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1981 BMW 635 (E12 based) lowering suspension advice

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julianonline
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1981 BMW 635 (E12 based) lowering suspension advice

Post by julianonline » Mon Jul 23, 2018 11:54 pm

Hello everyone, I am so happy to say that I purchased an awesome 1981 635 Euro from a good friend that had the car for 10 years, he was the second owner. The car came with many spare parts and even with a second engine.

The car has a huge potential, no rust that all in any of the trouble areas, paint job will be needed eventually. I will post more pictures in the next few days.

The suspension is one of the first things I want to upgrade (and also the brakes that feel they need to be improved... feeling is that takes long distance to break).

Being this a E12 based car and Euro, is there any recommendation about what suspension(springs + shocks) part numbers, manufacturer or any idea where to start?... I did a quick check in internet, honestly didn't spend that much time, but I am a little bit confused as my results in internet I believe are for a E28 based car, I may be wrong, but any guidance is very appreciated.

Also, is there any suggestion to improve the breaks, any upgrades from any other BMW series (including disc, break calipers, etc.) that would be a good replacement for a E12 based 635CSI?

Thank you for your support.

G03rt2
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Re: 1981 BMW 635 (E12 based) lowering suspension advice

Post by G03rt2 » Tue Jul 24, 2018 1:32 am

I have a 1981 euro as well and lowered the car earlier this year. I'm quite happy with my setup even though it's not correct (according to internet forum advice).

I mixed H&R part number: 29533-1 with Bilstein B6's (which are known as HD's and for non-lowered cars). The Bilstein part numbers I used are: 34-002292 & 24-008020. Ideally you want the Bilstein B8's but they were not available when I purchased mine.

The ride quality is great, no complaints. Firm, sporty, and not harsh at all. The only down side is what to do with the rear bump stops, and the rear spring will fall out of the perch when the car is jacked up. I plan to rectify this this coming winter by having the rears machined a bit.

It took me a while to find not only the correct part numbers but someone who stocks them. The E12 stuff is getting rare.

As far as brakes, the fronts are as good as they get if you have an 81 euro. Same caliper that is on the M6 from everything I read. The front rotors come cross drilled from the factory. I would just rebuild and refresh before looking at upgrades.

Oh... And we want pics!!!

bpoliakoff
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Re: 1981 BMW 635 (E12 based) lowering suspension advice

Post by bpoliakoff » Tue Jul 24, 2018 4:15 am

Euro brakes need no upgrading. Rotors are for sure not cross drilled from the factory. Lowering springs are hard to find and take patience. It took me 3 years to find a set of new B&G lowering springs. As you have noted they are same as for an E12 and even an E3. There is not a factory spring for lowering an e12 chassis. Bilstein sport shocks have to be used with lowering springs or the rear springs will come off their perches when you jack the car up because there is too much travel in a heavy duty Bil shock. A spil sport shock. the struts as well, have a shorter stroke,I have an 81 Euro that has been undergoing a total nut and bolt restoration and and am well versed in what will and will not work with these cars. Rebuild your existing brake system and you will be more than pleased. No reason for cross drilled or slotted rotors. The factory vented rotors are more than adequate.
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.

ron
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Re: 1981 BMW 635 (E12 based) lowering suspension advice

Post by ron » Tue Jul 24, 2018 4:09 pm

julianonline

Put your location in your profile as requested by Admin.
They are ALWAYS rustier than you thought!!!!!!
'88 High line.
'85 M #228
'85 M #207
'80 735i

GRNSHRK
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Re: 1981 BMW 635 (E12 based) lowering suspension advice

Post by GRNSHRK » Tue Jul 24, 2018 5:18 pm

I wonder how Bert knows this, since he has yet to drive his 6er #-o
The factory vented rotors are more than adequate.
That being said julianonline, the optimum would in fact be whatever lowering springs you can find, and Bilstein Sport struts =D>

As duly noted, the Sports for E12 chassis are scarcer than hen's teeth, you may have to go the used market :(

Here are a few suggestions for spring sources:
Suspension Techniques
Korman Autosport
B&G Springs (out of Sweden)

Also as duly noted, the calipers are already first rate, fixed type with 4 pistons up front (similar to M6) and 2 out back \:D/

The rotors are also vented on all 4 corners, but I did opt for cross drilled the last time I did brakes (not "breaks", BTW [-X ) photo below :-k

You also mentioned not much of brake feel, wherein I personally would opt for SS brake lines, the rubber ones you have may be original :shock:

Once again, there should be a few sources out there for these, remember that the set needs to include 6 lines, as there are 2 each side up front, to feed those 4 piston calipers :-({|=

Oh, and welcome aboard, please put your location in your profile like Ron asked, and keep the questions coming :wink:
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Front Brakes-sm.jpg (62.35 KiB) Viewed 510 times
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Bobbo
1980 633 CSi
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bpoliakoff
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Re: 1981 BMW 635 (E12 based) lowering suspension advice

Post by bpoliakoff » Wed Jul 25, 2018 2:41 am

I wonder how Bert knows this, since he has yet to drive his 6er "

Bert knows from listening to you, and many others, gas it up for years! LOL. Seriously the car is out to get finished now. We thought it would be running several weeks ago only to find the drain plug in the pan was stripped and oil was leaking so a new pan was bought and is going to the powder coater in the next few days. So yes Bobbo, I will get to drive it!! This year for sure. And I remember when Scott Andrews was active and he couldn't praise the brakes enough!!
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.

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zinnocoupe
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Re: 1981 BMW 635 (E12 based) lowering suspension advice

Post by zinnocoupe » Sun Aug 26, 2018 3:42 am

Bert I'm glad to hear you are getting close to being able to drive your car. I am hoping you will share some pics with us when its done. I will for sure be happy to congratulate you. Good luck finishing up!
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1979 Euro 635ci no longer a basketcase, just a running rust bucket!
1977 530i New addition ( nonrunner)
1987 635csi 60K KM Garage Queen

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Brucey
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Re: 1981 BMW 635 (E12 based) lowering suspension advice

Post by Brucey » Thu Aug 30, 2018 7:53 am

as with many 'upgrades' it isn't difficult to 'upgrade' over a load of knackered old sh*te; that is easy; one can be easily pleased.

What is more difficult is making an absolute improvement over OEM stuff that was in good condition to start with....

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

tmoretta
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Re: 1981 BMW 635 (E12 based) lowering suspension advice

Post by tmoretta » Sat Sep 01, 2018 6:11 pm

I have already removed the rear ALS on my '88 M6. Have gone to H&R springs and B8 Bilsteins in rear. I have the H&R front springs, but the B8's for the front are way back ordered (nobody has them). Anyone know if I can use the B6's (HD) in the front without causing the springs to come off the perches in full extension. I may have to wait months for the front sport springs.

bpoliakoff
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Re: 1981 BMW 635 (E12 based) lowering suspension advice

Post by bpoliakoff » Tue Sep 04, 2018 6:03 pm

I am not sure because of the way the front struts go together. But, cal Bilstein in Poway CA. They can always rebuild you a set with a shorter stroke through their rebuilding service there, in other words duplicating sports. Call them and find out the cost. It may make sense to just pick up a cheap used set of hds and have them do this for you.
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.

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