Hello everyone,
Simple question: are mustang and Cougar front coil springs the same? I emailed Espo spring about their cost for 600lb front coils, which are offered by many (Opentracker, Maier, SoT, ect…) for Mustangs, and the representative responded as if springs of that strength were unheard of… Which makes me wonder if there are any differences.
Btw, I know the leafs are longer, but does anyone know the original strength of one’s from a '69 XR-7 with AC, buckets, and a 351W? If you know that exactly, that’d be great. If not, ballparks are much appreciated.
Also, does anyone know a good place to get performance leafs around 165lb? The reason I ask for that strength instead of the lower 130-140lb range of the Competition Handling package is that I have personal experience in a mustang with a pair of Maier 165lb leafs in the back… I was stunned.
Mustang springs are physically the same, not sure about the ratings. The reason (I understand) that 620 lb (the common performance spring rating) is unheard of is that it is a misnomer. That rating is for BOTH springs together. Was Espo talking more in the range of 310 lbs? If yes, this is why.
Espo is more of an OEM type spring maker to my knowledge.
Any reason you are not just going with Grab-A-Tracks? That’s what I run and they are great.
Regarding rear springs, I bought and installed Espo comp handling units early this year. They too are great. Espo is much more reasonable than Eaton and they are ALMOST concours correct although they do not pass muster in that regard to my discriminating eye. For the price though, I like them, a lot.
Thanks for the info 1969XR7Vert, that makes more sense.
I’m not really one to care about concours, or really correctness at all… What can I say, I grew up around the best pro-touring '69 Mustang I know of!
Bearing that in mind, does anyone know of any place to get leaf springs in the 140-160lb range that are cheaper than that?
It may be a long shot, but is there an industrial spring supply in your area?
When I first got my '69 Eliminator, back in '83 or so, it was jacked up with the air shocks and rear spring shackles that were so common in the era. I couldn’t wait to get rid of them, but unfortunately the rear springs had sagged so badly that the shackles were necessary just to keep the car level. Being a dirt-poor college student unable to afford reproduction springs, I wound up at “City Spring” in nearby Oklahoma City. They were (and still are to my knowledge) primarily a truck/industrial spring supplier, in a gritty part of town. But they could make any sort of spring. I knew the place because, growing up on a farm, we’d used them for replacement springs for ancient hay wagons and such. I took them the springs off one side to look at, and a set of specs from the shop manual for the springs I wanted (for a CJ 4-speed hardtop, as I recall) and they made them right up. 30-odd years later, they’re still working great. Less than half the cost of “repo” springs, IIRC.
Whether places that do that kind of work at bargain basement prices still exist, I don’t know. But worth a try.
One source of confusion is that the spring number given is the spring diameter, not a weight rating.
#620 coil springs are .620 inches in diameter. In my '67 390, those were on the floor, but the big block (BB) ones worked great, and they are around .750 diameter (#750). Most suppliers say for the 351 you can go either way.
Went looking for information on this but nothing so far. I still think they are 620 lb (but have been wrong many times before!), can you cite a source Greg?
We offer stock replacement springs, two types of performance coil springs and progressive rate coil springs. > The terms used on the market today like 620 and 720 are not the spring rate. It is the diameter of the coil itself. > Upon testing various competitor’s spring rates, they are far less in actuality than what they’re advertised. Depending on the way they’re manufactured and number of coils, a 720 spring could actually be a lower spring rate than a 620. 1967-1973 Mustang cars can use the performance 65-66 springs for an approximate 2" drop.
Their ‘Progressive Springs’ were either mis-boxed or all wrong. I sent them back, and got the BB springs at W.C.C.C., but they all come from the same place. (They all had Scott Drake stickers and similar P/N schemes (BB, PR, etc) I measured them at around .750".
It does seem that many suppliers list the ‘620’ spring as a 620lb/in rate. Equally confusing is that the spring actually measures .620 in diameter.
Since I have an extra pair lying around I thought I would do the spring rate calculation on it, to see if the math explained anything.
(I put these in under the 390, and they were 1"drop springs, so it sat on the floor and was spongy to boot)
This spring has 8 and 1/8th active coils, a 5" outside coil diameter (4.38 Mean Diameter) and a .620 wire diameter, which yields a rate of 305lbs/in
The .750 diameter spring comes closer to being the actual spring rate (same numbers on coils and loop size) with a figure of 713lbs/in, so here we can see why they might use the diameter and rate numbers interchangeably.
Most steel has the same ‘springiness’ (modulus of rigidity), and mostly replacement springs have to be the same diameter, so the best way to change the rate is wire size or number of coils. Removing a coil makes the spring a bit stiffer, but only by a small amount (50lbs/in per coil in the .620 example), so wire diameter becomes the indicator of spring rate difference, all other factors being mostly constant.
I chose the stiffer ones (#8356, 0.65" bar diam. rated 418 Lbs/inch; #8330 are softer with 0.62" bar diam. rated 295 Lbs/inch).
These ratings seem to kind of match with Devildog’s maths.
