Thread: help with choosing a shock absorber

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I am rebuilding my 1948 vauxhall.
thred here. http://www.clubhotrod.com/forums/showthread.php?t=43857
I have fitted a complete volvo rear end, the coils have been shortened to get the ride height.
my problem is that i need to find some small shocks to complete the rear end install.
the coils are mounted at the rear of the diff, and the shocks are mounted at the front of the diff, as per factory volvo.
the lower shock mount is in the lower traling arm, and the upper shock mount is in the chassis.
the mounting points for the shocks from centre to centre are 300mm 30cm, or 12" at ride height whith the body fitted to the chassis.
I need to find some short shocks to suite, any ideas ?
thanks barnsey
photo of setup here.
http://i7.photobucket.com/albums/y28...tingpoints.jpg

I can't tell from the photos, what type top and bottom mounts do you need and how much travel do you need?

Originally Posted by techinspector1

I can't tell from the photos, what type top and bottom mounts do you need and how much travel do you need?

the shocks need to be loop to loop. or eye to eye,
I have an old set of VW bettle front shocks here that fit fine, but the travel down when fitted is only around just under 2" I would need about 4" down travel
the VW shocks that i have here measure.
fully closed 260mm 26cm a bit over 8 1/2 "
fully open, 410mm 41cm a bit over 16"
cheers barnsey
sorry if this don't make sense.

Originally Posted by barnsey

the shocks need to be loop to loop. or eye to eye,
I have an old set of VW bettle front shocks here that fit fine, but the travel down when fitted is only around just under 2" I would need about 4" down travel
the VW shocks that i have here measure.
fully closed 260mm 26cm a bit over 8 1/2 "
fully open, 410mm 41cm a bit over 16"
cheers barnsey
sorry if this don't make sense.

Going from your first post you need 12" static, and above you need 4" down travel and the VW shock has 16" extension. If you put that together you want a shock with 12" static, and 8" of travel, 8" compressed and 16" extended? Is that right? Do you really need that much travel?

from my first post.
I measured from the upper to lower mounting points where the shock will bolt on.
the car is sitting at ride height, so it is 12" from centre of loop to centre of loop.
so when the shock is mounted on the car it will be 12" between the two mounting points,
when i fit the VW shock to the mounts, there is only 2" travel down before the shock bottoms out.
hope that makes sense, if not I will try to get some better pics tomorrow and hold a tape between the mounting points to show it more clearley.
thanks heaps for taking the time.
cheers barnsey

Originally Posted by rspears

Do you really need that much travel?

This is what I was wondering also. If the diff itself will move up four inches and down 4 inches, for instance, and the mounting point of the shock is halfway between the pivot point of the arm it is attached to and the diff, then the shock will only see half that movement, or two inches up and two inches down.

I guess the question is, what is the amount of movement you are thinking at the diff itself, how long is the arm from the diff to the pivot point and where is the shock mounting point on that arm, how far back from the pivot point.

thanks again for your replies, I will get some measurements today and take a few pics.
I am pretty new to all this, and learning every day
cheers barnsey

I have an old pair of VW beetle front shocks that i have been using to try and work out what size shocks i need.
can you work anything out from this
cheers barnsey
http://i7.photobucket.com/albums/y28...shockmount.jpg
http://i7.photobucket.com/albums/y28...rideheight.jpg
http://i7.photobucket.com/albums/y28...ydepressed.jpg
http://i7.photobucket.com/albums/y28...rideheight.jpg
http://i7.photobucket.com/albums/y28...ebottomout.jpg
http://i7.photobucket.com/albums/y28...retocentre.jpg
http://i7.photobucket.com/albums/y28...ullyclosed.jpg
http://i7.photobucket.com/albums/y28...lyextended.jpg
http://i7.photobucket.com/albums/y28...yextended2.jpg

A shock needs 2" of compression and atleast 1" of rebound at minimum. All of this is from ride height. For your case you want to pick a shock with a collapsed measurement of 10" as a minimum and a extended measurement of 13" also as a minimum. If you can find a shock in one of the vendors list with a 3" collapse and a 2" extend = 5" stroke (9" and 14") this will work good and a 5" stroke is pretty standard. You want your axle to bottom out on your snubbers not the shock or will destroy your shocks. Longer stoke is not actually better for performance so measure them up and pick appropriate stroke length to suit your needs. The vendors have many lengths and strokes to choose from. I run Bilsteins on my coupe with 2-1/2" collapse and 1-1/2" extend and it rides nice and even better when loaded for rod run.

You might look at Speedway - http://www.speedwaymotors.com/Pro-St...DisplayId=2183 Pro Street SM500 (click the chart), 12" ride, 9.5" compressed, 14.5" extended. They also have a non-chrome "Speedway Brand" with the same specs and $3 cheaper, but back ordered right now.

thanks heaps guys for all your help.
I checked out that link and they look great,
I also found these ones on the so cal site http://www.est1946.com/speedshocks.aspx
I would like to try and get a pair with the dust cover. If its not too much trouble, could you take a look at that link,
If these don't suit, i will order a set of the SM500 Type.
sorry i am not more mathematica,l I AM NOT GOOD AT INCHES LOL
thanks again barnsey
Speedshocks in Steel:
We are proud to introduce our new line of Speedshocks in steel. These nitrogen filled gas shocks are engineered specifically for hot rod applications and offered in the “Standard” length of 9 1/4" closed and 14 1/4" extended or in the "Shorty" length of 7 7/8" closed and 11 1/4" extended. They are manufactured with or without dust covers and can be run on the front or rear end of the car in either configuration. The distinctive design of the dustcover is reminiscent of the “airplane shocks” used on early hot rods during the 40’s and 50’s. Other features are 90 durometer replaceable 5/8" ID lower and 7/16" ID upper neoprene rubber bushings and they come finished in either high gloss SO-CAL red or show chrome.

SOLD IN PAIRS

Inch to cm converter: http://manuelsweb.com/in_cm.htm

thanks Henry

I had this queued up when the server crashed....another approach:
Speedshocks in Steel:
We are proud to introduce our new line of Speedshocks in steel. These nitrogen filled gas shocks are engineered specifically for hot rod applications and offered in the “Standard” length of 235mm closed and 362mm extended or in the "Shorty" length of 200mm closed and 286mm extended. They are manufactured with or without dust covers and can be run on the front or rear end of the car in either configuration. The distinctive design of the dustcover is reminiscent of the “airplane shocks” used on early hot rods during the 40’s and 50’s. Other features are 90 durometer replaceable 5/8" (~15.9mm) ID lower and 7/16" (~11mm) ID upper neoprene rubber bushings and they come finished in either high gloss SO-CAL red or show chrome.

SOLD IN PAIRS

Jack's more of a "Teach a man to fish" guy...

Came across this while surfing....
http://www.monroe.com/catalog/docume...engthSheet.pdf