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Old 07-11-2005, 09:18 PM
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Suicide front perch

While trying to setup the alignment on my 27 with a spring over axle suicide front I discovered that the front perch is not parallel with the ground. It is welded to the frame so it has about 10 dg negative caster in the spring. Eye ends of spring are tipped under the frame. This doesn't seem right to me. Methinks the spring should be vertical or maybe a couple degrees of positive caster. What say ye?

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Old 07-11-2005, 10:58 PM
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Actually

i woudl put about 5 degrees of positive castor in the spring perch..5 degrees of cator is about optimum on those to my way of thinking..Sounds like a bit of fabricating to fix that..Sorry about that..

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Old 07-12-2005, 10:51 PM
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Caster

You might want to check to see if the caster is built into the axle .If so the perch would have to be paralell to the ground . It does sound like you have some changin to do. Good luck , Jerry
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Old 07-13-2005, 07:16 AM
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IMHO, it is the caster - at the kingpin - that tells the tale. I don't recall seeing a spring or perch setup with that much neg. caster - but without seeing the rest of your setup maybe it was somehow necessary.

One other minor point...if you DO remove the neg. caster in your spring, it might be easiest to make a wedge piece to go on the underside of the suicide perch rather than removing the perch altogether. I would think the removal process might weaken the metal in you cross member (cutting, grinding, re-welding etc.). Hopefully you can leave the perch in place and fabricate from there.

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Old 07-13-2005, 03:33 PM
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getting somewhere

This car was built late 50s early 60s and the workmanship isn't exceptional. So the excessive perch angle didn't surprise me.
It has a straight tube axle located by hairpins. I know this is a , but after 40 years with no visible problem I'm not going to change it. The spring mounts on top of the axle with single stud hangers. These have to be loosened to adjust the axle caster. Caster adjustment is made via the hairpin clevises.
I plan to use 7dg as a base for the caster adjustment. Educated guessing says that it probably won't go beyond 9dg or less than 5dg to make optimum caster. Toe at 1/8th, tierod behind axle. Camber at 2dg for zero scrub.
After a couple replies to jumpstart my brain, I came up with this. Good thing I like doing fab work, both literally and figuretivly.
Logic tells me that the spring caster should be the same as axle caster or nearly so. This would put the spring on the same plane as the axle so rebound wouldn't put a side load on the hangers.
Putting a tapered shim in the hanger would probably be a problem because the shim would be a 19dg taper in the worst case scenario. This would present a tapered surface to tighten the bolts against and this would lead to loose or broken bolts.
Is there a fault in my thinking? Thanks for help.
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Old 07-13-2005, 03:43 PM
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Right on

I think if you look at your axle you will find that the kingpin bosses and the holes for the spring perch bolts are on the same plane..it would then follow to have the spring work well with no bind in the shackels that the axle..spring..spring and shackles woud need to be on the same plane to work well..

So remaking that spring perch so it is at a positive angle would be the right thing to do IMHO..

IMHO a lot of the work on one of the older rods is about "fixin" stuff..

Just my thoughts

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Old 07-13-2005, 05:36 PM
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Quote:
Originally Posted by 61bone
Putting a tapered shim in the hanger would probably be a problem because the shim would be a 19dg taper in the worst case scenario. This would present a tapered surface to tighten the bolts against and this would lead to loose or broken bolts.
If you use a shim on the underside of the perch (between the perch and leaf spring) and then an exact copy of that shim, except reversed front to rear, on the TOP of the perch - you will end up with the bolts being perpendicular to the leaf(s) and the bolt heads parallel to the leaf(s) - which should eliminate any odd stress points on the bolts or the heads. Obviously, the shims would have to be the same width and length as the perch and have bolt holes drilled to correspond to the holes in the perch itself. I hope you can vision what I'm describing. Let me know if not and I'll try to draw up something in photoshop.
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Old 07-14-2005, 06:56 AM
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Quote:
Originally Posted by cboy
If you use a shim on the underside of the perch (between the perch and leaf spring) and then an exact copy of that shim, except reversed front to rear, on the TOP of the perch - you will end up with the bolts being perpendicular to the leaf(s) and the bolt heads parallel to the leaf(s) - which should eliminate any odd stress points on the bolts or the heads. ......
Or sometimes you can find what our millwrights call "hillside washers" -- washers with a built in taper -- about 15 or 20 degrees if I remember right... but Dewey's double shim design would be cleaner, and a good machinist could whip it out quick.
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