Advice on rear suspension

[songzunhuang]

Ever since I got my car, I thought the back sat a little low compared to the front. Recently, I have noticed that going over dips seems to cause my rear to bottom out with a hard thump. This happens with or without rear passengers.
When I stopped and I push down on the rear, it doesn't oscillate at all. Maybe one tiny bounce.
So the questions are as follows.

Looking at the picture attached below, is the rear of my car sitting low? Or is the front high?

Is bottoming out caused by the shocks, springs, bumpstops or what?

Do springs really wear out? They seem so hefty. I would expect shocks and bumpstops to wear, but springs?
The springs control the height of the car right?

I want to get rid of the bottoming out, but I also want don't like the rear of the car being so low.
Thanks in advance for educating me.

Is my car's rear sitting low? This is lined up with a parking stripe so you can see the difference between the front and back.

Screen Shot 2016-01-08 at 11.17.10 AM.png (482.85 KiB) Viewed 12751 times

[tschultz]

IT does look low, yes. You should see about taking a photo of the rear shocks/springs. Maybe the rears were converted to sports (lower), and the fronts remained the stock height.

[ZROSSA]

I don't think it would be bottoming if it was just sports in the rear. There really is only three other things to check other than springs. Diff mount, Subframe mounts and the rear strut mounts at the top of the springs. Springs do were out and sag....Start with them.

D

[Da_Hose]

A slightly out of the box recommendation is to check your alignment. If you have excessive toe-in, not only do your tires wear faster, but the suspension can jack and cause the front to lift a bit.

Jose

[jps635]

In answer to your question the rear does look low compared to the front but otherwise no. For reference the underside of my rear guards measure around 636 mm off the garage floor through the wheel centre (ie vertical) with 255/40/17's - bilstein sports / H&R rear springs - I think on the 2nd lowest perch setting. I have never bottomed out.

[GripGreg]

It does look a tad lower but, you should measure with a metal tape at the front of the rear wheel well body to ground.
Then, measure at the rear of the front wheel well to the same place. Make sure the tape measure is straight up & down.
Pictures can play tricks. The whole parking lot appears to be on a slant, lower left & higher right!

[tschultz]

I stand by my statement, as this is what my 633CSi looks like with stock front springs and lowered rears:




Either way, taking a look at the back end of the car will allow you verify if this is the case or if something else back there is messed up.

[jps635]

To clarify, obviously my car is lowered so tschultz is correct, it is low compared to stock, but not unreasonably so for a lowered car (subjective)

[Ralph in Socal]

Front looks normal and the rear looks low. Take a couple of pics of the set-up and post. You may have Bilsteins set at the lowest point as well as a number of other reasons.

Yes springs do wear out (sag). American car springs are (were) the worst. They also break and the suspension is subject to all kinds of other problems. Read up on Bruceys post about our suspension and you will learn a lot.


Ralph

[Brucey]

it looks like it is dragging its backside down the road a bit to me.

Is the SLS fitted, and failed?

cheers

[songzunhuang]

Front looks normal and the rear looks low. Take a couple of pics of the set-up and post. You may have Bilsteins set at the lowest point as well as a number of other reasons.

Yes springs do wear out (sag). American car springs are (were) the worst. They also break and the suspension is subject to all kinds of other problems. Read up on Bruceys post about our suspension and you will learn a lot.

Ralph

As suggested, I am posting pictures of my rear shock setup. A couple of weird things are that I noticed that they do not match. Yellow shock is driver side (Monotube?) and black on the passenger side (Twin tube?).

Also, I had no idea that these could be adjustable. I do see that they both have Bilstein markings on them. I also see a B4 on the sticker on the passenger side which makes me think it's a original Touring shock as opposed to a Sport or Heavy Duty.

In any case, please take a look at the pics and any feedback would be appreciated.

This is the driver's side rear shock. It appears to be a mono-tube B4 (Touring) shock.

Drivers Side Rear.png (733.09 KiB) Viewed 12621 times

This is the passenger side rear shock that is black (Twin tube?)

Passenger Side Rear.png (867.16 KiB) Viewed 12621 times

Can these be adjusted for height? If so, how is that done? I see no obvious adjustment mechanism. Thanks.

[Brucey]

yeah, those shocks ain't matched; you need to get a matched pair of (preferably adjustable spring perch) shocks there.

You need bumps stops too.

To get another shock to match the extant monotube Bilstein, you need to

a) read the number off it and
b) make sure that the extant shock is OK.

Most folk would recommend that you replace the shocks in pairs, and it is good advice.

cheers

[Da_Hose]

I agree with Brucey. Always replace shocks in pairs. If get a new set.

Jose

[songzunhuang]

Thanks everyone for the feedback. I understand and agree that they should be replaced in pairs. I have been consuming all the information I can find about the suspension setup (including Brucey's excellent post) and I am just trying to decide how to proceed.

You see, now that I know more about these cars over the past 5 months, I would really like an M6. If this were an M6, I would sink the required dollars to do it once! Of course, this is not an M6 but a car I am using as a daily commuter. Also, I have to figure out where I want to put my bucks as I have limited funds allocated to the ongoing care and feeding of this car. Do I spend only a moderate amount and get it working like factory, or do I star hopping it up? I've seen cars in the Bay area that have been sitting and owners are willing to let go for a very reasonable amount. I could swap this to a 5-speed. I could get a front air dam with fog lights, etc. etc. But in the end, it's still not an M6.

So I part of me is saying that I will get the car to better than stock and just drive it. For those of you following along, I have got a really dependable driver now. I have fixed EVERYTHING on the car and all systems work (yes GripGreg, even the OBC). If for some reason a smoking deal comes up on an no-op M6, then I dive it big time. As far as I can tell, the M6 has good investment potential. The 633 is still a great car, but it'll always lag behind in desirability and dollar appreciation. OK, I am just rambling now.

[songzunhuang]

yeah, those shocks ain't matched; you need to get a matched pair of (preferably adjustable spring perch) shocks there.

You need bumps stops too.

To get another shock to match the extant monotube Bilstein, you need to

a) read the number off it and
b) make sure that the extant shock is OK.

Most folk would recommend that you replace the shocks in pairs, and it is good advice.

cheers

Hey Brucey, here's a picture of the sticker on the Xtant Bilstien mono-tube. As you can see, the "B4" appears on the sticker making me think it's a touring. In the end, I think I'll take everyone's advice and replace both.

Model or part # sticker on the Bilstein

Screen Shot 2016-01-16 at 11.24.27 AM.png (302.68 KiB) Viewed 12584 times

[Brucey]

in old Bilstein-ese that is a monotube B46-0610 'comfort' shock.

In terms of damping rate it isn't much different to the other rear shock options;

Model_____________Force (N)____Force (lbF)
B46 0607 Sport ____1605 / 805___361 / 181
B46 0608 HD ______1605 / 805___361 / 181
B46 0610 Comfort__1590 / 770___358 / 173

(forces @ 20" per second, Rebound/Bump)

But the 'comfort' has a longer stroke than some other models and may not have an adjustable perch (check this). Most folk fit the HD shocks (which have adjustable perches and will work with stock springs).

In general terms there are only two practical reasons for an M6;

a) you want to use the extra power/performance, or
b) you think it is a faster-appreciating asset.

If you spend a modest amount on a standard E24 it can handle, look and stop much like an M6 and for a DD that is probably good enough....?

cheers

[GripGreg]

Glad no, really glad you got your OBC working! I was starting to get concerned!

And, if there's a left & right they should be replaced in pairs.
Maybe not front seats or mirrors or doors or lights but, yes the tires & shocks.
Greg

Ps: I also agree with Brucey comparing the E24 to the M6! Once you get your car running right, you'll love it!
Even though it's 3.3.
To me, if you find a Euro 635CSi, you'll be very happy w/o the woes of the M6; meaning the maintenance.
I recommend the Bilstein HD's. And a four-wheel alignment?

[rhanley 635csi89]

The Bilstein US web site has all the info you need, products for the 6 series start on page 122. Go to downloads, product info.
FWIW, I replaced stock shocks (SLS) with HD's on the four corners (new bmw stock springs in the rear), I find the ride totally different now. I also replace all the bushings (front/rear), steering, car now has a "harder" "stiffer" ride.

http://www.bilsteinus.com/fileadmin/use ... e_2014.pdf

[Brucey]

The Bilstein US web site has all the info you need...

well sort of... it is no help at all in identifying the monotube shock the OP has (they don't list that one any more), the parts listing makes no distinction between monotube and twin-tube shocks, and there is absolutely no indication of damping rates or acceptable spring lengths, perch adjustability etc etc etc. To cap it all some of the information is wrong, too; they indicate the change from E12 chassis to E28 chassis as occurring 9/82 whereas in fact it was 5/82. Also Bilstein of course manufacture OEM BMW shocks (eg for the M6/M635) and they don't list all the part numbers that correspond with these... Apart from that it is fine!

I've cut and pasted the relevant E24 content below

from bilstein US website 1/2016

BMW630
1978 B4 Rear F4-BNE-2016-BE
1978 B6 (HD) Front 34-002292 Rear 24-008020
1978 B8 (SP) Front 34-193020
1977 B4 Rear F4-BNE-2016-BE From 10/77 To 9/82
1977 B6 (HD) Front 34-002292 From 10/77 To 9/82 Rear 24-008020 From 10/77 To 9/82
1977 B8 (SP) Front 34-193020 From 10/77 To 9/82

BMW 633CSi
1984-1983 B4 Front 21-030512 Rear 19-020174

BMW 633CSi (continued)
1984-1983 B6 (C) Front F4-P36-0239-H0
1984-1983 B6 (HD) Front 34-002339 Rear 24-006088
1984-1983 B8 (SP) Front 34-181546 Rear 24-006071
1982-1978 B4 Rear F4-BNE-2016-BE From 10/77 To 9/82
1982-1978 B6 (HD) Front 34-002292 From 10/77 To 9/82 Rear 24-008020 From 10/77 To 9/82
1982-1978 B8 (SP) Front 34-193020 From 10/77 To 9/82

BMW 635CSi
1989-1985 B4 Front 21-030512 Rear 19-020174
1989-1985 B6 (C) Front F4-P36-0239-H0
1989-1985 B6 (HD) Front 34-002339 Rear 24-006088
1989-1985 B8 (SP) Front 34-181546 Rear 24-006071

BMW M6
1988-1987 B6 (HD) Front 34-002339

E28 535
1988-1985 B4 Front 21-030512 Rear 19-020174
1988-1985 B6 (C) Front F4-P36-0239-H0
1988-1985 B6 (HD) Front 34-002339 Rear 24-006088Rear 24-007276 Parameter 270/100
1988-1985 B8 (SP) Front 34-181546 Rear 24-006071

528i
1981-1979 B4 Rear F4-BNE-2016-BE
1981-1979 B6 (C) Front F4-P36-0228-H0
1981-1979 B6 (HD) Rear 24-007306
1981-1979 B8 (SP) Front 34-193020
1981-1979 Variable depending on application
Front 34-003268 B6 (HD); Set Option: Variable depending on application

528e
1988-1982 B4 Front 21-030512 Rear 19-020174
1988-1982 B6 (C) Front F4-P36-0239-H0
1988-1982 B6 (HD) Front 34-002339 Rear 24-006088 Rear 24-007276 Parameter 270/100
1988-1982 B8 (SP) Front 34-181546 Rear 24-006071

cheers

[Ralph in Socal]

Just to FYI the group regards Rear Bilstein shocks. I recently picked up a set of H&R Springs with Bilstein Sport shocks from an 85 535i. I notified Song I would hold these for him until I could determine exact status and condition of each assembly. The fronts are fine and in excellent shape. The rears suffered from a previous spring perch failure due to the snap rings givng way. Please look at the pics below. The Spring and Shock Assembly for each side were intact and mounted up top when I removed them. First a deformed snap ring followed by the shocks and the damage caused by the failures.

Deformation appears to start opposite of the open end. Probably opened up too wide during assembly.

Snap Ring Failure.JPG (274.06 KiB) Viewed 12453 times

Sides of the shock body severely gouged and damaged from the snap ring getting pushed down the tube by the spring perch

Rear Billie Failure.JPG (241.67 KiB) Viewed 12453 times

I happened to also have a set of e39 Konis on hand so I was able to compare set-ups. Koni uses a 2 piece system for the perch to sit on. Koni uses an additional "Shroud" Ring above the snap ring. The shroud is designed to push the snap ring in the groove and provide a bigger landing step for the spring perch. I also placed the shroud ring on the Bilstein shock and it appears to fit exactly like the Koni system. I measured each shock body and they are identical at 50.1 mm. This may actually be what Bilstein should be doing as the failures do occur as I just found out.

2piece ring system which includes the shroud ring.

Koni 2 piece Snap Ring.JPG (210.68 KiB) Viewed 12453 times

Worth a try isn't it.

Koni Snap Ring Shroud on Bilstein shock.JPG (220.12 KiB) Viewed 12453 times

Ralph

[Brucey]

IIRC the bilstein perches have a small relief in the underside, specifically so that the snap ring can't spread and come out. It isn't as tapered as the koni one, so presumably isn't so secure. However, if

a) the snap ring is deformed when it is moved or
b) it is installed in a groove with too much paint in it

then the snap ring is liable to come out.

Note also that some spring/perch height combinations will allow the spring to go coilbound on full bump before the shock bottoms out. If the bump stops are in bad condition (or worse still, omitted....), then on full bump, the spring goes coilbound and the snap ring can be forced out. Better that than the top mounts punching through the bodywork, I guess....

cheers

[captain awesome]

Brucey,

Do the rear shocks not have internal bump stops like the fronts? Maybe I read that incorrectly in the installation instructions?

[GripGreg]

On my Buster, the rear Bilstein HD shocks have external bump stops that need to be added on.
My front Bilstein Sports have internal bump stops. E12 suspension though.
Greg

[Brucey]

Brucey,

Do the rear shocks not have internal bump stops like the fronts? Maybe I read that incorrectly in the installation instructions?

fronts have internal bump stops, rears use external bump stops. You need to use the standard bump stop or the M6/M635 bump stop depending on the ride height you use.

If the spring and the bump stop are matched then the bump stop is taking a large proportion of the load before the spring goes coilbound.

cheers

[Brucey]

Brucey,

Do the rear shocks not have internal bump stops like the fronts? Maybe I read that incorrectly in the installation instructions?

fronts have internal bump stops, rears use external bump stops. You need to use the standard bump stop or the M6/M635 bump stop depending on the ride height you use. [ A lot of people use standard bump stops with lowering springs- this will make the ride somewhat choppy IME, a little harsh even.]

If the spring and the bump stop are matched then the bump stop is taking a large proportion of the load before the spring goes coilbound, but the first 1/2" or so of suspension travel from normal ride height does not go into the bump stop.

cheers