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I'm working on the FC subframe swap right now and need some help.
1) To get the wheel centered, how far back do I need to set the subframe? I've read 1" but in my measurements last night I set the front holes 1 5/16" back and it still wasn't centered. The hole will wind up nearly 2" back. Am I measuring wrong? How far back should it actually move?
2) What's the best way to get working suspension for this swap under about $1000? If it's coilovers, which? I've read every thread here and there are a lot of opinions but I am not sure what actually works from a spring stiffness and ride height standpoint. The car isn't a race car but I don't want to totally ruin the suspension.
Wouldn't the position also be dictated by the shifter and how it sits in the trans tunnel opening?
Yes, from what I have read the only issue there is in the shifter position. Some people have take the tailshaft out and shortened it an inch or so to get the shifter back in the right spot. I haven't heard of instances of the transmission not fitting in the tunnel despite being a little more rearward but if anyone could confirm that I'd appreciate it
Yes, from what I have read the only issue there is in the shifter position. Some people have take the tailshaft out and shortened it an inch or so to get the shifter back in the right spot. I haven't heard of instances of the transmission not fitting in the tunnel despite being a little more rearward but if anyone could confirm that I'd appreciate it
Just in regards to this, I'm using a FC turbo gearbox, and I've moved it 30mm further back than the factory location. You can barely get your palm between the UIM and the firewall. It's so far back I had to cut the shifter remote and move it forward 100mm so it fits in the factory hole, and there's no issues with clearance around the tunnel/bell housing. Even the clutch slave clears.
I moved mine 25mm and it's centred perfectly. Maybe you're not measuring the wheel location correctly?
Awesome thank you. Because I don't have ball joints for my s4 control arms yet, or any form of FC strut, the best measuring I can do is to measure the control arm inside the wheel well and then try to compensate for the offset between the control arm and the center axis in the hub. I must be doing something wrong in there, because everyone says 1" so I'll just go with that. 25mm is basically 1"
Awesome thank you. Because I don't have ball joints for my s4 control arms yet, or any form of FC strut, the best measuring I can do is to measure the control arm inside the wheel well and then try to compensate for the offset between the control arm and the center axis in the hub. I must be doing something wrong in there, because everyone says 1" so I'll just go with that. 25mm is basically 1"
This is after moving it back 25mm. If yours looks like this then you're fine. You can see the spindle is canted a little forward as the strut isn't bolted in yet.
This is with cheap weld-on coilovers at maximum compression that I ended up scrapping and replacing with BC Racing Gold coilovers.
Thank you for this follow up. I figured out my problem.
Originally Posted by Jon_Valjean
You can see the spindle is canted a little forward as the strut isn't bolted in yet.
I don't have a strut for an FC yet, and I don't have ball joints either, so I was just sticking the hub on the control arm with a socket extension and looking at it. I failed to see that the hub was tilted forwards, and not in line with the strut tower. If I point it towards the back like it's supposed to go, it's perfect at 1" back. Dumb mistake, but I'm glad it was an easy one. Thank you!
These pictures show my mistake
Are the BC Gold coilovers working well? I still need to figure out what to do for the strut
Are the BC Gold coilovers working well? I still need to figure out what to do for the strut
Yeah they're magic. I tried using a frankenstein strut, half FC and half FB, which didn't get the car low enough, then I tried weld-on coilovers (same problem). It wasn't until I put the BC coilovers on that everything came right. You just need to file or burr out the four holes on the strut tower a few millimeters, but it's not a biggie.
Don't let anyone tell you the caster is a problem either, after my wheel alignment it's showing 3 deg caster and it steers beautifully.
I also got a local place to make some braided brake hoses, which has made a huge difference. Easy enough to do once it's all apart.
I'm working on the FC subframe swap right now and need some help.
1) To get the wheel centered, how far back do I need to set the subframe? I've read 1" but in my measurements last night I set the front holes 1 5/16" back and it still wasn't centered. The hole will wind up nearly 2" back. Am I measuring wrong? How far back should it actually move?
2) What's the best way to get working suspension for this swap under about $1000? If it's coilovers, which? I've read every thread here and there are a lot of opinions but I am not sure what actually works from a spring stiffness and ride height standpoint. The car isn't a race car but I don't want to totally ruin the suspension.
Thanks
****, I did the whole swap for under $300 and that included the parts FC.
I shifted my axle centerline an inch forward because it made the subframe swap easier. The forward subframe mounts line up with only a little ovalling that way.
For suspension, I used '91-02 Ford Escort upper mounts (cheaper than ZX2 for some reason) which use the same bolt pattern as SA/FB but use a fixed strut shaft D-hole like FC. Need to drill the strut towers for the 10mm studs and file out the mounts for the larger FC shafts. Then I made spring seats from some washers and 3/16 plate, and used 10" long 2.5" springs with the lower pigtail cut off.
I would try to link pics here but for some reason the forum won't show a reply entry box when I am on my computer and trying to post images from a tablet is frickin' impossible.
If you don:t want to ruin the suspension, don't do the swap. I am going to de-convert my car soon (or maybe just scrap it, I have an unmolested '81 now) because the FC subframe wrecks the geometry. The roll center is too low and it moves around too much with those short little contro! arms.
Probably not a problem if you stiffen the suspension to where it can't move, but if you find that acceptable then you probably don't care about handling anyway.
If you don:t want to ruin the suspension, don't do the swap. I am going to de-convert my car soon (or maybe just scrap it, I have an unmolested '81 now) because the FC subframe wrecks the geometry. The roll center is too low and it moves around too much with those short little contro! arms.
Probably not a problem if you stiffen the suspension to where it can't move, but if you find that acceptable then you probably don't care about handling anyway.
i actually saw another way to do the FC strut swap in a Japanese magazine. they used the FB subframe, control arms and steering, the FC strut, knuckle and brakes. the only fabricated part was a thing that bolted on the FB steering arm that had an FC ball joint stud on it.
That’s interesting. Most people seem to be very happy with the swap on this forum and it seems popular. At this point I’m in a little too far to stop, and aren’t there ways to correct the roll center?
I haven’t gotten rid of the FB Parts quite yet so we’ll see if I hate the swap. I’ll be able to fix it.
The main reason I did the swap was because I had a lot of problems with bending spindles, and RX-7 strut housings were getting hard to find. Plus abeomid on the old Mazspeed forum did it, and I thought I had an easier way of doing it than he did, and there was this $50 FC sitting there...
The easiest way to fix the geometry is to keep using the FB steering box and linkage, crossmember and control arms/tension rods, and just use the FC struts/uprights with Mazda 3 ball joints. The FC steering arms are, IIRC, 130mm ball joint to tie rod, and FB are 145, so the FC knuckles will get you slightly faster steering.
That was the other downside: The FC rack, even the three port one I used, is not as fast a ratio as an FB power box. I also plan on splicing a steering quickener into a manual FB box since power boxes are so hard to find.
The main reason I did the swap was because I had a lot of problems with bending spindles, and RX-7 strut housings were getting hard to find. Plus abeomid on the old Mazspeed forum did it, and I thought I had an easier way of doing it than he did, and there was this $50 FC sitting there...
The easiest way to fix the geometry is to keep using the FB steering box and linkage, crossmember and control arms/tension rods, and just use the FC struts/uprights with Mazda 3 ball joints. The FC steering arms are, IIRC, 130mm ball joint to tie rod, and FB are 145, so the FC knuckles will get you slightly faster steering.
That was the other downside: The FC rack, even the three port one I used, is not as fast a ratio as an FB power box. I also plan on splicing a steering quickener into a manual FB box since power boxes are so hard to find.
The main point of me doing this is to get rack and pinion though, so that wouldn't help me. I've always loved my FB except for the steering feel. I purchased the fastest FC power rack available, 15:1. Hopefully that's quick enough not to bother me!
The steering feel isn't as good to me because the front end wallows around a lot more, I had to go from 175lb springs to 250 to maintain the same feel.
The steering feel isn't as good to me because the front end wallows around a lot more, I had to go from 175lb springs to 250 to maintain the same feel.
Did you fit coilovers? The reason I ask is that it's always bothered me that the guides online that are most popularly indexed by google all seem to feature struts that have been cut and welded together, half FB, half FC, with the top hats swapped over. I tried doing that, and there's no way you can get the front to sit low enough without having essentially no travel. It's a physical impossibility, there's simply no room to position the spring perch low enough without using some kind of tiny short shock and remachining the shock tube for a new retaining nut. So if you've done the FC swap without coilovers, then yeah, I can see it would handle like total ***.
And if you don't do something about the rear, you're going to see an imbalance in the roll axis, whether or not that's a game changer I can't comment on as mine is IRS and I haven't driven a FC swapped first gen that retained the watts linkage, which has a ridiculously high roll center in itself. But my point stands, fitting coilovers allows the front to sit low enough and retain travel so that the roll center is more or less what the FC had from factory anyway. The only difference is that the strut towers are about 25mm further forward, which means you lose about 2-2.5 degrees of caster. As I said before, it still feels fine to me, but if that's a problem you could always rotate the hat 45 degrees, redrill the holes and use the camber adjustment plate to dial in a couple more degrees.
For suspension, I used '91-02 Ford Escort upper mounts (cheaper than ZX2 for some reason) which use the same bolt pattern as SA/FB but use a fixed strut shaft D-hole like FC. Need to drill the strut towers for the 10mm studs and file out the mounts for the larger FC shafts. Then I made spring seats from some washers and 3/16 plate, and used 10" long 2.5" springs with the lower pigtail cut off.
Ah missed this before, I see what you've done. Did you retain the FC shocks? Without going for a ride in the car it would be impossible to say what it might handle like, but I guess if you didn't like it, then there has to be something wrong somewhere. I guess it's all down to preference, and all I can say is that mine works really well, and there's no way in hell I would go back to the way it was before.
The issue is that the roll axis gets a very steep angle with the rear high and the front much MUCH lower. Not a problem with stock SA/FB since both are relatively high (at stock ride height anyway), not a problem with stock FC since both are down in the weeds, but when you mix the two you have problems.
It was sort of okay when I had a low Panhard rod, but it kept breaking and I went back to the Watts. That is when I started to get really dissatisfied with the FC front.
I tried moving the roll center closer to the center of gravity by using redrilled FC strut tops, which raise the front 40mm or so, but those broke a lot, so next I made new long travel struts out of GC Impreza rear struts, and used the 175lb springs. This gave the same initial ride height but allowed more bump travel, and it worked sort of okay, but the Koni shocks absolutely suck. That is what I have used until now. It is not ideal because Koni shocks suck, way too much initial damping. Also having the front end that high causes cooling system issues, air packs up under the car and it overheats on the highway unless you use the fans.
Last year, I finally got my Ford 9" in the car. When I constructed it, I put the Watts pivot on-center instead of 40mm over axle centerline like stock. This helped a bit.
My next trick is another pair of AGXs, with 225lb springs, because I am sick of those freaking Konis, and I want to try redrilling the control arms' forward pivots 20-25mm higher. This WILL require bumpsteer correction!
My ultimate goal is to be able to get good turn-in without having the front end jacked real high. If I can do that, I can finally get rid of the 175lb springs in the rear and go to 150s or 125s for more grip. As it is, with the 125s, the car understeers mercilessly.
The other thing that can help the roll center a bit is to move the strut top as far inboard as it can. Due to the way suspension geometry works, this will have a marginal effect of raising roll center.
The short control arms will still mean it will move around a bunch as the suspension moves, which is less than ideal, but at least with body roll reduced the suspension won't move as much with cornering loads.
Having a stable roll center is crucial for having the chassis "take a set" in a corner. You can get this with good geometry, or making the suspension so stiff that it doesn't move. Good geometry and a suspension that moves makes for a very fun, forgiving, livable car. Having a suspension that doesn't move makes for an evil to live with pig that is tiring to drive after a while.
I want something that I can spend 16 hours a day in.
04-30-19, 06:21 AM
