darrenhill39

I feel that my stock rear springs have become a bit "weak" after 148,000 miles and would like to replace them. Unfortunately they are discontinued by Ford and I can not find factory replacements with the same spring rate. None of aftermarket springs seem to differentiate the convertible from the sedan, despite it being at least a couple hundred pounds heavier right over the rear axle. Does any one have good information about replacements or has anyone good experience with replacing theirs? Thanks.

Bert

hmmmmm . . . I would be very surprised if the springs have actually "worn out" but I guess it is possible; more likely it is the shocks that are worn out

if you can find a reference on line, compare the part numbers to the GT500 springs; they might be the same because the GT500 is a bit heavier also (but GT500 is mostly heavier in the front)

I'm thinking a set of take-off GT500 or regular GT springs will probably get you close, and can be had very cheap if you watch your local Craig's List and check E-Bay

tbear853

More likely it's the shocks worn out. They'll let the car bottom on the stoppers easier and OEM Mustangs don't have an abundance of room between the axle and bump stops anyway.

My question, does or did Ford even use different springs for these GTs, whether coupe or convertible?

houtex

Howdy darrin. Welcome to the forums!

Yeah, another vote for the shocks, maybe the suspension parts. Rear springs, even on a vert, shouldn't wear out that quick... They'll settle, and eventually over a LOOOONG period of time will start to sag, but... yeah, not this early. It's way more likely you need suspension work.

That said, here's your rear coil springs, potentially. At least part numbers to chase on Ebay or whatever.
https://www.fordpartsgiant.com/parts...8602)&pnc=5560

Bear... yes. See that link, and look at the many springs. The first two are coupes, the third is convertible, and then back and forth from there. I suspect various special models like Cobra or Shelby GT or such. In any event, yes, yes they did.

And I knew this because of my investigation into the shocks. Turns out that Ford made *four* different sets of shocks for their prime models of Mustang: V6, V6 Convertible, GT, GT Convertible. Not including Shelby GT or GT500s or such. And you might ask 'why?!'. Well, I have no idea. My *suspicion* is that they're tuned to a certain ride height, and outside of that range they are simply no good. It's a fantastic shock, seems, when new and you don't mess with things...

I found it out the hard way by not changing the shocks out on Awesome when I put on the 1" lower Ford P springs. The shocks were fine at the time. I figured "they're still good, they're shocks, they'll stop the bouncing just like they oughtta." Well, no. Immediately the shocks were definitely NOT up to the challenge. I then looked into the situation, found the above to be true on the four different sets, put 2+2 together and probably got 5, but close enough.

I put up with it for a while, but then I got tired of overly bouncy pavement ride and bottoming out on speed bumps, and put the orange Konis on. MUCH better, they don't care about where the car's riding, they just wanna stop the bouncin'/jouncin'. I hardly ever hit a speed bump and definitely the pavement ride is smoooth.

As far as swapping for non-V6 Convertible springs... careful. The ride height from the V6 to a GT to a GT500 would likely change... and probably change upwards. Which, to me, makes the car look fast standing still, all nose pointy down like a cat gonna pounce on something... So I'm in, do it, but only on them rear ones. Front one, cut a coil or two. MAN. That car's gonna look aggressive as (insert aggressive type thing here).

In case any of that helps anyone, there ya go!

VGMStudios

They made 4 different springs because of the weight differences of each car. V6 are cast iron engines while v8 are aluminum. The rears tho should be relatively the same for each.
Too bad the V6 springs are discontinued.

tbear853

And now I know, Thank You Sir.

I cut mine a full coil plus an inch off the top, applied some rubber seats, which stiffens the rate fubar probably, but I couldn't tell it except when looking at that rear fender gap.
.

darrenhill39

Thank you much for all the information! I have replaced the struts, shocks, upper/lower rear control arms, both sway bars including end links and bushings. The "offending" spring seems to be on the drivers side which seems softer than the right. I wonder if after 148000 miles carrying the extra (shared) 180 lbs of the convertible combined with my 230 lbs (for a total of 320 lbs) has "sagged" as it sits 1/4 lower on drivers side and wgen I get it I can almost feel it "tilt". It is a possibility that I am just being a bit over critical.

darrenhill39

Thanks for the idea, I will make an effort to make an educated decision about swapping these out.

tbear853

1/4" ain't huge.

darrenhill39

True that, however, when I sit in it I'm at 1/2 and the "feeling" I get is slushy, for the lack of a better term. Maybe I'm expecting too much.

tbear853

I've set in and drove "slushy" feeling cars, worn out old police cars relegated to training, high miles, shot shocks, 4 of us troopers in there, chasing each other on the track, I know the feeling. Our '08 GT feels nothing near like "slushy", but ours has under 33,xxx miles. Maybe you do have a weak spring or two ... and maybe I just haven't reached that point with ours yet?

There is room in the rear coils for Air-Lift bags as I recall, I have them in my Mercury GM. They don't raise a car much, an inch if pumped up maybe, but can be adjusted to compensate for loading, etc as they really just stiffen the spring from compression loads. At 0 psi with no load, like not there as long as the valve stem is "out" so they can "exhaust" on bumps, but just putting the valve core in causes them to stiffen up on bumps (imagine if you will, a half inflated balloon, you squeeze it and it swells else where but these are inside coils of steel, your springs) and loads that would normally drop the rear just ride good & level at 8-10 psi. I pumped them to 25 psi once just for "Sh*ts & Gr*ns", it barely raised the car but it was like riding with wooden blocks instead of springs, it was "rock hard" unloaded.. The ones in our Mercury are 18 years old, red poly bags (not rubber that cracks) , been across country a few times, I've towed with them a few times, have had so much luggage in trunk had to compress clothes on top as shutting it. I've hauled several hundred pounds of bagged wood pellets or water softener pellets in the deep huge trunk from an hour or more away with just 12-15 psi with no sag. I do like about 5-8 psi if carrying four adults (in the passenger comp). .

I have them plumbed with a tee and then the line from tee to rear fill valve is 3/8" garden hose (35 is max psi in bags anyway) to another tee where I have a shrader valve, and a 3/8" copper exhaust that I block off with a bolt in use if carrying a load.

I recall a fellow here once took his whole family on a long long tour of the US, toured Rt 66, etc ... using two S197 Mustangs for them all & luggage, he run air bags in one of them as I recall.
Air Lift 1000 series # 60841.

2008 Ford Mustang Air Bag Suspension Kits | Air Lift Company