The Stovebolt Site Forums The Shop Area Driveline 1946 knee action shock replacement

In a quest to make my truck ( 1946 GMC 1/2 ton) ride and handle better I am going to install tube type shocks. Great improvements have been made so far with radial tires and a front anti-sway bar. I also replaced the shackles and spring bolts on the rear and this week the front end is getting the same treatment. I pulled some leafs out of the springs on the back and will remove one out of the front to soften the ride. The removal of the rear leafs didn't change the stance of the truck much at all but it made the ride much less harsh.

I couldn't find a single thread on the forum about doing this swap of tube shocks in place of knee action shocks. I took some measurements of the suspension bottomed out and then with the axle hanging and decided a 5 inch travel shock has plenty of travel. I chose a Monroe 5751 shock with Compressed Length 8.500 In. Extended Length 13.440 In and Travel Length 4.940 In. I'll weld up some mounts and report how it goes.

Does any have any thoughts on this endeavor? I know the knee action shocks supposedly work "just fine" but I have to give this experiment a try! I am open to any advice as I haven't ordered the shocks yet. One specific question I have concerns oil versus gas filled shocks. The fine folks at Detroit Eaton Springs say in one of their videos that older vehicles don't respond well to gas shocks and oil filled shocks are the way to go. Problem is , I can't find "oil filled" shocks anywhere. Actually I think all shocks have some oil in them but I don't know what Detroit Eaton is talking about and they didn't answer my email. Anyone know anything about "oil versus gas shocks?

Thanks for any input!

David

I have run into the same problem with gas shock verses oil shocks. I too was dealing with Eaton Spring trying to soften the ride. I went with four new custom made springs with a lot less spring rate at each corner, it then came to shock choice, like with you, they suggested getting rid of the gas shock and going back to plain old oil filled, trouble with that is, no one makes that type of shock anymore. I hunted for weeks on the web and never could find anything. I have a short travel shock so my choice was pretty narrow. One of these days I am going to raise the upper mount and find a different shock for the front. This time I will hunt for a car with the same weight and wheel base as my truck, and go from there.

I have been down the road you are traveling, I had three of the seven leaves out of the front and four out nine removed from the back. Each pack had teflon liner full length, and tube shocks on each corner. It rode pretty good, but I had some money to burn from a side job I did so I went four new springs, plus it gave me piece of mind since I had old springs with a lot less leaves in them. It rides much better all around town and really helped at highway speeds. At slow speeds, the front bounces more then I like so I hope a softer shock will take some of that out.

Back in the day, all shocks were oil filled, I don't know for sure when gas shocks came about, maybe when the radial tire came around? Now they are all about stiff ride for better handling.

Joe

All shocks are still oil-filled. The current buzzword is "Gas-filled" as it makes the suckers part with their money a little easier. The only difference is that the area of the shock above the oil is filled with some sort of semi-inert gas like Nitrogen instead of plain old air. The same sort of dummies are the ones who pay extra to have tire shops fill their tires with 100% Nitrogen instead of a 70/30 Nitrogen/Oxygen mixture! (air!)
Jerry

Thats true about the oil in the shocks, but you still can't find any with out it and the extra gas is what helps stiffen them up.

"Gas-filled" shocks cam be compressed by hand so the pressure inside can't be more than a few PSI. It doesn't make good nonsense that the minuscule amount of extra pressure makes much difference where a vehicle weighing several thousand pounds is involved, or when considering the shock load of hitting a bump on the springs and suspension is considered. The so-called advantage of putting an inert gas in a shock is supposed to prevent the oil from foaming. P.T. Barnum was right- - - - -"There's a sucker born every minute!"
Jerry

Joe H,
Thanks for sharing your experience. I ordered the shocks I was looking at and I'll install them in the next couple of weeks and report back. I think the weight of the car shouldn't matter much since the shock is damping the movement of the unsprung mass of the suspension but then again what do I know. One of my shackle bolts was seized in the front right frame bushing. I had to weld a nut onto the shackle bolt (the threaded part with the zerk fitting) to remove it (with a sledge and a long wrench). That in itself and fixing the egg shaped bushing in the opposite end of the spring should make a big difference!

Joe, why are you unhappy with your current shocks? Do I understand that you think the new springs improved your ride? If so, why do you think that is?

Jerry, what you said is what I suspected. I'll see how the new shocks compare to the stock units.

David

David, sorry it took awhile to get back to you. My new springs were made by Detroit spring. I borrowed a set of digital car scales and made a ton of checks to know just what I was dealing with, starting with all four corners with and without passengers ( driver to ), full tank of fuel, road ready so to speak. Then I lifted the truck up on stands and dropped the leaf springs at one end to measure the weight of axles, tires, brakes, and steering. With half the springs dropped and all the axle weight on the scales, the actual spring weight was split between sprung and unsprung weights. This let the spring guys know what the leaves were actually carrying. I then removed one front and one rear and made a makeshift spring tester using my Toyota for weight, and one digital scale. With solid roller bearings at each end of the leaf spring rolling on smooth concrete ( think of funny look skateboard ), I lowered the trailer hitch of the Toyota down on the scale which was setting center point of the leaf. Leaf spring rates are measure by how many pounds it takes to compress the spring 1 inch. With some steel rulers and careful control of the jack, I was able to get a fairly accurate front spring rate of 360 to 370 pounds per inch of compression. This is way less then the 475 it came with. My new springs are in the 275 range,much lighter, more give, better ride! I can get away with this due to the later model 250 weighing much less the 216 it came with and the fact GM under rated the load carrying capacities. The rear springs are about 2/3 of what the OEM spring rates are.

As far as shocks and the ride, I still feel they are to stiff for slow speeds. At highway speeds, 55 to 75 the truck handles the bumps like they are not there, it rides as good or better then my '03 Tacoma, but at slow speeds 40 and down, the front bucks up and down over every spot in the road, like the springs are still to stiff. I know they are not, so the shocks have to be holding to tight. My next move is to unhook them and go for a short drive on my local test track I have around my area. I picked roads close to home and travel the same direction when testing stuff. If the front stays steady and the springs take the bumps, then I know for certain the shocks are to stiff. If thats true, then I have to shop a different manufacturer or model, I don't really know what the next step will be. I am also looking at replacing the tires. They are 19 year old radials, garage kept, still half tread or more. The age is starting to worry me a bit. I also run 40 psi in the front to make it steer easier, so I have that to play with.

I am hoping new tires with less air will help and I don't have to mess with shocks, but the easy way never works out for me.

Joe,
Wow, you did a lot of good work and research! I'm just winging it by comparison! Thanks for letting me know your experience. I can't imagine I'll do much better than you did but I think my ride will have to improve from what it is. I'll let you know my failures and successes on the project.

David

I have rebuilt all 4 of my knee action shocks, but was wondering if they have to be removed to install HP590 lever action shocks we have in stock from Jim Carter? I am trying to keep the truck original, and I won't be hauling firewood or Gravel. Thanks Bill

Bill, You'll need to remove the stock shocks to install the new kit.
David

Here is my report on my quest to improve the ride on my 1946 GMC 1/2 ton. I am happy with the results! I outlined the different steps I've taken in the initial post. I went to Home Depot and bought some C-channel and made some mounts for the front shocks. Here's a picture of the result. Shock mount for tube shocks

The total cost to make the mounts was $14 for the steel and $44 for both shocks from RockAuto. I used the stock mounting holes so I didn't have to drill anything. I made a lower mount out of 1/8" steel. If anyone wants more info I can send my plans. For the rear shocks, I simply bolted a piece of angle iron that runs from frame tail to frame rail above the old shocks lower mounts. I drilled holes in the angle iron and used the stock lower mounts. The rear shocks I used were Monroe 31125 that cost $16 each. You'll notice that all the shocks had a stud mount (the end of the shock is just threaded) and that simplified everything.

The ride is much better and less harsh. The old knee action shocks only dampen on the rebound, not on compression. The new shocks also seem to dampen the body roll when going around corners.