5000 rear-end suspension upgrade

I am going to committee here for feedback on how best to upgrade my 5000's rear-end suspension. If anyone has upgraded with success please let me know the improvements you added and or parts setup.

Here is what I am starting with...

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I will appreciate any and all feedback-
Dan
Seattle

Hi Dan,
Have the same set up as yours and am happy enough with it for the kind of driving we do for the last 15 years. What are your goals for the type upgrades you want to do ? The later MX with the 4 link (?)and coil set up might be the easiest. Will require fitting and welding but there are a bunch of them out there to use as a guide. If someone on this forum will chime in with their thoughts I would also be interested if there is a real advantage. I did notice a difference when a got better tires, but we don't drive on the edge much.

Dan, I have already shared pics of my project with you, but if you don't want to get that deep into it, I have a few suggestions for easier improvements.

It appears from the picture you posted that you have the optional "3rd" link traction bar on the top of the rearend (hard to tell).  This should help, but there is a problem with it. If you have the Mustang II rear springs, then you have very large and soft rubber bushings in the front of the springs. These big mushy bushings deflect under the power of a V8 (especially with better tires) and cause the car to do strange things under hard acceleration. Mine would pull very hard to the left under full throttle starts requiring driver correction. If I wasn't careful to un-correct before chopping the throttle, the car would dart suddenly to the right. My car drove fine if all you wanted to do was get from point A to point B, but ask it to do something a sports car should do and it was very uncooperative.  

Before I went overboard on my rebuild, I was considering contacting a spring company like Eaton Detroit Spring and checking on some replacement springs with smaller bushings. Another option in this area would be to have some steel or aluminum sleeves made for the front spring eyes that would allow you to use a smaller rubber or poly bushing. Building the spring pack with half-leafs in the front section of the leaf will stiffen the setup and help with wrap up under acceleration. Mopar did this in some of their muscle cars from the 60's.

I was also looking at Cal-Trak type traction bars. My car did not have the upper link that yours appears to and I needed better traction. The Cal-Traks are said to be the most effective leaf spring traction bars out there since they just about completely eliminate spring flex or wrap up. They can also be carefully adjusted to not effect ride quality too much. I'm sure that for a Sebring, they would be a full custom build.

Fully adjustable shocks at all 4 corners will make a big improvement in both ride and handling. The shocks from Viking are made in the USA and are adjustable for both compression and rebound. They are about the most reasonably priced double adjustable shocks I have found and will be under my car when it's finished.

There are bolt on coil over conversions for the front suspension that are intended for the street rod market. A lot of street rods use Mustang II based front suspension, so the aftermarket has stepped up with a lot of high performance stuff. Everything from tubular upper and lower control arms to massive brakes. There is a fellow on here that goes by DrJ that has upgraded his front. Hopefully, he'll chime in with specifics.

As to upgrading to the Fox Mustang rear suspension that's under the MX. It would require pretty much disassembling the rear half of the body down to the frame to do right. That's why I went custom. There were better options for just a little more work. Well, a lot more work actually. Also, the Sebring body is narrower in the rear than the MX, so your wheel and tire options would be even more limited than with a regular 5000. Of course, you could always add even wider rear fender flares.

Not sure about a rear sway bar for a 5000 with leaf springs. There was a Cobra version of the Mustang II that might have had one that could be adapted.

Sorry for the long post.

I appreciate the dialogue....

What I am interested in is increasing the cars performance. I guess my thinking is suspension or maybe even (disc) brakes could be a start.

I attempted to upload a cleaned up version of the work I did, analysis included. If the upload worked (tech challenged at birth) you can digest the entire document which spells out why I did what I did or you can go to the summery at the end which lists the parts and part numbers I used. It has all worked out pretty well. The ride on mine, which was the primary problem, is much improved. Handling is as good as anything I will ever need short of competitive racing. The anti-dive I incorporated into the fabricated front upper control arm attachment mounts (thanks Hotrod), has solved the pronounced nose dive that had occurred during hard braking.

My car came with the typical 9" Mustang II front discs and the drum rears. I upgraded the fronts to a SSBC 11" disc with a 90mm piston, and purchased semi-metallic rear shoes at the rear. Went on to order new drums that are cross drilled so as to help eliminate the off gassing that occurred on drum brakes. From what I read, the off gassing is what is mostly responsible for fading. Regardless I am if anything over braked now. If I hit the pedal to hard it will launch me over the windshield. My approach was cheep and cheerful and stopping her is no problem. I had also replaced the booster and master when I did all that. Switching to a larger bore master would probably reduce the pedal sensitivity. A new master costs 125 bucks or so. I am moving on to a new project and will be selling mine this year so the master may end up being a decision for the next enthusiast.

If my document did not come up just PM me with your email address and I send it to you or anyone else that's interested. I have pictures for a lot of these mods I can send as well.

OK so the attachment did not work because of it's size. PM me if you like and I'll send it to you.

My 302 Austin Healey MX goes very well in a straight line on smooth asphalt, but that's about it.  Very scary over 60 mph.  So the first project is to get power steering [separate topic].

Current front/rear suspension is horrible.  I have 4 link/coil in rear and Mustang II up front.  Without doing a ton of research, I'm thinking coil over shock set up for the front [adjustable].  For the rear, I think I will have to change the coil springs to longer, softer ones.  I see Dr. J's calculations for 110 lb per inch.  But it seems he left out the placement of the coil midway down the trailing arm [geometry] and the effect of shock dampening.  Nowhere on this site can I find the OEM rear replacement shock brand/model [to give me a reference point, especially dampening characteristics].

Why all the references to the Fox Mustang rear suspension?  True it is a "similar" 4 link coil setup but Fox suspension retailers don't support Mustangs prior to 1979.  And my chassis is 1978 with the old leaf springs removed.

I trying not to make a career out of this.

It took me a while to figure out what you have, because your post says "lead springs removed."
Once I figured it was meant to say "leaf" I have to ask why this was done and how ? The "scary over 60"
statement leads me to believe it wasn't done properly. I've had mine over 100 many times with no ill effects at all and is also from a '78 with the standard leaf springs. Handles well for what it is. Maybe going back to stock could be consider and is pretty inexpensive.