I've been researching rear leaf springs for my 51 Chevy pickup. I am going to go with a later model differential and understand that I need to have the centering pin holes moved approximately 3 inches back from the stock location. 1 1/2" makes up the difference in the axle mounts and 1 1/2" makes up for the factory not centering the wheel in the opening. Now here is the question I know Posies makes a spring with this pin relocated 3" back and I have been talking with the sales people at Eaton spring, this is my first choice on buying. They have told me that on a stock spring the hole for the pin is further forward making the rear section of the spring longer then the front section. Now moving the spring pin back 3" will make the rear section shorter than the front and that's not recommended. He said it would loose it's stability. At 2" the distance would be the same from the pin. Would you go 3" or 2"? Will the inch difference be that noticeable in the wheel opening?
I'd center the wheel in the top of the wheel opening, not the bottom of the wheel opening. And I'd just drill the hole in the perch where it needs to be, and use a spring with the stock pin location. but I'm weird
If you need the full 3 inches to center the wheels in the openings, you might consider moving the pin 1/2 the distance, and relocate the hole in the perch to make up the other half. Moving just the hole in the perch will put it near the edge of the perch, and I am not a fan of that. Also, just moving the pin 1 1/2 inches, should keep the front shorter, and not change the dynamics of the spring too much.
3" sounds like a lot of mismatch. You could buy or make a plate like this one: http://www.classicperform.com/Store/1947_59_Trucks/4753LSC-K.htm Also, I've never checked this but I've heard you can reverse the spring front to back and move the locating pin in the right direction.
speedway sells a lowering block that has the adjustable centering pin . if you want to lower it also.
I made a set of those plates AND reversed the leaf springs on my 40 Ford ( 86 Ranger frame)pickup. Turning the springs around moved the axle back a little too far so I moved it forward somewhat with the plates. I'm looking at the front half of the spring being 29 1/2" from the center of the bushing to the center of the axle and then 27 1/4" from the center of the axle to the center of the rear bushing. So, I'm 1 1/8 off center. That is obviously having the front longer than the back. Is it stable? Who knows...I haven't had the thing on the road yet. Maybe another month or two. The thing I didn't like about the plates in the link is that there's nothing to keep the plates parallel to the leafs. I made my plates wider with U shaped notches milled into them where the U bolts would pass through, keeping the plates from shifting.
You can turn the top leaf only around, its the one that locates the axle, the others will stay in place. Before getting anything custom made, set the axle in place and double check that 3" measurement. My oder truck was only 1.5" to 1.75" out and I thought the newer ones like yours were about the same.
The first 1.5 is to get the later model rear end sitting where the stock torque tube rearend sits. Here's a picture of the stock 51 mount, the centering point is 1.5 inches ahead of the axle tube. The second 1.5 is to get it centered in the fender, stock from the factory has it to far forward. Here's an example If I turn the spring around it moves the diffie 4.25 inches back. I do need new springs my old ones have broken leafs and the eyes are worn because the bushings were shot .
The sales people at Eaton spring have given you good advice Usually the front 1/2 is shorter than the rear 1/2 of the spring , and the rear spring eye is higher than the front . There is a very good reason for this! During bodyroll the outside rear should not move rearward in an arc ,it should be either neutral or try to arc slightly forward. By raising the rear spring eye and shortening the front the "axle to front spring eye" is closer to a horizontal radius, this is to induce "Roll understeer" The rear end should to try and steer inwards on the corner and straighten the front up [ understeer ]The purpose of roll understeer is to load up the suspension with a little bit more bodyroll so it stabilizes the rear end and doesn't sway. If the suspension had Roll "Oversteer" the rearend would become loose and unpredictable on corners, but the real nightmare is in a straightline when bodyroll and roll oversteer cause the rearend to sway back and forth [ the rollsteer and bodyroll work opposite to each other ] Have too much arc in the rear springs [ at normal ride height ] can cause the rear to "bump steer" or "roll steer" causing many novices to scratch their heads looking for solutions at the front end This is a major design fault on most homebuilt trailers and hotrods ,because people think the suspension should arc rearward over bumps to reduce the "Jarring" effect I think the best solution, if you are already using a known spring from a vehicle you can take measurements from is to move the front hangars and rear shackles to get the wheels [ and the spring eyes ] in the correct position Shit , I still have nightmares about when I lengthened spring shackles in the 70's to "improve" my car
Thanks Kerrynzl, that's a very good explanation of what goes on. I am thinking the fender can be moved ahead with some shorting of the running boards and filler panel. Or I can live with the tire off center. Being safe is better than looking cool.
If this is worring you so much then why not just relocate the front spring mount and rear shackle mount. Hell of alot easier than all those body mods. It's your truck do what you will. But think of this for a moment, your not making a 150 mph racer that needs to be 100% correct to be safe.
here's a drawing from Chevy's engineering data for the 54 truck, the 51 is similar but the available drawing is not so easy to see. http://www.gmheritagecenter.com/gm-heritage-archive/vehicle-information-kits.html Note how the wheel is centered with the top of the wheel opening, when the truck is loaded. You probably are trying to get it to look like this, when it's not loaded. Just something else to think about....
Johnny, moving the fender forward is something I was giving thought to anyway. The fender would be closer to center of the box sides. I'm not worried about going strait it's the curves I am thinking about. I want to pull a trailer with this truck. Squirrel thanks for the drawing, I have also given thought to how much the wheel will move back under load.
I understand your concern. Just stop and think a moment about what I said on making or have made the extended pad with pivot. The load will be setting in the correct location on the spring. The spring wont know any differant. Only you. Correction I'm refering to the photo of stock rear in the above statement. Your going with later open drive shaft correct? Then a offset with the correct contact surface spring perch is all that is needed.
If you're going with an open driveline, you need to disable the ability of the spring perches to pivot. A guy I knew was doing this on an early 50's Chevy truck, took it out for it's first drive and made it about 20 feet before the rear axle rotated on the pivioting spring perches and wrecked his new driveshaft. From the looks of things, it may be better to cut off the old perches and weld new, solid perches in place while positioning the axle where it needs to be.
I had my drive line built and in before mounting the bed. I then figured out the fenders were not centered over the tires so I moved the fenders forward. It was a new bed with no holes and the running boards were rough anyway, so I cut the running boards. Even setting next to a stock truck, you can't tell. I even have 2" wider fenders. Joe
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