Construction Zone
Don\
Welcome! Log In Register

Advanced

Shock stem machining

Posted by camdenthrasher 
camdenthrasher
Camden Thrasher
Godlike Moderator
Location: Atlanta
Join Date: 09/13/2017
Posts: 7

Rally Car:
BMW 2002


Re: Shock stem machining
November 21, 2017 09:32PM
Here's the service manual section regarding spring rates. Sorry for the tiny font and crap quality My front springs are the "red/blue" marked ones on the bottom. Notice how none of the of the measurements in any force unit are provided with a corresponding length unit. AKA it's not listed as lbs/in or N/mm or anything like that. Also it lists a range for each force unit give toon Not much sense I can make from that. MAYBE these are the total compression force of the spring at block height, but a ~600lb force over 6.9" travel (I don't know exactly what the max spring travel is but that's the stock damper travel listed elsewhere in the document. It couldn't be much less that that) equals about 85lbs/in which doesn't make much sense either. The total weight on the front axle would almost fully compress two springs of that rate.


I took the front spring to Motion Control Suspension here in Atlanta to measure it on their shock dyno / load cell and they came up with a roughly ~250lb/in rate. That measurement corresponds pretty closely with calculations I did of the suspension sag (or whatever the correct term is) at normal ride height based on a rough guess of the vehicle weight.

I only acquired the car 10 years ago so I don't know it's full history. However, the car isn't lowered at all, it doesn't have any other suspension upgrades so I can't imagine these are anything but the stock springs.
Please Login or Register to post a reply
Attachments:
open | download - Screen Shot 2017-11-21 at 10.20.17 PM.png (13.2 KB)
Screen Shot 2017-11-21 at 10.20.17 PM.png
john vanlandingham
John Vanlandingham
Mod Moderator
Location: Ford Asylum, Sleezattle, WA
Join Date: 12/20/2005
Age: Ancient
Posts: 14,064

Rally Car:
Saab 96 V4



Re: Shock stem machining
November 21, 2017 10:03PM
Can't read the text, type it out and post those PNs on the Einsatz patrone und hinterachse dämpfer.
ACHTUNG! careful with the decimal.



John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.
Please Login or Register to post a reply
Philippe Bellefleur
same as above
Infallible Moderator
Location: Laval (slowly moving back towards the woods)
Join Date: 03/12/2016
Age: Settling Down
Posts: 84

Rally Car:
Volvo 740 imposed by vince, might be a 240... I think it will be a 240.



Re: Shock stem machining
November 22, 2017 05:11PM
Well, there seems to be a problem here because hooks law states that if 600 lb force compress a spring 6.9 inches then the constant should be close to 87 lb/in.

What were the dyno figures in terms of force & deflection? I mean, load cells calculate force so the 250 lb/in figure came from a calculation. Was it right?

You can get the numbers yourself with weights and a tape measure, no need for a dyno...
Please Login or Register to post a reply
john vanlandingham
John Vanlandingham
Mod Moderator
Location: Ford Asylum, Sleezattle, WA
Join Date: 12/20/2005
Age: Ancient
Posts: 14,064

Rally Car:
Saab 96 V4



Re: Shock stem machining
November 22, 2017 05:54PM
.
Quote
Philippe Bellefleur
Well, there seems to be a problem here because hooks law states that if 600 lb force compress a spring 6.9 inches then the constant should be close to 87 lb/in.

What were the dyno figures in terms of force & deflection? I mean, load cells calculate force so the 250 lb/in figure came from a calculation. Was it right?

You can get the numbers yourself with weights and a tape measure, no need for a dyno...

Phil, you're geekin' out..
You don't understand this stuff, no need to corn-fuse things..
Wait for info from the guy.



John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.
Please Login or Register to post a reply
Philippe Bellefleur
same as above
Infallible Moderator
Location: Laval (slowly moving back towards the woods)
Join Date: 03/12/2016
Age: Settling Down
Posts: 84

Rally Car:
Volvo 740 imposed by vince, might be a 240... I think it will be a 240.



Re: Shock stem machining
November 22, 2017 05:58PM
You're right, we obviously need a bigger version of his screenshot.
Please Login or Register to post a reply
camdenthrasher
Camden Thrasher
Godlike Moderator
Location: Atlanta
Join Date: 09/13/2017
Posts: 7

Rally Car:
BMW 2002


Re: Shock stem machining
November 22, 2017 11:48PM
There is no bigger version of the chart. It's from a crappy web scan of the service manual, but I'll type out what it says for the "red/blue" spring:

" Coil spring rating N (kpl) [lbs] 2649...2737 (270...279) [505...614.8] "



However, no reason to really argue about it too much. The measurement on the shock dyno at MCS as well as my own rough calculations agree on a ~250lbs/in rate.


For John: the part # of the front dampers I have is 34-000243.
Please Login or Register to post a reply
Sorry, only registered users may post in this forum.

Click here to login