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Discussion Starter · #1 ·
Hi all, I just don't know!?, I'm in the habit of replacing old stuff IF it needs it, and do not know the age of the rear springs, but they are definitely not new..! what is the tipping point for replacement?
They rarely bottom out, and seem to sit ok height wise, but what tests do you all live by, when determining the time for new springs?

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Are you okay with "okay"? I don't think ever bottoming out is acceptable under normal driving. Does it have the stance and ride you want? For a modest investment, it can be juuuuuust riiiiiiiiight.
 

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It would be helpful if you posted some close up and detailed pics of the springs you have now, we could see if they are of OEM style anyway. How many leafs are they? Your car was originally a six cylinder so the factory spring rate would have been a relatively light 85lbs. Now you have a V8, possibly a 22gal. fuel tank, and who knows what else added (lowering blocks?), so that's something to consider. If your wheels/tires/back spacing are all within acceptable fitment specs and you are bottoming out at times the springs are indeed worth taking a look at. You may want/need more performance type or GT spec springs back there. Post pics and provide more info.
 

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A ride-height measurement would determine whether new springs were needed. This was done with the stock tires, inflated to their recommended pressure. You can look up the stock tire diameter/circumference and calculate the difference between those and what you have on, currently, to figure out how much to add/subtract from the spec. If the car is below spec or there is a significant difference between sides, then new springs may be indicated.

 

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New leafs can be a crap shoot for rate and ride height so if you like yours keep em. I have 5 leafs and they feel soft to me - but they are not Eatons or a high quality brand.
Crap shoot for sure. I have new "stock" height 5 leaf. They are firm and sit higher than stock. Luckily I wanted some rake.
 

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New leafs can be a crap shoot {snip} IF {snip} they are not Eatons or a high quality brand.
Fixed it for ya

It also doesn't help when places sell "65-73" leafs, or "65-70 HD" coil springs. There isn't a single application from a '65 that is comparable to anything in a 73. There are also hundreds of different leaf and coil part numbers.
 

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Are you okay with "okay"? I don't think ever bottoming out is acceptable under normal driving. Does it have the stance and ride you want? For a modest investment, it can be juuuuuust riiiiiiiiight.
Not to hijack :pirate:your Thread, just want to take it little further...........
OKAY I'll bite, what's the investment and the parts? inquiring minds wanna know. I have new springs, what I mean by that is they have less than 200 miles on them but have been on the car for over 15 years. And today while driving I bottomed out. We have famously terrible roads in Houston. I also have a new set of Scott Drake leaf springs, I'll need to check if there 4 or 5 leaf - But maybe I'll want to go a different route.
 

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Discussion Starter · #9 · (Edited)
So, bottoming out is probably not the correct term, I should say very occasionally I will get rear tyre scrub through a fairly large dip in the road..

I'll get some pics of the springs after work and get some more advice..

Have read a lot of threads here regarding trying to choose the correct springs, and that's what concerns me..(not the $)

 

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Well, @tmadden, the springs may have 200 miles but they've been holding the rear end of the car all this time.
Modest investment is a few hundred bucks for new springs, shackle bushings and front eye bushings.
My springs have been on since 1993 and don't sag, and @watto1, I don't think tire scrub is ever good. I am running a 225/70/14 rear tire and mine never scrub, even with my wife and sons in the car going over bumps and bridges. Tire scrub is what made me go ahead and rebuild my entire suspension back in the day.
Most of what I read on here says the best stuff is from Eaton Spring or from OpenTracker, but some are just fine with off-shore stuff from Scott Drake , Summitt Racing, whatever.
 
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The axle should hit the bump stops before scrubbing the tires regardless of the springs. Springs can sag over time but the rate does not change. If you're OK with the current height and spring rate, keep your springs and look into a taller bump stop.
 

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That seems like fixing the symptom, not the problem.
When I was a teen and my rear end was sagging and my tires scrubbed on hard bumps, I was surprised my Dad said just put some longer shackles or air shocks on it. I saved the money and replaced every single suspension and steering component. It rode like a new car. And looked better, too. Those springs still riding fine.
 

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Discussion Starter · #13 ·
The axle should hit the bump stops before scrubbing the tires regardless of the springs. Springs can sag over time but the rate does not change. If you're OK with the current height and spring rate, keep your springs and look into a taller bump stop.
Agree, if running 14" rims.. 17" changes things a bit..
I do have recent new rubber on now, which, on reflection, I'm not sure has rubbed..
I do see cracked front rubber bushes tho..


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Discussion Starter · #14 ·
A few more pics for those in the know regarding springs..
Also, for info.. no lowering blocks, standard 16 Gal fuel tank..


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Those are the original springs, or exactly like them anyway. That type of rebound clip and tapered and rounded leaf end say so. Your ride height/stance looks good back there though. Assuming those are the originals they were an 85lb. rate, meaning it would only take 85lbs. of weight to deflect them 1" and they were the standard springs back then. The GT Equipment Group springs would have been 110lb. rate and new ones just like them, made of SAE-5160 steel (the best) are made by Eaton Detroit Spring and stocked/sold by NPD. Their part number is 5560-23. They run about 3 hundred smackers a pair and you will want new bushings, and I would get new shackles too as long as you're at it, you can get both in a kit.

There are many cheaper springs you can buy, no question. The principal difference is in steel grades. Eaton uses only 5160 from North American mills and it has a chromium content other springs lack. 5160 will perform better and last longer than any other grade.
 

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Discussion Starter · #18 ·
Those are the original springs, or exactly like them anyway. That type of rebound clip and tapered and rounded leaf end say so. Your ride height/stance looks good back there though. Assuming those are the originals they were an 85lb. rate, meaning it would only take 85lbs. of weight to deflect them 1" and they were the standard springs back then. The GT Equipment Group springs would have been 110lb. rate and new ones just like them, made of SAE-5160 steel (the best) are made by Eaton Detroit Spring and stocked/sold by NPD. Their part number is 5560-23.
Thanks 4ocious, that's good info, yeah, thought they might be original..
It started life as a 6cyl, were they supplied 85lb springs too?
I'll have to see if anyone in Australia stocks the Eaton springs, seems most retailers here have the Scott Drakes..


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Thanks 4ocious, that's good info, yeah, thought they might be original. It started life as a 6cyl, were they supplied 85lb springs too?
I'll have to see if anyone in Australia stocks the Eaton springs, seems most retailers here have the Scott Drakes..
As far as I know all the '65/66 mustangs came with 85lb. rate springs, unless it was a GT which wasn't an option for 6 cylinder mustangs of any body style. Drake springs are foreign made and those same springs are sold under other brand names too. The Drake name is simply stamped on 'em. At last report they are made of EN45a (also called 9260 but going from memory here) steel, an acceptable grade with a high silicon content but not as good as 5160, no chromium content.
 

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The axle should hit the bump stops before scrubbing the tires regardless of the springs. Springs can sag over time but the rate does not change. If you're OK with the current height and spring rate, keep your springs and look into a taller bump stop.
Agree, if running 14" rims.. 17" changes things a bit..
I do have recent new rubber on now, which, on reflection, I'm not sure has rubbed..
I do see cracked front rubber bushes tho..
The axle should hit the bump stops before scrubbing the tires regardless of the springs, wheels, tires, load, political leaning, music preference, favorite food, pets, etc.

Possibly this could be a non-issue if you go to higher rate springs. A properly sized bump stop allows a lighter spring rate if preferred.
 
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