Rear Leaf Springs worn out?

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digithead

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Is there a definitive way to determine if rear leaf springs are worn out? I love my 1973 but boy it rides a bit rough. My clue is if you stand band and look at it , I'd say the rear end is sitting "lower" then I would imagine it should. So I thought of getting longer shackle kits to fix it. But now I realize maybe its just better to bite

bullet and new leaf springs and fix the ride and the stance?

 
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Is there a definitive way to determine if rear leaf springs are worn out? I love my 1973 but boy it rides a bit rough. My clue is if you stand band and look at it , I'd say the rear end is sitting "lower" then I would imagine it should. So I thought of getting longer shackle kits to fix it. But now I realize maybe its just better to bite

bullet and new leaf springs and fix the ride and the stance?
 I'd replace them or have them rebuilt and recurved by a spring shop if you have one nearby.

When I did mine on my 71 Mach, I wanted 4.5 leaf to try to overcome spring wrap-up. I have manual trans with open dif and it tends to hop the rear right wheel,

I bought from Mustangs Unlimited (if I remember). The ride is really good now, even the wife noticed the difference!! I did need to use 1" lowering block as the curve of the new springs is greater than the worn out ones, but should settle in time. I'll remove the blocks at that point. 5 leaf will be a bit too hard I think.

If you want the correct springs, definitely contact Eaton Detroit Springs. They will for sure set you up with the proper rate for your car. Once you know what you need, you can probably order from them or go to your local vendor, NPD, CJ Pony etc.

 
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I have had a 73 mach 1 since I ordered it new. These cars always sat lower in the rear. I actually put helper springs around the rear shocks to change the stance of mine when brand new. The springs do not really wear out but like stated they loose their arch and can be fixed by a spring shop. Great shocks make a huge difference in the ride also.

David

 

Hemikiller

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I use the 429CJ spring in my 71-3 cars, Mustangs Unlimited part number 42-547. I have had excellent luck with them, they did not sag or have any issues in the six years they were on my old '71 sportsroof and I currently have a set in my '71 Mach. They are a 138lb rate and the ride is firm, but not harsh. Buy a new set of rear shackles, u-bolts& front eye bolts to complete the job. They seem to have free shipping and it looks like the springs are included in that deal.

BTW, the MU part # is the spring industry standard part number, so if you do buy them from another source, they should have a mfr's label with that number on them.

http://www.mustangsunlimited.com/Mustang/Suspension/Leaf-Springs/Leaf-Springs/Rear-Leaf-Spring-1971-Mustang-V8-Coupe-Fastback.axd

You could also opt for the Eaton Detroit Spring exact reproductions. They are more money and I have no experience with them.

Whatever you do, don't be fooled into buying the 71 Boss / 72 HO spring. Those cars had a slightly lower ride height.

 

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The rubber components of the rear springs may need to be replaced. My experience has been that the front sat too high from the factory. one half coil removed fro the front springs with a cut off wheel lowers the front of the car about .75 inch. The small increase in spring rate will not be a problem. https://www.eatondetroitspring.com/cutting-coil-springs/  Chuck

 
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The resulting ride height after replacing the springs is a big unknown for us that are pondering the idea of new springs. Is it better to buy mid eye springs and raise them if they ride too low, or buy regular eye spring and lower them if they ride too high?

Sent from my SAMSUNG-SM-G930A using Tapatalk

 

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Thank you all for your input and feedback.

 
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The resulting ride height after replacing the springs is a big unknown for us that are pondering the idea of new springs. Is it better to buy mid eye springs and raise them if they ride too low, or buy regular eye spring and lower them if they ride too high?
 Thanks for reminding me. I neglected to mention in my post that the 4.5 leaf springs I used were standard eye. If I'd known that I would (temporarily) need lowering blocks, I would probably have bought mid eye springs.

Also, I misspoke. The springs (kit) I got were from Mustangs Plus, not Mustangs Unlimited. They are Grab-A-Track which turned out to be Scott Drake, or at least the kit components were. I bought the complete kit by the way. I reused my original shackles as they were still pristine and twice the thickness of the SD ones. Go figure!!

Geoff.

 
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I would use the mid eye if I did it again. Lowering blocks are more detrimental to handling than long spring shackles. It is best to have neither, but if you are going to correct an error, better to do so by raising it up with the shackles.

I have 5 leafs with the 195 pound rating- too harsh for most people in my opinion, I would consider taking a leaf out if I wasn't so lazy.

 

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I have seen many restored cars that are beautiful except for they sit WAY too high because they used after market springs. Reuse the originals or buy from Eaton spring. Nothing else looks right, unless you want the four wheel drive look. Chuck

 
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I have seen many restored cars that are beautiful except for they sit WAY too high because they used after market springs. Reuse the originals or buy from Eaton spring. Nothing else looks right, unless you want the four wheel drive look. Chuck
 Chuck, doing it again I would go with the proper Eaton ones. I still have the originals, but my local spring guy will not put in the extra 1/2 leaf I feel it needs for the wrap-up issue.

 I also agree that too high is ugly!!! Hence, the lowering blocks temporarily installed. As for handling, as long as it's all tight and pinned in, I don't see too much problem with handling for the driving I do. Long shackles look like crap and only raise the back end. My 72 had these and I hated them, but then I should have done a lot of thing to that car including NOT selling it!

 

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I have seen many restored cars that are beautiful except for they sit WAY too high because they used after market springs. Reuse the originals or buy from Eaton spring. Nothing else looks right, unless you want the four wheel drive look. Chuck
 Chuck, doing it again I would go with the proper Eaton ones. I still have the originals, but my local spring guy will not put in the extra 1/2 leaf I feel it needs for the wrap-up issue.

 I also agree that too high is ugly!!! Hence, the lowering blocks temporarily installed. As for handling, as long as it's all tight and pinned in, I don't see too much problem with handling for the driving I do. Long shackles look like crap and only raise the back end. My 72 had these and I hated them, but then I should have done a lot of thing to that car including NOT selling it!
I just spoke to "William" at Eaton Spring. He said they have a 4 leaf that is 11% stiffer (thicker leafs) at 158 lbs. vs. stock at 138 lbs. He also said it could be made to stock ride height. They also offer urethane front spring eye bushings to cut down on axle tramp (spring wrap up). Chuck

 
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I have seen many restored cars that are beautiful except for they sit WAY too high because they used after market springs. Reuse the originals or buy from Eaton spring. Nothing else looks right, unless you want the four wheel drive look. Chuck
 Chuck, doing it again I would go with the proper Eaton ones. I still have the originals, but my local spring guy will not put in the extra 1/2 leaf I feel it needs for the wrap-up issue.

 I also agree that too high is ugly!!! Hence, the lowering blocks temporarily installed. As for handling, as long as it's all tight and pinned in, I don't see too much problem with handling for the driving I do. Long shackles look like crap and only raise the back end. My 72 had these and I hated them, but then I should have done a lot of thing to that car including NOT selling it!
I just spoke to "William" at Eaton Spring. He said they have a 4 leaf that is 11% stiffer (thicker leafs) at 158 lbs. vs. stock at 138 lbs. He also said it could be made to stock ride height. They also offer urethane front spring eye bushings to cut down on axle tramp (spring wrap up). Chuck
 Yeah, thanks Chuck. I really wish in hindsight, I'd looked closer at Eaton. I do have all the data for front springs and some for rears from them. For now the budget is gone for a while, so re-doing them is not an option at this time, BUT if the Grab-A-Trak don't drop as I hope they will, I may consider changing them. I think it goes to show that OEM parts are usually the best option when available.

Geoff.

 

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This is my car with the 429 leaf springs. The nose is a little high as I rebuilt the suspension with a 351C in mind and it currently is still running the wheezy 302 with aluminum intake and water pump.



 

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You gotta love the blue! Chuck

 
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