BMR boxed LCA's

Which causes the least noise?
Which performes better?

 

Rubber/Poly will bind less. You'll get some bushing deflection at the rubber end, but it stops the binding problem. I'd go with rubber/poly if I were using one of the two.

Good luck!

 

They have one with a spherical bearing at one end that should eliminate bind and allow for proper suspension travel
Then you could get poly for the body attachment end for the perfect combination for this part. It should be quiet as well.

 

I've had both the BMR poly/rubber and the G2 poly/rod. I would definitely recommend the G2's. Both the BMR and the G2 were/are as quiet as stock. Either one will work, but IMO stay away from the poly/poly unless your car is drag-only or something.

 

TB ... I've seen you post this several times.
What's your reasoning behind that statement?

Let me voice mine ...

Remember, the center bolt in the bushing is nothing more than a location and pivot point. The inner sleeve and bushing all move as the LCA goes up and down.

A non-metallic bushing binds because the LCA twists in the mount when the body rolls like through a corner, jamming the bushing compound into the side of the mount, creating friction and thus increasing effective rear spring rate. And we all know that a increased rear rate will cause the car to push, especially on corner exit, under power.

A poly pushing is harder and less pliable. Therefore would slide easier on a metal surface of teh mount, under a given load, than would the softer rubber compound. The softer rubber would be "stickier" because it's softer.

I equate it to softer and harder compound in tires. The harder the compound, the less traction it will have, while a softer compound will grab a lot better.

What are your thoughts?

 

One of the reasons the stock control arms don't bind (ok, don't bind that bad) is due to the rubber bushings and the flexibility of the control arms. If you drop one wheel into a pothole, the front and rear mounting bolts are no longer parallel. This will require something in the design of the control arm to allow this misalignment. We know that boxed control arms are quite rigid, not a good place to get our required flex. Poly bushings are also very rigid (semi-solid?), also not a good place to expect flex. That leaves either a spherical bearing (heim joint, rod end, etc) or a rubber bushing. The heim joint is the best solution (and is practiced by LG Motorsports and many others) or rubber works as a poor alternative. Rubber is soft, not good for locating things, but it is good for a joint that has to experience "twisting".

I agree with that statement, but consider that a rubber bushing is pliable and will not try to twist in the bushing mount as much (due to internal give), this will place less side load on the "side of the mount". Basically, if you jam a stick into a block of rubber, you can move that stick a reasonable distance before you see much surface distortion. If you do the same to a block of poly, you will either break the stick or move the whole block of poly. It is this "give" that helps the rubber to eliminate bind. Unfortunately, it is simply due to rubbers lack of structural integrity.

Given only those choices, I feel the poly/rubber would be less detrimental to handling. I don't consider either to be "winners", but I feel that the poly/rubber is "less bad". Everyone who has read my ramblings already knows that I am a proponent of the spherical bearing for LCA use. I feel that it is the only proper solution, the downside is noise. I'll trade the noise for proper handling.

I'll correct that statement. It will not eliminate binding, sorry, I'll correct myself (or Mitch will.... ). It will reduce binding or bind less than poly. This is one of the reasons that many racers say to stay away from the 1LE rear bushings, they help locate the axle at a cost of increased suspension bind. Ground control (www.ground-control.com) says this about poly bushings (in their F-body catalog, online):

Basically, they use poly in one end and a spherical bearing in the other. Problem solved (or mostly solved). From the sounds of that statement (above), ground control would take stock 1le bushings over poly.


Anyway, these are my thoughts on the matter, sorry for the novel. Did I make any sense at all? (It is 1:42 am and I just installed an adjustable clutch quadrant and clutch cable in a friends Mustang GT....so, I may be a little tired right now...if so, I'll correct the errors tomorrow).


Kevin

 

Kevin, Given those 2 choices is no choice at all, though.

Sure rubber is more pliable. But where in heaven's name can the rubber move? The entire bushing is clamped between two pieces of metal, one on either side ... the mount.

So, if a twisting force is applied to the LCA, either the mount has to give, the bolt has to fail, the arm itself has to twist or it remains rigid.

I contend it remains rigid ... but the forces that are trying to twist it are still there. That will add even MORE effective "torque" to the mount against the bushing ... i.e. more clamping force ... i.e. bind. And the bushing can't deflect because it's clamped in all that metal.

So what happens when the suspension attempts work as the car goes over a small bump in the pavement? Or the body just tries to roll normally when transfering weight in a turn? It can't because it's all bound up. It can't move with the normal spring rate ... this increased rate equates to bind in EITHER bushing type ...

The world as I see it ... open my eyes, please!

M

 

You'll get no arguement from me there. I guess I tried to answer the question and only the question (for once).

I agree that the rubber has little room. However, GM got smarter (or tried to) on the latest control arms (off of my 2002), the rubber is not round, it is missing on the top and bottom of the bushing. It appears that GM tried to make the bushing more effective in thrust, front to rear, and leave room for some twisting motion. How effective is it? It's hard to say.

All that aside, I am not a fan of rubber or poly. My thoughts on the rubber may require you to look at it from a different perspective. You are looking at the properties rubber and poly strictly as they relate to side loading and bind (that increases spring rate). If we eliminate the spring rate part for a minute, consider simply the twisting action that a control arm (and bushing) sees during body roll or when one wheel hits a speed bump, etc. There has to be some give to allow the axle to move in a way that allows the bolts to be "non-parallel" to each other. I simply contend that rubber more easily allows this rotation than poly. Poly will increase your rear roll rate considerably, it simply dosen't want to allow any rotational motion. The rubber will give. That was my main point for picking it as "the lesser of two evils" (though, admittedly, it is not that much less evil). I would suspect the binding with regard to spring rate to be very similar between the two bushing types. Poly has very little "give" which will place substantial "side loading" (bind) against the metal surfaces that it rides against. However, poly is more slippery (back to your thoughts on tire compounds...it has less grip). Rubber will give somewhat (and even more with the new bushing that GM is using, compared to what was on my 3rd gen), but has more "grip". I'd like to measure the difference in energy required to move a LCA vertically while it is twisted with say...15 degrees of "twist". And then do this for both bushing types. I am starting to wonder what the results would show.

So, basically, we agree....(we just view the finer points differently, I think the result is the same). Rubber and poly are poor choices for LCA bushings. I would take my chances with the rubber over poly since I think the rubber will have less effect on "roll stiffness" (it won't try as hard to keep the rear parallel to the chassis). If we think of the lower control arms on the Fox bodied mustangs that the drag guys used (solid bushings or poly/poly), they were cracking the mounting points on the chassis due to twisting loads. I don't think there is any danger of a rubber bushing doing this damage and that, simply put, may be the beauty of a rubber bushing (it simply sucks "less bad").

I say this somewhat jokingly...Have you ever looked at rubber bushings that have lived under a car for a few years. They are usually anything but "pliable" (usually they are hard as a rock and don't resemble rubber at all, and they have very little grip). Maybe the rubber bushings get better with age....

These are just my thoughts, let me know what you think.

 

OK ... I see where you are coming from ... the lesser of 2 evils is a good way to put it.

And thanks for the tech on the new bushing design in the LCAs. I wasn't aware of that.

Bushing use is somewhat of pet-peeve of mine. I spent hundreds of dollars on poly/poly LCAs, searching for an LCA that woukld actually work.

The problem was, I didn't fully understand (assuming I do now ) the physics that was going on back there.

When I see someone about to plunk down $150 for poly or rubber bushing LCAs, I have to chime in and explain that for another $50, an LCA can be had that actually does what ALL it's intended to do.

 

Absolutely. My BMR's rattle, but they don't bind....

 

And my G2s don't rattle nor do they bind ...

 

Thanks for the lesson !

 

I have been thinking about trying LG's new Heim/Heim LCA's. I just haven't taken the time to order any yet. I guess Lou needs to call me up....lol.

Ryabut98, that's why the message boards are here. Besides, Mitch and I seem to have the most interesting conversations. If I ever find myself in Texas, I may have to look Mitch up.

 

You do that, Kevin.

I look forward to it ....

 

Trackbird I would say you have articulated the problems with this part of the suspension quite well.

If a spherical bearing is placed at one end ( the diferential side ) and poly at the body attachment end would this be enough to eliminate bind.
I building some prototypes with these very features
I believe this binding to be detremental to the longevity of the LCA mounts.

 

The poly/heim design is already in use by several of the sponsors on this board and is the best compromise for street use thus far. We had a long discussion about the merits of the spherical bearing on the chassis to allow the rear to articulate correctly (the LCA's scribe an arc as viewed from behind), and most said they used the poly on the body for noise reasons. This was finally clarified by Lou from LG Motorsports who mentioned that the arc of the panhard rod will cause some slight binding during vertical suspension travel with the poly on the body (the rear axle will move from side to side as the Panhard bar travels in it's arc), but it seems to be fairly minimal and that is why the poly was to be placed on the body end. I am of the opinion that the only way to truly free up the rear suspension is to use hiem joints (rod ends, etc) on both ends of the LCA. This results in some degree of noise transmission. I'm on my second set of heim/heim LCA's. The first set were not noisy at all (Herb Adams LCA's and Panhard bar), but, when I sold that car, I sold the LCA's. I now have BMR LCA's and PHB (heim joints on all ends) and they "rattle". This seems to be caused by a fairly inexpensive rod end that is being used by BMR (I believe it is a QA1 rod end, they are usually pretty good, but these rusted in a few weeks and have rattled since new). Though they are noisy, they work well so I have not changed them (thus far).

Possibly, but over time poly will "cold flow" and the fit will become "sloppy". It is easy enough to replace an $8.00 bushing every few years, so it is still not such a bad thing. It could place undue loads on the mounting bolts, but I suspect the shock loads from a spherical bearing are not any better for the mount. I've never broken a mounting point (neither has anyone I know) with any type of LCA, but is it a potential concern.

Just my thoughts...

Kevin

 

Holy crap!!! When I clicked on this thread, I didnt know I would be on it for 15 mins.! Believe me I read every bit of it, but Im slow so youll have to break everything down for me in Lamens terms! Shorten everything up from B I G to small. Im in the same boat with the LCAs and PHB! The car is a daily driver, but I plan to take it to the track a few times out of the month. So bascially, I want it to perform well at the track, but want it to be streetable. I dont mind a little noise, but I dont want to be driving down the street while people stare because my car is squeeking and rattling as if something was wrong with it. I dont mind replacing the ends, but it all depends on how often. I know that there were many good points from above (none that I caught because I dont follow), but Im totally lost. I just want to get the right stuff on my car. Im trying to understand, but remember, Im slow. I think I have ADD!

 

Basically, we have determined (assuming we all agree) that spherical bearings (rod ends, heim joints....all the same thing) are the only way to make a high performance LCA that works "correctly".

We then decided that if you must have a quiet (stock type) ride and refuse to use a Heim joint, you are left with rubber/rubber or poly/rubber for your bushings (one type on each end or both poly). This dosen't seem to be much of a choice, but out of the two, I'd take my chances with a rubber/poly in an effort to minimize the effect that either type of design has on handling. Basically, both are a compromise, we just decided (or I think we did) that rubber is "less bad". The fact that rubber is soft helps the suspension move with less resistance, it also allows the suspension to move in ways you don't want it to. But, that is pretty much the definition of compromise, it does everything and none of it well.

Does that clarify it somewhat?

If not, just ask...

 

Kevin, we need to start charging for these seminars ...

 

Mitch....My wife was telling me the same thing yesterday while I was talking to SStolen on the phone about his alignment....We'll just change our signatures to say "Donations accepted, please mail to....."