I’d like to raise the rear of my 51 Chevy about 1"-2". I’ve already re-arched the springs. Also, I know you can flip the shackles from the stock position, but sometimes they flip back, and I don’t want to have to deal with that. Looking at the rear shackles, I was thinking about changing the rear mount. Currently looks like this: I’m thinking about cutting up the stock rear spring mount. I'd use the "tube" and base, some 3/16 plate and build them like the aftermarket ones pictures below: (The leaf springs I've got are good stockers 1.75" wide and I want to use them. The mounts below are for 2.5" wide leaf springs, otherwise I'd just buy them.) It would allow the shackle to point up and lift the rear of the car a little bit. Also, I could build the rear mount to whatever small amount of lift I want. Any thoughts on using the stock springs with new fabbed rear mounts?
If you were to flip the springs to put them below the shackle mounts, you would see that is is literally impossible for them to flip back up into their stock position. I would do that first.
Yea, swinging the shackles down instead of up will give you the same smooth function of the suspension. But the shackle hole centers look to be about 2+ inches so flipping will raise the chassis about 4+ inches. If you want less than 4, blocks are your only option.
Since the shackle flip only changes the position of one end of the spring, and the axle is in the middle of the spring, the lift will be less than that. There is no way to compute it without accurate measurements of all dimensions. The easiest thing is to just try it.
Sounds like good advice, thanks. Do you know about how much it’ll raise the rear? Also what’s the easiest way to flip them? With the frame on jack stands and the rear suspension hanging, the shackles point straight forward (horizontal). Do I use a pry bar to pull the rear spring eyes down as I lower the car weight onto the tires? Thanks again for your help.
If I were to hazard a guess, I would say that the lift at the axle would be about the length of the distance between the pins in the shackle. Jack the car up. Put it on stands, with the axle hanging. That will pull the shackles down a bunch. You will need to carefully lever them the rest of the way. Once there, put the car back on the ground, and see if you like the results.
That is the best way to flip them. I used a tire iron when I first got my 52. The drivers side of the car seemed higher than the passenger side. Once I looked under, I saw the drivers side shackle was down where the passenger side was correct. I jacked the car up and with the rear hanging, I "slowly" worked it back up to where it belonged. You'll have to do the opposite. Be aware they are going to spring back towards the rear and possibly towards you!
Thanks everyone! Today is a do stuff with the wife day, but will get out in the shop tomorrow and see how it works out.
Worse than that..........Usually the centrebolt is a lot closer to the front eye [to control axle torque reaction] Usually a 1" lift would require 2-1/4" + at the rear shackle. This is not the correct approach as it will alter pinion angle, bur worse than that it will cause the wheelbase to lengthen during suspension compression [resulting in a very unstable roll-oversteer] Manufacturers mount the leaf springs at an angle like this [below] for a very good reason. @Hot Rod Dan , you would be better off raising the front spring hangers [or both] We have just gone through the same exercise on a tandem trailer with rocker equalizer leaf springs. Trailer suspension is a nightmare [which is why torsion axles reign supreme] We needed to raise the trailer 15mm which required lifting the hangers 35mm and not touching the shackles at all. This fixed the fenders rubbing over bumps, BUT as a side bonus there was less axle walk [roll steer] so it improved the handling a lot ,even with a higher CG.
How would you raise the front spring hangers? We are talking about the rear end of this car. The front hangers can't be raised. Or am I missing something?
It could be extra-worse on this car, depending on what spring perches we're used in the axle swap. Given that this car left the factory with a torque tube rear, with pivoting mounts to the spring, the spring pack bolt wasn't centered under the original axle, but forward of it. If the fixed perches didn't have a forward hole, to put the axle where it belongs, it is about 1-1/2" too far forward. I have seen tires strike the wheelhouses where this mistake was made. That offset would make the shackle-only lift even yet less.
Yep haha Hangers vs Shackles The Rear has front hangers and rear shackles and to confuse them on some beam axle pickups They have "Rear Hangers" on the front [with front shackles]
Put a spacer on front hanger also. We're just talking spacer blocks on the leaf spring mounts. Not longer shackles or flipping anything. Air shocks also work. Try not to over think things.
I won't set the pinion angle & weld the spring perches to the axle until the build in near complete, so I should be OK on pinion angle. Help me understand the "wheelbase to lengthen during suspension compression". Doesn't that normally happen regardless of shackles pointing up or down as the spring flattens? And haven't 1949-54 Chevy owners been doing this for years? (not sure how it effect the ride though) Good point, I did drill new locating holes in the perches & lower mounts to account for this.
Have a good look at the schematic I posted #10 When the spring compresses/flattens out it will lengthen along the "datum line" What manufacturers do is lower the front eye and raise the rear eye so the axle will arc forward . This angle counteracts the spring lengthening along the datum line. Manufacturers also have the front half of the spring [from the axle centreline] substantially shorter than the rear half. This helps stiffen the spring for rotational torque like a ladder bar, but doesn't affect total spring stiffens. A side affect of this offset is the spring doesn't lengthen as much between the spring eye and axle centerline. Crawl under any leaf spring vehicle and you will observe this ^^^ [offset and height difference]
Good information, thanks for the explanation. I think I understand it now. So if I take your graphic and explanation, as the axle moves closer to the front due to suspension travel the leaf spring lengthens and keeps the wheelbase relatively the same.
Mimilan - Thanks again, I understand what you are saying now. But as I think about this I also wonder if flipping the shackles is going to make that much of a difference in handling. This car has a straight axle on the front with 15x4.5" wheels and skinny tires. On the rear it'll have large tires and slapper bars. It'll probably ride and steer like an old Jeep and as a Jeep owner/enthusiast I don't mind. I may just try flipping the shackles and see how it rides. I can always change it back and add spacers between the frame and front & rear spring mount
You can try it and see..........but word of caution ! Do one mod at a time and test. Roll oversteer is unstable because the axle steering always transfers weight to the opposite side [oscillating back and forth] This usually requires opposite lock to correct. Roll understeer [wheelbase shortening] is more stable but needs more steering input. This ^^^ is only an issue with rear live axles because the wheels are always perpendicular to the axle. If the front axle has been setup to correct bump steer it won't roll steer at all [the axle, tie-rod, and spindles act like a parallelogram] Back in the 70's single axle travel trailers [towed behind British cars] were the curse of NZ roads. They would sway at speeds above 40mph and were road hogs. A simple fix was to have the hangers at the rear and the slippers/shackles at the front [turn the axle/suspension around 180 deg] and it changed from oversteer to understeer. We had a utility trailer that swayed badly when towed behind a 4 x 4 SUV , but when we towed it behind a Nissan Bluebird the swaying disappeared [even when loaded] The difference was approx 12" lower towball /hitch height changed the angle of the suspension. It made that much of a difference. [below is a typical trailer setup] Most trailers are built with Neanderthal skills On our O/T race car [a road racing FR500C] it has a lot of rear roll understeer. This car is quite bad at "tramlining" on bumpy straights. But roll understeer self corrects [We can take our hands off the wheel at 170mph even though it is darting around over bumps] Roll understeer is great for mid corner "side bite" allowing more aggressive throttle oversteer corner exit.
You were just changing the caster of the axle and just adding more. That’s all you did. I have added shims to axles on trailers to change the caster for years. Old timer taught me that trick.
Caster doesn't apply to rear axles [or trailer axles] What we were changing was the arc [or path of travel] of the suspension. On trailers they arc rearward causing roll oversteer. similar to below [showing a RH corner] With roll oversteer , the bodyroll transfers to the opposite side causing the other side to compress [and steer] with then bodyrolls back again. [oscillating side to side] With roll understeer the vehicle wants to straighten up in a corner requiring more steering input [or throttle oversteer in our race car] This is only a problem with axles where the wheels are fixed perpendicular to the axle centreline [rear axles] Trailer torsion axles don't roll steer, and car IRS don't roll steer
Dan I own a 51 hard top. Would like to chat with you. I’m having a hard time figuring out how to post questions! Thanx
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