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Leaf spring rate recommendations

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dan0R30 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dan0R30 Quote  Post ReplyReply Direct Link To This Post Topic: Leaf spring rate recommendations
    Posted: 25-July-2020 at 3:01AM
I've been comparing various replacement rear leaf springs for my '70 Torino 2drHT, and I'm seeing numbers all over the map. At a high level, it looks like members here have used both Eaton Detroit Springs and General Spring KC with good results. The TLDR, what's your preferred spring rate? But to work through the ordering process for my vehicle/project, please keep reading!

Eaton appears to be more OEM matched (hence the MANY part numbers for different model/engine combos), while General KC offers options for a standard, convertible, or a GT/convertible with a 429 motor. Eaton only appears to list spring rates, but General additionally provides the spring capacity. I think this is where the differences in part numbers are possibly abstracted by Eaton, since all the factory leaf springs I believe are interchangeable between models regarding fitment...  I could be wrong here.

I currently have the factory 351C motor, and both companies offer a standard duty 94 lbs/in spring rate. Eaton also offers increments of 119 and 195 here (in addition to ride height). Since I am planning on swapping my 351C with my 429/460 block, I noticed that  the Eaton part numbers for a 429 are different for the same spring rates of 94 and 119 (they do not offer an option for 195). Again, are the actual part numbers differences due to spring capacity or are the fitment/dimensions actually different? Comparatively, General KC's 429 motor option is only 195 lbs/in (opposite of Eaton!), and they also have 100lb less capacity than the standard duty. Fastbacks/sportsroof models weigh more than the hardtop so this seems opposite to me... moving on...

I then decided to change my body style to the Torino Cobra on Eaton's site, and now I get another unique option which is a spring rate of 211 lbs/in (same P/N for all various 429 motors). I know the Cobras are a fastback body, so perhaps I could believe that the fitment is actually different here, but I am suspect of that that.

Assuming that all these options really will install on my 2drHT, I think it just comes down to the spring rate for me; hence the handling and comfort level. I don't plan on having filling every seat so the total capacity factor may not be of real interest.

If I am mistaken in any of this, please correct me! Otherwise, back to the original question: what spring rates have you all tried and how do you like them?
Dan

1970 Ford Torino 2drHT - Original 351C 4V - FMX - 9" 3.00
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 25-July-2020 at 10:05AM
When I have a chance, I will look up the springs in the Ford parts catalog and see if the original rates are listed.  The problem with aftermarket springs is that they consolidate springs.  For example they will make one part number cover three OEM springs.  So often times, the after market springs aren't exactly as the OEM springs are.

As for the spring rate, a lot of that will depend on your goals for the car. What will it be, a smooth riding cruiser, a street strip car, or built for best handling?  Also what are your front springs?  You want to match the front and rear springs to some degree.  If you have super stiff rear springs and soft front springs, your going to end up with a handling mess.

I have never messed with spring rates on a 1970-71 Torino, but from my experience with the later cars,  I would think that the 94 lb/in springs would be very soft and boaty while the 195 in/lb springs would be very stiff, something that a station wagon would have used.  My '72 uses coil springs but it is similar in weight to a 70.  I had run 183 in/lb springs and found them too stiff.  The rear end hopped and it was too easy to induce oversteer.  I went down to a 158 in/lb spring and found it much better. With poly bushings and a rear sway bar, the handling is great and the ride is still firm, but not hopping about on rough roads.


Vince

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Post Options Post Options   Thanks (0) Thanks(0)   Quote dan0R30 Quote  Post ReplyReply Direct Link To This Post Posted: 25-July-2020 at 1:26PM
Vince, thanks for your input. Please let me know what the catalogs say when you are able to get a chance!

To answer your questions (great follow-up by the way), I am looking to build mostly a mean street cruiser that can be taken to the drag strip for some occasional fun. So I won't be concerned as much about taking a hard corner as opposed to a good launch, if I had to choose. 

As for the front coil springs, they are most likely stock from what I can tell. I am planning on replacing them with stiffer springs when I swap the motor, but you bring up a good point about the mismatch. It may be worth replacing now along with the leaf springs, since I plan to drive it on the street while I take my time building the 429.

The 94 lbs/in springs don't sound too different than my current worn-out springs! Wink  Perhaps at minimum the 119 will be a decent option for me. I'll have to keep looking around, since the next jump from both of these vendors is 195 lbs/in.
Dan

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 26-July-2020 at 10:15AM
Hey Dan, 

so I checked the Parts Catalog and as I suspected there were quite a number of options through Ford from the factory.  There were a total of 14 springs offered in 1970 Torinos, including station wagon springs.  Eliminating the springs used only on station wagons, that leaves 8 part numbers.  See them listed in these charts below:





From the parts catalog, it looks like the 429 base suspension cars had a spring specific to them.  The numbers in brackets are the body styles, with 63 being the fastback models (station wagons are all the 70's).  

63C = Torino Fastback
63F = Torino GT
63H = Torino Cobra

Unfortunately, there is no spring rates listed from Ford. All they list is the load rate, which basically is the load the spring was designed to carry.  Generally, all else equal, a higher load rate would equate a higher spring rate, but since all else is rarely equal, this may not always be the case.

To decipher this info into a more readable format, here is what you have for 1970 fastback cars only:

Base Torino with 6 cylinder or 302 - C9OZ 5560-C - 645 lb load rate spring
Base Torino with 351 or 429, Torino GT with 351 - C9OZ 5560-D - 677 lb load rate spring
Torino GT and Torino Cobra with 429 (except CJ) - D0OZ 5560-C - 660 lb load rate spring
Base Torino HD spring (except 429) - C9OZ 5560-M - 740 lb load rate spring
Base Torino 351-4V, Torino GT (except 429) HD Spring - C9OZ 5560-R - 780 lb load rate spring

I am not sure if this info helps you or not, I hope it does.  I would think with your goals in mind you'd want a fairly stiff rear spring, but not so stiff that it hampers the ride or the launch on the strip.  Too soft and you might have wheel hop issues.  The one difference with your car over a 4 link coil suspension is the leaf spring cars won't have the binding effect of the 4 link adding to the spring rate.  So maybe you will have to go up the the 195 in/lb springs to meet your goals, since the other options seem really soft to me.

Hopefully some of the 70-71 owners chime in for you one what they are running.  Good luck.






Vince

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Post Options Post Options   Thanks (0) Thanks(0)   Quote dan0R30 Quote  Post ReplyReply Direct Link To This Post Posted: 26-July-2020 at 2:45PM
Thank you Vince, this is great! I appreciate you taking the time to look through this. I've been looking over it as well after you posted it. If I throw my body code into the mix (65C) and my factory motor (351C-4V), it looks like it should have had the 677 lb load rate (C9OZ 5560 D). For whatever reason (perhaps being it wasn't a "performance" body style), it didn't use the HD spring option like they did for the fastback/cobra.

What it does confirm for me though is that since the fastback w/ 429 (non-CJ) also used the 677 lb load rate, I should be able to install the fastback's HD springs no problem (i.e. my assumption earlier about the fitment between a hardtop and fastback).

With this information, I am inferring that Eaton's 94 and 119 lbs/in spring rates roughly translate to the 645 and 677 load rates, so the 119 would be closer to what was installed in my model Torino from the factory. The 195 lbs/in looks to be the 740 lb HD load rate, and finally the 211 lbs/in may be equivalent to the Torino Cobras and GTs that were advertised as performance models.

Until any other 70/71 owners have some input, I'm leaning towards the 195 lbs/in spring rate. Thanks again for your input!
Dan

1970 Ford Torino 2drHT - Original 351C 4V - FMX - 9" 3.00
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Wubbington Quote  Post ReplyReply Direct Link To This Post Posted: 02-May-2022 at 12:40AM
Did you ever settle on springs? I'm trying to figure out what to put in my 71 302 formal roof.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dan0R30 Quote  Post ReplyReply Direct Link To This Post Posted: 02-May-2022 at 4:38AM
I did, but I realize now that I put my decision/updates in my other project thread instead of here.  I went with the Eaton extra heavy duty springs (195 lbs/in) with a +1" lift to get my desired rake. I decided to stick with rebuilding my 351C instead of converting to the 429, so I just used the part numbers for the 351. The springs took a couple weeks to ship (made to order), but they are great and the ride was just what I was hoping for! The one issue I ran into was with their install kit. The front eye bolt was WAY too long. I used my old bolt with the new nut, but I was still surprised by it.









And welcome to the forum!
Dan

1970 Ford Torino 2drHT - Original 351C 4V - FMX - 9" 3.00
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