pressure.

[Kubricks]

Originally Posted by Ginger_Extract

For those who are curious, I can now say that this install IS possible. A friend stepped in and came to the rescue, so we were able to manhandle the strut assembly and get everything bolted together.

Set the negative camber to maximum, which with stock springs/dampers, should be around -2 according to Vorshlag. The front wheels are now SERIOUSLY tucked in. I would say it's every bit of -2. Will be getting the car aligned tomorrow since the toe is visibly out on both sides.

Drove the car around the block a few time to listen for any catastrophic noises and all seemed well. Got it up to 70mph on the freeway for a few minutes. There is a definite increase in NVH, on compressions/dips where both wheels are loaded simultaneously, you can hear and feel the dampers in action. Lock-to-lock, the steering action is buttery smooth. Chalk that one up to Vorshlag's bearing top plate. When the suspension loads unequally, say having one tire hit a manhole cover, the plates themselves make a bit of noise. It's not terrible, but certainly not as quiet as the OEM strut tops.

Once I get the car aligned, I'll actually push it a bit and get more impressions about the changes made.

A quick question, does your front ride height increase after the Vorshlag camber plate installed?

I am also on non-adjustable damper (Bilstein, custom valved), I wish to have more camber but I am not sure whether the stack height increase will throw the balance off, I have no other means of adjusting the ride height.

[yllwwgn]

fe1rx, just wanted to say thanks for sharing and documenting all the details so far! It's information like this that helps others in the community learn from others' "doing".

Although I personally would not be running the stock dampers with ANY kind of aftermarket spring (I dislike them with even the stock springs, ha ha), it's interesting nevertheless to see how the OEM strut was designed.

[Ginger_Extract]

Originally Posted by Kubricks

A quick question, does your front ride height increase after the Vorshlag camber plate installed?

I am also on non-adjustable damper (Bilstein, custom valved), I wish to have more camber but I am not sure whether the stack height increase will throw the balance off, I have no other means of adjusting the ride height.

Not at all. If you read Vorshlag's literature on the E90/E82 plate design, they made a notable effort to not change stack height/available travel.

[Hops128i]

after installing vorshlag plates on a OEM suspension, my before alignment results were very close to OEM specs on the fronts.

[Kubricks]

Originally Posted by Ginger_Extract

Not at all. If you read Vorshlag's literature on the E90/E82 plate design, they made a notable effort to not change stack height/available travel.

Thank you very much, placing my order now.