what exactly is the difference (besides the obvious rod ends) between the LCAs that bmr sells?

what are the pros and cons to each?

i have heard the "race" LCAs are really noisey, is this true?

i am wanting to make a mean street machine, should i just go with the tubulars with poly bushings or is there actually a $130 difference in feel that i would need on a street car?

Ty

 

The difference is basically the rod ends.

The spherical (heim joint) rod ends have no cushioning. This makes them much firmer, which reduces unwanted flex in the suspension. This makes the suspension work better--it improves traction.

On the other hand, the lack of cushioning makes the ride harsher. You will feel more irregularities in the road. It will also increase road noise in the cabin.

The adjustable LCAs allow you to adjust the pinion angle of your rear axle. This is useful if you're optimizing your car for the drag strip, but it's not neccisarily unless you lowered the car (or are planning on lowering in the future).


If you want a mean street car I'd recommend the tubulars with poly bushings...or at most the "combo" type with the Poly bushing on one and and the heim on the other.

 

those are the ones i was kind of leaning towards because they are adjustable. i am planning on lowering my car and going with an aluminum driveshaft. i have heard there are some vibration problems when the pinion angle isnt perfect with the alum d/s.

i was just afraid they would be noisey because of the rod ends.

Ty

 

They'll probably be somewhat louder than stock, but I don't think it would bother you too much. A little noise is to be expected: after all, it's a sports car, not grandma's Cadillac.

The driveline vibration should't be dependant on the driveshaft. Aluminum or steel, it shouldn't make any difference. Angle is angle, I'd make sure it was set right with steel or aluminum.

 

Besides the rod ends, they are generally offered in mild steel and chromoly, which is lighter and stronger, but more costly.

 

That is actually NOT true The Chromoly is not lighter it merely has a thinner wall than the mild steel but since it is a denser metal it still retains it's weight. No biggie really but it is a big misconception. And the cost differance is about 2.00 per foot

Richard

 

The BMR race version is noisey as hell !! My race version is now sitting on a shelf I ended up buying a set of Motoblue LCA'S .

 

Besides the rod ends, they are generally offered in mild steel and chromoly, which is lighter and stronger, but more costly.
[/quote]

That is actually NOT true The Chromoly is not lighter it merely has a thinner wall than the mild steel but since it is a denser metal it still retains it's weight. No biggie really but it is a big misconception. And the cost differance is about 2.00 per foot

Richard

[/quote]

Sorry, but neither of these are true.

Chromoly steel is STIFFER than mild steel, but it's ultimate strength is basically the same. That means that if you apply a lot of load to otherwise identical specimens--one each of chromoly and regular steel, the Chromoly one will hold it's shape longer, then suddenly break. The "ordinary" steel one will deform a bit first, then break. But they will both break at about the same load. As a quick note, most people are actually thinking about stiffness when they say "strength", but this is actually a misnomer.

Chromoly and "mild steel" are almost exactly the same density.

If you want to check out this information you can look this up in the CRC Handbook of Chemistry And Physics, Mark's Handbook for Mechanical Engineers, or just about any College materials & engineering textbook.

If you are designing a part based on ultimate strength, then the two are about the same. (except the Chromoly costs more).

You are designing a part based on deflection/stiffness, which is very common, then the Chromoly is "better". That means you can make your part stiffer, but the same weight (by using the same size part, made from Chromoly) or you can make it lighter (a thinner part made from Chromoly). Take your pick: stiffer or lighter, but not both.

For the purposes of LCAs, I would imagine they use the same size tubing as the mild version (thereby keeping the threaded inserts the same). Therefore the Chromoly part would be stiffer. However, I don't think you would ever notice a difference. That is because the differance in stiffness would only become apparent at very high loads (high enough to permanently stretch the mild steel) and even if those loads were to occur, other things such as poly bushings or even the unibody are going to give (flex) well before the LCA would be loaded that much. You MIGHT notice a tiny difference in the race version with heims at both ends, but I doubt it. As for the weight savings, if they designed for that it would be minimal at best because there is so little material involved. Take a leak before you get in your car and you'll be better off.

I'd save some $$$ and stick with the mild steel version.

 

on a previous post chevy killer said he installed an alum d/s and because of the pinion angle the alum d/s caused a lot of vibration at high speeds where the steel one didnt.

 

Right, but the problem causing the vibration must have been there in either case. The vibration comes from the pinion angle being incorrect. If he didn't feel it with the steel driveshaft, the steel must have been damping the vibration. But that doesn't mean that it was "OK". The problem was still there, he just didn't notice it.

I think the pinion angle should be set properly, regardless of driveshaft material. Improper alignment is a bad thing wether you feel it or not. Even if you don't feel it, it's still putting more load on the driveline parts and it's costing you a bit of power.