Strut Mount Question

[Tommm]

Background: I bought a set of Koni Sports, to go with the 135 springs I had in the garage. Instead of using the old hardware, I bought everything new from FCP, including the Lemforder strut mount (Lemforder 31306775098). I wanted to save the strut assemblies in case I found an high mileage 1 or 3 for my daughter when she gets her license in about a year I would have a 53k mile suspension for her to get a few years use out of.

I assembled the now strut and hardware in September, and put the four shocks on a shelf. Yesterday I started to tackle the job. I watched the videos and got the old strut out just like they said.

PROBLEM: I cant get the new one in. The new one is taller, and I cant get it under the lip of the fender without removing the wheel hub/knuckle. I then took apart the old strut (dreaded spring compressor again) and took apart one of my new assemblies to see if I had an extra part/washer/??? making it taller.

Turns out the rubber on the new strut mount is beveled, making it taller. I am attaching a picture of the two side by side. Here is the page from FCP https://www.fcpeuro.com/products/bmw...60-31306775098 It cross references the PN in realoem.

I would rather not install a 52k mile strut mount with my new shocks, and I also don't want to have to remove the control arms to free/basically remove the whole hub/knuckle, hang the assembly from the car, then install the hub by sliding it up the strut and then re assemble the control arm.

But, if that is the way the strut mount comes, that is what I will do unless you have a better way besides removing the fender which a friend semi seriously suggested.

Here is a link to the album with three pictures http://www.1addicts.com/forums/album.php?u=316886

Tom


https://www.youtube.com/watch?v=4YkVs_jm9R4. At about ten minute mark.
https://www.youtube.com/watch?v=KmZvggTxrKU

[sprp85]

There is an angle that the strut will go in with some effort.

However, what I did was, compress the spring as assembled, slip the assembly in past the fender and then un-compress it.

Good luck

[Tommm]

Originally Posted by sprp85

There is an angle that the strut will go in with some effort.

However, what I did was, compress the spring as assembled, slip the assembly in past the fender and then un-compress it.

Good luck

Was your mount thicker? I tried all angles and it cant get past the wheel well because the assembly is about 1/2" taller.

What do you mean compress the spring as assembled? If I have a spring compressor on the spring when I install the strut will I be able to get the compressor off?

Thanks

[gjm120]

I think the only difference in the strut mounts is 53k miles and age. They wear.

[Tommm]

Originally Posted by gjm120

I think the only difference in the strut mounts is 53k miles and age. They wear.

So its me. "User error". It should fit, push harder on the hub?

[fe1rx]

Originally Posted by Tommm

So its me. "User error". It should fit, push harder on the hub?

No, change your method.

Loosen the inboard suspension arm bolts (tension arm and wishbone) so they are free to rotate. Fighting those bushings is ridiculous, not to mention bad for them. Once you have done this:

Install the strut into the strut tower first.

Then put slide the knuckle onto the strut tube. If I recall correctly, this is easiest if the steering is turned a bit inboard on the side you are working on.

(Life is simpler if you also take the brake rotor and caliper off because things are lighter, but this is not strictly necessary.)

Done this way it is an easy one-person job. Without the rotor and caliper on the knuckle it can be done with one hand. No spring compressor in your wheel well is required. Bentley recommends this method, which probably means BMW does too.

I have also done it the way you are trying (and internet wisdom suggests), but it is a ridiculous use of force over brains. Others will disagree, having ultimately succeeded, but frankly if you have to fight with something to remove it, you are doing it wrong.

Of course if you had loosened those bolts initially, the removal would have progressed with removing the knuckle from the strut first, then removing strut from the strut tower.

[gjm120]

Question for fe1rx: what's your opinion on the need to replace the arm fasteners once you've loosened them ? Given that they are a torque + 90deg I'm assuming they are stretch bolts.

[Tommm]

It's got to be me. I hung the assenbky and it didnt work. I probably didn't loosen the inboard bolts enough. They are very loose now.

I will reassemble the assembly and try again.

Did you just jack up the hub to where it would be loaded to tighten the inboard bolts?

[Tommm]

Originally Posted by gjm120

Question for fe1rx: what's your opinion on the need to replace the arm fasteners once you've loosened them ? Given that they are a torque + 90deg I'm assuming they are stretch bolts.

The videos dont say replace but they do say loosen

[gjm120]

Originally Posted by Tommm

The videos dont say replace but they do say loosen

Right. Just thought I'd ask fe1rx since he has shown much engineering knowledge on some postings here.

I will say when you re-tighten the fasteners on the subframe/bushing side, do it with the suspension at ride height. It's easier and safer to do it on ramps.

[fe1rx]

Originally Posted by gjm120

Question for fe1rx: what's your opinion on the need to replace the arm fasteners once you've loosened them ? Given that they are a torque + 90deg I'm assuming they are stretch bolts.

Bentley says to replace these bolts. I am sure BMW does too. Conventional wisdom says that when a bolt is set by torque + angle it is torqued to yield (i.e. you are actually permanently stretching the bolt). For a true torque-to-yield bolt, you should change it every time.

The question is - are these bolts actually yielding at the specified torque + angle? Possibly not.

These bolts are M12x1.5 class 8.8. They can be safely torqued to 64 ft.lbs. without damaging them. The specified torque is 50 ft.lbs. +90 deg. If you don't exceed 64 ft.lbs. in achieving that 90° it is safe to say you haven't actually yielded the bolt.

I guess I should perform that experiment some time (or maybe you can).

In any case, I don't replace these particular bolts every time they are torqued on my own car.

[fe1rx]

Originally Posted by gjm120

will say when you re-tighten the fasteners on the subframe/bushing side, do it with the suspension at ride height. It's easier and safer to do it on ramps.

Ramps are a great solution to achieving ride height and still having access to torque the fasteners.

[gjm120]

Originally Posted by fe1rx

Bentley says to replace these bolts. I am sure BMW does too. Conventional wisdom says that when a bolt is set by torque + angle it is torqued to yield (i.e. you are actually permanently stretching the bolt). For a true torque-to-yield bolt, you should change it every time.

The question is - are these bolts actually yielding at the specified torque + angle? Possibly not.

These bolts are M12x1.5 class 8.8. They can be safely torqued to 64 ft.lbs. without damaging them. The specified torque is 50 ft.lbs. +90 deg. If you don't exceed 64 ft.lbs. in achieving that 90° it is safe to say you haven't actually yielded the bolt.

I guess I should perform that experiment some time (or maybe you can).

In any case, I don't replace these particular bolts every time they are torqued on my own car.

Thanks for the input!

[fe1rx]

I decided to put my engineering judgement to the test as I had a used bolt on hand to experiment with. I made a 90 mm long tube to provide a representative gauge length for the bolt clamping dimension.

Measured:

122.55 mm original length
122.77 mm at 50 ft.lb. (delta = 0.22 mm or 0.24% of gauge length)
122.89 mm at 50 ft.lb. + 90° (delta = 0.43 mm or 0.48% of gauge length)
incidentally this took about 80 ft.lbs. to achieve
122.58 mm after relieving torque (delta = 0.03 mm or 0.03% of gauge length)

In US measurements that is 0.001" of permanent stretch.

I call this permanent deformation negligible, meaning these bolts can be retorqued to this spec a few times in their life.

[Tommm]

I just got the evil strut on. Now on to the other side. I feel like a butcher with a jack to push the hub in place while you are doing real science.

Thanks for your help.

[juld0zer]

I thought it's the coating which wears off which mandates replacement? As you have proven, the fasteners are more than adequate.

However, the locknuts must be replaced. They are the egg shaped ones and the nuts with nylon lock rings in them.

It has been covered here or on the E90 forum before - the front strut mounts compress with age and wear/tear.

[ianc]

Hmm, very interesting post. I'm measuring a front ride height of only 24" at the fender lip: too low. At first I thought it was just that my Eibach springs had sagged after 7 years and ~68K mi, but now I'm wondering if my strut mounts aren't just shot instead? Maybe both?

Could a worn-out top hat make a half inch difference in ride height? Spring pads?

ianc

[asbrr]

Originally Posted by ianc

Hmm, very interesting post. I'm measuring a front ride height of only 24" at the fender lip: too low. At first I thought it was just that my Eibach springs had sagged after 7 years and ~68K mi, but now I'm wondering if my strut mounts aren't just shot instead? Maybe both?

Could a worn-out top hat make a half inch difference in ride height? Spring pads?

ianc

I would say a bit of both but the spring pads won't be much, it will mostly be the strut mount and maybe a little on the springs. Just from the picture in this thread you can see how much the mount compresses over time.

[ianc]

I don't have the strut mount in front of me, but after looking a little further at a few pics of the assembled stack, I'm having difficulty understanding why a worn mount would cause the ride height to decrease? Doesn't the spring pad sit right between the spring and the metal portion of the mount?

If so, the spring height should be the same, and only the central rubber damping portion shown in the pic at top by the OP would get smashed down over time.

Or am I just missing something obvious?

ianc

[asbrr]

Originally Posted by ianc

I don't have the strut mount in front of me, but after looking a little further at a few pics of the assembled stack, I'm having difficulty understanding why a worn mount would cause the ride height to decrease? Doesn't the spring pad sit right between the spring and the metal portion of the mount?

If so, the spring height should be the same, and only the central rubber damping portion shown in the pic at top by the OP would get smashed down over time.

Or am I just missing something obvious?

ianc

You know, looking at the stack picture on RealOEM, I started doubting myself. I still think it's a factor, maybe someone else could weight in?

OP's pic shows the mount upside down, imagine it right side up - the lock nut at the top of the strut holds the assembly together, and keeps the mount pressing down on the upper spring cup (the pad is between the cup and the spring). So in effect, the rubber inner portion of the mount (the same part that looks compressed in OP's picture) is all that is holding the top of the entire strut in place. So the inner rubber portion of the mount is helping absorb vibrations in both lateral loads as well as vertical loads.

Over time my interpretation is the constant weight/load compressing the mount vertically (down) into the upper spring cup will indeed reduce overall stack height when the rubber on the inside of the mount weakens.

This pic shows the "right side up" view of the mount, the inner rubber piece is what gets compressed over time: https://goo.gl/images/AcqhSz

I don't know if this makes better sense now or if I've confused the issue more!

[ianc]

Hmmm... So the contact between the guide support (1) and upper spring plate (8) is not metal-to-metal, but rather only the conical rubber surface in the OP's first pic? Can anyone confirm this? If that's the case, I could see it decreasing the car's ride height since the top of the upper spring plate would now be pulled up closer to the strut tower mount on the body?

ianc

[Tommm]

Part 8 spring plate compresses the spring. Part 8 is at a set place on the strut rod-the end of the threads. On my volvo there ia a nut on top of part 8.

The mount is on top of that. If it was compressed i would have gotten the assembly under the wheel well . So yes the mount will compress like in my picture. I put them upside-down so you see they are identical untul the rubber.