I am about to pull the trigger on a 911 front suspension. It is billed as being from a 72-74 911S (no the aluminum calipers are gone and I will be using regular A calipers instead) as it has KONI struts with the 3.5” spacing. Ultimately I am looking to install KONI Sport (aka Yellow) struts that have the adjustment knob on the top. I have read a few quality threads such as…

http://www.914world.com/bbs2/index.php?sho...c=390&st=20

This answers a lot of questions, but that thread mostly talks about Boge struts, spindle mods, etc. and doesn’t 100% clear up a question I have about KONI insert compatibility.

My confusion comes from the KONI application guide http://www.koni-na.com/pdfcatalogs/2007applguide.pdf (approx 1 MB PDF). If you don’t want to look at the PDF here is a summary of the KONI document …

65-68 911
Boge strut 86-1394 Classic
KONI strut 86-1308 Classic

69-74 911
Boge strut 8641-1039 Classic
KONI strut 86-1638 Classic

75-89 911
Boge strut 8641-1039 Special
KONI strut 86-1942 Special
(footnote) 8641-1039 Sport

914 and 914/6
All (Boge?) 8641-1077 Sport

To translate KONI types, Classic = “Black”, Special = “Red” and Sport = “Yellow”.

The implication is that "it appears" that you are really limited if you want to use the “Sport” insert as they only list the “Sport” strut for the 914 and 914/6 as well as for the 75-89 911 (but with a cryptic footnote). The 911 footnote says…

“Ext. adjust Sport alternative (both Boge and KONI) for OE KONI struts, gland nut 73.25.01.011.1 must be ordered separately”

My confusion/questions…

• Is the dimensions/structure of all Boge struts the same and all KONI struts the same (I understand that Boge and KONI struts are not the same)? If so, using Boge struts as the example, ANY Boge “compatible” insert will “fit” ANY Boge strut regardless of the year of strut and model of insert?
• That the KONI strut has a larger internal diameter and that the Boge is smaller? That the special gland nut they mention is first threaded into the KONI strut (Its external thread match the KONI struts threads) and then the Boge compatible KONI insert screws into the gland nut?
• I am making a lot of assumptions here, but if the above is true about the gland nut, does that mean that you can take ANY of those KONI inserts and using the special gland nut use it in ANY of the Boge struts?
• That the KONI application guide actually lists recommendations based upon OEM replacement and insert valving. For example if all of my above leaps of faith are correct (in that you can really mix and match) that if you do, you may just have incompatible insert valving that will affect handling dynamics. BUT it also means that you can use the proper 914 KONI "Sport" insert (that is properly valved for the 914) in any of the Boge or KONI 911 struts!?!?
• This is more of a question for someone at KONI, but they list the 8641 “series” as being externally adjustable. Basically it looks like all of 8641 inserts are “sport” types. But the above into lists the KONI insert for the 75-89 Boge strut as “Special”, but not “Sport” even though it is an 8641 series insert. Maybe this is a misprint and it really is a Sport insert?

I know someone is going to say “Just use Boge struts”. I understand that my options are greater with the Boge, but I am really trying to settle my own confusion regarding the KONI struts. And if it works as I think it might, and then I may just go with the KONI struts front end that I am looking at.

One last thing…

I have tried to document everything that I have learned on the 914 Wiki. Please feel free to look at that article and if you think you know what you are talking about, correct any mistakes.

http://www.roadglue.com/wiki/index.php/911_front_suspension

Didn't the 3.5 spacing come on the later cars? I thought they had only the 3" spacing up to 74. I could be mistaken, it's happend before.

3.5" began in 1969 with the first Koni strut and S-Calipers.

I have fairly early (still have the late model ball joint pins though) Koni struts on both of my cars. Both have had the spindles raised. I say this because on a Koni strut, you have a reduction in the tube where the spindle slips on. You can literally only raise it 18mm before you hit the flare. Boge's are different.

A 911 Boge strut is basically the same as any 914 Boge strut except the spindles are beefier on the 911 variety.

The main difference between the two is the fine (Koni I believe) threaded top and a more coarse threaded top on the Boge. That and the caliper mount spacing of course.. the Koni and Bilstein struts have the 3.5" mounts.

I'm no expert on this but, from working with mine, that's what I saw.

If you are planning on buying Koni's new, you may want to have them special ordered with the 914 valving. It's not "that" much different (only the high-speed rebound is different from what the Koni engineer told me) but it may make a difference.

Here's a bad picture that shows the difference in the tube (that old camera was actually dying Aaron... so don't post the flower icon macro bla,bla,bla ):

Actually, this shows the flare in the tube better (just above the spindle mount)

Eric, thanks for jumping in!

The photos of the KONI strut is interesting. You mention (and the photo shows) that they have a flare, but the Boge does not. Implication here is that the Boge strut has a smaller diameter than the KONI strut?? I wonder if this is some evidence toward my idea that the KONI insert that is designed to fit the more common Boge strut have a smaller diameter (same size as Boge OEM insert?) than the direct replacement KONI inserts for KONI struts. So if you wanted to use a Boge "style" insert (of which there seems to be more options available even from KONI) in a KONI strut, you would use the special gland nut they mention?

Where I am going with this if my posts are not clear enough is that I would like to be able to use the KONI strut, use the special gland nut and then use the 914 KONI Sport insert that is already valved for the 914, but is intended to be used in a Boge strut. I am making a LOT of assumptions here which might be really wrong.

I really don't think you'd be able to use that insert. Call Jason at Paragon for all the Koni details.

Personally, I'd get the proper Koni/Koni insert and be done with it. I'd have them specially valved for the 914 (ask me how I know that's what I'd do )

Ok, I talked to Bob at KONI and Jason at Paragon (both were VERY helpful and answered any question I came up with). Here is what I found out.

1. It sounds like the 69-89 Boge 911 struts are dimensionally the same, so you can mix and match inserts regarding fitment. However valving may be incorrect. I think the same holds true for the KONI struts of the same time period as well. I think the 68 and earlier 911 struts may be different (we didn’t talk much about them). So while the KONI application chart does not list a sport insert for the 72-74 KONI strut, you can use the insert designed for the 75-89 KONI strut in the 72-74 KONI strut. Basically the KONI charts are going to list OEM replacements (if they provide them) as well as upgrades to something like the Sport insert, but they it must both fit AND have proper valving before they are listed on the chart. Also, there might be a model that works (both fit and valving) for the front, but they don't have a model for the rear of the same type, so they will not list the front if they don't have a matching rear. Basically they are not going to recommend a Sport for the front if they don’t offer a Sport for the rear even if one of the other front Sport models would be just fine.

2. My quest to use the 8641-1077 914 Sport insert (which is should fit into a Boge strut) in the 911 KONI strut by using the special gland nut to convert from one thread pattern to another almost works, but there is a problem in that for some reason the 914 insert necks down much lower (near the bottom) on the insert than the 911 insert. This means that as you slide the insert it, it may bottom out before it is in position. Apparently it is VERY close to working as is, and that you can machine some metal off of the necking on the insert and it will fit, but at the risk of destroying or shortening the life of the insert. Apparently this used to be an issue with some of the 911 inserts and KONI moved the necking farther up the insert. But they haven't done the same for the 914 insert. So close, but no cigar. It is not a recommended solution.

3. I asked about the difference (if any) between the "8641-1039" and the "8641-1039 sport". I found it odd that there was an 8641 series insert that was not a "Sport" insert. They are different, but only in valving. Both have the same basic construction (single adjustable via the top screw), but the non-sport has less aggressive valving.

4. While I can use the 75-89 insert in the 72-74 strut and put it all in the 914 the valving is not going to be ideal. So while I can get that insert revalved to match the 914, there is another route as well. That would be to use the body of the 86-1638 (this is the natural replacement for the 72-74 KONI strut) and have it rebuilt using "Sport" internals (and of course valved appropriately)

What am I going to do?

I am going to pull the trigger on the 73 S front end that is available to me locally. I am going to eventually be buying the 8641-1039 Sport inserts. Eric will say that I will not be happy with the valving and if he is right, I will eventually get them revalved.

No I won't...

After my chats with Koni they stated the valving was only minor and it was the high speed rebound. I only changed mine because I had a bad shock and, they were the old style inserts. They put the new rods in and changed the valving at the same time. I thought if you were buying new ones and talking to Koni you might want to go that route.

I doubt you (or I) would be able to notice the difference.

Richard, et al... Was there ever a solution to this match ?
I find myself in a similar quandry.

Rich,

I am not sure what your question is. You quote the section about trying to match the KONI insert designed for the 914 Boge strut with the 911 Koni strut. As mentioned in my post above, the information that was given to me is that it will almost fit, but not quite due to differences in location of the neck on the strut vs the insert. I ended up buying the 8641-1039 Sport insert which fits in either a 911 Boge or 911 KONI strut. You just need a special gland nut if you are using it with the KONI strut.

Here is a photo of my KONI strut and the 8641-1039 Sport insert. You can see the where the strut necks down. The insert also has a slight neck, but it is high up enough to not bump into the neck on the strut. I wish I had the 914 specific insert so I could see the difference, but my understanding is that the neck on the 914 insert just barely hits the neck on the strut. But just enough to not make it work.

Click to view attachment

Danm~!

Apologies for the hijack but I think I might be able to learn something from you guys. I have acquired a pair of Koni struts with the 3.5" spacing. I have had these soda blasted. These are the adjustable type where you have to turn the whole thing. Is there an insert I can put into this which is no longer adjustabke or is adjustabke at the top? If so any suggestions as to the part number. I have read this and another thread and I am more confused then before. The part number on my struts is 911 341 042 10.

Or should I just get a replacement pair and set them to the softest setting?

Thanks


Roman

Those are non-usable junk. Please send them to me for proper disposal.

Page 2. (as Paul Harvey would say)

If the inserts are still good, I would set them at the softest setting and forget them. Keep in mind, that is my personal recommendation for "street" driving. This gives a firm yet compliant feel. YMMV.

If they need a rebuild, I would send them to Koni and have them both revalved for the 914 and have the top adjustable shaft installed at that time. I believe the cost on the adjustable shaft was around $70.00. Revalving is not "needed" but, the high speed rebound values are a little different for a 914 as mentioned herein.

Let me come back around to this...

If they need rebuilding, just get new ones. I believe all of the new Koni's are top adjustable (with the exception of their vintage series). New one's are often less expensive than repairing old ones.

Roman,

That is the exact same strut that I have (same part number). So pretty much everything discussed in this tread applies to your struts.

One thing to note is that I mention above that Koni has two top adjustable inserts that would work in that strut. They are the "8641-1039" and the "8641-1039 sport". They are the same construction except that the "sport" has more aggressive valving. And as Eric says if you are not happy with the valving as delivered (as these are valved for 911), Koni will re-valve them for you (for a fee). I would also agree that it might be more cost effective to buy new and revalve later if your unhappy vs. having the guts of the strut rebuilt. Assuming your struts haven't been touched since new, the guts are not an "insert", but rather the damper internals. You just yank all of that out and slide a complete self contained replacement insert into the strut body.

Richard

Forgot to mention this. You need to fill the space between the insert and the strut with something. I have heard that you should (1) don't put anything in (2) use oil (3) use antifreeze.

The answer is (3) antifreeze. Putting in nothing just allows water to work it's way in and rust the strut from the inside out. Using oil allows water to get in and float the oil out the top and allow the water to rust the bottom of the strut. Using antifreeze prevents freezing and rusting as I think antifreeze has anti rust agents in it as well.

This was told to me by tech person at Koni.

It's listed, with the fluid volume needed, in the instruction sheet that comes with the inserts. 50ml (1/4 cup) if I recall.

You guys are great, so I could just order two 8641-1039 inserts and two gland nuts 73.25.01.011.1 and that should be it? I assume that the pitch on the top of the insert is the same or do I need something else. Nice to see I have done something else right, or maybe as right as somebody else.

This is very helpful indeed. All I need now is to get the rest of the car done.

Roman

You're going Koni to Koni so your pitch on those struts will be the same. Why would you need a new nut?

I'm rather taken aback that you're not sending those to me.

Oh well, I think you should hurry and finish them off, display them quite proudly in your house and take a picture of them. Then... every time you visit Marke, whip out the picture and tell him to "hurry up... the struts are waiting!"

I wish I was still living in the US, all this would be far cheaper as it is I am living back here where well it isn't. Does not look like I am going to make the 40th anniv but thena agin. I have also sent you a PM so I can spend lots of money... The pound is at a three week high WoooHoooo

Roman

Joking... I meant "I'm rather taken aback that you're not going to give those to me!"

Spend all you want! We'll make more. Thanks for doing your part to stimulate me the US economy!! (Now, if I can just find a bank to give me a 3 year balloon and about $500k over my valuation in an equity loan. Hookers and whiskey for all my friends!)

I think the vast majority of the replacements struts sold are for Boge struts since those are the most common type. So I believe that when Koni packages up the inserts, they include a centering ring and nut that works with the Boge strut (or maybe you re-use the Boge nut, I am not sure). Regardless, if you are going to use the OEM Koni strut, then you need the special gland nut because the Koni strut nut is different than the Boge strut nut (different thread, etc.) You also can't reuse the nut that is on the OEM strut as it has the right threads but otherwise the wrong shape to hold the newer insert into place. The Koni application PDF list the gland nut and I think Roman has the right number in his earlier post.

So in short, there is slightly more work/parts needed to put a Koni insert into a Koni strut.

Eric Shea;

Aren't you out of the business now? Rumor has it you no longer are around?