Rear Coli Overs

[Grande]

Hey guys, a question concerning rear coil overs. I built my FFR Mark 4 using a 1995 donor, rear solid diff and rear donor coils setup. I did like the ride for what i use the car for, a daily road driver. But I decided to go rear coil overs and new control arms to clean up the look and hopefully get a better ride. A few concerns, I had to mount them body side down otherwise they touch calipers, which seems like it isnt a big deal. Which upper mount holes are used , pic shows upper holes but manual states lower holes. Also the ride is so unpleasant it bounces me out of car. I used the recommended 350 pounds coils. So any suggestions on these questions,1 - which coil recommended for daily acceptable ride (loved the donor ride) 2 - which upper mount hole to use?, 3 - I removed the quad shocks otherwise touch, big deal? , Thanks.

[CraigS]

First what brand are the coilovers? If they are FFR Konis, did you check that they were on their softest setting before installing them? Go to 200-250 springs. You may get more wheel hop w/o the quad shocks. Also check if you mounted them in the other direction would that give enough clearance?

[OSU Cowboy]

From my own experience - I highly recommend the rear lower control arms from Breeze Automotive with the heim joints.

When we first got our MK3.1 on the road - the ride was pretty harsh. I spoke with Mark at Breeze, was going to get softer springs and QA1 adjustable shocks along with the lower control arms. He was out of stock on the shocks at the time - so I went with just his lower control arms to see what difference that would make. It was a night and day difference. Running the Koni's and springs from FFR, along with those heim joint lower rear control arms, transformed the ride from harsh to what I think is very reasonable for the sort of car this is.

[PG_Cobra]

What control arms did you fit? Is your setup 3 link or 4 link?
If its 4 link you may have a serious binding problem if you have hard urethane bushes in the control arms.

This write up from Maximum Motorsports explains what hard urethane bushes do to a Mustang 4 link:

https://www.maximummotorsports.com/Adjustable-Rear-Swaybar-solid-axle-Mustang-1979-2004-P546.aspx

Select "Instructions" and open the pdf

[Grande]

Thanks for replies, I will clarify, Yes they are Konis from Factory Five, Craig I see no adjustment on my konis, . I have 4 link from donor setup, and Factory Five new lower aluminum control arms. I removed quad shocks for clearance. They also mention that the calipers should be swapped from left to right in order to fit the coil overs in the manner the manual states. I did not swap calipers, simply inversed coils direction. Thanks

[AC Bill]

I wonder what the spring rating on the donor coil springs were, after however many miles may have been put on them? I believe the 94 Mustang stock rear springs when new, were variable type (progressive), starting at a pretty low 165 lbs, and a maximum of 250 lbs. So new 350 lbs springs on a lighter car would make for a pretty stiff ride, when you're not used to it. it. The stiffer ride really enhances the performance handling, but might not be everyone's cup of tea.
The Koni coil over shocks can be installed in either direction, and will still function fine. I can't say all shocks can be though, if the shock's valving make compression damping stiffer than rebound damping. 50/50 would be ideal. What make did your buy?

The quad shocks may help prevent wheel hop, which is what they were designed to do, but you may have clearance issues with the new coil over springs. Not sure with the MK4's, but I think they are usually left off.
Can't answer the, which hole to use to mount shock, as my Mk3.1 was factory ordered for the 3-link, so it only had one hole. Looking at the mounting bracket for a 4 link set up, I would think the lower hole would be the better choice. Least it would be more approximate to where my shock is mounted.

[J R Jones]

AC Bill's comments are appropriate. The two layed-down shocks are for axle tramp (wheel hop) on acceleration, they have little effect on ride quality.
Photos I found show progressive springs on the Mustang rear suspension. The visible characteristic is a close stacked coil section and a wider stacked coil section. That is a more expensive spring to make, in order to get improved ride quality. Bill's numbers, 165-250 is a big difference from 350.
The upper hole setting with a coil over contributes to ride height. The upper hole drops the chassis, the lower hole raises it.
You have a choice to make, your comfort or under car aethetics.
The change in performance handling is realized when racing or driving at the limit. Actually that will be beneficial on a smooth track. Most road surfaces are rough enough that stiff suspensions skip off the bumps more than softer suspensions and loose traction when the bumps loft the tires and the chassis.
jim

[Grande]

Thanks for everyone’s input, I had Koni shocks from factory five, and eibachs for coils 350 lbs, used upper holes but will switch to lower holes as others suggested, will try ordering 250 lbs coils , the ride is not suitable for everyday driving in the city at the moment.I regret the change for anyone driving there car as a daily driver . Was very impressed before this mod for my purpose

[J R Jones]

Grande, The progressive springs react to much of the road surface with the 165 lb rate. When the bump height is greater, the 165 coil section bottoms-out and the 250 lb section compresses.
250 lb springs will not feel like your progressive springs.
I do not know if there are progressive options for your new shocks, look into it. That concept could be a spring like your Mustang springs or perhaps you can stack a short 165 lb spring and a short 250 lb spring on each shock.
jim

[Jeff Kleiner]

I have to wonder if you have something bound. I’ve driven a bunch of solid axle roadsters with 350# springs and they are not “unacceptable”. Heck, I run 500# in the rear of mine and am comfortable.

Jeff

[Grande]

Thx for all the replies , all I know is it was a nice ride before with all donor parts , for everyday driving and after the conversion find it hard and harsh on bumps. For binding components , all I replaced were the 2 lower control arms with FFR cobra lowers , and both arms were torqued at ride height , so arms should not be binding I would believe.

[CraigS]

Here is the procedure to check the adjustment on the Koni shocks.
https://www.koni-na.com/en-US/NorthAmerica/Technology/Adjustment-Guides/
It is a pain in the neck but it could be important. All the pics in the FFR instructions show them mounting in the upper holes at the frame bracket.
https://www.factoryfiveparts.com/content/instructions/14675-koni-rear-coil-overs.pdf

[J R Jones]

Grande, Not being a Roadster guy I had to review photos to understand the physics of your suspension rework. In addition to installing different shocks with different damping, and coil springs with higher spring rate, you have relocated the spring/shock to a location where it has more control on the wheel/tire. Even if you had the same shock and spring characteristics, you now have more "wheel rate", making the ride stiffer.
With the coilover further to the outside you have more roll control.
With the coilover further aft you have more bump control. Apparently it all added up to the result that you have experienced.
jim

[Norm B]

I did the upgrade from donor shocks and springs last year. The car had some twitchy handling characteristics with the donor set up during spirited driving. The ride was much softer but in a hard corner the rear would sag and cause very uneven loading on the fronts with their stiffer springs.
The car handles much better now. Here’s a picture. Note I was able to retain the quad shocks by relocating the frame shock brackets further to the rear.

HTH

Norm