Another mystery part...this time inside a Boge strut

[Franks89-911]

89 3.2L Targa, pre 962/964.

So I am replacing my front shock absorbers. (not entire strut assembly). Removed the casing that covers the top of the shock. Part # 5 on the PET diagram below.

A round hard rubber disk came out of the left one. And then, apparently dryrotted, promptly crumbled in two when I looked at it funny. It says on it "Caution gas pressure / achtung gasdruck". It apparently sits on the top of the round cap that screws on top of the strut assembly to hold the shock in. On the reverse side it is notched. See pics. Oddly, my right shock did *not* have this disk at all.

The PET does not list this part. My new Sachs replacement shocks I bought from yonder Host do not include this hard rubber disk. I could not find it for sale on yonder Host either (except possibly under the Koni red shock package sold here, the white disk could be it? - But my car didn't have Konis, it came with Boges as OEM and I know were never replaced by dad/prior owner).

Anyone know what it is/part #? I may go to the Stealership and ask but thought I would consult my friends first. You likely know more than they do anyway! ;-)

Don't want to put my new shocks in without this part - it serves a purpose, otherwise it's just metal on metal (cap against casing).

Thanks,
Frank

[Porboynz]

There is a part like that on a Koni strut between the rubber donut and the strut housing, made of a nylon plastic material. Seems to be a nice surface for the rubber snubber to bear on when you hit that really big bump, or when you hit that not so big bump after lowering the ride height more than you should have for the street. (I'm guilty, but it just looks so much better that low)

[djpateman]

That ring is an important part. It sits between the nut (4) and the snubber (3). If the shock bottoms out the purpose of the snubber is to cushion the action. In doing so it will become compressed and can act like a bellows. As the shock rebounds the snubber can create a bit of a vacuum. The disk is there to provide a vent to prevent the vacuum from sucking the shock oil from around the shaft seal. The slots that you see go towards the hard surface of the nut and provide the venting action.

[Franks89-911]

Originally Posted by djpateman

That ring is an important part. It sits between the nut (4) and the snubber (3).

Thank you your explanation is very helpful. Do you know the part # by chance or where I can get two?

[Porboynz]

Originally Posted by djpateman

That ring is an important part. It sits between the nut (4) and the snubber (3). If the shock bottoms out the purpose of the snubber is to cushion the action. In doing so it will become compressed and can act like a bellows. As the shock rebounds the snubber can create a bit of a vacuum. The disk is there to provide a vent to prevent the vacuum from sucking the shock oil from around the shaft seal. The slots that you see go towards the hard surface of the nut and provide the venting action.

I always wondered what the slots were for, live and learn.

[djpateman]

Yes, the real mystery is the part #. AFAIK every shock needs one of these, but hard to find a diagram that shows one. A part # that I came up with is 901 333 511 00 for Boge & 901 333 511 12 for Koni, but cannot confirm if this is the correct part or if it is available. Later cars have 911 333 511 00 for all shocks. Surely Pelican can come up with something.

[Franks89-911]

Originally Posted by djpateman

Yes, the real mystery is the part #. AFAIK every shock needs one of these, but hard to find a diagram that shows one. A part # that I came up with is 901 333 511 00 for Boge & 901 333 511 12 for Koni, but cannot confirm if this is the correct part or if it is available. Later cars have 911 333 511 00 for all shocks. Surely Pelican can come up with something.

Once again, djpateman, my sincere thanks. Next stop, Stealership, I hate it but they may be able to help get me back on the road.

[Franks89-911]

Update: just spoke to our host. Part numbers provided by djpateman are apparently spacers for rear shocks.

They also said the Boge original front inserts (and Sachs replacement inserts) don't come with these disks. Koni replacements do, however. I would swear on a stack of Bibles that Dad never replaced these front shocks, and the originals to the car were Boge assemblies (it says so on them) and hence Boge inserts. Host folks pulled up PET, and say I can install the Sachs replacements without disks without a problem. We'll see...

[75 911s]

I can't speak for the Sachs, but in my research for my midyear that had Boge struts I found several how to threads that explain that modern inserts/shocks have the bottom out bumpers inside. In the case of my Bilstein inserts, the shock is positioned upside down. If the lower portion of the casing were removed, you would see the rubber bumper inside. Since the (bilstein) insert is self contained, it isn't part of the earlier style 2 part system of 1. the strut housing containing oil and 2. the insert. Since the inserts are all self contained, install is simplified. Part 3 in your diagram is not used. The part you speak of - I would think that it is not needed because based upon DJpateman's description of that part, it helps alleviate vacuum caused by the snubber (part 3). No snubber, no disk.

This is conjecture and based upon Bilstein inserts. My info is based upon rebuild threads on this forum and my own I don't know Sachs. Perhaps reach out to the manufacturer?

The 101 book doesn't mention specifics about removing/keeping the oil, or the bumpers. It refers to the o ring...what o ring he is speaking of though? The top one that part of the tower on the underside of the car? The dust cap rides in that.

You spoke of metal on metal and that disk serves a purpose, if your sachs shock has the bumper built in, the dust cap should never strike the nut. Was this the metal on metal you are referring to?

I wonder if some of the shop guys on here can clarify who have done hundreds of insert replacements.

[Franks89-911]

Update: went to Jim Ellis Porsche here in Atlanta. Also went to RS Motorwerks in Sandy Springs. Neither of them knew what this part was, nor could they find it in any database or in PET. Then RS called me back and told me they think it's part of the Rubber Bump Stop (part #3 above in PET). Will revisit dealership to see if they have this bump stop in stock, to verify.

THANK YOU to everyone who replied and helped me out! This forum is amazing. I'll get her back on the road soon. Wish I could do it today - it's Dad's birthday and he would have been 86 today, wanted to honor him with a drive.