Rear Spring Top Mount Angle Question

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ByronB
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Rear Spring Top Mount Angle Question

Post by ByronB »

I forgot to mark the orientation of the three bolts of the top mount before I dropped the rear shocks, so now after swapping the springs on to the new Bilsteins I have a 33% chance of getting it right! These old Boge's were installed about 70k miles ago in 1997 according to the records on the car so they may not have been installed properly then, who knows.

I tried lifting the shocks into all three positions, and none of the positions really seem to have the bottom bolt hole line up that close. I can put the bolt in pretty easily by simply moving the bottom of the shock in place but I just don't want to have it binding or torquing the top of the shock unnecessarily. They angled the top mount slightly for a reason.

Any tips or tricks to this?? THANKS!
1981 Euro 635csi Dogleg 5-speed, Recaros, LSD, Sunroof & A/C
GRNSHRK
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Re: Rear Spring Top Mount Angle Question

Post by GRNSHRK »

Byron, I recently replaced my rear springs, and there is one photo in the attached link, but I'm not sure that will be of much help :-?

I seem to recall rotating the assembly until the top 3 studs went up through the holes, then rotated the lower portion of the strut until the bottom aligned with the trailing arm :-k

viewtopic.php?t=32980

Anyhoo, hope this helps [-o<
:mrgreen:
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ByronB
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Re: Rear Spring Top Mount Angle Question

Post by ByronB »

Yes, but unfortunately the top spring perch is at an angle so there must be a "right" way to insert it into the three holes: one that is correct, one that is 1/3 off, and one that is 2/3 off of the correct angle, right?? :-?

To further complicate things, there are actually TWO sets of three holes, but only one has a hole above it accessible from the back seat, so that must be the one intended to line up with one of the studs. Why the other three holes? I have NO idea!! :-k
GRNSHRK wrote: Thu Feb 02, 2023 10:00 pm Byron, I recently replaced my rear springs, and there is one photo in the attached link, but I'm not sure that will be of much help :-?

I seem to recall rotating the assembly until the top 3 studs went up through the holes, then rotated the lower portion of the strut until the bottom aligned with the trailing arm :-k

viewtopic.php?t=32980

Anyhoo, hope this helps [-o<
1981 Euro 635csi Dogleg 5-speed, Recaros, LSD, Sunroof & A/C
GRNSHRK
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Re: Rear Spring Top Mount Angle Question

Post by GRNSHRK »

Byron, correct, only one out of 3 rotational positions is correct :roll:

And I have no idea why there are 2 sets of 3 holes ( :shock: ), as you duly noted the others won't work and I have no idea why they are there either :-({|=

But to reiterate, I held the entire strut/spring assembly up into the strut tower and rotated it until I achieved the correct orientation, then secured the top before addressing the bottom :-"

Then, IIRC, I turned the lower half of the strut until it lined up with the mount in the trailing arm, slid the giant bolt in place and tightened things up :wink:

Again, been a while, and I stand corrected if others have a different solution or experiences [-o<
:mrgreen:
Bobbo
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ByronB
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Re: Rear Spring Top Mount Angle Question

Post by ByronB »

I agree on all points, and thank you kindly for your input. I just am not able to identify any significant difference at the bottom of the shock from all three top positions is why I am confused.

I was just hoping to learn some tips or tricks from the experts here but I guess I'll just have to find the orientation with the least resistance in putting the lower bolt in, although none seem to have much resistance from best I can tell. We'll see!
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86_6series
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Re: Rear Spring Top Mount Angle Question

Post by 86_6series »

I can stand corrected, but I don't remember a difference in the rotation of
the guide support while installing the rear struts. Well I hope not or else
I got it wrong all these years.
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plip1953
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Re: Rear Spring Top Mount Angle Question

Post by plip1953 »

I don't think there is a specific orientation for the top mount.
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Ralph in Socal
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Re: Rear Spring Top Mount Angle Question

Post by Ralph in Socal »

plip1953 wrote: Sat Feb 04, 2023 10:34 pm I don't think there is a specific orientation for the top mount.
This is correct for rear struts. Fronts do have an angle in the top hat that the strut bearing bolts to

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86_6series
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Re: Rear Spring Top Mount Angle Question

Post by 86_6series »

Ralph, +1 on the fronts.
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Re: Rear Spring Top Mount Angle Question

Post by Ralph in Socal »

I have to add - I happen to have the e12 on stands sans suspension so I had a serious look. There are 2 sets of holes in my 81 e12 also. I didn't realize that was the case. The strut top fits in all possible positions of the two different sets of holes. Meaning orientation is not specific. BMW would have
engineered specific hole settings if it required a specific orientation

Ralph
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
81 633 csi (retired)
ByronB
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Re: Rear Spring Top Mount Angle Question

Post by ByronB »

Thank you very much gentlemen!!! I imagine the slight camber to my strut top is just from the spring compressing the rubber a bit over the years. This makes me feel MUCH better! I just got all the parts in from Germany to finish the brake job, so with that and this rear strut info I will finally be able to put it all back together and hopefully be road worthy very soon. :D
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Sbeaud
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Re: Rear Spring Top Mount Angle Question

Post by Sbeaud »

Just for a point of reference here are some pictures of a 1988 M6. Taken during last year's partial suspension rebuild.

Scott



BMW M6 Rear Strut Tower-1.jpg
BMW M6 Rear Strut Tower-1.jpg (411.58 KiB) Viewed 1880 times
Attachments
BMW M6 Rear Strut Top Mount.jpg
BMW M6 Rear Strut Top Mount.jpg (503.56 KiB) Viewed 1880 times
1988 M6
jsspagg
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Re: Rear Spring Top Mount Angle Question

Post by jsspagg »

I currently have the rear suspension out of the car and got one of those "ah ha" moments as I did not mark the orientation that the rear shocks came out. When I read this post I took a look at my situation and discovered that I have the "six hole" dilemma. After studying the top of the mounting surface for a minute, I surmise that the holes for access from the rear shelf area provides a window on which holes to use. In my image, looking from the top down, you can see I broke out the insulation material to get access to unbolt the shock. You can also see washer weaar marks in the paint of the three holes used.

In the images that Scott posted above, you can see the opening cut-outs with the insulation still covering the holes.

At some point I will study the top mounting of the shock assembly to see if I can make any determinations as to a specific orientation. If I figure something out, I'll post here.

Jeff
Attachments
Rear Shock Mount.jpg
Rear Shock Mount.jpg (2.4 MiB) Viewed 1358 times
1980 635 Euro
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jsspagg
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Re: Rear Spring Top Mount Angle Question

Post by jsspagg »

Marked up images.
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Rear Shock Mount Marked up Scott.JPG
Rear Shock Mount Marked up Scott.JPG (87.17 KiB) Viewed 1358 times
Rear Shock Mount Marked up.JPG
Rear Shock Mount Marked up.JPG (118.75 KiB) Viewed 1358 times
1980 635 Euro
Under restoration
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