FC3S Rear Suspension Explained/Demystified
 

Rear FC suspension explained/demystified

This is a result of rebuilding and working with FC rear suspensions for the past 8 years. I'm seeing a lot of new drifting and other enthusiasts (even some old) having no idea what they are talking about and rely on the large range of info found all over the internet. Here is everything you need to know (There is other crazier stuff you can do like changing suspension points and total redesign but this is the average stuff anyone can do/have done)

Attachment 755240

Pink : DTSS Bushings. Fancy Mazda rear steering bushings that where designed to help with the limitations of semi trailing arm suspension. Works great when NEW and when running factory tire widths. Terrible in drifting as it will make the rear end dance all over during transitioning and when gripping hard with wider/stickier tires and 20 year old bushings car will be rear steer heavy and be awkward and unpredictable. I prefer the racing beat version over other delrin ones due to the metal insert. Solid aluminium is fine aswell. Be careful during install/removal as the knuckle can split. Mazdatrix has some, RacingBeat, PBM. Common part.

Blue : Lateral Rods. Holds the control arm in place as far as toe is concerned. Would recommend newer/aftermarket ones as the older ones can have slot in the balljoints and allow for the rear toe to wander. I had one get all sloppy and allow for 5-10deg in toe change. You can use them to adjust tow aswell but its moreso meant to adjust the dynamic tow with your ride height change. When you lower/slam your car the dynamic tow can change and this can help even it out. (OEM at mazdatrix or aftermarket at AWR or PBM)

Red: Control arm Links? / Jangle Rods. Determines the camber of the car at the specified ride height. Unless your running 14s and your frame is on the ground you can usually have these shortened enough to have 0 camber. Mazdatrix has adjustable ones and PBM has shorter ones. I usually opt for sorter ones to keep it simple. If you need/want adjust-ability then go all out. (NOTE: Changing the length of these links changes the axis of rotation of the control arm bushing and will cause binding/damage to solid/polyurethane bushings. If modifying these links it is highly recommended to get spherical control arm bushings or stay with the stock rubber ones.)

White: Control arm Bushing. This is where toe is traditionally set. There is an eccentric bolt that allows for toe to be adjusted. most people set to zero, some like a bit of toe out as the FC rear suspension toes in under accel or they like the back end to be "happier" for when drifting. You can use stock bushing and still be able to adjust camber with the jangle rods as the rubber bushings have lots of play but i wouldn't recommend it as it makes them rotate way out of axis. Spherical bushing is the way to go if you want to adjust camber. (Via the jangle rods) I don't know if anyone else makes them anymore. (I have old MMR ones, but they are discontinued, and I have energy ones for the stock jangle rods) I know PBM makes spherical ones now.

Grey: Subframe stay/mount. Factory subframe bushings have lots of compliance so this is here to have a physical limit to the subframe deflection. Some people use this to adjust camber by pulling on the entire subframe. When doing it this way with stock subframe bushings you'll have uneven camber due to the offset location. In reality it is a terrible way to adjust camber and just a cheap way. Can be removed all together if you have solid subframe mounts or left in place for peace of mind. You can find these all over the internet. Dont waste your money. But hey, its your money.

Yellow: Subframe mounts. PMB makes weird moving ones. Its a feature that adds unnecessary play/another degree of freedom in your subframe. You can get the PBM diff mounts and just drill them to 20mm to fit the subframe studs. Or get any other solid subframe mount. Adjusting camber by cranking on the subframe is terrible way to do it. Not saying you cant, just saying you prolly shouldn't. Hard to find these anymore in solid form.

Green star!! : Front subframe mount. Bane of all FC owners. Break all the time or are broken and you just can't tell anymore/ignore it. The one in my turbo car wasn't broken but had so much compliance that the diff would actually move enough to hit things. Unless you have solid rear mounts dont waste your time and solidly mount this. I have seen some hokey "fixes" to this mount over the years from pinion snubs to complete mount redesigns. Honestly easiest way is to have the stock mount boxed in and welded. Reinforce the mounting tab on the subframe because that is the next thing to go. Pinion snubbers "work" sortof. The floor above is thin and not reinforced by anything so I doubt it will do anything other then delay the inevitable. If you use a solid front mount and still have stock rears then the diff will pop out of the subframe no matter how tight you put it. Its slotted so nothing is really holding it down. I had to cut an "access hole" in my floor to put it back into place after every run at an event. (Drifting an n/a car but the clutch kicks alone where enough) Solid mounting the diff seems to be the only way to help alleviate the front mount problems. Would recommend solid mounting diff to everyone regardless of driving style. Solid mounted it on my street car, I don't hear anything with my quiet exhaust. If you do then change your diff oil. (You may still hear some diff noise at a certain RPM/gear but its the nature of the beast. Drive your corolla/civic if your sensitive to these noises)

(People have argued that you can change camber with the rear camber adjuster. I'm not saying you cant, just recommending you don't.

People have also argued that the PBM subframe bushings are "solid as hell". Thats fine, but I'd rather not have an extra point that can potentially/is moving when I setup my suspension. I want it solid, with as little moving parts/adjustment areas as possible. Keeping it simple is key to eliminate as many variables as possible. Even "solid" bushings/mounts deflect to a certain degree.

Please feel free to add suppliers

86-92 Suspension Parts

Suspension Components - 1986-92 Mazda RX-7 Performance Parts

Multilink and Steering Angle for FC - Parts Shop MAX

AWR's E-Production parts for RX-7

Very good write up. Maybe archive?

Thanks for the info. Good to have in one place.

Nice Fleemer, generally good info except for this. Sounds like you're missing the dual-hole oval washer that catches the lip of the subframe tab and prevents the diff mount from popping out of the slots.

As you said though, a solid front mount is probably the way to go if you're running >200 RWHP.

Sweet

Im sure he's using that, maybe his tab was broken off.

Pinion snubbers work very well actually. I have used then on multiple cars. If they are set up correctly they really don't take a lot of load they just reduce the strain on the stock mount. I have never seen any significant deflection of the body. I have however seen broken brackets from solid mounted solutions, but this vehicle was heavily road driven as well as drifted and did not have any other solid mounts. Point being is the snubber is not a bad solution for a street driven vehicle.

Its in place, it still pops out.

Attachment 755226

And its a PITA to put it back in place without dropping the subframe unless you cut a hole/inspection panel in the floor. Even then it needs some coaxing.

Its a good backup/stopgap. You would have to preload it and check it every once and a while like a belt as the metal stretches :P. I don't like it because I cant rely on it.

After seeing my diff popout of the front mount a whole bunch I doubt it could hold the diff in its entirety.

Never had an issue with my pinion snubber, and I launch on 255 drag radials constantly.

That lip is just bent metal for the double washer, so I ran a quick bead to make it thick enough so the diff cant jump out. If you don't like a snubber, then I'd suggest the Bikedad brace, (ironically enough, that's his picture you used)

I am also not a big fan of pinion snubbers just because I think the front diff mount should just be a better design, as well as the mounting tab. I'm sure pinion snubbers work great

Good write up.

Your subframe is screwed up, that is why your diff is sliding out. There is a small tab on the subframe that will prevent the diff from sliding out of the subframe if you use the OEM hardware to mount the diff. That is why people rip the mount off the subframe, with a solid front diff mount while you are just pulling the diff away from the subframe. See picture below.

I will add that if you use a solid front diff mount you MUST use solid subframe and rear diff mounts to keep from damaging the subframe long term.

Attachment 641731

I measured the bump steer of my rear suspension and it was, for all intents and purposes, zero.

I don't think he's talking about bump and/or travel, only that the rear wheels will tend to pull in or rather towards each other to the front under hard acceleration. Maybe he can clarify this.

I've got delrin in the yellow spot, diff mount I know, with Mazda comp "crowns" on the bottom of them and a Mazda comp up front in the grey. Good or bad? Your post confused me a bit on which way you don't want solids and non-solids.

With solid mounts, crowns up, tighten until they bottom out, then to torque spec if not already.

Same for solid rear diff mounts. They should look like this

Attachment 641346

dammit largeorange! Now I need to double check, I think I put the crowns on upside down. The crown "tongs" are facing down on mine. Easy quick fix, but I can not remember.

It felt like I was going to shear those bolts off before I bottomed them out so I stopped and made sure they were at the torque.

If it feels that way you can cut down the rubber crowns slightly so the mount will touch the bushing. If you install them with the crowns facing down you can bend the metal part of the crown.

Yeah, They torqued up fine, but the metal part did indent as you mentioned. Its holding fine for me however.

Question for you. So can you really buy the PBM rear solid diff mounts and drill then to 20mm and use them for solid subframe mounts? I have bought everything from PBM but the subframe risers because I have been trying to find solid subframe mounts and can't find any. I just want to be sure before I buy them. Has anyone done this before? Maybe a picture of it?

Thanks in advance!!

You can. Same bushing outer diameter. I measured them myself with my calipers. You can find delrin ones on eBay if you don't think you can find a 20mm drill bit in the US :). (Some local machine shop should be able to put it in a lsth and sort it out for you for next to nothing. )

I noticed that you appear to be using the PBM moveable front subframe risers. Those are the ones that have the half-sphere two-piece shape, right? Only reason I ask is because you said that you can open up the diff bushings for use there. Was it just because you already purchased the subframe risers and didn't want to send them back for another set of diff bushings?

Recommend solid mounting the diff and/or subframe to everyone?!

Any solid mounted diff or subframe car I have driven or has sounded like a bag of spanners being dragged down a gravel road. Solid bushings transmit every little noise the drivetrain makes right to the big resonating chamber at the rear of the car. In my opinion it's possibly the worst mod one can make on a street car. Right up there with removing the sound deadening, removing the cold start cam and/or BAC, or running a straight pipe from the header to a dump in front of the rear drivers tire.

Now I'm sure there are people out there with higher tolerances for driving a tin can than I, in fact I know it, because some of these people with the aforementioned mods seem to have no issue with them.

However I'd wager that most would get very tired of driving around with solid mounts after a short while.

There are owners of 100% track cars (trailered to the track) who have complained to me that their solid diff/subframe cars are too tiring to drive for extended periods on the track and have subsequently switched to competition rubber mounts. They are faster because they are happier.

I just want to keep people reading this topic from making a very annoying mistake.

In my opinion, solid suspension mounts are not suitable for street car use.

After 3500 miles on the full PBM Solid mounts this last year, I agree and will be switching everything back out with comp rubber. I can vision a perfectly smooth freshly paved race track being tolerable for a brief while, but paired with stiff coilovers it is just not bearable for street use long term and you WILL regret buying them. I do.

Based on how the subframe mounts to the chassis, I wouldn't expect the NVH to go up that much over poly bushings if the subframe was solid mounted and the front diff mount, rear diff mounts, and control arms to the frame were all rubber bushings. Now, if the diff also had solid mounts, absolutely it would have large amounts of NVH.

My hypothesis here is that if the subframe risers were solid and an adjustable camber arm was installed simply to triangulate the frame for support there, not adjustment, then all the control arm bushings were rubber and the diff mounts were rubber, it shouldn't add any more than factory noise. It would also eliminate any flex in the rear suspesion side to side from the subframe wiggling around, but it would require toe arms and camber links on the inboard side of the control arms.

I know that on plenty of vehicles, the rear control arms mount to ears that are welded to the body itself from the factory, like the FB RX-7, so I at least would like in put on my little "theory".

No racer wants a harsh/hot/uncomfortable car...they put up with it because they have to.
Putting race parts on a street car means you're adapting to meet requirements that the car will literally never see, but you'll pay the price constantly.

Besides, compliance is vastly underrated.
Recall back in the 80's (well, I can recall that far back...) when Honda decided that stiffness was the be-all/end-all of GP bike frame design, a decision which lead to the era of ferocious highsides as the chassis absorbed stress until it wound up and spit the rider over the bars. They had to selectively weaken parts of the frame to solve the problem, a counterintuitive but ultimately successful strategy.
Also bear in mind that as Honda worked through the problems, they had direct access to suspension/tire engineers who helped cope with the energy transferred by the frame. After all, if the chassis ain't gonna absorb the energy, it'll just find another outlet and new tires and suspensions certainly help.
This level of follow through is rarely available to a normal street car.

So, just don't do it.

If you just installed solid rear subframe mounts (preferably not aluminium ones) that would be the least reduction in NVH. It wil still transmit a little more noise than stock.

Without everything in the rear suspension solid, you probably won't notice any appreciable difference in handling from just subframe bushings. OE toe rods are fine if they aren't worn, but you'd want a spherical bearing in the rear trailing arm, a solid center link, and DTSS deletes at a minimum.

I agree with all you stated above. I wouldn't expect a huge change, but the idea is to reduce flex and maybe one less point of failure. I know that FC's are plagued by uneven camber, so I would figure that solid mounting might fix that issue. I forgot to add in my theory above that DTSS deletes would be installed, but I am curious as to why shperical trailing arm bearings are needed. Is it because the lack of movement in the subframe would cause binding in the control arm under load?

I get the solid center link, but the only reason I suggested adjustable was to make it so that it's has the solid-ish spherical bearings and it can allow the bolts to line up due to the frame being solid mounted and not all frames are perfectly straight.

Is the reason against aluminum subframe bushings due to the possiblity of failure? The way I see it, if the mounts are solid and torqued, they shouldn't move or wear out. I do appreciate all of your input though, and I want to be well informed. Also, this topic should help others who want to set up their rear ends as well.

The aluminium subframe bushings will transmit more noise than Delrin or UHMW.
The rear camber on an FC should only be set with different length camber links. Ronin Speedworks makes a bad ass set of solid camber links to adjust the camber. PBM makes their solid link as well but they are only one length and the PBM link is durable but heavy.

When you adjust the rear camber by changing the rear camber link length, it puts a twisting load on the rear control arm bushing. Only the OE bushing or a spherical should be used in that location. Poly or Delrin in that area will bind the suspension if you adjust the camber with non stock camber links.

Leave the sub link rod where it is, and do very little or no adjustment to it. Adjusting the sub link excessively can mess up up pinion angle. I suggested to use an aftermarket adjustable sub link to make a small camber adjustment if needed, and to solidly brace the subframe. The stock sublink is not quite solid.

This was pretty much my understanding, but thanks for clarifying. What is your opinion on the adjustable camber links?(Not the Ronin solid ones, great product from the pics BTW) The little ones on the trailing arm, not the center one that we have already addressed shouldn't be used.

Only issue with the individual adjustable camber links for our cars is that the ones available don't come with spherical bearings. I also heard issues of them breaking, which I think is related to the fact they bind because they don't have bearings in then.

I work with a lot of bmws, and we recommend factory differential bushings. Our customer's cars we noticed solid subframe bushings haven't transmitted much noise over factory. The new f80/f82 m3 come with subframe that have no bushings, solid. For our fc, we would have to make sure the height in the did and subframe spacing give the proper pinion angle. So it would not be recommended to do subframe rising bushings and stock diff bushings

The adjustable links need maintenance and proper setup in the car. If they are installed too tight they will bend and break. The AWR/Mazdatrix ones can bend. You can reduce that possibility by keeping them lubed and running short rear shocks (coilovers). MMR made a set when they were in business. They had a spherical bearing on one end. They were slightly better, but they also needed maintenance and proper setup so they did not bind and break.

I have found with the solid links you have about 1 degree of positive camber adjustment just in the slop of the bolt holes on the arm and subframe. You need to loosen the link with the car in the air, pull the wheel down toward the ground and retighten the link. So if you go with solid links you want to have slightly more negative camber than your desired setting. Do this by installing the links with the rear wheels on the ground. Then jack the rear of the car up, and pull a bit of camber out to get it where you want it.

Good to know. Now I just need to convince the wife that a second mortgage is a good idea.

So i have the PBM toe rods/ lateral rods anybody have issues the it actually hit floor? from their website "Requires chassis clearancing when paired with subframe risers. The arms may hit the bottom of floor if not clearanced, causing damage to arms and hardware" I don't have subframe risers at all.

So, you have had no issues with the PBM lateral links? How long have you been running the PBM lateral links? Looks like a good upgrade over the stock Mazda lateral links.

I've been using it for 5 years already, street and track driving. I just noticed it yesterday when I put it on the alignment rack and did the alignment myself noticed that its so close or actually hitting the bottom floor.

Great info, thanks for posting.

My apologies in advance for reviving an old but an insanely informing thread.

For the Camber Arm Links - Are the PBM links the same length as the oem camber links? I'm using the Energy Poly Bushing kit and don't want to experience any binding.
For the Battle Version or PBM Lateral Rods - I'm not trying to adjust any toe on the rear but I would like to refresh these parts. Would these also cause binding with my Poly Bushing Kit?

Just to confirm you're referring to this spherical bearing conversion?
https://store.partsshopmax.com/shop/...ng/FCTAFB.html

The only rear subframe bushing I see on the site is as follows
https://store.partsshopmax.com/shop/...g/FCTARUB.html

You need the trailing arm (control arm bushing, in white on the picture thing from years ago) bushing : https://store.partsshopmax.com/shop/...ng/FCTAFB.html as it will bind in stock / poly form if you change the camber links (jangle rods in red) : https://store.partsshopmax.com/shop/...le/FCTACL.html

Does it matter that it says forward bushings? It's a tad misleading
https://cimg3.ibsrv.net/gimg/www.rx7...7e5a324487.png

A word of advice when installing the PBM spherical control arm bushings:
Press in the bearing/both cups at once from one side of the control arm. If you try to press in one cup from one side and then the second cup from the other side, they will NOT meet in the middle. FWIW, PBM will sell you new cups without the bearing or spacers for ~$35. Ask me how I know…

How do you know? Also just to confirm the "front spherical bearings" work in the rear control arms to prevent binding when using the lateral rods and and trailing arm camber links?

Well, I botched a pair on my first install attempt and had to buy more.



Shorter camber links tilts the axis of the main (front?) bushing on the rear control arm. With rubber bushings, the axial misalignment is just taken up in the bushing compliance. With sphericals, the axis can shift to be where it needs to be with the shorter links and not cause binding.

Bringing this back again from the dead, I have am the pbm camber links and sub frame camber arm. The rear control arm bushing is oem rubber with the cam bolt. If I were to get the pbm Trailing Arm Forward Bushings, Spherical Bearing I assume the oem cam bolt would either not work or fit, so then would I have to get adjustable rear lateral rods so I can adjust toe? Also with these mods it should also prevent any binding issues as well?

I have the AWR spherical bushings and retained the OEM Bolt and eccentric to adjust rear toe.
I recall the AWR bushing hole was larger than the stock bolt diameter so I used a thin metal “shim” sleeve around the OEM bolt to take up the slop and retained the adjusting eccentric. No problems for years now.
If I ever got adjustable lateral rods, then I would swap out the OEM bolt for a larger one and adjust toe using the lateral rods.

As listed on the 1st post that when changing the camber links (NOTE:Changing the length of these links changes the axis of rotation of the control arm bushing and will cause binding/damage to solid/polyurethane bushings. If modifying these links it is highly recommended to get spherical control arm bushings or stay with the stock rubber ones.)

so sticking with the oem rubber control arm bushings and not using the adjustable lateral rods, I should be fine and not have any binding issues