Rear suspension bushings, etc.

[ChipG]

Hi all,

I'm getting BMR springs installed on my car in a week or two, and am adding in cradle centering bushings at the same time. As I look into the next phase I'm planning on "locking down" the IRS. I don't want to change everything all at once so I'm looking at sensible clusters of mods to do.

BMR, FTBR, Steeda, SPL, Cortex and others offer various combos of bushing and lockouts for the IRS: cradle bushings or lockouts, diff bushings or lockouts, IRS braces, vertical links and various levels of bushing (poly, delrin, billet, spherical...). Here are some of my assumptions and my tentative plan, feedback welcome.

First question is which things to do at the same time. My thoughts are cradle/diff/bracing and vertical links, and then I'll address rear control arms later and at the same time as front control arms. Sensible or am I missing something?

For the cradle, my understanding is that there isn't much NVH risk there so going stiffer isn't a big deal, but for the diff there's more significant NVH risk, so I'm thinking I'll go a bit more aggressive on the cradle than on the diff. Also assuming vertical links aren't a significant NVH concern.

My understanding is that the bracing/lockout kits in large part cover for soft bushings because changing the bushings is a PITA.

So, what I'm thinking at the moment, with Qs:

• Cradle centering sleeves, already ordered from BMR.
• Cradle bushing lockout kit or cradle bushings? Poly or Aluminum? I'm leaning BMR aluminum bushings.
• Diff bushing lockout or diff bushings - poly. Skip this? I'm leaning BMR poly bushings.
• Vertical links with rod/spherical ends from SPL or Cortex. Does it make sense to do these at this point?
• Do I need an IRS bracing kit (BMR or Steeda)?
• I'm leaning to waiting on lower control arms/bushings as well as sway bars and end links for next phase.

For context, the car is a 2020 GT350 that is a combo street and HPDE car. I track it roughly monthly, but also put 20k miles on it last year. I want to continue to improve its capability (while I improve mine) and am willing to accept some tradeoffs, but I have no plans to go "full race car" with this one - it needs to remain street friendly. Current mod list focuses primarily on durability, reliability, maintainability, and safety. Performance mods at the moment are limited to GT350R splitter, GT4 hood vent, gurney flap, alignment mods (camber plates, camber bolts, camber arms, toe links) and wheels/tires. Springs and E85 flex tuner are being added shortly.

Thanks for all input.

Chip

 

[Beermoney]

Not all that great with the hierarchy of mods for an S550, but have you looked at Full Tilt Boogie? They make some nice parts and keeping most of the parts from the same manufacturer so you know they work together may make dialing it in easier on you in the long run.

 

[ChipG]

Not all that great with the hierarchy of mods for an S550, but have you looked at Full Tilt Boogie? They make some nice parts and keeping most of the parts from the same manufacturer so you know they work together may make dialing it in easier on you in the long run.

I have and was leaning BMR as I have a couple of their parts already, but not enough to make it a real issue yet. They have adjustable vertical links (not that I'd know quite what to adjust or why ), diff bushings they say are only needed for drag racers, and one bushing kit (which I think Honeybadger is running) without info but appears to be aluminum.

Chip

 

[TMSBOSS]

Chip

My first question regarding parts and suppliers is "What are you trying to Fix"? Answer that and then tailored advice is much easier.

You seem to have the same goals as I do. Own a streetable machine that does well on track. So track the car and see what is the first obvious shortcoming. Does it push through a corner? Does it tear up the outside of the tires(My current issue), over heating, braking or power issues/desires?? Then address the issues as they pop up. Seat time first. Wheels and tire are the simplest and usually the best bang for the buck. You seem to have a good handle on that. Although I am looking at 315 SC2's for my next street tire. They should fit on the wheels you have.

This past weekend I had a educational conversation at the track with a local vender who has tracked his own GT350. His advice was to go gently into the mods "Catalog". The car is fairly sound as delivered. His experience with removing rubber and replacing it with aluminum was that it will improve performance....minimally. It will destroy street manners and comfort. This is a guy who knew he would be selling me parts. I assume he feels sound advice and spending my money like it was his was a good thing. Hope so.

My Symptom: Tires wearing on the outside edge. Fix. I will be adding camber both front and rear. The rear I can simply adjust. The front will require cutting the shock tower (Adjusting the top side) or replacing the lower control arm and tension rod with adjustable pieces. One I can reverse simply by removing the new and putting the originals back on. Cutting will require welding to but back to stock. So now I have to budget for new lower arms and an alignment.

I saved a lot of money and aggravation by going slowly down the mods path. Sticking with one manufacturer who builds a system for your car often pays for itself. Ford comes to mind. Cortex has a great handle on the S197 platform. Others build "Some" of the needed components for our cars. Finding the "Right Combination" can be much more expensive than buying a system ONCE.

A good path for progression is:
Safety
Tire's and wheels
Seat time
everything else.

BTW. You have a gorgeous machine.

 

[Tractor Junk]

Changing the diff bushings isn’t difficult, but very time consuming. The problem is that once you remove the cradle from the car, you get into the “might as well” phase.

You’ll be disconnecting the driveshaft while doing diff bushings, so you might as well do a carbon driveshaft…

Since the driveshaft is out, you might as well replace the shifter…

Of course the exhaust has to removed for this, so you might as well… etc. etc.

If you do diff bushings, you’ll be deep in “might as well” territory.

 

[blacksheep-1]

FTBR makes awesome small parts for our cars, Bruce is just not as well known as some folks, I would offer one caveat on the carbon driveshaft, which is the same one I offer for the carbon wheels. All it takes is a chip in the coating and you start the downhill slide to a catastrophic failure. I would not recommend them for the street, and I'm not sure I know of any competition cars that run them (maybe the Gt4 car, but I'm not positive, I don't recall the last time I was under there) but none of the S197s run them, and the Gt4 spec cars also run aluminum wheels in 18inch.
This has just been my experience with carbon fiber parts, once the "gel coat or whatever you want to call it" is compromised, you get oil and water intrusion and the fibers are affected.

 

[Scootsmcgreggor]

It depends like said above on what your goals are.
My goal was the most precision in the back end to make steering with the throttle more predictable. Having done most of the popular stuff out back and some of it twice with different manufacturers I would recommend spherical RLCA bearings and spherical rear upper shock mounts as the top two from a performance standpoint. The only reason you don’t read more about the rlca bearings is they’re not an easy bolt on so far fewer people do them. Huge improvement though in precision of the rear under power. More so than the rest of the rear ended mods I’ve done combined probably. And the rear shock is in binding stock so a spherical upper mount takes that bending force away and also the rubber mount that moves around back undamped. Much better damping on and off track as a result.

 

[ChipG]

Chip

My first question regarding parts and suppliers is "What are you trying to Fix"? Answer that and then tailored advice is much easier.

You seem to have the same goals as I do. Own a streetable machine that does well on track. So track the car and see what is the first obvious shortcoming. Does it push through a corner? Does it tear up the outside of the tires(My current issue), over heating, braking or power issues/desires?? Then address the issues as they pop up. Seat time first. Wheels and tire are the simplest and usually the best bang for the buck. You seem to have a good handle on that. Although I am looking at 315 SC2's for my next street tire. They should fit on the wheels you have.

This past weekend I had a educational conversation at the track with a local vender who has tracked his own GT350. His advice was to go gently into the mods "Catalog". The car is fairly sound as delivered. His experience with removing rubber and replacing it with aluminum was that it will improve performance....minimally. It will destroy street manners and comfort. This is a guy who knew he would be selling me parts. I assume he feels sound advice and spending my money like it was his was a good thing. Hope so.

My Symptom: Tires wearing on the outside edge. Fix. I will be adding camber both front and rear. The rear I can simply adjust. The front will require cutting the shock tower (Adjusting the top side) or replacing the lower control arm and tension rod with adjustable pieces. One I can reverse simply by removing the new and putting the originals back on. Cutting will require welding to but back to stock. So now I have to budget for new lower arms and an alignment.

I saved a lot of money and aggravation by going slowly down the mods path. Sticking with one manufacturer who builds a system for your car often pays for itself. Ford comes to mind. Cortex has a great handle on the S197 platform. Other build "Some" of the needed components for our cars. Finding the "Right Combination" can be much more expensive than buying a system ONCE.

A good path for progression is:
Safety
Tire's and wheels
Seat time
everything else.

BTW. You have a gorgeous machine.

Thanks, as is yours! I've been tracking it, and I've got alignment (-3.5* front and -2.2* rear for the track) and tire wear in a good place thus far. What I'm looking for is to get the rear end "set" better - more stability, predictability, and ability to get into the throttle on corner exit without the rear being unsettled. I agree with your order of operations. I put in safety gear, got some good wheels and tires (I do run 315s except when I get a deal on takeoffs or on a brand without 315 option), did about 12 days on track last year, and am getting prepped for this season when I plan to get about 20 days on track (one weekend a month through the season typically).

Chip

 

[ChipG]

Changing the diff bushings isn’t difficult, but very time consuming. The problem is that once you remove the cradle from the car, you get into the “might as well” phase.

You’ll be disconnecting the driveshaft while doing diff bushings, so you might as well do a carbon driveshaft…

Since the driveshaft is out, you might as well replace the shifter…

Of course the exhaust has to removed for this, so you might as well… etc. etc.

If you do diff bushings, you’ll be deep in “might as well” territory.

It is really hard to avoid "while-I'm-at-it-itis"! If the diff bushings are that much of a hassle, maybe I'll skip those for now as I'm not a drag racer, nor am I ready for a driveshaft swap.

 

[ChipG]

FTBR makes awesome small parts for our cars, Bruce is just not as well known as some folks, I would offer one caveat on the carbon driveshaft, which is the same one I offer for the carbon wheels. All it takes is a chip in the coating and you start the downhill slide to a catastrophic failure. I would not recommend them for the street, and I'm not sure I know of any competition cars that run them (maybe the Gt4 car, but I'm not positive, I don't recall the last time I was under there) but none of the S197s run them, and the Gt4 spec cars also run aluminum wheels in 18inch.
This has just been my experience with carbon fiber parts, once the "gel coat or whatever you want to call it" is compromised, you get oil and water intrusion and the fibers are affected.

I'm somewhat familiar with FTBR since the days of looking at their bushing sets for an IRS SN95 build. Just didn't see as many options in this case, but I've no negative perception on them and would happily consider their parts as appropriate.

I've heard similar on CF and would lean towards aluminum once I get to that point (and I'm not there yet).

 

[ChipG]

It depends like said above on what your goals are.
My goal was the most precision in the back end to make steering with the throttle more predictable. Having done most of the popular stuff out back and some of it twice with different manufacturers I would recommend spherical RLCA bearings and spherical rear upper shock mounts as the top two from a performance standpoint. The only reason you don’t read more about the rlca bearings is they’re not an easy bolt on so far fewer people do them. Huge improvement though in precision of the rear under power. More so than the rest of the rear ended mods I’ve done combined probably. And the rear shock is in binding stock so a spherical upper mount takes that bending force away and also the rubber mount that moves around back undamped. Much better damping on and off track as a result.

Goals above but similar to what you've said - get the "slop" out of the rear. Interesting that you've found the control arms and shock mounts more effective. You're right that I've not heard nearly as much about them. Do you think they'd be as effective with stock rubber bushings elsewhere in the IRS or is it perhaps an aggregate effect? As in my first post, I was considering the control arms as a following phase but perhaps should swap the order and consider the shock mounts with them.

 

[Scootsmcgreggor]

Goals above but similar to what you've said - get the "slop" out of the rear. Interesting that you've found the control arms and shock mounts more effective. You're right that I've not heard nearly as much about them. Do you think they'd be as effective with stock rubber bushings elsewhere in the IRS or is it perhaps an aggregate effect? As in my first post, I was considering the control arms as a following phase but perhaps should swap the order and consider the shock mounts with them.

yeah FTBR and BMR have some videos showing various bushing deflections under load. The RLCA bushing deflection is huge. The bushings are massive and that gives them a lot or room to deflect. Much more so than vertical link, toe link, or camber arm bushings. The RLCA bushings are also way out of plane so without them being sphericals the bushings are fighting eachother when cycling the RLCA. Vorshlag has a picture in their build thread of a guy hanging from the rear rear lower control arm and there’s so much bind that the arm isn’t at full droop with him hanging from it. Also with the orientation of the forward rlca bushing and the way it reflects it creates primarily toe changes. So I figured let’s see if changing it is worth all the work and it really was.

 

[Tractor Junk]

Rear shock mounts are worthwhile but can be a tricky install on the GT350 (mag ride). You’ve got to disassemble/ reassemble the connectors coming out of the top of each shock.

I destroyed a shock during my install by not being careful. FYI.

 

[RES_22]

Installing the RLCA inner spherical bearing is not simple but (in conjunction with sphericals in toe link, shock top mount and outer RLCA) it tranforms the car...esp on good tires (old or new) and on high speed entries/throttle tip-in. Biggest gain.

Permits you to experiment with (and trust) aggressive toe settings w/o fearing weird behavours related to toe changes that occur when all the oem rubber bits deflect under lat/vert loads.

Lap times come from confidence in the rear on entry.

NVH: No increase to speak of.

 

[blacksheep-1]

I'm just happy that you guys are using the term "control arm" in its' proper form.

 

[TMSBOSS]

I'm just happy that you guys are using the term "control arm" in its' proper form.

What do you call the part of the arm closest to the Rims?? Lol.

 

[TeeLew]

It is really hard to avoid "while-I'm-at-it-itis"! If the diff bushings are that much of a hassle, maybe I'll skip those for now as I'm not a drag racer, nor am I ready for a driveshaft swap.

IF you can avoid most of the project creep, it is a good time to put Poly bushings in the rear subframe and better bolts in the diff. I know you're talking about centering sleeves and the lockout kit, but I just went straight to replacing the bushings. They're cheap and I feel it's just a little better way of solving the issue. It's also a good time to install rear subframe supports from either Steeda or BMR.

 

[TeeLew]

I would not recommend them for the street, and I'm not sure I know of any competition cars that run them (maybe the Gt4 car, but I'm not positive, I don't recall the last time I was under there) but none of the S197s run them, and the Gt4 spec cars also run aluminum wheels in 18inch.

I'm aware of several race cars which use a carbon fiber driveshaft, but they all use a torque tube connecting the engine and the transaxle (not just rear end) which completely protects the driveshaft from road debris. Your point is completely valid. Any surface damage will be a dotted line on a highly stressed part, and no one wants that.

If you have a way to protect the shaft in the driveshaft tunnel, it's easier to justify the use.

 

[Casultenbeers]

Hi all,

I'm getting BMR springs installed on my car in a week or two, and am adding in cradle centering bushings at the same time. As I look into the next phase I'm planning on "locking down" the IRS. I don't want to change everything all at once so I'm looking at sensible clusters of mods to do.

BMR, FTBR, Steeda, SPL, Cortex and others offer various combos of bushing and lockouts for the IRS: cradle bushings or lockouts, diff bushings or lockouts, IRS braces, vertical links and various levels of bushing (poly, delrin, billet, spherical...). Here are some of my assumptions and my tentative plan, feedback welcome.

First question is which things to do at the same time. My thoughts are cradle/diff/bracing and vertical links, and then I'll address rear control arms later and at the same time as front control arms. Sensible or am I missing something?

For the cradle, my understanding is that there isn't much NVH risk there so going stiffer isn't a big deal, but for the diff there's more significant NVH risk, so I'm thinking I'll go a bit more aggressive on the cradle than on the diff. Also assuming vertical links aren't a significant NVH concern.

My understanding is that the bracing/lockout kits in large part cover for soft bushings because changing the bushings is a PITA.

So, what I'm thinking at the moment, with Qs:

• Cradle centering sleeves, already ordered from BMR.
• Cradle bushing lockout kit or cradle bushings? Poly or Aluminum? I'm leaning BMR aluminum bushings.
• Diff bushing lockout or diff bushings - poly. Skip this? I'm leaning BMR poly bushings.
• Vertical links with rod/spherical ends from SPL or Cortex. Does it make sense to do these at this point?
• Do I need an IRS bracing kit (BMR or Steeda)?
• I'm leaning to waiting on lower control arms/bushings as well as sway bars and end links for next phase.

For context, the car is a 2020 GT350 that is a combo street and HPDE car. I track it roughly monthly, but also put 20k miles on it last year. I want to continue to improve its capability (while I improve mine) and am willing to accept some tradeoffs, but I have no plans to go "full race car" with this one - it needs to remain street friendly. Current mod list focuses primarily on durability, reliability, maintainability, and safety. Performance mods at the moment are limited to GT350R splitter, GT4 hood vent, gurney flap, alignment mods (camber plates, camber bolts, camber arms, toe links) and wheels/tires. Springs and E85 flex tuner are being added shortly.

Thanks for all input.

Chip

So I ended up rambling on with my post as things came to mind:

I’ve been slowly building and tracking my 2017 GT350 for almost 5 years now. I can share my experiences in regard to some of your inquiries. Other items I am also curious about. I have the Steeda vertical links installed, no added NVH in my opinion. Steeda recommends the polyurethane for road course applications so I went with that. Spherical end vertical links could add NVH. I have had the Steeda diff bushing inserts installed for years (black higher durometer, my idea was to test my NVH tolerance prior to installing full aftermarket bushings). Slight NVH gear whine at highway speeds. They cause clunkier parking lot speed shifts. Mind you my car is far from a daily here in Canada, but also far from a race car. The Steeda cradle alignment and bushing support kit seems to be effective and durable. As most of you know I had to cut the one diff bushing insert to fit the drivers rear side of the diff (GT350 bushing sleeve and rubber nibs are different from GT only on that one).

Now with all of that said I am preparing to drop my rear subframe to install the BMR polyurethane diff bushings (simply for reliability and longevity, a torn rubber bushing mid season is what I don’t want and aluminum here is likely way too loud for anything that’s not a dedicated race car). BMR Aluminum cradle bushings as well (Personal opinion that NVH is less of a concern here VS diff bushings). With the solid cradle bushings bracing isn’t needed so much and potentially saves weight going this route.

Great that you already have the camber arms and toe links. I ran a few years on stock parts and am now upgrading to the BMR camber arms and toe links for adjustment and locking out the subframe adjustment points as I’ve had camber slip after a road course day.

Hope this helps. I also have one inquiry of my own that should support this topic.

Has anyone confirmed fitment or installed the BMR Polyurethane diff bushings BK049 in a GT350? I’m curious about the fitment as GT350s have a different subframe part# vs GTs and the many bushings inserts don’t fit properly just on that one rear drivers side bushing due to the reasons I mentioned. I haven’t looked lately but it seems just the bushing sleeve and rubber nibs are the only difference. Looks to me like once removed the opening would be a perfect circle and accept any aftermarket diff bushing same as a GT. I reached out to BMR could not provide me with a clear answer.

I’d recommend inspecting your sway bar end links as you may find the fronts are bent. Mine were after what I would call not severe track use.

Hope this helps and good luck with your build.

 

[TeeLew]

Now with all of that said I am preparing to drop my rear subframe to install the BMR polyurethane diff bushings (simply for reliability and longevity, a torn rubber bushing mid season is what I don’t want and aluminum here is likely way too loud for anything that’s not a dedicated race car). BMR Aluminum cradle bushings as well (Personal opinion that NVH is less of a concern here VS diff bushings). With the solid cradle bushings bracing isn’t needed so much and potentially saves weigh

The diff bushings are a good idea, but solid mounting the rear sub is a big NVH concern. Poly bushings there add a bit of noise with a substantial gain in feel. AL bushings in the subframe will feel good to drive, but it will not be quiet.