Author Topic: 6.9 front coil springs  (Read 257 times)

6point9kenya

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6.9 front coil springs
« on: 31 January 2020, 10:22 PM »
Good morning from Kenya,

The rebuild of the only 6.9 in Kenya is progressing well, the car is now running. It had been converted to coil springs and we have decided against re instating the hydropneumatic suspension as the car will see very limited and occasional use.
However the car is very low at the front as it uses 450SE front springs and the 6.9 engine is considerably heavy. I believe there is a company in the US that does front springs suitable for 6.9s that go racing, can anybody point me in the right direction?

J-P

Randys01

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Re: 6.9 front coil springs
« Reply #1 on: 01 February 2020, 09:28 PM »
This has some interesting connotations.
Assuming a professional outfit can calculate the spring rates to accommodate the heavier nose of the car, is it really that simple? Under the hydraulic system theoretically all the system carried all the unsprung weight equally.
That's no longer the case.
My  big question is who is going to calculate the shocker rates and where are they going to come from?  Banging in some good old W116 450 shockers is not going to really get the job done. The static load is the springs' job but once we are in motion the shockers control the show.  An extra 120 kgs at one end of the car is going to generate quite an influence once that mass starts to rise and fall down the long and winding road.
I had a [limited] association with the global Munro shock absorber manufacturer in the late 60's trying to develop local content shockers to replace the fabulous De carbone/ Bilstein  OE shocks used on the mercurial Renault 12, 16 and  P504.
Getting the 16 sorted was a nightmare. [now there's a yarn for another time!}
I took 2 years of field trials and countless hours in the test rigs/factory to come up with a satisfactory replacement..so it's not a walk up start  when we start swapping springs and shockers into the unknown.

I wish you well and of course you will come up with something satisfactory no doubt....bearing in mind the millions of Deutschmark DB spent on refining the hydro system to handle a 140mph 2 ton world beater sets a hi bar to emulate........and that was adapting an existing system.[thanks Mr Citroen .worked on that system too!!.uggghh ]
Please keep us posted as this project unfolds..I for one have a particular interest in this kinda thing.


Randys01

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Re: 6.9 front coil springs
« Reply #2 on: 01 February 2020, 09:45 PM »
Oops!!.yes you spotted the mistake. 2nd line should read "sprung weight".
Of course this raises the point that the unsprung weight  takes a notable increase in the rear suspension...........chassis experts out there among you will agree that a 10-15 per increase in unsprung weight  is some thing to be considered.

TJ 450

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Re: 6.9 front coil springs
« Reply #3 on: 02 February 2020, 10:55 AM »
Nice work!

Regarding the springs, I know coil-overs have been used in place of the struts although don't have any details of who did it. I think they were in the US though.

Regards,
Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

daantjie

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Re: 6.9 front coil springs
« Reply #4 on: 02 February 2020, 11:42 AM »
+1 for coil overs if you can make it work.  The fact that they are adjustable should make it easy to dial in the firmness and damping rate.
Daniel
1977 450 SEL 6.9 - Astralsilber

daantjie

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Re: 6.9 front coil springs
« Reply #5 on: 02 February 2020, 12:05 PM »
Found this on the m-100.co forum, I think it's likely the best setup I have seen, as it utilizes the top mount already in place, pretty genius:

https://www.m-100.co/content.aspx?page_id=2155&club_id=406485&item_id=825864&message_id=2055976&fs=1#req

Daniel
1977 450 SEL 6.9 - Astralsilber

john erbe

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Re: 6.9 front coil springs
« Reply #6 on: 10 February 2020, 03:33 PM »
JP. I answered your inquiry on the M-100 website. Relatedly, a 600 lb. rated spring (coil over) compressed 3" so, you've got 1800 lbs. on the front end.

6point9kenya

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Re: 6.9 front coil springs
« Reply #7 on: 10 February 2020, 09:16 PM »
Thank you John. I have emailed Eibach, fingers crossed!

john erbe

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Re: 6.9 front coil springs
« Reply #8 on: 11 February 2020, 12:49 PM »
Hope to swing by the local Eibach dealer myself this week. However, there may be a problem with their stud mounted shock in that the top of the shaft thread probably metric, which would require machining a new adapter as the QA1 shocks are SAE.