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Print Page - 6.9 suspension conversion

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Garage => Mechanicals => Topic started by: john erbe on 27 February 2008, 07:17 AM

Title: 6.9 suspension conversion
Post by: john erbe on 27 February 2008, 07:17 AM
 Purists read no further. However, in the event that someone is out there about to junk or sell his 6.9 too cheap because of endless suspension repairs and doesn't have a fat wallet -STOP! Just completed conversion, total cost about $900 in parts and that's with double adjustable coil overs in front. Had I used standards cost would be around $600. Instalation easy, and I'm just a shade tree mechanic with a floor jack and blocks. Put it this way, if I saw a 6.9 in junk yard with crapped out suspension and had all the parts in hand plus spring compressor for rears, I could drive car out in two hours and never have to worry about suspension again. Hopefully, this will keep more 6.9's on the road. If you want details send me a pm, glad to help.
Title: Re: 6.9 suspension conversion
Post by: john erbe on 27 February 2008, 03:34 PM
Michael:

I live in Vallejo, California. Yes, I have part numbers for the non-mercedes shocks and springs. Thinking about going one size smaller in front spring but first want upgrade the Bilstein/Mercedes spring set up in rear, see how it looks and then make decision. Will take some photos. Its real easy. Guy that told me about it just said he used coil overs in front, upper mercedes rubberized bracket off hydraulic strut, and had to machine brackets and a spacer. That was all the info I had to go on. Once I removed the upper bracket from from the 6.9's strut and laid it side by side a coil over shock with the "stud" mount on the top (and a few beers) Bingo! it came to me. Not knowing what the size springs, shocks or the rate of the spring, I had to do alot of running around. The machine work was easy. I didnt need a spacer, so his set up is probably a little different. Ironically, and here's the kicker, the front conversion is easier than the back.
Title: Re: 6.9 suspension conversion
Post by: john erbe on 27 February 2008, 07:27 PM
Just took pic's will send tomorrow. If any questions, just get back. Based on just a couple of test drives I would summarize accordingly: the old hydraulic had a smoother ride in that you did not feel the road and all the little bumps however in the dips you get that big gondola, riding the waves rebound and the excessive roll in the turns. The rebound and the roll are now history. You feel the road but I think going with a higher profile tire will help address that issue. Also, I took the easy way out and went with rear springs off of a junk yard 450sel, they're in all likelyhood, thirty years old. The 15" Yoko's currently mounted were a good match for the old system. I just need to fine tune the whole set-up. Best hing I ever did, no regrets. Now a new paint job and smaller repairs will be falling in place.
Title: Re: 6.9 suspension conversion
Post by: oscar on 16 March 2008, 05:56 AM
Hi John,

Wilst removing springs off a wrecking 280, your post came to mind.  Looking at the metal mounts that hold the upper rubber shims and the lower metal brackets for coil sprung w116's, it made me wonder what a 6.9 with only strut mounts needed has.  Are these metal mounts still there on 6.9's?  If not I'm still not sure how you achieved to seat the coils.  Can you elaborate?  Please ;D

It sounds like an interesting conversion and although I've perhaps unfairly screwed my face up at 6.9's with coils appearing for sale in the past, you've got me thinking about the whole idea in a different light.  I suppose I'd want to have control over how the conversion was done rather than buying a 6.9 already done.

Another question - what about the hydro pump.  Did you just remove it and all the ancillaries then buy a blanking cap to cover the whole where the pump would go?  If so, did you have trouble getting the blanking plate?



Title: Re: 6.9 suspension conversion
Post by: john erbe on 16 March 2008, 06:40 PM
The rear is no problem in that the 6.9 has the upper spring perch. Shims and springs are available in different sizes and in different materials form other makers. I've ordered some shims from a company called energy suspension. The only diff. from the 4.5 is that the holes in the rear subframe for the bolts for the shock are not threaded but no big deal. I can tell you how I did mine if interested. Regarding front, you dont need the spring perch in that you are simply replacing the hydraulic strut with an adjustable coilover shock which fits in the exact same location using the rubberized top bracket on the 6.9 for attachment at the top. You will need a machinist to make the lower bracket for the lower attachment.
Title: Re: 6.9 suspension conversion
Post by: john erbe on 16 March 2008, 06:44 PM
Oscar: Regarding the blanking plate, some guys have used one from another model MB that apparently fits. In that I have a machinist that lives a few blocks away, I brought him an extra pump and he made a plate to match the pattern.
Title: Re: 6.9 suspension conversion
Post by: oscar on 17 March 2008, 03:21 AM
Thanks very much John.  I had to google what a coil over was would you believe ::) but having done so and knowing what a McPherson strut looked like it all makes sense now.  Simple really, I should've known.

The only diff. from the 4.5 is that the holes in the rear subframe for the bolts for the shock are not threaded but no big deal. I can tell you how I did mine if interested.

No need really unless someone else wants to know.  It'll all be lost on me unfortunately without the real thing to go look at and compare so I wont push you.  All I got to look at is the subframe and axles from 280's and a 350 which I think are different from a regular 450 anyway.  It's an interesting mod and something I'll consider and revisit if I come across one that needs a suspension overhaul.

Re the blanking plate, true probably just about any 70's or 80's m110, m116 or m117 with a blanking plate will be interchangeable with the pump of a 6.9 and anything else that used the same pump and manufacturing a plate shouldn't be too difficult.  As long as it doesn't leak, all's good.  :)




Title: Re: 6.9 suspension conversion
Post by: brandily on 08 April 2008, 03:37 PM
John,
I just got a 6.9 last week, the car has not been used for a couple of years, I just got the car started, but it it sitting all the way down, I was beginning the think that I should do something else with the car, because it does need to be worked on, the problem is that in Mexico that kind of car was not sold here, , just a couple of imported ones, therefore it is very difficult to find replacement parts here, I would be very thankfull to have some of the pictures of that conversion.   
Title: Re: 6.9 suspension conversion
Post by: john erbe on 09 April 2008, 08:02 PM
Will send tomorrow.
Title: Re: 6.9 suspension conversion
Post by: john erbe on 10 April 2008, 08:24 AM
Brandily: Send me a PM and I'll send pics.

John
Title: Re: 6.9 suspension conversion
Post by: ALV148 on 12 June 2020, 09:03 AM
The rear is no problem in that the 6.9 has the upper spring perch. Shims and springs are available in different sizes and in different materials form other makers. I've ordered some shims from a company called energy suspension. The only diff. from the 4.5 is that the holes in the rear subframe for the bolts for the shock are not threaded but no big deal. I can tell you how I did mine if interested. Regarding front, you dont need the spring perch in that you are simply replacing the hydraulic strut with an adjustable coilover shock which fits in the exact same location using the rubberized top bracket on the 6.9 for attachment at the top. You will need a machinist to make the lower bracket for the lower attachment.

John  what size and rate were the springs you used??
Title: Re: 6.9 suspension conversion
Post by: rumb on 12 June 2020, 10:30 AM
You are unlikely to get a reply as the previous posts are 12 years old and I dont think those members are around anymore.
Title: Re: 6.9 suspension conversion
Post by: john erbe on 12 June 2020, 01:40 PM
ALV148, still alive. Timely question as I just made a re-do of my conversion putting in shorter shock and softer spring. Rides much better. Installed a 10" by 450 lb. 2.5 ID Eibach. However, if I can locate a spring compressor I will go with the 12" spring. Dont like having to screw-up, if I remember, about 21/2 inches on shock.  Ride in fron is lower than standard which I prefer. Height from deck to center of wheel well is 24 3/4". I can give you info on shock if interested.
Title: Re: 6.9 suspension conversion
Post by: ALV148 on 12 June 2020, 02:07 PM
Hi John thanks for the reply. I have use the inner wing turret Shock fitting point which has allow me to use a 12/19” coil over shocks which gives me more travel with a 13”  2.5” 425lb spring. But the spring is far to soft travelling 5” to rest. On my cals I need a 850lb to sit with 2.5” travel at rest. (1 inch lower than rear.  Any tech info would be great fully received. Thanks
Title: Re: 6.9 suspension conversion
Post by: john erbe on 12 June 2020, 03:40 PM
ALV...having trouble attaching photo. Send me a PM and Ill pass some along. I just installed the QA1DD403 which is single adjustable. My compressed height of shock, measured from center of bottom eyelet to top of spring is 11 3/8" with a compressed spring height of 6 1/8". Have about 2 1/2 " of thread showing on shock below bottom of adjustment washer. Approximately 12mm between coils, once again all this is at ride height/grounded. If you check the QA1 catalogue they've come out with a new advanced coil over, which is in the patent process but pricey. Mention because one of the size options would be more ideal, just slightly taller. My calc's showed a 500lb would also work fine.
Title: Re: 6.9 suspension conversion
Post by: john erbe on 12 June 2020, 04:04 PM
I note in your photo that the base of the shock appears attached on the arm in a more interior position than mine which I positioned in it's original place using the same bolt holes.
Title: Re: 6.9 suspension conversion
Post by: john erbe on 12 June 2020, 04:14 PM
Test. Mine at ride height.
Title: Re: 6.9 suspension conversion
Post by: john erbe on 12 June 2020, 04:57 PM
Better photo.

(http://)
Title: Re: 6.9 suspension conversion
Post by: ALV148 on 13 June 2020, 04:38 AM
Hi John. Thanks for the photos and reply
I am inboard as I am using the inner wing turret fixing to give longer travel hence keeping spring side clearance. As the original HPF set up give 2.25” of both upward and downward movement from sitting position. I have 6” in total but with a 425lb spring it uses 5 “ of that when sitting. I note your 10” spring is also very compressed?? Is the photo in sitting position ?? Do you still have 2.25” of travel left?? I need 2.75” of compression to have Sitting at the right level. Therefore 425x5 divided by 2.75= 772lbs. Does that sound right?? Cheers
Title: Re: 6.9 suspension conversion
Post by: john erbe on 13 June 2020, 08:28 AM
ALV..photo is with car down on ground. Attached shows measured shock eyelet to eyelet fully extended. Same measurements as given in catalogue but didnt help in my case because I dont use the upper eyelet rather the "stud mount" and inasmuch only interested in measure from bottom eyelet to underside of nut at bottom of thread. Travel is 4 7/8". A more ideal ride height for this shock would be higher toward the standard but I wanted lower in front as shown in photo taken of 6.9 with a 12" 450 rated spring and if I recall only two threads showing below bottom adjustment washer. That spring compressed to 8 1/4 " when loaded. However, the shock in that picture was the next size up and too big. Photo of side by side comparison to hydraulic strut prior to install. Found that out when I shot off a bridge at speed and clunk! Assumed incorrectly that went spring bound when in fact the shock probably bottomed out. Never said I was the smartest guy in the world. Swiched to 600 lb spring which compressed to 9" and subsequently drove for years. Result, higher in front more like standard ride height but stiff ride, tight handling, no body roll etc etc. Hence the change to the 450 which required a shorter shock. Hope this helps.

(http://)
Title: Re: 6.9 suspension conversion
Post by: ALV148 on 13 June 2020, 01:18 PM
Hi John.
Interesting that you thought the 600lbs were to hard. You say 4” Travel with 450lb. And 3” travel with 600lb  which makes sense as they both equate to 1800lb load. I need to double check the springs I had in stock? As i was sure they were 425 which travel 5 “ to standing which equates to a 2125lb load??I
May be they were only 360lbs 🤷🏼‍♂️🤷🏼‍♂️will let you know how I get on
Thanks again for info and photos. 👍🏼
Cheers
Title: Re: 6.9 suspension conversion
Post by: john erbe on 13 June 2020, 05:24 PM
i'll post photo when I get the 12" spring installed.
Title: Re: 6.9 suspension conversion
Post by: raueda1 on 13 June 2020, 07:53 PM
ALV..photo is with car down on ground. Attached shows measured shock eyelet to eyelet fully extended. Same measurements as given in catalogue but didnt help in my case because I dont use the upper eyelet rather the "stud mount" and inasmuch only interested in measure from bottom eyelet to underside of nut at bottom of thread. Travel is 4 7/8". A more ideal ride height for this shock would be higher toward the standard but I wanted lower in front as shown in photo taken of 6.9 with a 12" 450 rated spring and if I recall only two threads showing below bottom adjustment washer. That spring compressed to 8 1/4 " when loaded. However, the shock in that picture was the next size up and too big. Photo of side by side comparison to hydraulic strut prior to install. Found that out when I shot off a bridge at speed and clunk! Assumed incorrectly that went spring bound when in fact the shock probably bottomed out. Never said I was the smartest guy in the world. Swiched to 600 lb spring which compressed to 9" and subsequently drove for years. Result, higher in front more like standard ride height but stiff ride, tight handling, no body roll etc etc. Hence the change to the 450 which required a shorter shock. Hope this helps.

(http://)
Feel free to send me your old struts for proper disposal and to ensure that they don't fall into the wrong hands. ;D
Title: Re: 6.9 suspension conversion
Post by: john erbe on 29 June 2020, 07:40 AM
In response to a PM asking how I made the upper connection: First I'll give credit where due to the guy down in Texas years ago who explain the concept, key of which is to take advantage of the rubberized boot up in the fender to which the strut is attached. Dont know how he he made the connection but here's mine. And, secondly to the local machinist used by the local NHRA guys who apprenticed as a kid in the German navy and without asking made all the parts out of crankcase steel. Quite simple, took strut with upper boot, shock, spring and spring perch to machinist. He made a cone which copies the upper end of strut. The base is turned to seat snugly in the perch.
Title: Re: 6.9 suspension conversion
Post by: ALV148 on 08 July 2020, 03:02 PM
HI John

Sorted !!! here is mine with 12" 725lb Springs
Title: Re: 6.9 suspension conversion
Post by: ALV148 on 08 July 2020, 03:04 PM
photos
Title: Re: 6.9 suspension conversion
Post by: ALV148 on 08 July 2020, 03:07 PM
the photos have to be opened as they look squashed otherwise  :D
Title: Re: 6.9 suspension conversion
Post by: john erbe on 08 July 2020, 04:52 PM
ALV,

725 lbs. !!! How's the ride?  Looks like you chassis sits much higher.
Title: Re: 6.9 suspension conversion
Post by: ALV148 on 09 July 2020, 04:30 AM
Yes  the 450SEL rear springs sit the rear up and therefore i have had to match the front, the front now sit 3/4" lower than the front

however the car rides high but fine

If i were to go again the 12" length is right, i would use 550 to 600lb springs instead and use shorter springs on the rear

but this is just temporary for me to get the car on the road

i am currently amassing and refurbing the part to reinstall the HPF suspension

here wheres i'm at

thanks 
Title: Re: 6.9 suspension conversion
Post by: daantjie on 09 July 2020, 10:58 AM
Nice work on those original leak lines, they are now NLA from Benz :'(
Title: Re: 6.9 suspension conversion
Post by: rumb on 09 July 2020, 03:04 PM
I have quite a few of the hard lines if you are interested.  PM me.
Title: Re: 6.9 suspension conversion
Post by: john erbe on 09 July 2020, 03:53 PM
Here's a suggestion which I  considered back in the day: That last short bit of line with the fitting that screws into the accumulator, replace it using a braided stainless high pressure hose that you can have made up at your local hydraulic shop. That way you can have them put a swivel at the end and now, combined with the flexibility, it's a thousand times easier to screw in the fitting to the accumulator.