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Project Grey Mustang 5.0: Part 7 – Testing BMR Suspension’s Rear Control Arms

by Vince Illi

When designing an automobile, engineers have to make compromises or tradeoffs to satisfy performance, longevity, reliability, and comfort objectives.   Perhaps one of the best examples of these compromises is in suspension bushing design.   A bushing is an isolator (usually rubber) that serves the purpose to both isolate noise and vibration (comfort) and allow a measure of articulation (performance).  The problem with a rubber bushing is that the softness required to reduce noise, vibration, and harshness (NVH) and provide a cushy ride is the exact opposite of what is necessary for good performance.

Read more about Project Mustang 5.0 here!

 

This is the stock rubber bushing on one of Project Mustang’s stock control arms.  You can see that it is made of rubber for isolation from NVH and has voids cut into it on the top and bottom to allow the control arm to articulate in those directions.

The problem with a rubber bushing is that it is “squishy.”(I apologize for using such a difficult and technical word.)   Squishiness is good for a comfortable ride and stuffed animals, but it’s not good for performance.  Soft bushings create a feeling of slop in a suspension.  This is because any forces transmitted through the bushing must first compress or stretch the bushing before they can act on the vehicle.  In the case of the control arm pictured above, when the axle pushes the car forward, it must first compress that squishy bushing before it can push the control arm and then the car.   

As an example, imagine that you are pushing a heavy, wheeled cart.   But instead of pushing on the actual cart to move it, you are pushing on a spring that is, in turn, pushing on the cart.  Before the cart will move much, you must first compress the spring.  Some of your effort in pushing the cart is lost in compressing that spring.  The compressing of the bushing is what creates slop, because there is a short time between the driver’s inputs (such as steering and braking) and the car actually reacting to these inputs while the bushings in the suspension compress.

So the solution from a straight-line standpoint would seem to be to simply eliminate the bushing and directly bolt the control arms to the car.  This would allow all of the acceleration and braking forces to be transmitted directly to the chassis.  However, that would create bind, because during cornering the control arm needs to articulate around those bolts.  That requirement for articulation is the second reason that bushings are used.

It is possible to replace rubber bushings with ones that are harder by increasing the durometer of the material.  The durometer is a measurement of how difficult it is to deform a material, so the higher the number the “less squishy” it is.  Polyurethane is a popular material choice for more performance-oriented bushings.  It has a higher durometer than rubber but still allows some deformation and thus doesn’t completely compromise ride quality.

 

This polyurethane bushing from BMR Suspension replaces a factory rubber bushing.

The advantage of polyurethane bushings is that it is stiffer than rubber, removing a lot of slop from the suspension.  The disadvantages are increased NVH, increased maintenance requirements (polyurethane must be lubricated regularly to prevent squeaks), and less articulation if the bushing is not designed correctly.  Many combination street/race applications use polyurethane bushings, as they are a very good compromise of performance, comfort, and ease of maintenance.

The ultimate solution from a performance perspective is the use of spherical bearings or Heim joints.  Discovered by the British in World War II from a captured German fighter plane, Heim joints allow articulation with zero compression.  Heim joints are the best of both worlds in terms of performance: in one direction, you can have zero compression and in another you can have articulation.  The problem with Heim joints is that they are very noisy and uncomfortable—every bump and vibration is transmitted directly through them, since there is zero compliance to act as an isolator.

 

This Heim joint from BMR allows articulation with zero slop.
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Comments
Basshed
Basshedlink
Wednesday, July 02, 2014 11:57 AM
I'm very curious: what led you to replace the Whiteline lower control arms/brackets & pan hard bar/brace with the BMR? It's definitely appreciated reading about all the different brands for sure - helps my purchasing decisions for my '14. Thanks for these updates!
Dusty Duster
Dusty Dusterlink
Wednesday, July 02, 2014 1:28 PM
Whiteline's parts are great! The "other" Mustang still uses them. We're just testing BMR's parts now, as well!
warmmilk
warmmilklink
Wednesday, July 02, 2014 3:44 PM
I have the same lower control arms on my Mustang and I gotta take a couple issues with this article...

Another negative of spherical rod ends is that they wear fast. I even have boots from SealsIt on mine, and they started the tell tail rod end "clicking" about 3 weeks after install (prolly 1k miles or so)

BMR doesn't recommend the grease that you said they do. Everytime I talked to them, they said any synthetic grease, when pushed further, they said AMSOil everytime...

The gear whine, while not loud, its easily audible with the windows up, you do not at all have to listen for it unless you have horrible hearing. And I only have the LCA's with the stock UCA, which I imagine makes things even louder. But its not loud like you said, turning on the radio even quietly covers it up.


PS
I like the "other" UCA's having issues breaking... way to protect the sponsors... but its been redesigned since so its no longer and issue...
Dusty Duster
Dusty Dusterlink
Wednesday, July 02, 2014 8:33 PM
Gear whine is more noticeable with non-stock gears; I still have the stock ones in mine. It's also very subjective: everyone has different tolerances for noise levels. What I think is completely fine might be absolute torture for you.

BMR personally told me to use motorcycle chain lube. They do recommend Amsoil. My local powersports shop didn't carry the Amsoil lube, so I bought what they recommended. I've also put quite a few miles on it and haven't noticed any clicking... yet.

There have been multiple failures of UCAs from many different manufacturers. BMR makes one of the sturdiest out there, however.
warmmilk
warmmilklink
Wednesday, July 02, 2014 8:58 PM
Well my gears are stock, but I do have the 3.73's... so maybe thats it...

They told me about the chain lube also, but said the SealsIt boots are better, and prolly not a good idea to use both.

I've only heard of Whiteline UCA's failing, but that could be the only 2 I researched were Whileline and BMR
Dusty Duster
Dusty Dusterlink
Wednesday, July 02, 2014 9:11 PM
I've heard people complain about gear whine with 3.73s and stock control arms, actually!
John Swan
John Swanlink
Tuesday, July 08, 2014 2:58 PM
Vince glad to see you trying out the BMR stuff. I have been running those control arms for probably about 60000+ miles. Have replaced both the Poly and Spherical bushings once. I definitely recommend putting the boots on, the weather/roads/salts around here will do the rod ends in quickly. They are a PIA to get on but I have not had any problems with them since adding them.

I actually had a UCA fail although the circumstances are vague. I had what I thought was a driveshaft failure 6 months after getting the car and Ford even replaced it under warranty. I was lubing up the bushing on the UCA and noticed 'new' weld lines on it. I removed it and asked the Ford dealer about it, they admitted to 'repairing it'. I don't know if it failed and took out the driveshaft or if, and I cannot really fathom how, they somehow broke it. But if it had failed I would not think the dealer would have warrantied the replacements.

Anyway, that was NOT a BMR UCA. I was using another brand at the time and have since switched to BMR and never looked back. Kelly @ BMR really knows these cars well and has given me a lot of good advice in the past.
Dusty Duster
Dusty Dusterlink
Tuesday, July 08, 2014 3:49 PM
They just WELDED the old one back together?! They clearly have no concept of the stresses the UCA sees. It's one of the most stressed parts in the car!
John Swan
John Swanlink
Tuesday, July 08, 2014 4:04 PM
Tell me about it! I replaced it as soon as I saw that. Of course they never told me it had to be repaired, there was no mention of it on the repair ticket, the whole thing was very fishy...
warmmilk
warmmilklink
Tuesday, July 08, 2014 4:38 PM
So I take back the worn rod end comment, turns out I just got a defective one as the other is still tight. No fault of BMR as this is a QA1 part... But they are sending me out a new rod end...
Dusty Duster
Dusty Dusterlink
Tuesday, July 08, 2014 5:12 PM
I'm curious what you fellows use as a basis to tell when a rod end needs to be replaced. Do you check for play in the bearings? Wait until the noise gets unbearable?
warmmilk
warmmilklink
Tuesday, July 08, 2014 5:31 PM
I could hear it clicking at low speeds where there's not enough road noise to drown it out. Then when I finally got around to getting my car up on a lift I grabbed it and shook it and could hear it clicking. Which doesn't necessarily mean a bad rod end, people who don't care about the noise keep driving them like this (mostly race cars), but it shouldn't be this loose after 3 weeks...
John Swan
John Swanlink
Tuesday, July 08, 2014 10:24 PM
Yep, the clicking, then a clunking, then I was looking for the hammer banging around in the trunk. Only really notice it at slow speed over drops like a pothole. There is not really any noticeable play in it, but when I sprayed a little silicone lube in it it would quieten up for a day or two.
Kelly@BMR
Kelly@BMRlink
Thursday, July 10, 2014 10:23 AM
Great article Vince! I am glad to see you using our components, and I know you will thoroughly enjoy them. We have as much or more experience with the S197 Chassis as anyone out there, and it will show when running our components.

warmmilk; yes, unfortunately sometimes rod-ends can develop play prematurely. It is not super common, but can and does happen. It is rare enough, that I typically remember each and every time/customer. Yours for example, I shipped it out via USPS Priority, and you should have it any time now. You are all the way across the country, so give it a little bit of time. I appreciate the video you took, it REALLY helps when a customer contacts me and is prepared - it makes the process quick and simple.

John Swan, I am happy to hear about your experiences with our components and service! You are an example of why we are, where and who we are today.

If anyone has any questions about S197 Suspension, our products, etc. - please do not hesitate to contact me. My E-Mail is Kelly@BMRSuspension.com
warmmilk
warmmilklink
Thursday, July 10, 2014 12:23 PM
Yeah, thanks for taking care of me Kelly. In the past all the rod ends I've used developed this kinda play so I didn't pay much attention to it until I had it up on a lift and noticed it was only one side (I made the first couple posts here before that).

Another plus for BMR is great customer service!
Dusty Duster
Dusty Dusterlink
Thursday, July 10, 2014 2:22 PM
BMR has the best customer service of any company I've ever worked with.
Kelly@BMR
Kelly@BMRlink
Friday, July 11, 2014 2:53 PM
Thanks Dusty Duster! That truly means a lot to me.

priapism
priapismlink
Tuesday, August 19, 2014 12:56 PM
I see lots of posts about LCAs and UCAs on the forums, thanks for helping me understand what everyone's complaining about. Seems most of these upgrades aren't applicable to my '12 LS Boss, however. Nice writeup.
Dusty Duster
Dusty Dusterlink
Tuesday, August 19, 2014 1:22 PM
Thank you for the kind words!

I disagree about these upgrades not being applicable just because you have a BOSS. Your car still has the same control arms as a GT Mustang and still has issues with geometry in corners and squishy bushings.
priapism
priapismlink
Tuesday, August 19, 2014 1:33 PM
Some of those parts aren't available for my Boss, I'm not saying it doesn't have the issue.
Dusty Duster
Dusty Dusterlink
Tuesday, August 19, 2014 2:15 PM
All the parts for the GT bolt onto the BOSS, and vice versa.
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