- Nov 22, 2019
- #1
mrbone
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Hey all! So, I am in the process of replacing the worn out leaf springs on my 68 RR..
Ran into a crazy problem. The leaf springs are too short!!
I have Mopar Performance bracket set PN: P4120105 for the B-body 116" wheel base.
The springs are PN: P3690454 & 455 and bolt right up to the MP hanger bracket.
I am told the super stock spring should be 56" which, unless I am measuring wrong- they appear to be.
And, the MP extended bracket is 2" longer than my factory bracket.
But as the photos show- they are short.
Not sure what to do?? Any advise? What am I missing?
HELP!
- Nov 22, 2019
- #2
Lefty71
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Look up the part number for the springs... I thought that 454 and 455 were for 62-65 Plymouth "B", and maybe plymouth only, so shorter front segment. Look it up tho, dont quote me on it!
- Nov 22, 2019
- #3
mrbone
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That's what I thought was wrong at first too.
Mopar Performance P3690456 & P3690457 are listed for 1964-65 B-body.
The MP 454 & 455 is for B-body rated at 3800#. So, the springs should fit..
- Nov 22, 2019
- #4
33 IMP
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Have you put weight on the new springs? With car weight on the springs the arch gets shallower and they effectively become longer.
If that doesn't help, I'd guess you need different hangers.
- Nov 22, 2019
- #5
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Daves69
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As you lower the weight on to the spring, pry/leverage the shackles rearward till they go past center for you. Maybe that will help.
- Nov 22, 2019
- #6
snakeoil24
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Springs should connect with out putting weight on the arch. Sounds like wrong or mislabeled springs
- Nov 22, 2019
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Daves69
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FWIW, Some prying reference on SS springs…….
https://www.forabodiesonly.com/mopar/threads/leaf-springs-for-dart-swingers.445041/#post-1972662122
BTW, The 56" length mentioned is correct per MP Chassis book. 20" front, 36" rear segments. Likewise the 2" longer front hanger. Should go.
Compare the length to the old spring.
Last edited:
- Nov 22, 2019
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ddpsnake
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weight on the car been there befor,sure freak me out the first time.
- Nov 22, 2019
- #9
VANDAN
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I had bought MP SS springs for my '65 Coronet, thru Summit Racing, and they were incorrectly tagged, so make sure you have the correct springs before you beat yourself up. Took a bit, but they corrected the error...
- Nov 23, 2019
- #10
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andyf
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mrbone said:
Hey all! So, I am in the process of replacing the worn out leaf springs on my 68 RR..
Ran into a crazy problem. The leaf springs are too short!!I have Mopar Performance bracket set PN: P4120105 for the B-body 116" wheel base.
The springs are PN: P3690454 & 455 and bolt right up to the MP hanger bracket.
I am told the super stock spring should be 56" which, unless I am measuring wrong- they appear to be.
And, the MP extended bracket is 2" longer than my factory bracket.
But as the photos show- they are short.
Not sure what to do?? Any advise? What am I missing?HELP!
View attachment 869633 View attachment 869635 View attachment 869636
Compare the rear segment length to the springs you took off. If they are the same length then you are good to go. Also compare the front segment length. The SS springs should be two inches shorter which is why you have a two inch longer hanger. If everything checks out correct then go ahead with the install. If not then you have some problem. Maybe mislabeled springs or some other unknown issue.
- Nov 24, 2019
- #11
mrbone
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OK, as usual you guys are right on the money.
Sorry it took me a couple days to get back to you, (work & kids).
After a lot of measuring, staring and actually setting the old leaf's next for comparison..
I put a jack underneath the Super Stock Spring and started compressing it. Sure enough, the rear shackles went right into position.
It was also clear the new springs have much more ARCH than the old ones. Obviously, they will 'flatten' out after they are 'broke in'.
Thanks for all you're help as always! AJ
- Nov 24, 2019
- #12
PLMHEMI
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Be prepared to check and change your pinion angle....
- Nov 24, 2019
- #13
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Ceedawg
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When shocks are installed the hanger will stay back where it’s supposed to be. Too long a shock, then it could lock forward on a hard launch or just jacking up to change tire, a no no. Now, removing shocks is a good way to remove tires that are snug-tight up in the wheel well.
- Nov 24, 2019
- #14
33 IMP
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Agree with PLMHEMI. I needed 3° down shims to get mine where I wanted it, with super stock springs .
- Nov 25, 2019
- #15
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miller
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mrbone said:
Sure enough, the rear shackles went right into position.
You won't know that, until the rear axle is in place, wheels on the ground, and weight of the car is in place.
- Nov 25, 2019
- #16
mrbone
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You are right!! Thanks for the heads up.
33 IMP, where did you get the shims? Did you make them out of aluminum?
- Nov 25, 2019
- #17
33 IMP
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I have made my own spacers, and wedges to alter pinion angle, but I think the ones on my 62 were purchased. Summit and jegs both sell them, I'm sure.
- Nov 25, 2019
- #18
Fran Blacker
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Know what shims you need before ordering $30/40 a pair.
- Nov 25, 2019
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bearman
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Don't forget to box up the spring perches.
- Nov 26, 2019
- #20
mrbone
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bearman said:
Don't forget to box up the spring perches.
What is "boxing up the spring perches"?
Never heard of that.. of course I never heard of spring perch shim's either.
Pretty sure I'll need to shim, without measuring, looks like my pinion angle is least 2 degrees higher now.
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