Is it important to get a new spring pin to match the larger hole that comes on new spring perches? Someone told me that it’s not necessary because it’s the u-bolts that place the rear where it needs to be and don’t worry about it. Bolt er’ in and forget about it.

Thoughts?

I just went through this on my Dart. I like them to be centered. I cut a couple spacers out of 3/8 pipe, I think it was. Got lucky as it fit great over the pin and in the hole. They centered the perches up on the springs.

How big is the hole??

I'd want to drop the rearend on there, bolt it up, measure the wheelbase.
Get that right & equal both sides.
If the holes are concentric, I'd want to sleeve the locating pins for race use so the axle can't re-locate itself.
If not concentric, double-check measurements, break out a die grinder & bit, make them concentric, and sleeve 'em.
For street use, sleeving is probably not necessary, depends on power/shock loads/grip.

I bought the next size up bolt with a larger head to fill the hole in the spring pads, and then had to drill out the register holes in the springs to fit the bigger bolt diameter. Spring steel does not drill very fast!

So who is reinventing the wheel??? We been stickin it in the same hole for over 50 years

Seems some of the replacement perches have a larger hole. I have inboard springs with new perches. There was a lot of slop. I wanted it all centered up so it didn't go down the road sideways like an old Chevy truck.

Mine were like 1/2"

I would push or pull the rear end perches forward to get the most traction on it I could get with them

Yup, that’s what I do on all the street car rears I narrow, you can buy the tubing by the foot and just tack weld a 3/4 “ on inside of perch. Moroso or Competition Engineering make em with 1/2” hole, but they used to be spendy. That is by far the quickest and most cost effective way to do it. Jim

I bought new springs from Eaton and the register bolt was smaller than the stock one for some reason. I just went up a bolt size and drilled the holes in each leaf bigger.

Aftermarket parts always have to have at least one thing not quite right about them.

Thanks guys. I think I’ll try the 3/8 black pipe trick to keep things in line. Makes you wonder why something as simple as a hole can’t be made right after all these years. Always something.

I don’t understand the concern?
Once the U-bolts are tightened, where’s it going to go?
I highly doubt the 1/16” is going to make a difference.

Morroso perch
Mopar perch

The nut on the bottom of the leaf spring pin will/should center itself to the mounting plate.

I stopped buying the Mopar perches and switched to the Moroso for that reason. On the several spring, and axle swaps I have done I have never once had the Mopar perch sized centering pin. It hasn't mattered if the springs were stock 30yr old or brand new aftermarket, the locating pin has always been the smaller diameter.

Those Mopar perches look like they are for the 73-up B Isolation setup.

hi , the P4120074 mopar spring seats have a .625 or 5/8" center hole . the ones you want are mopar P5007857 with the .500 or 1/2" center hole . ronnie

The bigger hole perches from Mopar are from their truck parts bin, resold as Performance Parts.

I love the cut pipe spacer idea. Why build a car and allow the rear housing not to be accurately located? No wonder some of the Mopars out there are crapboxes.

As much precision that can be controlled by me, gets the go ahead.

The large hole perches are for the isolator type attachment. They are later production, therefore probably more common. I've been using the 3/8" pipe as a spacer for years.
Doug