rear spring and shock

Morning,

Been away for a few weeks, so now getting back to the car project. We picked up our rebuilt 302 from my Speedy Racing Engines yesterday, looks awesome in black and red, now to go shopping for performance parts!

We're also working on completing the rear suspension so we can get wheels on etc etc.

Question: We've gone with the 4 link hook up in the rear on a ford 8.8 rear end, I've been looking at coil and spring options, but not sure what height I should go with as we don't have wheels and weight on the car. What have others used?

I'm thinking of a medium spring - 110lbs range with a QA1 double adjustable shock 13" compressed, 20.5" extended?

Cheers in advance,

Mark

i have the same set-up and went with the air bag for the same reason. not sure how light the rear is and its adjustable. I am not done with my build so dont have info on how it works

Measured unsprung weight Drivers side on mine was 152.25 lbs; Passengers side at 148.50 lbs. Sprung weight was 487.75 drivers; 420.50 passengers. I removed the separate OEM spring (spring rate undetermined) and shock, fabricated and welded in attachment points for coil-overs. Used Vi-King units (double adjustable) with 12" 110 lb/ft spring rate.
You want to use a spring in the rear that has a higher natural frequency than the front spring. Doing that minimizes pitching which is an undesirable ride characteristic.
I converted the front as well on mine to compliment the rear. When purchased my MX had the ride characteristics of a Mac Truck. Substantially better ride now. The short wheel base is another ride issue with our cars but there is nothing to be done about that.

I am working on my rear suspension. It is a Ford 9 inch rear end. Rear end is a little wider than it should, therefore the tires that I have in the rear stick out a wee bit too much. Tire size is 255-60-R15. This axle came off a 79 Lincoln Versaille. It came with disc brakes. I need a smaller tire size and I hope this solves the problem. Thinking of replacing Mustang coil spring to "coil overs". Need advice.

Will try, what questions specifically?

What I need, before I can go any further is the exact part numbers QA 1 coil overs. I think if I can adjust the height up or down, I'd be good to go. I don't want to guess as I depend on a shop to do the work. I assume there are members who have gone through this or want to. Anyway, I could listen to anyone who knows from their experience. I talked to QA1 techs and they want more info as this is more or less a custom setup. Thanking you in advance. Sorry I was so late in responding. Tony McFarland, WI 608/ 838-1106.

I went with Vi-king coil overs because they have a working relation with Gayle Bridges who has access to springs the rate of which met my specifications. He is also super knowledgeable and helpful (read that as patient...I was new to suspension engineering when I started this project). Anyway I believe Vi-king was started by former QA1 guys. I liked the fact that their units are adjustable in both bump and rebound. Being coilovers they all permit ride height adjust-ability. Give them a look/call and if any of that works for you I can give you the part specifications and numbers. Just got back with mine from a 1,200 mile tour of the Adirondack mountains, the subject of a piece I will write up and post. Spoiler Alert...she came back on four wheels and not a flat bed!

Thank you D. J. I talked to the tech guy at Fabquest today and got a little more info. He gave me some basic specks, depending on the measurements, I'm going to give him. Thanks again, I'll let you know.

So I'm stuck with the rear suspension. Called jegs and they asked if its a stock rear shock and spring sizing form the 89 mustang with the two eyelet pickup or i need something else and to measure the size? I literately have the frame on axle stands, so not sure what to measure, do I go with a single adjustable stocker star - compressed height at 13.5" and extend to 21" then a coil spring of some size......ideas?

When I dissembled my 4-link coil spring rear this is what I found:
OEM Springs: .50" od wire with slight taper down to 5/16" on the last two coils
Overall length out of the car was (D) 13" (P) 12.5", due to age probably
OD of spring: 4.75"
ID of spring: 3.75"

Sprung weight rear: (D) 487.75 lbs (P) 420.50 lbs, that with a (Ford 8" posi)

OEM Shocks: Brand and numbers missing
Out of car and measured eye to eye
Extension: 16"
Compressed: 12.5"

Now with all that said it is generally accepted that the OEM specifications for the MX was stiff and harsh, mine certainly was. Converting to coilovers generates the flexibility to adjust the ride height, the shocks stiffness in one or both functions depending on which one you go with and it opens the door to selecting softer springs more commensurate to the cars actual sprung weight. It also allows you to establish the proper natural frequency for the springs, the car itself and one another (front vs rear). By doing this you can engineer out a lot of the OEM's shortcomings. One should accept that there are going to be limitations on how well a car with a short wheel base and a live axle is going to drive. It will never be a Miata, but it does not have to shake the fillings out of your teeth either. Mine no longer does.

fantastic DrJ! that really helps us out over here.

This is what I needed. Thanks for all your help. Tony

I have a few more questions
1. Regarding mounting of new coilover. Is it mounted where the existing coil spring is now?
2. Does the replacement coilover assembly be mounted where the existing shock Is?

Thanks a lot TONY

P.S. Do any members live in the Madison, Wisconsin area?

The OEM rear spring is nested between the trailing arm and a perch mounted to the frame rail. That real estate could be modified to accept a coil over. I chose to abandon that location and fabricate/weld in mounting points just aft of the axle using 3/16" channel. I did that to create a structure where the mounting bolt is in double shear at both ends. That may have been overkill but I am pretty sure that it is not going anywhere. I have pictures which I could try to email to you, having a little tech trouble with my laptop lately. PM me with your email address and I will try to get you what I have if interested. There are other way's to do it. If you are OK with the sprung corner weights I gave you being similar to yours, you could divide them by the spring rate of the springs you intend to use. That would give you the static compression. ex: an average rear corner sprung weight of 450 lbs and a 110 lbs/inch spring that has an unloaded length of 12" ends up being compressed down to 8" in the car under that load. The shock should be adjusted so as to allow 60% of it's travel be available for "bump", 40% for rebound. The adjustable lower spring saddle will allow you to tune that in once installed. So with all that in mind you mock up the rear so that the rear tire is where you want it relative to the fender well, you make sure that there is acceptable clearance between the top of the axle and the rubber bump stop on the frame rail at rest (because the bump stop is what will limit your travel in bump, not the shock as that could damage it). You determine the length of your coil-over, shock eye to shock eye, in its statically compressed length and you mark where the mounting bolt holes on your brackets need to be positioned for welding. That should get you close and adjusting the spring should get you home.

So we have our QA1 spring and QA1 shock (which can be adjustable) but we decided that we would mount the spring into the upper and lower rear control arm, and mount the shock using upper and lower eyelets from the rear of the axle up into the frame mount. This will require us rotating the lower shock pick up so its angled slightly to mate up with the frame. If that makes any sense! LOL.....I have attached an image showing what I'm thinking. What is missing from the image is the attachment point the upper part of the spring sits in. Its a bracket with a 4" diameter circular cupe which the spring is supposed to sit inside.

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I'm upgrading my 1988 MX rear suspension too.  It is a CR OEM 4 link with a "pan hard bar" and what appears to be progressive coils.  The shocks are cheap Monroes #32191.  I wear a kidney belt over 40 mph ;0]  And Marilou refuses to ride with me.

I think the OEM copied the Fox Mustang 4 link TRX suspension from 1979 - 1984.  But it was modified for the Mustang II chassis [circa 1974-1978].  So my lower trailing arms are heavy production stampings that look like the Fox Mustang's.  My upper control arms are very short [6"] and tubular as is the pan bar.  And crude.  Functional but certainly not pretty [like the photo above].  A graduate from Welding 101?  The arms actually bind and keep the 8" axle from hitting the floor of my garage when body is raised [tires & shocks off].  But I'm keeping all the various "arms".  Just blasted and primed the lower control arm last night.  Yellow, just like the OEM.

I have to recommend using an air chisel fitted with these 1/8" diameter rods [about 12 of them] that reside in a steel cylinder.  A great alternative to sand blasting [a dreaded mess, sand everywhere].  The actuated rods just destroy rust and paint.  Really works great on the bottom side of your mower deck too.  Northern Tool I think sells the attachment.

Enough for now.  Marilou said if I get my butt moving on this rear suspension issue then she would wear that short, tight black leather skirt and heels for a "soft" ride...

Fox Mustang TRX Suspension similar to Sebring MX:
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SEE:
See
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My Sebring MX:

I typed this all up yesterday but don't see here this morning....did I forget to 'send' it?  Did it get deleted for some reason?
I dunno but I'll re-do it as there may be some useful info  for someone.

My MX rode so bad I was afraid I was going to crack the windshield!  So took some measurements on the existing 250# springs, 11.625" free height, 8.750" loaded height.
Difference of 2.875" X 250# spring rate = 718.75# per spring for a total rear end sprung weight of 1437.5#.
This seems very heavy to me as the whole car only weights 2440#...and considerably heavier than what Dr J determined with his car.  I only took one measurement and this could account for some error but I wouldn't think that much.
Anyway, that's what I got so going with those specs I sent the spring off to have a pair of new coils made.  They came back with 167# variable rate springs, 13.8" free height, 9.5" design loaded height.
The car sits about 2" inches higher with no passengers and the ride is 150% better!  The short wheelbase is still responsible for some porpoising but overall, nothing like it was before.

Dannymax
Your move from 250 to 167 lb springs was is the right direction.  But they are variable rate springs so the first 2 inches of travel are far less than 167.  After 2 inches you get into the hard stuff [my opinion].  I think Dr. J calcs and 110 lb spring selection are pretty close.

I need to finish my post above yours but not today.  I put 90 lb Moogs on the rear.  But they are constant rate springs.  They are long so I have quite a bit of pre-load.  I gained about an 1 1/2" of height too.  Now it matches the front fender clearance.  I put adjustable AGX KYB shocks on the rear and set the dial at 3 out of 10 positions.  Rear end is much softer now.  But the front end is killer.

John,
I don't think my sprung rear end weight is accurate, don't see how it can be. But the proof is on the blacktop and the darn thing really rides and handles well. My wife and I are both very pleased with the result.

For now I don't see any changes on the horizon but should that change, as things often do, I agree with you that the direction to go in has been successfully identified.

By the way, I have non adjustable, low end, KYB gas shocks and surprisingly they seem to work really well with these springs.