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Rear left suspension sag problem

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Danny Wilde
Posts: 73
Joined: Wed Apr 18, 2012 8:44 pm
Location: Italy

Rear left suspension sag problem

Post by Danny Wilde » Thu Apr 18, 2019 3:40 pm

Hi to all :D , I hope you can find a minute to share your view on this sagging issue I have.

7 years ago I installed new Bilstein B4 shocks and bump stops on all 4 corners (I like the stock ride), after installing the LPG (5 years ago) I noticed a 2cm sag on the rear left (where the LPG tank sits in the spare tire space) and got my mech to insert some SPACERS to balance in up again to eliminate the sag.

Now after 5 years the rear left is sagging again for about 13mm, and looks pretty awful :-?
Height is measured from middle of wheel arch:

FL 69,5 mm
FR 69,4 mm

RL 66,6 mm
RR 67,9 mm


Considering that:

1) all 4 shocks and bumps stops are 7 years old (and I don't use the car much)
2) replaced FRONT strut top mounts 2 months ago, but NOT the rear ones
3) never changed the SPRINGS, afaik they might have beet there for the best of 32 years..


That said, would any of you advice to insert even MORE SPACERS on the rear left again?

Or could it be the rear SPRINGS need to be replaced? Should I consider reinforced springs on account of the LPG tank?

thanks for your precious help!
my best regards :D
Danny
9/1986 euro 635CSi manual Diamantschwarz

bpoliakoff
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Re: Rear left suspension sag problem

Post by bpoliakoff » Fri Apr 19, 2019 9:36 pm

How heavy is the LPG tank loaded.? Good place to start. If heavy enough, it's like having 2 drivers in the car at once. Answers itself. I know a barbecue sized tank must weigh close to 35#s loaded at least. Go from there. Give the springs a break!! They are probably shot and could be broken. I pulled the rears out of my 81 10 years ago and they were broken in 1/2
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.

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Danny Wilde
Posts: 73
Joined: Wed Apr 18, 2012 8:44 pm
Location: Italy

Re: Rear left suspension sag problem

Post by Danny Wilde » Sat Apr 20, 2019 11:53 am

Dear bpoliakoff thanks for your answer :D , yeah the weight is about that heavy, I guess you're right, I think I'll just bite the bullet and replace the springs! (By the way I had a look at your total restoration project and it looks awesome 8))

As a matter of fact in the past few days I've been searching around in the forum (including Brucey's very detailed front spring guide) for some info on the correct serial n° for stock height springs (I have stock Bilstein B4s) and I found there are loads of different options, especially for the rear ones, could you or anyone please confirm that these are the correct serials for stock ride height springs for my 9-1986 euro manual 635?

front springs: 31331127662
rear springs: 33531125326

Correct?

I guess, since I'm there, I also should replace the rear top mount PERISHABLE parts (I've already replaced the front ones), could you be so kind of pointing out which numbers of the pic below I should replace?

Image

http://www.realoem.com/bmw/enUS/showpar ... Id=33_0248

Thanks, I really appreciate your help! :D
Danny
9/1986 euro 635CSi manual Diamantschwarz

bpoliakoff
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Re: Rear left suspension sag problem

Post by bpoliakoff » Sun Apr 21, 2019 2:18 am

Danny just go with what realoem says. Replace the top mounts as well like you said. Bil B4s are really not the way to go. If you can afford it, B6s ,which are heavy duty is what you should use. A firmer ride than the B4s which are no more than a bone stock shock but again heavy duty and a firmer ride and really the way to go
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.

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Danny Wilde
Posts: 73
Joined: Wed Apr 18, 2012 8:44 pm
Location: Italy

Re: Rear left suspension sag problem

Post by Danny Wilde » Fri May 10, 2019 9:31 am

bpoliakoff thanks again, I'll follow your advice :D
cheers
9/1986 euro 635CSi manual Diamantschwarz

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