The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - 55.2-59 1955-59 Chevy 4x4 Power steering problems

leegreen · 11-01-2022, 01:42 AM

Is that the factory rear spring mount location or did it get moved rearwards for a longer spring?

I think the problem is the different length of radius between spring mount and axle (red line below) and on the drag link (blue line)

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Name: Capture.jpg
Views: 278
Size: 35.9 KB

so as the axle moves up and down on a large radius and the drag link moves on a small radius the link end at axle moves front-back. This is bump steer. In a perfect setup the steering box is vertically in line with the fixed end of the spring and the drag link is the same length as fixed spring end to axle. Check a AD GM setup where the box is on top of frame right above spring. The TF trucks were less ideal with box in front of pivot, but remember the factory springs did not deflect much except on huge bumps, bias ply tires took some of the hit out of small bumps and trucks were slower.

leveling the drag link if it is not may help a bit as the further it is from horizontal the more for-aft movement there is to any given up-down travel. But the essential problem will remain unless you can get fixed spring pivot and steering box closer together.

Also, how much arc is in your springs at ride height, more arc means more back-front movement of the axle. If you have a lot of arc the axle will move forward on compression as the spring flattens and backwards on rebound as the spring bends. In this case a bit of downwards angle on the drag link may help, and in your picture you look to have upwards angle.

11-01-2022, 01:42 AM	#7
leegreen Registered User Join Date: Mar 2022 Location: Surrey BC Posts: 726	Re: 1955-59 Chevy 4x4 Power steering problems Is that the factory rear spring mount location or did it get moved rearwards for a longer spring? I think the problem is the different length of radius between spring mount and axle (red line below) and on the drag link (blue line) so as the axle moves up and down on a large radius and the drag link moves on a small radius the link end at axle moves front-back. This is bump steer. In a perfect setup the steering box is vertically in line with the fixed end of the spring and the drag link is the same length as fixed spring end to axle. Check a AD GM setup where the box is on top of frame right above spring. The TF trucks were less ideal with box in front of pivot, but remember the factory springs did not deflect much except on huge bumps, bias ply tires took some of the hit out of small bumps and trucks were slower. leveling the drag link if it is not may help a bit as the further it is from horizontal the more for-aft movement there is to any given up-down travel. But the essential problem will remain unless you can get fixed spring pivot and steering box closer together. Also, how much arc is in your springs at ride height, more arc means more back-front movement of the axle. If you have a lot of arc the axle will move forward on compression as the spring flattens and backwards on rebound as the spring bends. In this case a bit of downwards angle on the drag link may help, and in your picture you look to have upwards angle. Last edited by leegreen; 11-01-2022 at 02:09 AM.