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Oil for Lever/Knee Action Shocks


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I've read advice that for lever/knee action shocks ( eg  1937 Special ) that motorcycle fork oil is good to use

 

And I plan on following this advice.....but what weight ?    10W ?  or  20W?  or 30W?  or  what?

 

Jack Worstell

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Use motorcycle fork oil.....comes in about ten different weights. 10 is what the original viscosity would have been pre war. I have used it many times. A small increase in weight drastically changes the action of the shock.  Weights are available in 5,10,15,20,25,30,40.

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Lazar at Apple Hydraulics recommended this to me when I needed a heavier oil for my rear shocks:

 

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ISO 100 is about 30 weight. They also make ISO 32, ISO 46, and ISO 68, which are obviously thinner. Apple fills shocks with the ISO 32 when they rebuild them, but I wanted more damping in the rear.

 

Unfortunately, this stuff appears to only be available by the gallon, so it's not particularly economical if you just need a few ounces at a time for shocks. I suspect that gallon will be a lifetime supply for me.

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17 hours ago, edinmass said:

Matt......that’s why I recommended the fork oil.........

 

Basically have a gallon of Mobil DTE chainsaw bar lube at this point.

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So   ISO 32 is about 15W     and this would be good to use in the shocks in a 1937 Special ?

( in other words...15W motorccyle fork oil would be about right ?)

 

Jack Worstell

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Posted (edited)

15 could be a bit heavy............but mostly it's trial and error.....till you find what you like. If it were me I would start at 10, drive it a week or two to get the feel.....and then decide if I want to go up. Better to start off lower than higher. 

 

 

PS- I have mixed 10 & 15 50/50 to split the difference........not sure if it was an improvement or not. 

Edited by edinmass (see edit history)
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ISO 32 is what Apply Hydraulics uses as standard fill in the shocks they rebuild. It's what I'm running in the front shocks on my '41. Since my car is a limousine and often has my whole family on board, it would bob up and down more than I liked when there were passengers in back. The ISO 100 added the damping I wanted yet didn't kill ride quality. It's nice to be able to fine-tune the shock response using oil, and I agree that ISO 32 is probably the right place to start since that's what the rebuilders use. As I said, I'm pleased with the way my front shocks work with the ISO 32--it rides really well and doesn't bob or bounce down the road.

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Jack, do yourself a favor, pull one shock, and test it by hand with two or three different rated oils. It will give you a much better understanding of where your heading with viscosity changes. It’s been about five years since I have done it. The ten to twenty weight jump is HUGE.

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Remember also that how many times you bounce the car or operate the arm to bleed the air out has a direct impact on how the vehicle will ride.  You can get the air out and add fluid until the shock is almost solid.

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7 minutes ago, Tinindian said:

Remember also that how many times you bounce the car or operate the arm to bleed the air out has a direct impact on how the vehicle will ride.  You can get the air out and add fluid until the shock is almost solid.

 

Good point! Leave some room in there for expansion or else the oil will have nowhere to go and it will lock up.

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7 hours ago, Tinindian said:

Remember also that how many times you bounce the car or operate the arm to bleed the air out has a direct impact on how the vehicle will ride.  You can get the air out and add fluid until the shock is almost solid.

My technique is to replace the plug not-even-finger-tight and drive once around the block. Repeat if you've burped air out and need to top off further.

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