Technical Chev threaded shackle bushes How, Why

I am working and learning on my 41 Chev truck project with I beam front.

I see the shackle bushes for the front spring are a threaded design. It looks like the bush is pressed into the hanger or eye, and then a threaded pin is screwed in for the shackle.

In normal operation it would appear that the thread is actually the bearing surface. Please let me know if I have this wrong and explain how they actually work.

This appears a more complex setup than a latter car with a bush and pin. What are the advantages of this setup as there has to be some reason for the extra complexity. Is there any tricks when checking for wear? If you were to replace them would you keep original.

Thanks

Steve from down under

 

They sounds like the same as ones used on Mopars of the same era. Basically make sure the outer surface the bushing is threaded into has not gone oblong. Also lot if you replace these there are lefts and rights. The are reverse threaded so they don’t back out by themselves.
I believe they are called silent blocks. There are different lengths on the shackle part. But most all drew bushing are the same size.
Willys Jeeps used these and probably the most common and best prices on them.

 

This is what the front shows in a rebuild kit, the shackle rides on the smooth part

 

Those are different from the silent blocks C hangars. These look way beefier. Again if you see oblonged holes are funny where. Then time to replace otherwise grease them up. You may want to raise the front and see if the left/right play in the suspension also.

 

The shackle bushings pivot on the threaded portion and the tapered smooth sections are drawn into and lock in the sideplates

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• http://chevy.oldcarmanualproject.com/shop/194/index.htm
  
• http://chevy.oldcarmanualproject.com/chevyresto/41index.htm

 

Thanks for the photo.
I have a paper copy of the manual and have read the section on how to replace the bush.
What I am trying to work out is what the advantages of a threaded bush are since other cats I have seen just use a plain bush and pin. Also how much wear is to much. There is a little bit of play in one end of the pins, but without ever felt a new set this may be normal.

They seam a complex solution for a simple job, but someone has decided it is the was to go. I am constantly trying to understand design principles, but that is just me.

Thanks

Steve

 

I have the same setup on my '50 Chevy truck. The threaded pins and bushes are also used on some Brit cars of the 30's

I understand that the reasons for their use are: Firstly, the use of a thread form increases the bearing area for any given diameter as against a plain pin. Secondly, the fact that they're threaded means that any sideways movement of the shackle is restricted to the clearance of the threads; restricting excessive movement on a semi elliptic setup would require shimming for plain pin shackles if there is any significant sideways clearance from the shackle to the spring or ch***is.

When I bought it, the bushes and pins on my truck (probably the originals fitted at the factory) had more forward and backward movement at the spring hanger end than up and down play. This resulted in the truck pulling randomly\wandering under heavy braking, changing all the bushes and pins fixed this issue straight away.

 

I think a good test of whether or not they're worn out, is if you can move them end to end. If so, replace them. If not, they should last a long time with proper lubrication...which means, grease them every 1000 miles, or as often as the factory manual says to.

I expect there is an SAE paper about them in an archive somewhere.

 

If there is a better way to do it, someone would have built them, and so far, no one has come up with it yet. My '37 uses the same design, keep them greased and they last forever.

 

GM used that concept in their front suspension until at least 1972. The A arm pivot in my suburban had them.

 

Highway tractors still use them. I would say they last longer if they are kept greased, I would also say they went away in light duty stuff because they need to be kept greased and they would be more expensive than rubber bushings.


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...when you grease these, the grease gets into every thread groove for a better working shackle...check out the cut-a-way..

 

Really? My '69 Suburban doesn't have anything like my '39 Chev has? My Suburban has pressed in rubber bushings on upper and lower control arms that go over a smooth shaft with nuts on each end. No threaded bushings anywhere.
This is the Moog kit I bought:



I believe Chevy stopped using these threaded bushings in 1954. I know my '57 Suburban, and my '55 Chev 150 didn't have them.

 

He might be talking about the 3/4 ton version, eh?

 

Mine were way past worn out so I replaced them with rubber bushings.

 

Surface area would be my guess, add up all the thread sides and you gain quite a bit of contact area.

 

also no lateral movement

 

Chevrolet used the old treaded style in pickups till 73. Suburban until 80 something.
Very good design. Lasted forever if greased. Have seen these threaded bushing still good after a good cleaning. If you can’t get them to take grease a little well placed heat will soften the old grease and let you pump fresh grease in. P***enger car change in 55.