Bump Stops and Dust Sleeves for Front Strut Assembly???

[BHT2109]

Greetings All!

Currently rebuilding suspension on 1991 BMW 318is, and there seem to be multiple part#s and discrepancies with regard to bumps stops and dust sleeves within the front strut assembly. Basically, I need to know what to purchase in order to bring the suspension to OEM stock specifications. NOTE that I will also be installing new KYB shocks and struts along with various other parts. Please refer to these realoem.com diagrams:

https://www.realoem.com/bmw/enUS/showparts?id=AF93-USA-07-1990-E30-BMW-318is&diagId=31_0211

https://www.realoem.com/bmw/enUS/showparts?id=AF93-USA-07-1990-E30-BMW-318is&diagId=31_0111

In the first diagram, we have a bump stop with part#s 31331124449 AND 31331133513 (#11). In the second diagram, only 31331133513 (#5) is represented. First of all, how many total bump stops do I need? I am assuming only one per side, correct? Furthermore, which one is most appropriate; what is the difference?

To further add confusion, KYB (and other sites) dictate that I should purchase a "Boot Kit" if installing KYB struts (which I am), and this kit seems to have the bump stop in it - is this a direct replacement for one of the part#s listed above? In other words, does the kit take care of the bump stop question? ALSO, WHICH kit should I buy?: some sources say "KYB-SB101" will fit, others say "KYB-SB105" is appropriate.

Confused yet? How about dust bellows? In the FIRST diagram, part# 31331134314 (#12) looks VERY different from the SAME part# in the SECOND diagram (#8)! What is going ON here? One has a long accordion structure, the other is a short sleeve. How many dust bellows do I need? Does the KYB Boot Kit take care of everything? Currently I have part# 31331134314 in my cart ready to purchase, as well as KYB-SB105 kit - will these take care of everything?

Sorry for the long and confusing message; seems silly to be so anal about a few pieces of foam and plastic, but I'd really like to get this right the first time. (I suppose I could just go ahead and disassemble the strut assembly and inventory what's there, but how would I know if the previous owners didn't screw with it?).

Thanks guys!

Ben

[D.Martijn]

Greetings All!

Currently rebuilding suspension on 1991 BMW 318is, and there seem to be multiple part#s and discrepancies with regard to bumps stops and dust sleeves within the front strut assembly. Basically, I need to know what to purchase in order to bring the suspension to OEM stock specifications. NOTE that I will also be installing new KYB shocks and struts along with various other parts. Please refer to these realoem.com diagrams:

https://www.realoem.com/bmw/enUS/showparts?id=AF93-USA-07-1990-E30-BMW-318is&diagId=31_0211

https://www.realoem.com/bmw/enUS/showparts?id=AF93-USA-07-1990-E30-BMW-318is&diagId=31_0111

In the first diagram, we have a bump stop with part#s 31331124449 AND 31331133513 (#11). In the second diagram, only 31331133513 (#5) is represented. First of all, how many total bump stops do I need? I am assuming only one per side, correct? Furthermore, which one is most appropriate; what is the difference?

To further add confusion, KYB (and other sites) dictate that I should purchase a "Boot Kit" if installing KYB struts (which I am), and this kit seems to have the bump stop in it - is this a direct replacement for one of the part#s listed above? In other words, does the kit take care of the bump stop question? ALSO, WHICH kit should I buy?: some sources say "KYB-SB101" will fit, others say "KYB-SB105" is appropriate.

Confused yet? How about dust bellows? In the FIRST diagram, part# 31331134314 (#12) looks VERY different from the SAME part# in the SECOND diagram (#8)! What is going ON here? One has a long accordion structure, the other is a short sleeve. How many dust bellows do I need? Does the KYB Boot Kit take care of everything? Currently I have part# 31331134314 in my cart ready to purchase, as well as KYB-SB105 kit - will these take care of everything?

Sorry for the long and confusing message; seems silly to be so anal about a few pieces of foam and plastic, but I'd really like to get this right the first time. (I suppose I could just go ahead and disassemble the strut assembly and inventory what's there, but how would I know if the previous owners didn't screw with it?).

Thanks guys!

Ben

As RealOEM states it. (I don't think there is much difference when you Google search both part numbers)
31331133513 is for sport suspension
31331124449 for regular

As your car is an IS, I would use 31331133513

For the dust covers, I think BMW changed the design because the old dust cover, covered the whole strut which made it prone to rusting.
This is the newer design:


In short, get the 31331133513, 31331134314 (short ones). Ditch the KYB boot kit as it has the longer sleeves.
only one cover is needed per shock.

[BHT2109]

As RealOEM states it. (I don't think there is much difference when you Google search both part numbers)
31331133513 is for sport suspension
31331124449 for regular

As your car is an IS, I would use 31331133513

For the dust covers, I think BMW changed the design because the old dust cover, covered the whole strut which made it prone to rusting.
This is the newer design:


In short, get the 31331133513, 31331134314 (short ones). Ditch the KYB boot kit as it has the longer sleeves.
only one cover is needed per shock.

Perfect - this is precisely the kind of answer I was hoping for. Thanks so much for the help.

Didn't realize that bit about the dust boot redesign - good to know I only need the smaller type. I'm glad, because some of the reviews of the KYB kit I've read mention that the boot seems like plastic junk. Happy to know I don't need it.

[GoldMember]

Hi, just reading this older thread and have the same question. I'm putting H&R OE sport springs and Bilstein B4 shocks on my '85 325e, so I'll need bump stops. Since the OE Sports only lower a little, I'll use the 31331124449 bump stop? Or should I get 31331133513?
Also, what is the correct orientation/assembly of this short dust cover and bump stop? My guess is that the bump stop fits totally inside the dust cover and sort of "clips" into it with the slotted end up and the tapered end down? I've not done this job before, having trouble visualizing. Thanks!

[roguetoaster]

The technically correct way is tapered end of bump stop towards strut body, multiple ridges of the dust boot just on the end of the bump stop. Ultimately it doesn't matter since the stop will function either way, and the dust boot will unclip in short order and just float wherever.

[twenty]

I hit this thread when Googling for the same issue.

In summary, the longer dust cover is actually for the so called tropical version - although it'll fit the bump stop fine. The shorter version is for non tropical versions. I assume the BMW logic is that in tropical counties there's more risk of dirt/sand/moisture externally than it developing internally, so longer cover protects the shocks from the elements.

It it helps, KYB has a great video (for the E36, but the principle is the same) that shows the longer dust cover in action.See https://www.youtube.com/watch?v=hZSEHQYFxxk