Rear Cross Brace

[satan_srv]

I was looking at the Lower Rod A that connects all four corners of the cross beams and I was thinking that it looks slightly bent. It's number 2 in this picture:

Or you can see it behind this S-TAI exhaust pic the straight bar that is going across under the exhaust:

I'm assuming this bar helps limit the torsional flex on turns by crossing out the cross beams...a straight X would be a better design but there probably was not room due to the engine.

Anyway it's made of aluminum and doesn't seem to be very big...should I just replace it with the OEM part or could I just design a new one out of Aluminum tubing? Other companies already make aftermarket cross braces for cars like the S2000 and they really help.

Thanks for the input!

 

[Larry Bastanza]

If you look at items #1-6 (excluding#3) they form a box. This will give the most rigidity, other then your comment about using an X. I would put your original piece is a light press and straighten it, it should be fine. JMO. BTW, list price is 578.52US

HTH,
LarryB

 

[satan_srv]

If you look at items #1-6 (excluding#3) they form a box. This will give the most rigidity, other then your comment about using an X. I would put your original piece is a light press and straighten it, it should be fine. JMO. BTW, list price is 578.52US

HTH,
LarryB

Thanks Larry, I guess I will press it out. Based on what you said I think you are agreeing with me in that it doesn't appear to do too much in the rigidity department as the big cross beams do most of that.

 

[LJSB]

I'm assuming this bar helps limit the torsional flex on turns by crossing out the cross beams...a straight X would be a better design but there probably was not room due to the engine.

The way I see it is that the folks at Honda had a clean sheet of paper and could have designed anything they wanted to on this car.That includes a "x" brace instead of this trapezoid shaped thing. Another would be a more powerful engine but that's another matter all together.

I recently replaced this item on a car becuase of a similar condition.
I'm not a engineer and don't know what this part is really designed to do but it looks like it's intent is more likely structural.
I bet it cost a pretty penny to design and manufacture and it is expensive to buy as Larry mentioned. Darn if I know for sure why it is there or for what practical purposes( read daily over the road driving) it is needed. I do know that aluminum doesn't exhibit the impact of stress the way steel does and bending it does compromise its strength and molecular structure. The information I've gleaned from the classes I've attended on aluminum repair(I-CAR) and info from "Tech-Core" caution against it. If this part is bent and then bent back to "look" okay it might not mean sheep dip.
If I get to ask one of their engineers (Honda/Acura) why it's there and what it's intent/function is I will, because I'd like to know too.

 

[satan_srv]

right...that's why I was thinking replace or create a steel piece originally. I'll look around for a replacement

 

[titaniumdave]

I would agree with the idea of straightening the brace. This part appears to handle compression and tension loads only, so having it straight will make it work more efficient in tension mode. It does not have to straighten before it can transmit load. The brace maintains the distances between the mount points on the cast members, I don't believe you will get increased rigidity out of a different design unless it was quite a bit larger and taller, plus this is an area which Honda has desinged very well. You would get more improvement in rigidity by using a direct mount strut brace in the engine compartment with a targa brace to the front of the compartment if you want to make a part.

 

[satan_srv]

My brother fabricates all kinds of aluminum and SS stuff (he programs robotic welders which is really scary) so I could talk to him...

conflicting viewpoints so far, which is always good for discussion

 

[Larry Bastanza]

I guess one thing that might be worth noting is your intentions for the car. First let me say that pbassjo has significantly more structural/metalury knowledge that I do. He is a pro. Titaniumdave (I know he is involved as well in titanium and metalurgy) makes a good point about the structure and it's function, so the real question is what are you planning to do with the car?

If you plan on stressing this structural part often, such as drive the car at it's limits regularely on the racetrack, replace it. If street driving is your intention I would straighten it.

As Dave mentions it will keep the lower suspension points aligned and spread apart(this goes back to my "box" comment). If you push the car hard, you will increase stress and pressure on this part and straightening may not be the best route.

HTH,
LarryB

 

[titaniumdave]

The question about straightening and strength loss can not be answered with out knowing the heat treat of the part. I think it is safe to assume the part is 6061 Al, but I don't know if it was heat treated to T6 condition. If it was not, the part will age to T4 naturally and you can bend it slight amounts and there is no strength loss to speak of. If it has been aged to T6 then Joe is correct as far as molecular structure loss of integrity and there will be a tendancy for the part to be brittle in the location of the bend. Either way, the amount you need to straighten it, if the picture is accurate, is so slight I would not be concerend if it were on my car. The place this part should fail is at the edge of the weld where it meets the mount plates, on the plate. This tube is very heavy wall on the side toward the car and should not be the weak link in the structure. If the part should ever go into a failure mode, it should be a crack forming, and slow propagation, not catastrophic failure.

I would straighten it, drive it and clean and inspect it like the rest of you suspension parts. I wipe down part of this bar every 3,000 miles when I change my oil, pretty easy to keep an eye on it if you are concerned. I would guess it will never fail no matter how hard you drive it, if you race it, you will be inspecting it pretty often any way and you can fix it if it cracks.

 

[LJSB]

I have the NSX body repair manual. I'll look up to see what the rating is of this piece if it's there I'll also look in the other manuals on a course I took. It listed the grades for the different body/structure panels on the NSX though I don't know if this one is listed.

I can't say and am not saying one way or another that this part shouldn't or couldn't be bent back in the event of a slight bend as described and be just fine and no pose no compromise in regard to safety.
I just don't know but when it comes to structure and customer liability I'd rather err on the side of caution. I am curious what Honda thinks and what this part was really meant to do.
Sitting where it is it sure can be bent easily.
They list different part numbers for this item for the targa and non-targa in the crash manual by the way.
It's grouped as 1991-1994 for one number and another for 95-98 targa and yet another for 95-98 coupe if that means anything.
Dave's suggestion seems to make sense.
Wouldn't mind knowing who's pissing the furthest on this.

 

[satan_srv]

I have the body repair manual as well..i didn't find it...it's just a suspension piece it seems..and minor at best IMO considering the crossbeams already box out the car...it's probably just excessive but i'll keep an eye out for a new one