Rear Suspension mushiness question

[tvjake2]

I searched for info on this but couldn't find anything on point. I've just replaced the front control arms, sway bar link, shocks and rear trailing arm link on my '89 635CSi. The mechanic said he filled the reservoir for the SLS system and said that they seemed to work but the shocks did leak a bit. After driving the car for a few days it seems that the front suspension is fine but the rear drives like the tires are at about 15 lbs of pressure (they are not). The rear end mushes (technical term) sideways if you make a quick direction change. It also seems to float a bit on the highway and doesn't feel planted. I don't hear the pump engage when I start it up and I don't feel any motion associated with start up. Should I hear anything from the rear suspension pump? Could I hear something if I went to the trunk and listened?

This is my first 6 Series and I'm not familiar with any eccentricities yet. Is this normal for this suspension system or should I just be replacing the rear shocks.

[dcains]

Common solution is to replace the rear shock - not with another set of self-levelers, but with the conventional version. One less headache to worry about, and a one-time fix.

[bkats]

If/when the SLS engages, it's obvious. You can usually hear the pump and feel the system adjust. The SLS rear is kind of squishy by nature, but it shouldn't be that obvious. Try putting a bunch of heavy stuff in the trunk (enough to compress the rear) and start the car. There should be visible and audible operation.

The symptoms you describe could be rear sway bar related (links or bushings). An improperly installed trailing arm link can be the culprit, but not likely.

[tschultz]

Rear subframe bushings shot?

How about dog bones?

[tvjake2]

Common solution is to replace the rear shock - not with another set of self-levelers, but with the conventional version. One less headache to worry about, and a one-time fix.

My mechanic said there was a lot of work involved in replacing the SLS with standard shocks. I understand that BavAuto has a kit ($217) that provides support parts. If I got shocks, springs and the kit is it that hard to convert? I think the conversion is cheaper that a rebuild if my math is correct.

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If/when the SLS engages, it's obvious. You can usually hear the pump and feel the system adjust. The SLS rear is kind of squishy by nature, but it shouldn't be that obvious. Try putting a bunch of heavy stuff in the trunk (enough to compress the rear) and start the car. There should be visible and audible operation.

The symptoms you describe could be rear sway bar related (links or bushings). An improperly installed trailing arm link can be the culprit, but not likely.

I will test this out. If the pump is not working that is at least half the problem. Also, if the pump is not working that would definitely make up my mind to convert rather that deal with that also. I'll check the sway bar bits and pieces. The trailing arm link is new. It seems a pretty straightforward installation.

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Rear subframe bushings shot?

How about dog bones?

I have seen this word "dogbone" several times and assume its' part of the suspension. What technical part of the suspension is the dogbone?

[roger hanley]

I'm no expert, however, I have been replacing everything on my 89 635 for the last year, I've replaced all my suspension front and rear plus all bushings. Replaced the SLS with Bilstein HD, much stiffer ride, my gut tells me I should have stayed with the SLS and replaced the front with Bilstein Touring.
Regarding the rear suspension, enter your vin in RealOEM and review the suspension, rear axle, stabilizer rear and front suspension. Dog Bones reference components the resemble "dog bones". Rear stabilizer part #33551124375(stabilizer link) and rear axle support #33321125665 (Pitman arm). They both most likely need replacement.

[alpinacsi]

If you replace the dog bones: don't buy the cheap ones (uro, ocap, karlyn). They will last about 6 mo if you are lucky. Also check your rear diff mount while you are working one the rear.

[braol]

Common solution is to replace the rear shock - not with another set of self-levelers, but with the conventional version. One less headache to worry about, and a one-time fix.
I second this motion.

[bkats]

My mechanic said there was a lot of work involved in replacing the SLS with standard shocks. I understand that BavAuto has a kit ($217) that provides support parts. If I got shocks, springs and the kit is it that hard to convert? I think the conversion is cheaper that a rebuild if my math is correct.

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I have seen this word "dogbone" several times and assume its' part of the suspension. What technical part of the suspension is the dogbone?

Replacing with a standard suspension will include shocks and springs. The sls springs are too soft and will sag without the sls. Replacement is usually cheaper if at least one hydraulic component is dead. Pretty much Springs would be the only viable replacement, financially.

It usually involves just capping the accumulators in the rear wheel wells and disconnecting the electric harness to the pump. You can actually leave it all in place.

I removed the pump from the trunk, because I needed the space for my emergency kit. And I removed the accumulators for easier cleaning of my wheel wells. This is all optional.

The dog bones are usually the rear pitman arms. I believe you replaced yours already.

[tvjake2]

Replacing with a standard suspension will include shocks and springs. The sls springs are too soft and will sag without the sls. Replacement is usually cheaper if at least one hydraulic component is dead. Pretty much Springs would be the only viable replacement, financially.

It usually involves just capping the accumulators in the rear wheel wells and disconnecting the electric harness to the pump. You can actually leave it all in place.

I removed the pump from the trunk, because I needed the space for my emergency kit. And I removed the accumulators for easier cleaning of my wheel wells. This is all optional.

The dog bones are usually the rear pitman arms. I believe you replaced yours already.

I'm going to jack up the rear and get under and inspect, test the pump action and try to isolate the issue in the rear. I'll probably replace the stabilizer links and the large rubber mountings that are on either end of the rear axle carrier just because they are rubber. It almost feels like the stabilizer bar is not doing its job, replacing the links may fix that. Anyway, I'm glad to know its not a characteristic of the car and can be fixed. Now to just figure out what it is.

[Sansouci]

I've replaced my LAD system on my E32 and regret it. For your system, if the SLS shocks are not leaking, look at all the fixing points which are rubber bushings and refresh those, including the aforementioned Pittman Arms. Even if you were going to swap out the SLS for standard shocks, you would replace these parts anyway. Typical LAD failure (and maybe on the SLS) is the accumulators loose their charge. But in that case, they tend to make the ride hard, not mushy. That's my $.02
--Ken

[tvjake2]

If you replace the dog bones: don't buy the cheap ones (uro, ocap, karlyn). They will last about 6 mo if you are lucky. Also check your rear diff mount while you are working one the rear.

I agree, I got the BMW dogbone. I stay away from wonky parts.

[RSheiman]

Rear accumulator issue I had was car going up and down on its own, don't know other symptoms of bad accumulators but they do often need replacement. Nobody mentioned subframe bushings which probably need to go unless recently replaced (bet yours are original).

[tvjake2]

So...the saga continues. I've been generally disappointed with this car. It rides poorly (in spite of the repairs in the #1 comment) steers loosely and just isn't what I expected. After several months of putting up with this I'd had enough and took it into my repair shop. As it turns out the lead mechanic, who works on both of my cars, worked on these cars when they first came out in the late '80's. Nice. We went over a long litany of repairs that surfaced. The SLS was toast as were a number of other suspension parts. His words to me were "this car is unsafe to drive". Uh,oh. I've know these guys for quite a while and if they say it's not safe I tend to agree with them. So I left it.

After a week and a nice large bill I pulled out of the garage with pretty much a new undercarriage...and no SLS. Hartage springs, Bilstein shocks, suspension repairs and some very nice brake work plus a bunch of odds end. The car lowered about an inch with these changes. The change in the car is dramatic. Where the rear end previously felt like jello it now feels well planted. The steering has improved and the brakes are dramatically better. I like to work on all my cars but being lift-challenged these types of repair just aren't feasible.

Everyone working in the shop, and some visiting customers, all were impressed with the general condition of the car (no rust anywhere). The mechanics told me that the engine and trans ran as well as, and maybe even better, than any other 635CSi they had driven. All of this cudoesque adulation certainly made for a feel good day when I picked the car up. The road feel when I drove home wasn't too bad either. I'd say the SLS was interesting from a load leveling standpoint but that's about it. Performance handling was not good, but it did have a nice mushy ride. When it goes bad, unless you can afford the repair, get rid of it.

All of this goes to show that if the car doesn't feel right...you won't feel right. I'm glad I got the work done. Next - maybe Ireland Engineering sway bars.

[n2bimmer]

Absolutely, if your car is taken care of you feel good about it.

[1986series6]

+1 on Ireland Engineering sway bars.

[FernandoBunster]

I believe it's time for rear subframe bushings, swayer links and bushings and rear pitman arms (dogbones). By refreshing the front suspension your rear suspension's issues have been magnified.

[bkats]

Sway bar links and dogbones are easy enough. I'd do them just to get all your rubber up to scratch at the same time. I did both at once and got a noticeable difference, and my old parts were still decent. Nothing dramatic, but now it drives like a new 80's car.

Btw, this car just isn't fantastic for steering. It's got that 80's/90's dead spot, and the steering box has never been anyone's source of pride. Combine that with a heavy nose that takes a while to load up.

[tvjake2]

I believe it's time for rear subframe bushings, swayer links and bushings and rear pitman arms (dogbones). By refreshing the front suspension your rear suspension's issues have been magnified.

We checked all that and it passed inspection...for now. These guys are pretty particular, if something weren't right they'd tell me. We did the dogbones a while back. The whole car now feels pretty good. I've tried some off ramps at a quick pace and there was no drama.

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Sway bar links and dogbones are easy enough. I'd do them just to get all your rubber up to scratch at the same time. I did both at once and got a noticeable difference, and my old parts were still decent. Nothing dramatic, but now it drives like a new 80's car.

Btw, this car just isn't fantastic for steering. It's got that 80's/90's dead spot, and the steering box has never been anyone's source of pride. Combine that with a heavy nose that takes a while to load up.

Definitely. The steering is not a high point in the car. If you think the nose on this car has understeer you should try the 8 Series. After autocrossing the 840Ci I figured out some tricks to adjust my driving to compensate for an overloaded front. The 840Ci has Bilsteins and M Sport springs so it handles a bit better than stock. I'm taking the 635 on my next autocross and I'll use that experience to see how it does. Gotta get those IE sway bars though.