Eaton leaf springs for a 71 429

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Jan 4, 2012
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My Car
1966 coupe - 347w
1971 Mach 1 - J code
1972 Mach 1 - Q code
G'day All, I want to lower [by 1'] and stiffen up the rear of my 71 429CJ a little, I was looking at the Grab-A-trak springs - 4.1/2 leaf 175lb/in. BUT the Eaton springs look like a better product,

My question is, my research tells me OME spring are rated at around 133-138lb/in [ so looking for somthing a tad stiffer] Eaton list their OEM replacement springs at 138 and their special 1' lowered spring at 138...

But the NPD catalog lists a Eaton 1' lowered spring for the 1971 Boss 351 rated at 152lb/in, Can anyone see or know of a reason why this spring wouldn't fit my 429 Mach 1??

Also they list different part numbers for car built before and after 10/09/70.. My car was built on 10/08/70 and released on 10/09/70 Can anyony tell me what the difference is in parts and compatabilty??

Any insight or help would be very much appreciated, I'm in Australia and the car is still in the USA, I'm trying to buy as much as possible for the car, to be shipped with it to OZ, as parts for 71-73 mustangs are very limited and hard to get over here..

Plenty of stuff for 64 1/2 to 70 tho...

Sep 30, 2010
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Mustang, OK.
My Car
1972 Mach 1 Q code
2007 GT
1969 Cougar Eliminator B302
CSX 7000 Shelby Cobra FIA
2020 Edge ST
2002 F250 V10
You are correct about Eaton being the better product and the look correct as well. Why do you want to increase the spring rate? Do you want it to handle better? More isn't always better. Invest in an email or phone call to Eaton Spring to benefit from their knowledge. Chuck

Sep 7, 2011
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Wake Forest, NC
My Car
1971 Sports Roof Fastback (early model)
1973 Coupe -Under rebuild/restore

I agree with c9zx! There is a lot more to just the engine size. Call Eaton Detroit Springs and talk to the tech dept. The leaf springs are designed to hold the car up while the shocks and sway bar do the handling.

mustang7173. :D