Iso-delete Options

Duke5A

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I've got a buddy who is a Chrysler mechanic who will be rebuilding it for me. I would imagine he could weld new perches, but im trying to see how I can avoid that

You need to ask your buddy what the easiest option is then. Welding or fabrication, but it's going to be one of the two so as long you want to do an ISO delete with a factory F/J/M axle.
 

BudW

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A couple of different issues at hand here.
The “centering bolt” on older leaf springs use a smaller head/nut than what the centering bolt uses on FMJ springs. If I remember correctly, it is like 1/2” on older springs and 5/8” on FMJ springs – but don’t quote me on that measurement (just going by memory).
For a person to re-use FMJ leaf springs and older shock plates, a person will either need to enlarge the bolt hole on the older shock plates to match the FMJ centering bolt OR replace the centering bolt to older style springs. The centering bolt shaft diameter is the same, only the FMJ bolt and nut is larger diameter.

To change a centering bolt, a person needs to get two clamps and clamp down the spring (on or off the car) with differential removed. Tighten the clamps down snug (enough they will not “pop” off). Remove old bolts and replace with new bolts. Remove clamps and that job is completed.
Center Bolt.png

Black - leaf spring
Red - centering bolt
Blue - spring clamps (should already be in place)
Green - one version of a clamp to use (C-clamp) but there are others that will work
Note: there usually is not any space between the leaves. I left the space for clarity.

It might be easier (and cheaper?) to just drill out the centering bolt hole on older shock plates.

There can be an issue of differential movement if you use a small centering bolt inside a larger hole, a person can’t/won’t be able to get differential in there straight and keep it that way.

Now the FMJ differential perch hole. The 8¾ (or Dana 60) spring perches are all drilled to the smaller/older centering bolt. In this case, if replacing both the differential and shock plates, I would use new centering bolts. No drilling would be needed.

If using an FMJ differential, a person will need to find a piece of metal and fill in the large hole (which I “think” is 1-7/16” in diameter – but don’t quote me on that). Once welded in place – re-drill the hole in the center. The side to side is not as big of an issue as the front to rear location is drilled at – but if using wider than normal tires, the side to side position might also be critical.
BudW
 

brotherGood

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I've got a new centering pin coming, and ive picked up some scrap metal from work to cut out my spacers that'll fit in the FMJ perches. I'm hoping to get out to the garage and flip the axle on the bench to measure the hole in the perch so I can order the correct size hole saw.
 

Duke5A

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Just remember you're going to have to plug weld your biscuits to the heads of your new locating pins, or they'll just fall out when driving. You still plan on running an adapter plate between the axle and spring to attach the factory rear sway bar links? If so, you now also need to drill out that plate to fit over the diameter of the biscuit.

I'm still recommending you take it to a shop and have them replace the pads with older A/B/E pads and then use the correct locating pins.

Mopar Spring Perches

mopar-spring-perches-7.jpg
 

brotherGood

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Wouldn't I just need to essentially fill the hole in the perch? I am running the E body sway bar plate, and have the new centering pin due in tomorrow.

I dont disagree that new perches would solve this problem much easier and quicker, but they guy doing the axle rebuild has already essentially been volunteered to do more than he signed up for, and welding perches on may me more than he really wants to screw with...even if he has a welder to begin with.
 

BudW

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If using new centering bolts/pins, an option you have is to attach your “spacer” on top of spring when installing the centering bolts. That way the differential will not be altered. It also allows for removal/reinstallation without issues.

I can understanding flipping differential over for measurements, test fits, etc. – but before you invest in a hole saw that you might only use once, I might recommend purchasing a short piece of steel bar stock, say ¼” (6.4 mm) thick (or so) that is 1” (24.5 mm) wide (or so) and file off corners of a square (or rectangular) piece to fit the holes.

Example:
Perch Hole.png

Black is differential perch hole.
Red is square or rectangular metal stock.
Green is corner either cut off or filed off to fit the hole.
Orange is lines/scribes cutting the circle exactly in half – to locate the center to aid drilling your new center hole. You do not want the center of your square (or rectangle) for that might not be the center of the hole, possibly.

You now have the option to weld those to differential perches or just bolt them on using your new centering bolts. I agree with Duke5A the blocks/spacers will work for initial bolt-up, but will fall out over time if not secured somehow. The differential doesn’t have a lot of stress in that area – but if there was nothing to hold it in place at all times, it will start to walk around, causing your rear alignment to change.
BudW
 

brotherGood

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I've got 1/8" thick piece of steel that I was planning on cutting and stacking. I just wasnt sure how they mounted as to whether itd be better off being bolted to the upper plate, or to the perch.
 

brotherGood

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For some reason, it just hit me..and if it was explained already, I apologize.

To avoid all of this, and the need for new perches, I can just drill out the upper and lower plates to accept the FMJ centering pin, correct?
 

Duke5A

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For some reason, it just hit me..and if it was explained already, I apologize.

To avoid all of this, and the need for new perches, I can just drill out the upper and lower plates to accept the FMJ centering pin, correct?

The lower shock plate you shouldn't have to touch, only the upper plate that the sway bar end link attaches to because it needs to slip over the top of the bolt with large spacing biscuit you have to make and weld to it.

If you want later tonight we can do a video chat and I can show you how my car is setup. What you're looking to do is basically what I had to do just last week to get the Dana 60 installed. For some reason the perches the shop welded to the axle tubes had the larger locating hole.
 

brotherGood

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The lower shock plate you shouldn't have to touch, only the upper plate that the sway bar end link attaches to because it needs to slip over the top of the bolt with large spacing biscuit you have to make and weld to it.

If you want later tonight we can do a video chat and I can show you how my car is setup. What you're looking to do is basically what I had to do just last week to get the Dana 60 installed. For some reason the perches the shop welded to the axle tubes had the larger locating hole.

Crap, I just saw this..I hope you weren't waiting around for me.

If I drilled the top plate, would I still even need to fab anything up?
 

Duke5A

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Crap, I just saw this..I hope you weren't waiting around for me.

If I drilled the top plate, would I still even need to fab anything up?

No problem. Offer is still on the table for as long as my car is on jack stands. I'm free anytime after 8pm.
 

BudW

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Well . . . you can have/will have movement (walking) between the top plate and differential perch if there is not something to prevent it.
I forgot about the top plate (for sway bar) – which may make a difference.
For some reason, brain fog maybe, I can’t picture how the top plate center hole is made to comment further at this moment.
BudW
 
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